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10, , 2, m, Ter, , CBSE, , 2021-22, , Science, (As per the Latest CBSE Syllabus Released in July 2021), , Shivanshu, , B.E., M.B.A., , Visit https://telegram.me/booksforcbse for more books., , Full Marks Pvt Ltd, (Progressive Educational Publishers), An ISO : 9001-2015 Company, , New Delhi-110002

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Published by:, , An ISO : 9001-2015 Company, , 9, Daryaganj, New Delhi-110002, Phone: 011- 40556600 (100 Lines), Website: www.fullmarks.org, E-mail: info@fmpl.in, © Author, All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without, permission. Any person who does any unauthorised act in relation to this publication may be liable to criminal prosecution, and civil claims for damages., , Branches:, • Chennai • Guwahati, Marketing Offices:, • Ahmedabad • Bengaluru • Bhopal • Dehradun • Hyderabad • Jaipur • Jalandhar • Kochi • Kolkata, • Lucknow • Mumbai • Patna • Ranchi, , New Edition, , “This book is meant for educational and learning purposes. The author(s) of the book has/have taken all reasonable care to, ensure that the contents of the book do not violate any existing copyright or other intellectual property rights of any person, in any manner whatsoever. In the event the author(s) has/have been unable to track any source and if any copyright has, been inadvertently infringed, please notify the publisher in writing for corrective action.”, , Printed at:, , (ii)

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Preface, Science-10 (Term-2) is based on the latest curriculum guidelines released by the CBSE in July, 2021 for the examination to be conducted between March–April 2022. It will certainly prove to be a torchbearer for those who toil hard to achieve their goal., This All-in-One Question Bank has been developed keeping in mind students’ requirements for Board, Examination preparations like learning, practising, revising and assessing their progress., Salient Features of the Book:, ●, Each chapter is designed in a ‘Topicwise’ manner where every topic is briefly explained followed by, Exercise to that topic., ●, Topics presented in easy-to-understand points that help in memorising and retention., ●, Answers are written in lucid language and according to the student’s level of understanding., ●, Every exercise covers all possible varieties of questions with answers in the form of Multiple Choice, Questions, Assertion-Reason Type Question, Very Short Answer Type Questions, Short Answer Type, Questions and Long Answer Type Questions., ●, Case Study Questions have been provided in chapterwise manner., ●, All important NCERT Textbook questions are covered with answers., ●, Previous Years’ Board Questions and latest CBSE Board Questions with answers are also included., ●, Answers have been given as per the CBSE Marking Scheme where needed., ●, Chapter Map and Quick Revision Notes have been given for student’s benefit., ●, Common Errors by the students are provided to make students aware what errors are usually committed, by them unknowingly., ●, Assignment is given at the end of each chapter., ●, Three Sample Papers (2 Solved + 1 Unsolved with Answers) are given for self assessment., ●, The book has been well prepared to build confidence among students., We earnestly hope that this book will prove to be highly useful for students., Suggestions for further improvement of the book, pointing out printing errors/mistakes which might have, crept in spite of all efforts, will be thankfully received and incorporated in the next edition., –Publishers, , Visit https://telegram.me/booksforcbse for more books., , (iii)

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CBSE CIRCULAR 2021-22, , osQUnzh; ekè;fed f'k{kk cksMZ, (f'k{kk ea=kky;] Hkkjr ljdkj osQ v/hu Lok;Ùk laxBu), , Central Board of Secondary Education, (An Autonomous Organisation Under the Ministry of Education, Govt. of India), CBSE/DIR (ACAD)/2021, , Date: July 05, 2021, , All the Heads of Schools affiliated to CBSE, Circular No: A cad-51/2021, Subject : Special Scheme of Assessment for Board Examination Classes X and XII for the Session 2021-22, COVID 19 pandemic caused almost all CBSE schools to function in a virtual mode for most part of the academic session of 202021. Due to the extreme risk associated with the conduct of Board examinations during the second wave in April 2021, CBSE had, to cancel both its class X and XII Board examinations of the year 2021 and results are to be declared on the basis of a credible,, reliable, flexible and valid alternative assessment policy. This, in turn, also necessitated deliberations over alternative ways to, look at the learning objectives as well as the conduct of the Board Examinations for the academic session 2021-22 in case the, situation remains unfeasible., CBSE has also held stake holder consultations with Government schools as well as private independent schools from across the, country especially schools from the remote rural areas and a majority of them have requested for the rationalization of the syllabus,, similar to last year in view of reduced time permitted for organizing online classes. The Board has also considered the concerns, regarding differential availability of electronic gadgets, connectivity and effectiveness of online teaching and other socio-economic, issues specially with respect to students from economically weaker section and those residing in far flung areas of the country., In a survey conducted by CBSE, it was revealed that the rationalized syllabus notified for the session 2020-21 was effective for, schools in covering the syllabus and helped learners in achieving learning objectives in a less stressful manner., In the above backdrop and in line with the Board’s continued focus on assessing stipulated learning outcomes by making the, examinations competencies and core concepts based, student-centric, transparent, technology-driven, and having advance provision, of alternatives for different future scenarios, the following schemes are introduced for the Academic Session for Class X and Class, XII 2021-22., , 2. Special Scheme for 2021-22, A., , B., , C., , Academic session to be divided into 2 Terms with approximately 50% syllabus in each term: The syllabus, for the Academic session 2021-22 will be divided into 2 terms by following a systematic approach by looking into the, interconnectivity of concepts and topics by the Subject Experts and the Board will conduct examinations at the end of, each term on the basis of the bifurcated syllabus. This is done to increase the probability of having a Board conducted, classes X and XII examinations at the end of the academic session., The syllabus for the Board examination 2021-22 will be rationalized similar to that of the last academic session to, be notified in July 2021. For academic transactions, however, schools will follow the curriculum and syllabus released by, the Board vide Circular no. F.1001/CBSEAcad/ Curriculum/2021 dated 31 March 2021. Schools will also use alternative, academic calendar and inputs from the NCERT on transacting the curriculum., Efforts will be made to make Internal Assessment/ Practical/ Project work more credible and valid as per, the guidelines and Moderation Policy to be announced by the Board to ensure fair distribution of marks., , 3. Details of Curriculum Transaction, ●, ●, ●, ●, ●, ●, , Schools will continue teaching in distance mode till the authorities permit inperson mode of teaching in schools., Classes IX-X: Internal Assessment (throughout the year-irrespective of Term I and II) would include the 3 periodic, tests, student enrichment, portfolio and practical work/ speaking listening activities/ project., Classes XI-XII: Internal Assessment (throughout the year-irrespective of Term I and II) would include end of topic or, unit tests/ exploratory activities/ practicals/ projects., Schools would create a student profile for all assessment undertaken over the year and retain the evidences in digital, format., CBSE will facilitate schools to upload marks of Internal Assessment on the CBSE IT platform., Guidelines for Internal Assessment for all subjects will also be released along with the rationalized term wise divided, syllabus for the session 2021-22.The Board would also provide additional resources like sample assessments, question, banks, teacher training etc. for more reliable and valid internal assessments., , 4. Term II Examination/ Year-end Examination, ●, , ●, , At the end of the second term, the Board would organize Term II or Year-end Examination based on the, rationalized syllabus of Term II only (i.e. approximately 50% of the entire syllabus)., This examination would be held around March-April 2022 at the examination centres fixed by the Board., , (iv)

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●, ●, ●, , The paper will be of 2 hours duration and have questions of different formats (case-based/ situation based, open, ended- short answer/ long answer type)., In case the situation is not conducive for normal descriptive examination a 90 minute MCQ based exam will be, conducted at the end of the Term II also., Marks of the Term II Examination would contribute to the final overall score., , 5. Assessment / Examination as per different situations, A., , B., , , C., , , D., , , , , In case the situation of the pandemic improves and students are able tocome to schools or centres for taking, the exams., Board would conduct Term I and Term II examinations at schools/centres and the theory marks will be distributed, equally between the two exams., In case the situation of the pandemic forces complete closure of schools during November-December 2021,, but Term II exams are held at schools or centres., Term I MCQ based examination would be done by students online/offline from home - in this case, the weightage of this, exam for the final score would be reduced, and weightage of Term II exams will be increased for declaration of final, result., In case the situation of the pandemic forces complete closure of schools during March-April 2022, but Term, I exams are held at schools or centres., Results would be based on the performance of students on Term I MCQ based examination and internal assessments., The weightage of marks of Term I examination conducted by the Board will be increased to provide year end results of, candidates., In case the situation of the pandemic forces complete closure of schools and Board conducted Term I and, II exams are taken by the candidates from home in the session 2021-22., Results would be computed on the basis of the Internal Assessment/Practical/Project Work and Theory marks of Term-I, and II exams taken by the candidate from home in Class X / XII subject to the moderation or other measures to ensure, validity and reliability of the assessment., In all the above cases, data analysis of marks of students will be undertaken to ensure the integrity of internal assessments, and home based exams., , CBSE CIRCULAR 2021-22, , osQUnzh; ekè;fed f'k{kk cksMZ, (f'k{kk ea=kky;] Hkkjr ljdkj osQ v/hu Lok;Ùk laxBu), , Central Board of Secondary Education, (An Autonomous Organisation Under the Ministry of Education, Govt. of India), NO.: F.1001/CBSE-Acad/Curriculum/2021, All the Heads of Schools affiliated to CBSE, , July 22, 2021, Cir. No. A cad-53/2021, , Subject :, , Term wise syllabus for Board Examinations to be held in the academic session 2021-22 for, Secondary conduct of the Internal Assessment/Practicum/Project., This is in continuation to Board’s circular num regarding Special Scheme of Assessment for Board Examination for Classes X and, XII for the Session 2021- 22. The subjects for classes IX to XII are hereby notified vides syllabus for term end board examinations,, guidelines for the conduct of Internal Assessment/Practicum/Project are also enclosed., Schools are requested to share the term wise syllabus and guidelines for the conduct of board examinations and Internal Assessment, / Practicum / Project available on CBSE Academic Website http://cbseacademic.nic.in at the link http:/chseacademic.nic.in/Termwise-curriculum 2022.html with all their teachers and students., , (v)

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Syllabus, (TERM – II), , , Unit, , Term-II, , Marks: 40, Marks, , I, , Chemical Substances-Nature and Behaviour: Chapter 4 and 5, , 10, , II, , World of Living: Chapter 8 and 9, , 13, , IV, , Effects of Current: Chapter 12 and 13, , 12, , V, , Natural Resources: Chapter 15, , 05, , Total, , 40, 10, , Internal Assessment: Term II, Total, , 50, , Theme: Materials, Unit I: Chemical Substances - Nature and Behaviour, Chapter – 4 Carbon and its compounds, • Carbon compounds: Covalent bonding in carbon compounds. Versatile nature of carbon.Homologous series., Chapter – 5 Periodic classification of elements, • Periodic classification of elements: Need for classification, early attempts at classification of elements (Dobereiner’s Triads, Newland’s Law of Octaves, Mendeleev’s Periodic Table), Modern periodic table, gradation in properties, valency, atomic number, metallic and non-metallic properties., Theme: The World of the Living, Unit II: World of Living, Chapter – 8 How do organisms reproduce?, • Reproduction: Reproduction in animals and plants (asexual and sexual) reproductive health-need and, methods of family planning. Safe sex vs HIV/AIDS.Child bearing and women’s health., Chapter – 9 Heredity and Evolution, • Heredity: Heredity; Mendel’s contribution- Laws for inheritance of traits: Sex determination: brief introduction;, Theme: Natural Phenomena, Unit IV: Effects of Current, Chapter – 12 Electricity, • Ohm’s law; Resistance, Resistivity, Factors on which the resistance of a conductor depends. Series combination of resistors, parallel combination of resistors and its applications in daily life. Heating effect of, electric current and its applications in daily life. Electric power, Interrelation between P, V, I and R., Chapter – 13 Magnetic effects of current, • Magnetic effects of current: Magnetic field, field lines, field due to a current carrying conductor, field due to, current carrying coil or solenoid; Force on current carrying conductor, Fleming’s Left Hand Rule, Electric, Motor, Electromagnetic induction. Induced potential difference, Induced current. Fleming’s Right Hand, Rule., Theme: Natural Resources, Unit V: Natural Resources, Chapter – 15 Our Environment, • Our environment: Eco-system, Environmental problems, Ozone depletion, waste production and their solutions. Biodegradable and non-biodegradable substances., , (vi)

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ONLY FOR INTERNAL ASSESSMENT, Note: Learners are assigned to read the below listed part of Unit V. They can be encouraged to prepare a, brief write up on any one concept of this Unit in their Portfolio. This may be an assessment for Internal, Assessment and credit may be given (Periodic assessment/Portfolio). This portion of the Unit is not to, be assessed in the year-end examination., Chapter – 16 Management of natural resources, • Conservation and judicious use of natural resources. Forest and wild life; Coal and Petroleum conservation., Examples of people’s participation for conservation of natural resources. Big dams: advantages and limitations; alternatives, if any. Water harvesting. Sustainability of natural resources., Assessment Areas (Theory) 2021-22, (Class X), Science (086), , Theory Total, Competencies, , Maximum Marks: 80, Marks, , Demonstrate Knowledge and Understanding, , 46 %, , Application of Knowledge/Concepts, , 22 %, , Analyze, Evaluate and Create, , 32 %, , Note: • Internal choice would be provided., • Internal Assessment – Term I and II (10 Marks each), • Periodic Assessment - 03 marks, • Multiple Assessment – 02 marks, • Subject Enrichment (Practical Work) - 03 marks, • Portfolio - 02 marks, , (vii)

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Contents, Unit-I: Chemical Substances-Nature and Behaviour...................................................................... 9-52, 1. Carbon and its Compounds............................................................................................................................. 9, 2. Periodic Classification of Elements.............................................................................................................. 21, , Unit-II: The World of the Living....................................................................................................... 53-99, 3. How do Organisms reproduce?......................................................................................................................53, 4. Heredity and Evolution..................................................................................................................................83, , Unit IV: Effects of Current............................................................................................................ 100-157, 5. Electricity......................................................................................................................................................100, 6. Magnetic Effects of Current.........................................................................................................................134, , Unit V: Natural Resources........................................................................................................... 158-192, 7. Our Environment ....................................................................................................................................... 158, 8. Management of Natural Resources (This chapter to be assessed in the Periodic Tests/Portfolio Only).177, , • Sample Paper 1 (Solved)........................................................................................................ 193, • Sample Paper 2 (Solved)........................................................................................................ 198, • Sample Paper 3 (Solved)........................................................................................................ 203, , (viii)

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Unit-1, Chemical Substances-Nature and Behaviour, , 1, , Carbon and its Compounds, , Topics Covered, 1.1 Bonding in Carbon–The Covalent Bond and Versatile Nature of Carbon, 1.2 Homologous Series, , C hapter map, , Bonding in Carbon, , Covalent Bond, , Allotropy of Carbon, , Electron Dot Structure, Diamond, , Graphite, , Fullerenes, , Large Number of Carbon Compounds, , Catenation, , Tetravalency, Hydrocarbons, Chains, , Branches, , Rings, , Homologous Series, , in Carbon: The Covalent Bond and Versatile, Topic 1. Bonding, Nature of Carbon, Carbon: Carbon has atomic number 6, mass number 12. It has 6 protons, 6 electrons and 6 neutrons. Its, electronic configurations is 2, 4. It has four valence electrons. It belongs to group 14 and second period of the, periodic table., Organic Compounds: Those compounds which contain carbon essentially alongwith hydrogen and mostly,, oxygen, sulphur, nitrogen, halogen, etc., , Covalent bond: The bond which is formed by equal sharing of electrons is called covalent bond., Covalency of Carbon: Carbon has four valence electrons. It cannot lose 4 electrons because high energy is, needed to remove 4 electrons. It can share four electrons to form four covalent bonds, therefore its covalency, is equal to 4, i.e. it shows tetravalency., , Single Covalent bond: The bond formed by sharing one electron each is called single covalent bond, e.g. the, , following molecules have single bonds., , 9

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H, H H, , Cl Cl, , H–H, (Hydrogen), , Cl–Cl, (Chlorine), , H C H, H, , H O H, , H Cl, H–Cl, (Hydrogen Chloride), , H–O–H, (Water), , H, , H, , H, , C, , C H, , H, , HH HH, , H–C–H, H, (Methane), , H–C–C–H, HH, (Ethane), , Double Covalent bond: When two atoms share two electrons each, double covalent bond is formed., O O   , ,   , ,   , , O=O, (Oxygen), , Triple covalent bond: When two atoms share three electrons each, triple covalent bond is formed., , Properties of Covalent Compounds:, (i), (ii), (iii), (iv), , They are insoluble in water but soluble in organic solvents., They do not conduct electricity as they do not form ions., They have low melting and boiling points., They exist in solid, liquid as well as in gaseous state., Allotropes: The property due to which one element exist in more than one form, which differ in physical, properties but have similar chemical properties. These forms of element are called allotropes., , Allotropes of Carbon: Diamond, Graphite and Fullerenes are crystalline allotropes of carbon., , 340 pm, , 154 pm, , Structure of diamond, , Structure of graphite, , The structure of C60, (Buckminster, fullerene): Note that the, molecule has the shape of a, soccer ball (football), , Catenation: The property due to which an atom can form stable covalent bond with the atoms of same element., I. Multiple Choice Questions, , Exercise 1.1, , (1 Mark), , Choose the correct answer from the given options., 1. A molecule of ammonia (NH3) has, (a) only single bonds , (b) only double bonds, (c) only triple bonds , (d) two double bonds and one single bond, 2. Which of the following is the correct representation of electron dot structure of nitrogen?, (a), (b), (c), (d), 3. Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g., hydrogen. After the formation of four bonds, carbon attains the electronic configuration of, (a) Helium, (b) Neon, (c) Argon, (d) Krypton, , 10, , Science-10

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4. The correct electron dot structure of a water molecule is, (b), (c), (d), (a), 5. The molecular formula of ethene and its electron dot structure is, (a) C2H4,, , , , (b) C2H4,, , (c) C2H2,, , , , (d) C2H6,, , II. Assertion-Reason Type Questions, , (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Carbon forms covalent compound with chlorine of formula CCl4., , Reason: Carbon has 4 valence electrons, valency 4, chlorine has 7 valence electrons, valency 1., 2. Assertion: Carbon forms very large number of compounds., , Reason: It is due to property of catenation and tetravalency, , III. Very Short Answer Type Questions, , (1 Mark), , 1. Draw electron dot structure of NH3 molecule. Predict the total no. of bonds around N-atom., , [Delhi 2016], OR, A molecule of ammonia has the formula NH3. Predict the total number of bonds present around nitrogen, atom. , [CBSE 2016], 2. Why covalent compounds are poor conductors of electricity?, [CBSE 2020], 3. What would be the electron dot structure of carbon dioxide which has the formula, CO2?[NCERT], 4. Which element exhibits the property of catenation to maximum extent and why?, [Delhi 2016], 5. State two characteristic features of carbon which when put together give rise to large number of carbon, compounds., 6. Explain why carbon generally forms compounds by covalent bonds or do not form ionic compounds., Or, 4+, Give reason why carbon neither forms C cations nor C4– anions but form covalent compounds which, are bad conductors of electricity and have low melting and boiling points., [Delhi 2013], Or, Carbon has four electrons in its valence shell. How does carbon attain stable configuration?, [Delhi 2015], 7. Why are most carbon compounds poor conductors of electricity?, [CBSE 2018], 8. Define catenation., [CBSE Sample Paper 2019-2020], 9. Covalent compounds have low melting and boiling point. Why?, [CBSE 2020], 10. How are covalent bonds formed?, [CBSE 2020], , IV. Short Answer Type Questions-I , , (2 Marks), , 1. Carbon, group 14 element in the periodic table, is known to form compounds with many elements., Write an example of a compound formed with (i) Chlorine, (ii) Oxygen., [NCERT Exemplar], 2. In electron dot structure, the valence shell electrons are represented by crosses or dots., (i) The atomic number of chlorine is 17. Write its electronic configuration., (ii) Draw the electron dot structure of chlorine molecule., [NCERT Exemplar], 3. Compare the ability of catenation of carbon and silicon. Give reasons., [NCERT Exemplar], 4. Give a test that can be used to confirm the presence of carbon in a compound. With a valency of 4, how, is carbon able to attain noble gas configuration in its compounds?, [CBSE Sample Paper 2020-21], 5. The number of carbon compounds is more than those formed by all other elements put together. Justify, the statement by giving two reasons., [CBSE Sample Paper 2020-21], , Carbon and its Compounds 11

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V. Short Answer Type Questions-II , , (3 Marks), , 1. What are covalent compounds? Why are they different from ionic compounds? List their three, characteristic properties., [Delhi 2016], 2. (a) Explain why carbon forms covalent bond? Give two reasons for carbon forming a large number of, compounds., (b) Explain the formation of ammonia molecule., [CBSE Sample Paper 2018-19], 3. Carbon, a member of group 14, forms a large number of carbon compounds estimated to be about three, million. Why is this property not exhibited by other elements of this group? Explain., [CBSE 2020], 4. Atoms of an element contain five electrons in its valence shell. This element is the major component of, air. It exists as a diatomic molecule., (i) Identify the element., (ii) Show the bond formed between two atoms of this element., (iii) Write the nature of bond between the two atoms., 5. (i) Explain the formation of calcium chloride with the help of electron dot structure. (At numbers: Ca, = 20; Cl = 17), (ii) Why do ionic compounds not conduct electricity in solid state but conduct electricity in molten and, aqueous state?., [CBSE Sample Paper 2020-21], , Answers 1.1, I. 1. (a) It has three single bonds and one lone pair., , 2. (d), It has triple bond, , 3. (b) Carbon attains 8 electrons after sharing four electrons and acquire stable configuration of Neon., , 4. (c), , , , 5. (b) C2H4,, , II. 1. (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., , 2. (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., III. 1., , , It has 3 bonds around N-atom., , , 2. It is because covalent compounds do not form ions., , 3., 4. Carbon since it forms strong covalent bond, due to smaller atomic size., , 5. (i) Catenation, (ii) Tetravalency of carbon., , 6. Carbon as 4 valence electrons. It cannot lose 4 electrons because very high amount of energy is needed. It, also cannot gain four electrons because 6 protons cannot hold 10 electrons., It can share four electrons to form four covalent bonds. Covalent compounds do not conduct electricity, because they do not form ions. They have low melting and boiling points due to weak forces of attraction, between molecules., 7. Carbon compounds form covalent bonds/do not dissociate into ions/do not have charged particles (ions)., , 8. The property of self-linking of atoms of an element through covalent bonds in order to form straight, chain, branched chains or cyclic chains of different sizes is called catenation., , 9. It is because they have weak van der Waal’s forces of attraction between molecules therefore have low, melting and boiling points., , 10. Covalent bonds are formed by equal sharing of electrons., 4+, O2–, Cl1– C, C4+, (ii)  , 2. (i) Cl (2,8,7) (ii), IV. 1. (i), CCl4, , 12, , Science-10, , CO2

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3. Carbon shows catenation property to more extent than silicon. It is because C–C bond is stronger than, Si–Si bond because carbon is smaller in size than silicon., 4. – Burn compound in air/ oxygen; Gas evolved turns lime water milky, – By sharing its four valence electrons with other elements., 5. • Due to self linking ability of carbon/catenation, , • Since carbon has a valency of four it can form bonds with four other atoms of carbon or atoms of, some other mono-valent element., • Due to small size of carbon it forms very strong and (or) stable bonds with other elements, V. 1. Those compounds which are formed by equal sharing of electrons are called covalent compounds., They are different from ionic compounds since ionic compounds are formed by transfer of electrons from, one atom to another., , Properties:, (i) They have low melting and boiling points., (ii) They do not conduct electricity in molten state and in aqueous solution., (iii) They are mostly insoluble in water but soluble in organic solvents except glucose, sugar, urea, ethyl, alcohol, etc., , 2. (a) Carbon has electronic configuration 2, 4. It could gain four electrons forming C-4 anion or lose 4, electrons to form C+4 cation . Both are not possible due to energy considerations. Carbon overcome, this problem by sharing electrons and forming covalent compounds. Two reasons for forming large, number of compounds:, (1) Catenation   (2) Tetra valency, (b) Formation of NH3 molecule, Three hydrogen atoms each share their 1 electron with nitrogen to form three covalent bonds and, make an ammonia molecule (NH3)., , 3. Carbon shows the property of catenation., It forms strong covalent bonds with other atoms of carbon forming long straight, branched and closed, chain compounds., Carbon is smallest in size in group 14 with tatravalency, it can form double as well as triple bonds,, therefore, it can show property of catenation to maximum extent and forms 3 million compounds other, elements cannot show property of catenation to this extent due to larger size form weaker covalent bond, and cannot form double or triple bonds., , 4. (i) Nitrogen, , (ii), , (iii) Triple covalent bond, , C2H4 is molecular formula of Ethene, , 5., , Z, Ca – 20, Cl – 17, ××, × Cl ×, ×× ×, Ca + ××, Cl ×, × ××, ×, , (i), , :, , Electronic configuration, 2881, 287, , ×× –, Ca+2 2 × Cl ×, ×× ×, Ca+2 2Cl–, CaCl2, , , (ii) Ionic compounds do not conduct in solid state due to absence of free ions but they conduct electricity, in molten and aqueous state due to presence of free ions., , Carbon and its Compounds 13

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Topic 2. Homologous Series, , Isomerism: Those compounds which have same molecular formula but different structural formula are called, isomers. This phenomenon is called isomerism., , Straight Chain Compounds: Those compounds which have carbon atoms linked in a straight chain are, called straight chain compounds, e.g., H H H H, H C C C C H (Butane), H H H H, , Branched Chain Compounds: Those compounds which have carbon atoms linked as branched chains, e.g., H H H, H C C C H is a branched chain compound., H, H, H C H, H, , Saturated Closed Chain Compounds: Compounds having carbon atoms arranged in the form of a ring, e.g., cyclohexane has the formula C6H12. It has single bonds only., HH HH, C C, H, H, C, C, H, H, C C, HHHH, Aromatic, Closed Chain Compounds: If closed chain compounds contain double or triple bonds, they are, called unsaturated closed chain compounds, e.g. Benzene (C6H6). It is also called an aromatic hydrocarbon., , Hydrocarbons: The compounds formed by carbon and hydrogen only are called hydrocarbons., Heteroatoms: In a hydrocarbon chain if one or more hydrogen atoms is replaced by halogens, oxygen, nitrogen, or sulphur, then these atoms replacing hydrogen are called heteroatoms, , Functional groups: These are the atoms or groups of atoms or reactive part of the compound which determines, O, , O, , the properties of organic compounds, e.g. Cl, OH, C H, C OH, etc., The functional group is attached to the carbon chain by replacing one or more hydrogen atoms., , Homologous series: The series of organic compounds having same functional group and similar chemical, properties is called homologous series., Characteristics:, (i), (ii), (iii), (iv), (v), , Each series has a general formula, e.g. alkane has CnH2n+2 as general formula., Each series has same functional group, e.g. alcohols has –OH group., Successive members differ by CH2 unit, e.g. CH4 and C2H6 differ by CH2 unit., Successive members differ by 12 + 2 = 14 u by weight, e.g. CH4 has 16 u, C2H6 has 30 u weight., There is a gradation in physical properties, e.g. there is an increase in boiling point with the added carbon, chain, i.e. with the increase in molecular weight., , General Formula: The formula from which all the members of homologous series can be derived, e.g. CnH2n, is the general formula of alkenes, CnH2n–2 is the general formula of alkynes., , 14, , Science-10

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Exercise 1.2, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. Structural formula of benzene is, , (a), , (b), , (c), , (d), , 2. Which of the following is not a straight chain hydrocarbon?, (a), , (b) H3CCH2CH2CH2CH2CH3, , CH3, |, (c) H2 C − H2 C − H2 C − CH2, |, CH3, , (d), , CH3, CH3, , CH − CH2 − CH2 − CH3, , II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: C6H12, C2H4, C4H8 are alkenes and have double bond., , Reason: C3H4 and C5H8 are alkynes and have triple bond., 2. Assertion: Following are the members of a homologous series:, , CH3OH, CH3CH2OH,CH3CH2CH2OH, , Reason: , A series of compounds with same functional group but differing by – CH2– unit is called a, homologous series., [CBSE 2020], III. Very Short Answer Type Questions, , (1 Mark), , 1. An alkene ‘P’ has three carbon atoms and an alcohol ‘Q’ has four carbon atoms. Write the formulae of, P and Q., 2. Write the molecular formula of benzene and state the number of double bonds in its structure. [Delhi, 2013], 3. What is homologous series?, [Delhi 2016], 4. The molecular formula of two members of a homologous series are C3H4 and C6H10. Write the molecular, formula of a member of this family with five carbon atoms in a molecule., 5. Write the general formula of alkenes. Write the name of the simplest alkene., [Delhi 2015], 6. Write the next homologue of each of the following: (i) C2H4, (ii) C4H6[Delhi 2016], 7. Write the structure of an alcohol with three carbon atoms in the molecule. , 8. Write the molecular formula of alcohol derived from butane., [Delhi 2016], , Carbon and its Compounds 15

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9. Write the molecular formula of an alkyne containing 10 atoms of hydrogen., 10. Write the name and molecular formula of the fourth member of alkane series. [Delhi 2016], 11. Write the name and formula of second member of homologous series with general formula CnH2n+2, [Delhi 2015], 12. Write the name and formula of second member of homologous series having general formula CnH2n–2., [Delhi 2016], 13. Which of the following organic compounds belong to the same homologous series:, C2H6, C2H6O, C2H6O2, CH4O, 14. The formula of citric acid is shown below:, COOH, |, CH2, |, HO − C − COOH, |, CH2, |, COOH, State the name of —COOH functional group in citric acid., , [Delhi 2014], , 15. The molecular formula of ‘A’ is C10H18 and ‘B’ is C18H36. Name the homologous series to which they, belong.[Delhi 2014], 16. Write the next homologous of CH3CH2OH and HCOOH., 17. Write the molecular formula of first two members of homologous series having functional group Cl., [Delhi 2017], , 18. Write the molecular formula of the 2nd and the 3rd member of the homologous series whose first member, is methane (CH4)., [AI 2017], 19. How many covalent bonds are there in a molecule of ethane (C2H6)?[NCERT], 20. Write the electron dot diagram of ethane (C2H6) molecule., , [Delhi 2011], , 21. Write the number of covalent bonds in propane, C3H8.[Delhi 2016], 22. Write the number of covalent bonds in the molecule of butane (C4H10).[Delhi 2015], 23. State the valency of the carbon atom in (i) an alkane (ii) an alkyne., 24. Name a cyclic unsaturated carbon compound., [CBSE 2020], 25. Which of the following is not observed in a homologous series? Give reason for your choice., , (a) Change in chemical properties, (c) Gradation in physical properties, IV. Short Answer Type Questions-I , , (b) Difference in -CH2 and 14u molecular mass, (d) Same functional group [CBSE Sample Paper 2020-21], (2 Marks), , 1. The general formula of three compounds A, B and C is CnH2n. ‘B’ has the highest boiling point and ‘C’, has the lowest boiling point., (i) Mention the type of compounds A, B and C., (ii) Which of these has minimum number of carbon atoms?, (iii) Name the homologous series to which A, B and C belong , [Delhi 2016], 2. Select alkenes and alkynes from the following:, C2H4, C3H4, C2H2, C4H8 , Write their structural formula also. , [Delhi 2014, 2015], 3. An alkane has molecular weight 86. Write its molecular formula. What will be its physical state?, [HOTS], , V. Short Answer Type Question-II, , (3 Marks), , 1. What is homologous series of carbon compounds? Give an example and list its three characteristics., [CBSE 2019], , 16, , Science-10

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Answers 1.2, I. 1. (c) It has 6 C–C bonds, 6 C–H bonds and three C = C bonds., , 2. (d) It is branched chain hydrocarbon., II. 1. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , 2. (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., III. 1. ‘P’ is CH3–CH=CH2, ‘Q’ is CH3CH2CH2CH2OH, , 2. C6H6, It has three double bonds, H, H, , , H, , H, H, , H, , , 3. It is a series of organic compounds having same functional group and similar chemical properties., , 4. C5H8, , 5. CnH2n, Ethene is simplest alkene., 6. (i) C3H6, (ii) C5H8, H H H, , 7. CH3CH2CH2OH or H C C C OH, H H H, Propan-1-ol, , , 8. C4H9OH or CH3CH2CH2CH2OH (Butan-1-ol), , 9. C6H10 , 10. C4H10, Butane (CH3CH2CH2CH3), , 11. C2H6, Ethane, 12. C3H4, Propyne, , 13. C2H6O (C2H5OH) and CH4O (CH3OH) , 14. Carboxylic acid, , 15. ‘A’ belongs to Alkynes, ‘B’ belongs to Alkenes., , 16. CH3 – CH2 – CH2OH. Propanol and, CH3COOH ethanoic acid, , 17. The general formula of the compounds having – Cl functional group is CnH2n + 1Cl. Its two members, are:, , (i) CH3Cl, , , (ii) CH3 – CH2 – Cl, , 18. (i) CH3CH3 (Ethane); where n is 2, (ii) CH3CH2CH3 (Propane); where n is 3, , 19. There are 7 covalent bonds. , H H, , 20., , H C C H, H H, , 21. There are 10 covalent bonds. 22. There are 13 covalent bonds., H H H, H H H H, H C C C H H C C C C H, H H H, 23. (i) Four, (ii) Four, , H H H H, , , 24. Benzene is cyclic unsaturated carbon compound., , H, H, H, , H, H, , H, , 25. (a) It does not occur due to the presence of the same functional group., , Carbon and its Compounds 17

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IV. 1. (i) Unsaturated hydrocarbons with double bonds., (ii) ‘C’ has minimum boiling point, so ‘C’ has minimum no. of C-atoms., (iii) Alkene, , 2. C2H4 and C4H8 are alkenes, C3H4 and C2H2 are alkynes., H H H H, H H, | | | |, | |, HC ≡ CH, HC ≡ C − CH 3, H− C = C −H H− C= C− C− C−H, , (C4 H8 ), (C H ), (C3H 4 ), (C2H4 ), | |, 2 2, H H, , 3. C6H14 has molecular weight of 6 × 12 + 14 = 86u., It is in liquid state at room temperature., V. 1. The series of organic compounds having same functional group and similar chemical properties is called, homologous series. For example,, Alkane: CH4 C2H6 C3H6, Methane Ethane Propane, , , Characteristics: • Each successive member differ by CH2 unit., • They have gradation in physical properties., • They have similar chemical properties due to presence of same functional group., , C ase study question, , 1. Water is a simple molecule consisting of one oxygen atom bonded to two different hydrogen atoms. Because, of the higher electronegativity of the oxygen atom, the bonds are polar covalent (polar bonds). The oxygen, atom attracts the shared electrons of the covalent bonds to a significantly greater extent than the hydrogen, atoms. The molecule has a bent structure, the H—O—H bond angle is about 105°., (i) Which of the following statement is true regarding the electronegativity of atoms in water molecule?, (a) Hydrogen is more electronegative than oxygen, (b) Hydrogen is less electronegative than oxygen, (c) Electronegativity is same in Hydrogen and oxygen, (d) Hydrogen and oxygen do no show significant electronegativity in water, (ii) What is the shape of water molecule?, (a) Linear, (b) Trigonal planar, (c) Bent, (d) Octahedral, (iii) Select the correct type of bonding in a water molecule, (a) Ionic Bonding (b) Covalent Bonding (c) Hydrogen Bonding (d) None of these, (iv) The correct electron dot structure of a water molecule is, (b) H O O, (c) H O H, (d) H O O, (a) H O O, (v) The H—O—H bond angle in water molecule is, (a) 109.5°, (b) 180°, (c) 90°, (d) 105.0°, Ans. (i) (b), (ii) (c), (iii) (b), (iv) (c), (v) (d), , Quick revision notes, • Carbon is a versatile element that forms the basis of all living organisms and large number of materials we, use in our daily life., • Carbon shows allotropy. Diamond, graphite, Buckminster fullerene are allotropes of carbon., • Diamond is hard, lustrous and used in jewellery., • Graphite is soft and used as electrode in cells, lead of pencil, lubricants in machines., • Diamond has octahedral structure, graphite has hexagonal structure and fullerenes have football like, structure., • Carbon forms large number of compounds due to the property of catenation., , 18, , Science-10

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•, •, •, •, •, , Covalent bond is formed by equal sharing of electrons between the combining atoms., Carbon can form covalent bond with hydrogen, oxygen, sulphur, nitrogen and halogens., Carbon also form compounds having double and triple bond between carbon atoms., Carbon can form straight chain, branched chain, closed ring compounds., Carbon compounds belong to homologous series which have common functional group and similar properties., , Common Errors, Errors, , Corrections, , • Students write structural formulae of compounds, wrongly., , ☞ Write skeletal formulae of compounds, making, all the carbon atoms having tetravalency, e.g., H H H, H C C C H, , • Students do not write ‘ane’ and ‘ene’ clearly., • Students write chemical reactions wrongly., • Students leave some parts of 3 mark or 5 mark, questions., • Students do not depict electrons properly in, electron dot structures., , • Students write wrong structural formula of, functional group., , H H H, ☞ Write them clearly. You may use block (capital), letters to avoid confusion., ☞ Do lot of practice by writing equations again and, again., ☞ Do not leave any part. Check whether you have, attempted all the parts or not., ☞ Always depict electrons in pair, e.g., , ☞ Write correct structural formula by keeping in, mind carbon always has tetravalency, i.e. form, four covalent bonds., , important Formulae, S.No., , Formula, , Compound, , 1., , CH4, , Methane, , 2., , CH3—CH3, , Ethane, , 3., , CH3—CH2—CH3, , Propane, , 4., , CH3—CH2—CH2—CH3, , Butane, , 5., , CH3—CH—CH3, , 2-methylpropane, , 6., , CH2 CH2, , Ethene, , 7., , CH3—CH CH2, , Propene, , 8., , CH2 CH—CH2—CH3, , But-1-ene, , 9., , CH3—C CH2, , 2-methylpropene, , CH3, , CH3, CH3, 10., , CH3—C—CH3, , 2, 2-dimethylpropane, , CH3, 11., , H—C C—H, , Ethyne, , Carbon and its Compounds 19

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12., , CH3—C CH, , Propyne, , 13., , HC C—CH2—CH3, , But-1-yne, , 14., , HC C—CH2—CH2—CH3, , Pent-1-yne, , 15., , HC C—CH2—CH2—CH2—CH3, , Hex-1-yne, , 16., , CH3—CH2—Cl, , Chloroethane, , 17., , CH3Cl, , Chloromethane, , 18., , CH2Cl2, , Dichloromethane, , 19., , CHCl3, , Trichloromethane, , 20., , CCl4, , Tetrachloromethane, , 21., , or, , C6H12, , Cyclohexane, , 22., , or, , C6H6, , Benzene, , 23., , CH3OH, , Methanol, , 24., , CH3CH2OH, , Ethanol, , 25., , CH3CH2CH2OH, , Propan-1-ol, , Assignment, I. Multiple Choice Questions, , Total Marks : 20, (1 Mark), , Choose the correct answer from the given options., 1. Which of the following does not belong to the same homologous series?, (a) CH4, (b) C2H6, (c) C3H8, (d) C4H8, 2. Which of the following is the first member of alkene?, (a) CH3, (b) CH2=CH2, (c) CH3–CH=CH2, (d) CH2, 3. How many valence electrons are present in carbon?, (a) 2, (b) 3, (c) 4, (d) 5, 4. Graphite conducts electricity because, (a) it has free carbon atoms, (b) it has free electrons, (c) its one layer can slip over another layer (d) None of these, , II. Assertion-Reason Type Questions, (1 Mark), Note: Use instructions as given in exercises of the chapter., 1. Assertion: H2O has two covalent bonds and two lone pair of electrons., , Reason: CnH2n is the general formula of alkene., 2. Assertion: Carbon has a strong tendency to either lose or gain electrons to attain noble gas configuration., , Reason: Carbon has four electrons in its outermost shell and has tendency to share electrons with, carbon or other elements., III. Very Short Answer Type Questions, , 1. What do you mean by catenation ?, 2. Draw the electron dot structure of propyne., , IV. Short Answer Type Questions-I , , 1. How are covalent bonds formed?, 2. Draw electron dot structure of H2O and NH3 molecule., , V. Short Answer Type Questions-II, , 1. Draw the structures of three allotropes of carbon., , VI. Long Answer Type Questions, , (1 Mark), , (2 Marks), , (3 Marks), (5 Marks), , 1. (i) What is homologous series of carbon compounds? Give an example and list its three characteristics., (ii) Compare the ability of catenation of carbon and silicon., , 20, , Science-10

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2, , Periodic Classification of Elements, , Topics Covered, 2.1 Early Attempts at the Classification of Elements, 2.3 Trends in the Modern Periodic Table, , 2.2 Modern Periodic Table, , C hapter map, Periodic Classification of Elements, Newland’s Law of Octaves, , Dobereiner’s Triads, , Limitations, , Achievements, Mendeleev’s Classification, , Mendeleev’s Periodic Law, , Mendeleev’s Periodic Table, Achievements, , Modern Periodic Table, Achievements, Limitations, , Modern Periodic Law, , Limitations, , Trends in Modern Periodic Table, Valency and Valence Electrons, Atomic Size, Metallic Character, Non-metallic Character, Reactivity, Tendency to lose Electrons, Tendency to gain Electrons, Acidic character of oxides, Basic character of oxides, , Topic 1. Early Attempts at the Classification of Elements, , Earlier attempts at classification: In 1803, Dalton published a table of relative atomic weights (now called, , atomic masses) which formed the important basis of classification at that time. The earliest attempt to classify, the elements resulted into metals and non‑metals., , Dobereiner’s Law of triads: When elements are arranged in a group of three, such that the atomic mass of, middle element is the average of the mass of first and third element, they were found to resemble each other, e.g., , 21

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Li, 7, , Na, 23, , K, 39, , Ca, 40.1, , Atomic mass of Na = 7 + 39 = 23, 2, , =, , Sr, Ba, 87.6, 137.3, Atomic mass of Sr, 40.1 + 137.3, 177.4, =, = 88.7, 2, 2, , Cl, 35.5, , Br, I, 79.9, 126.9, 126.9 35.5, = 162.4 = 81.2, Atomic mass of Br =, 2, , Limitations, • He could not classify all the elements discovered at that time. Hence, this system of triads was not found to, be useful., • Only 3 sets of elements forming the triads was found., , Newlands’ law of octaves: When elements are arranged in increasing order of their atomic masses, every, , eighth element resembled with the first, e.g. the properties of Li and Na are found to be similar, Be and Mg, resembles each other., sa (do), , re (re), , ga (mi), , ma (fa), , pa (so), , da (la), , ni (ti), , H, , Li, , Be, , B, , C, , N, , O, , F, , Na, , Mg, , Al, , Si, , P, , S, , Cl, , K, , Ca, , Cr, , Ti, , Mn, , Fe, , Co and Ni, , Cu, , Zn, , Y, , In, , As, , Se, , Br, , Rb, , Sr, , Ce and La, , Zr, , –, , –, , Limitations, • It was found that Newlands’ law of octaves was applicable only upto calcium. It worked well only with lighter, elements., • It was assumed by Newlands that only 56 elements existed in nature. But many elements were discovered, later, whose properties did not fit into the law of octaves., • Newlands adjusted two elements in the same slot, but also put some elements with different properties under, same place, e.g. Co and Ni are in the same slot with H, F, Cl and Br and these do not resemble with H, F,Cl,, Br. Iron resembles with Co and Ni but it is placed far away., , Mendeleev’s Periodic Law: Properties of elements are periodic function of their atomic masses ie. properties, of elements depend upon their atomic masses., , Mendeleev’s Periodic Table: He arranged elements on the basis of atomic masses and similarity in chemical, properties (formulae of oxides and hydrides)., • Mendeleev’s periodic table contains 8 groups and 6 periods., • It was based on increasing order of atomic masses and on the basis of formulae of oxides and hydrides., • Each group has been subdivided into A or B, except Group VIII., • Group VIII consist of three elements in each row, total 9 elements., • Hydrogen was kept in Group 1. It was the only element in first period., • Second period had Li, Be, B, C, N, O, F –elements., • Third period had Na, Mg, Al, Si, P, S, Cl –elements., • In group I, in the 4th, 5th, 6th period, Cu, Ag, Au were placed in Group IB along with K, Rb, Cs in Group IA., , 22, , Science-10

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Mendeleev’s Periodic Table, Groups, , I, , II, , III, , IV, , V, , VI, , VII, , VIII, , Oxide:, , R2O, , RO, , R2O3, , RO2, , R2O5, , RO3, , R2O7, , RO4, , Hydride:, , RH, , RH2, , RH3, , RH4, , RH3, , RH2, , RH, , Periods, , A, , B, , A, , B, , A, , B, , A, , B, , A, , B, , A, , B, , A, , B, , Transition series, , Ø, 1, , H, 1.008, , 2, 3, 4, , First, series, , Li, , Be, , B, , C, , N, , O, , F, , 6.939, , 9.012, , 10.81, , 12.011, , 14.007, , 15.999, , 18.998, , Na, , Mg, , Al, , Si, , P, , S, , Cl, , 22.99, , 24.31, , 26.98, , 28.09, , 30.974, , 32.06, , K, , Ca, , Sc, , Ti, , V, , Cr, , Mn, , Fe, , Co, , Ni, , 39.102, , 40.08, , 44.96, , 47.90, , 50.94, , 50.20, , 54.94, , 55.85, , 58.93, , 58.71, , Ru, , Rh, , Second, series, 5, , First, series, , First, series, Second, series, , Cu, , Zn, , Ga, , Ge, , As, , Se, , Br, , 63.54, , 65.37, , 69.72, , 72.59, , 74.92, , 78.96, , 79.909, , Rb, , Sr, , Y, , Zr, , Nb, , Mo, , Tc, , 85.47, , 87.62, , 88.91, , 91.22, , 92.91, , 95.94, , 99, , Second, series, 6, , 35.453, , Ag, , Cd, , In, , Sn, , Sb, , Te, , I, , 107.87, , 112.40, , 114.82, , 118.69, , 121.75, , 127.60, , 126.90, , 101.07 102.91, , Pd, 106.4, , Cs, , Ba, , La, , Hf, , Ta, , W, , Os, , Ir, , Pt, , 132.90, , 137.34, , 138.91, , 178.49, , 180.95, , 183.85, , 190.2, , 192.2, , 195.09, , Au, , Hg, , Tl, , Pb, , Bi, , 196.97, , 200.59, , 204.37, , 207.19, , 208.98, , • In group II, in the 4th, 5th, 6th period, Zn, Cd, Hg were placed in Group IIB along with Ca, Sr and Ba in, Group IIA., • In Group IIIB, Sc, Y and La are present, B along with Ga, In, Tl are present in Group IIIA., • Group IVA has Ge, Sn, Pb and Group IVB has Ti, Zr, Hf., • Group VA has As, Sb, B, along with Group VB has V, Nb, Ta., • Group VIA has Se, Te, along with Group VIB has Cr, Mo, W., • Group VIIA has Br, I with Mn and Tc in Group VIIB., Fe Co Ni, • Group VIII has Ru Rh Pd (9) elements., Os Ir Pt, , Achievements of Mendeleev’s Periodic table, • He could classify all the elements discovered at that time., • He gave preference to similarity in properties over increasing order of atomic masses., • He left gaps for the undiscovered elements and predicted their properties which made their discovery easier., Scandium, gallium, germanium which were discovered later, have properties as predicted by Mendeleev., • His periodic table helps in correction of atomic masses of some of the elements in the beginning., • Noble gases discovered later could be easily adjusted in his periodic table without disturbing the existing order., , Limitations of Mendeleev’s Periodic Table, • Position of hydrogen was not justified, because it resembles both with alkali metals (group 1) as well as, halogens (group 17)., • Isotopes of an element have different atomic masses but similar chemical properties that posed a challenge, to Mendeleev’s periodic law., , Periodic Classification of Elements 23

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• Increasing order of atomic masses could not be maintained., • Some elements having different properties like transition metals were kept along with alkali metals (Group 1), and (Group 2). Transition metals resemble each other but these were kept in different groups., , Exercise 2.1, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. Up to which element, the Law of Octaves was found to be applicable?, (a) Oxygen , (b) Calcium, (c) Cobalt , (d) Potassium, 2. According to Mendeleev’s Periodic Law, the elements were arranged in the periodic table in the order, of, (a) increasing atomic number, (b) decreasing atomic number, (c) increasing atomic mass, (d) decreasing atomic mass, 3. In Mendeleev’s Periodic Table, gaps were left for the elements to be discovered later. Which of the, following elements found a place in the perioidc table later?, (a) Germanium , (b) Chlorine, (c) Oxygen , (d) Silicon, , II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Increasing order of atomic masses could not be maintained in Mendeleev’s periodic table., , Reason:, , His periodic table helps in correction of atomic masses of some of the elements in the, beginning., 2. Assertion: Dobereiner adjusted two elements in the same slot., , , Reason:, , Dobereiner could not classify all the elements in triads., , III. Very Short Answer Type Questions, , [CBSE 2020], (1 Mark), , 1. Lithium, sodium and potassium form a Dobereiner’s triad. The atomic masses of Li and K are 7 and, 39, respectively. Predict the atomic mass of sodium., 2. Why was the system of classification of elements into triads not found suitable?, 3. Did Dobereiner’s triads also exist in the columns of Newlands’ octaves?, , [NCERT], , 4. What were the limitations of Dobereiner’s classification?, , [NCERT], , 5. Besides Gallium, which other elements have since been discovered to fill the gaps left by Mendeleev in, his periodic table?, [NCERT], 6. What were the criteria used by Mendeleev in creating the periodic table?, , [Delhi 2013], , 7. Why do you think the noble gases are placed in a separate group in the periodic table?, , [Delhi 2013], , 8. Write two reasons responsible for late discovery of noble gases., , [Delhi 2013], , 9. What was the basis of classification of elements by Newlands?, Or, , Define Newlands’ law of octaves., [Delhi 2014], 10. Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by, Mendeleev.[NCERT Exemplar], , 24, , Science-10

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IV. Short Answer Type Questions-I, , (2 Marks), , 1. Elements have been arranged in the following sequence on the basis of their increasing atomic, masses: F, Na, Mg, Al, Si, P, S, Cl, K, (a) Pick up two sets of elements which have similar properties., (b) The above given sequence represents which law of classification of elements?, 2. Can the following group of elements be classified as Dobereiner’s triads? Explain by giving reasons., (a) Na, Si, Cl   (b) Be, Mg, Ca, , [Delhi 2019] [NCERT Exempler], , 3. Write two drawbacks of Mendeleev’s periodic table., 4. What were the limitations of Newlands’ law of octaves?, , [NCERT], , 5. Use Mendeleev’s Periodic table to predict the formulae for the oxides of the following elements:,              K, C, Al, Si, Ba, , V. Short Answer Type Question-II, , (3 Marks), , 1. Study the data of the following three categories A, B and C., Category, A, , B, , C, , Name of the element, , Atomic Mass, , Li, , 7, , Na, , 23, , K, , 39, , N, , 14, , P, , 31, , As, , 74, , B, , 10.8, , Al, , 27, , Ga, , 69.7, , (a) From the given three categories A, B and C, pick the one which forms Dobereiner’s Triads., (b) Why did Mendeleev placed elements of category A, B and C in three different groups?, (c) Is Newland law of octaves applicable to all the three categories? Give reason to justify your answer., [CBSE 2020], , VI. Long Answer Type Questions, , (5 Marks), , 1. (a) Why do we classify elements?, (b) What were the two criteria used by Mendeleev in creating periodic table?, (c) Why did Mendeleev leave some gaps in his periodic table?, (d) In Mendeleev’s periodic table, why was there no mention of noble gases like Helium, Neon and, Argon?, (e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their, different atomic mass or in the same slot because their chemical properties are same? Justify your, answer.[Delhi 2012, 2013, 2015], 2. On the basis of Mendeleev’s Periodic table, answer the following questions:, (a) Name the element which is in, (i) I group and III period., (ii) VII group and II period., (b) Suggest the formula of the following:, (i) Oxide of nitrogen, (ii) Hydride of oxygen, (c) In group VIII of the periodic table, why does cobalt with atomic mass 58.93 appear before nickel, having atomic mass 58.71?, , Periodic Classification of Elements 25

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Answers 2.1, I. 1. (b) It was applicable up to Calcium, , 2. (c) Increasing atomic mass, , 3. (a) Germanium found a place below silicon., II. 1. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , 2. (d) ‘A’ is false but ‘R’ is true., 7 + 39, = 23, 2, , 2. It is because all the elements discovered at that time could not be classified into triads., III. 1. Atomic mass of sodium =, , , 3. Yes, e.g. Li, Na, K is a part of Newlands’ law of octaves., , 4. (i) All the elements could not be classified into triads., (ii) Only three triads could be identified resembling each other., , 5. Scandium and Germanium, , 6. (i) Increasing order of atomic mass, , (ii) Formula of oxides and hydrides, , , 7. It is because these are least reactive and resemble each other., , 8. (i) They are less abundant in nature., , (ii) They are least reactive., , 9. Elements were arranged in increasing order of atomic mass and every 8th element resembled with the, first element., 10. GeCl4, GaCl3., IV. 1. (a) (i) F, Cl (ii) Na, K, , (b) Newlands’ law of octaves, , 58.5, = 29.25, 2, which is nearly equal to 28 but these elements do not resemble with each other., , , 2. (a) No, because atomic mass of Si =, , , (b) Yes, atomic mass of Mg =, , 9 + 40, = 24.5, 2, , which is nearly equal to 24 and these three elements resemble with each other., , 3. (i) I sotopes challenged the basis of Mendeleev’s periodic table., (ii) Increasing order of atomic masses could not be maintained in classifying all the elements., 4. (i) It was applicable upto Ca, i.e. lighter elements only., (ii) New elements could not fit into Newlands’ octaves., 5. K2O, CO2, Al2O3, SiO2, BaO, V. 1. (a) ‘A’ forms Dobereiner’s Triad., (b) It is because they had different formula of oxides and hydrides., (c) No, it was not applicable to elements after Ca(20) because after Ca every eighth element did not, possess similar properties to first., VI. 1. (a) It helps to study the properties of elements in a simpler way by studying the properties of 118, elements by studying properties of 18 groups and 7 periods., (b) (i) Increasing order of atomic mass, (ii) Formula of oxides and hydrides of elements., (c) These gaps were left for the undiscovered elements., (d) Noble gases were not discovered by that time., (e) They will be placed in same slot due to same properties., , 2. (a) (i) Na belongs to 1st group, IIIrd period. (ii) F belongs to VII group, IInd period., , , (b) (i) N2O5 (ii) H2O, (c) It is because Co, Rh, Ir resemble with each other and Ni, Pd, Pt resembles with each other., Similarity in properties were preferred over increasing order of atomic masses., , 26, , Science-10

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Periodic Classification of Elements 27

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Topic 2. Modern Periodic Table, , Atomic number: It is equal to the number of protons. It is also equal to number of electrons in a neutral atom., Henry Moseley showed that atomic number is a more fundamental property than atomic mass of an element, ie. properties of elements depend upon atomic number, , Modern periodic law: Properties of elements are a periodic function of their atomic number., Modern periodic table (Features and Advantages), ●, ●, , ●, ●, ●, ●, , ●, , It is based on increasing order of atomic numbers., It could remove the anomalies of atomic masses, i.e. cobalt has higher atomic mass than nickel but has lower, atomic number and hence placed before nickel., Prediction of properties of undiscovered elements was more accurate., The position of elements was related to their electronic configuration., There are 7 periods (horizontal rows) and 18 groups (vertical columns)., Each period has elements equal to the maximum number of electrons in the shell corresponding to the, period, e.g. 1st period has 2 elements because 1st shell has 2 electrons, 2nd period has 8 elements because, 2nd shell has 8 electrons. 3rd period has 8 elements although 3rd shell can have 18 electrons (maximum),, but if it is the last shell, it cannot have more than 8 electrons. 4th and 5th period have 18 elements each,, although they could accommodate 32 electron. This is because if 4th and 5th shell are the outermost shell, and electrons are filled in the increasing order of energy they could accomodate a maximum of 18 electrons., 6th and 7th period have 32 elements, each., Each group has elements with same number of valence electrons and similar chemical properties but each, period have elements with different number of valence electrons and chemical properties., , The electronic configuration of some main group elements are given below:, Group 1, , Group 18, , H (1), , Group 2, , Group 13, , Group 14, , Group 15, , Group 16, , Group 17, , 1, Li (3), , He(2), , Be (4), , 2, 1, Na(11), , 2, 2, Mg(12), , B(5), 2, 3, , C(6), 2, 4, , N(7), 2, 5, , O(8), 2, 6, , F(9), 2, 7, , 2, 8, 1, K(19), , 2, 8, 2, Ca(20), , Transition, elements, , Al(13), 2, 8, 3, , Si(14), 2, 8, 4, , P(15), 2, 8, 5, , S(16), 2, 8, 6, , Cl(17), 2, 8, 7, , 2, 8, Ar(18), 2, 8, 8, , Group 3 to 12, , Ga(31), , Ge(32), , As(33), , Se(34), , 2, 8, 8, 1, , 2, 8, 8, 2, , 2,8,18,3, , 2,8,18,4, , 2,8,18,5, , 2,8,18,6, , Br(35), 2,8,18,7, , Kr(36), 2,8,18,8, , 2, Ne(10), , Exercise 2.2, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. Which of the following statement(s) about the Modern Periodic Table are incorrect?, (i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic, number, (ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic, masses, (iii) Isotopes are placed in adjoining group(s) in the Periodic Table, (iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic, number, (a) (i) only, (b) (i), (ii) and (iii), (c) (i), (ii) and (iv) (d) (iv) only, 2. Which of the following statements about the Modern Periodic Table is correct?, (a) It has 18 horizontal rows known as Periods, (b) It has 7 vertical columns known as Periods, (c) It has 18 vertical columns known as Groups, (d) It has 7 horizontal rows known as Groups, , 28, , Science-10

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3. Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong, to the same period?, (a) A, B, C, (b) B, C, D, (c) A, D, E, (d) B, D, E, 4. Where would you locate the element with electronic configuration 2, 8 in the Modern Periodic Table?, (a) Group 8, (b) Group 2, (c) Group 18, (d) Group 10, 5. Element ‘X’ forms a chloride with formula XCl2, which is a solid with high melting point. ‘X’ would most, likely to be in the same group of the periodic table as:, (a) Na,, (b) Mg,, (c) Al, (d) Si, [HOTS], 9, 6. On the basis of electronic configuration of 5 X, the group number and period of the element ‘X’ is:, (a) Group 15 period 2 , (b) Group 13 period 2, (c) Group 19 period 5 , (d) Group 13 period 5, [CBSE 2020], 7. An element ‘X’ with atomic number 11 forms a compound with element ‘Y’ with atomic number 8. The, formula of the compound formed is, (a) XY, (b) X2Y, (c) XY2, (d) X2Y3 [CBSE 2020], 8. An element ‘X’ is forming an acidic oxide. Its position in modern periodic table will be, (a) Group 1 and Period 3 (b)Group 2 and Period 3, (c) Group 13 and Period 3, (d) Group 16 and Period 3, [CBSE 2020], 9. Consider the following statements about an element ‘X’ with number of protons 13., (A) It forms amphoteric oxide, (B) Its valency is three, (C) The formula of its chloride is XCl3, The correct statements(s) is/are, (a) only (A), (b) only (B), (c) (A) and (C), (d) (A), (B) and (C)[CBSE 2020], II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 to 4 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: SiCl4 is covalent compound, , Reason: Si can lose electrons and chlorine can gain electron., 2. Assertion: Ionic compounds have high melting point., , Reason: , Ionic compounds do not conduct electricity in solid state., 3. Assertion: The formula of oxide of nitrogen is N2O5. and H2O is oxide of hydrogen., , Reason: N2O5 is acidic oxide H2O is neutral oxide., 4. Assertion: Element with atomic number 118 belongs to group 18., , Reason: Element with atomic number 118 has 8 valence electrons., , III. Very Short Answer Type Questions, , (1 Mark), , 1. State modern periodic law., [Delhi 2013, 2014, CBSE 2018], 2. Write the formula which determines the maximum number of electrons that the shell of an atom can, accommodate.[Delhi 2013, 2014], 3. The electronic configuration of two elements X and Y are 2, 8, 7 and 2, 8, 8, 3 respectively. Write the, atomic numbers of X and Y., [Delhi 2013], 4. Out of the three elements P, Q and R, having atomic number 11, 17 and 19 respectively, which two, elements will show similar properties and why?, [Delhi 2014], 5. Write the number of horizontal rows in the modern periodic table. What are these rows called?, [Delhi 2013, 2014], 6. Explain, why the number of elements in the third period are 8., 7. Name the element having electronic configuration 2, 8, 3. What is its valency?, 8. P(3), Q(12), R(13), S(20), which two elements have similar chemical properties and why?, 9. Where would you locate the element with electronic configuration: 2, 8 in the modern periodic table?, [Delhi 2013], 10. Give the number of elements in 2nd and 5th period of modern periodic table., 11. A metal ‘M’ belongs to 13th group in the modern periodic table. Write the valency of the metal., 12. What is the number of valence electrons in the last element of the 3rd period?, , Periodic Classification of Elements 29

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13. An element ‘X’ belongs to the second group of periodic table. What is the formula of its chloride?, 14. An element ‘B’ belongs to the second period and Group 13. Give the formula of its oxide., 37, and 17, Cl are isotopes of chlorine, would you place them in different slots because their atomic, masses are different? Or would you place them in the same position because their chemical properties, are the same?, [NCERT], 16. Is it possible to have an element with atomic number 1.5 placed between hydrogen and helium?, 17. If an element ‘X’ is placed in group 14, what will be the formula and nature of bonding of its chloride?, [NCERT Exemplar], 18. An element ‘A’ has atomic number 17. To which group and period does it belong?, [Delhi 2016], 19. Find the atomic number of the element whose electronic configuration is 2, 8, 5., [Delhi 2016], 20. An element ‘A’ has atomic number 16. To which group and period does it belong?, [Delhi 2016], 21. Name the scientist who first of all showed that atomic number of an element is a more fundamental, property than its atomic mass., [CBSE 2018], 22. How many metals are present in second period of periodic table?, [CBSE 2020], 23. To which group and period should hydrogen be assigned?, [NCERT], 24. Write the name, symbol and electronic configuration of an element X whose atomic number is 11., [Delhi 2019], , 15., , 35, 17 Cl, , IV. Short Answer Type Questions-I, , (2 Marks), , 1. Predict the maximum number of valence electrons possible for the elements in the first period of, periodic table. , [Delhi 2014], 2. Why lithium with atomic number 3 and potassium with atomic number 19 are placed in group one?, What will be atomic numbers of first two elements of second group?, [Delhi 2016], 3. List two anomalies of Mendeleev’s periodic table which were solved by modern periodic table law., [Delhi 2016], 4. (a) Among the following elements identify the one that would form anions:, , K, O, Na, F, Ca, Cl, Hg, (b) Write the electronic configuration of the anions identified above., [Delhi 2014, 2015], 5. An element belongs to third period and second group of the periodic table:, (a) State number of valence electrons in it. (b) Is it a metal or non-metal?, (c) Name the element. (d) Write the formula of its oxide., [Delhi 2011, 2015], 6. State the reasons for the following:, (a) The elements of the same group have similar chemical properties., (b) The elements of the same period have different properties., [Delhi 2012], 7. (a) State two main characteristics of elements on which modern periodic table is based., (b) No fixed position can be assigned to hydrogen in the periodic table. Why?, [Delhi 2012], 8. (a) State modern periodic law., (b) Elements A, B, C and D have atomic numbers 1, 8, 11 and 19 respectively. Choose the odd element, and give reason for your answer., [Delhi 2012], 9. How it can be proved that the basic structure of the Modern Periodic Table is based on the electronic, configuration of atoms of different elements?, 10. The electronic configuration of an element is 2,8,4. State its:, (a) Group and period in the Modern Periodic Table., (b) Name and write its one physical property., [Delhi 2019], 11. An element ‘X’ has atomic number 13., (a) Write its electronic configuration., (b) State the group to which ‘X’ belong., (c) Is ‘X’ a metal or non-metal?, (d) Write the formula of its bromide.[Delhi 2012], , 30, , Science-10

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12. Choose from the following: 6C, 8O, 10Ne, 11Na, 14Si, (a) Elements that should be placed in the same period., (b) Elements that should be placed in the same group., State the reason for your selection in each case. , , [Delhi 2016], , V. Short Answer Type Questions-II, , (3 Marks), , 1. The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1, 3,, 5 and 7 electrons in the outermost shell respectively. State the period in which these elements can be, placed in the modern periodic table. Write the electronic configuration of the atoms A and D and the, molecular formula of compound formed when A and D will combine., [Delhi 2014, 2015], 2. (a) Predict the following which will form anions and which will form cations:, , (i) Na (ii) Al (iii) Cl (iv) O, (b) Name two elements that are inert., 3. An element P (atomic number 20) reacts with an element Q (atomic number 17) to form a compound., Answer the following questions giving reason:, Write the position of P and Q in the Modern Periodic Table and the molecular formula of the compound, formed when P reacts with Q., [Delhi 2017], 4. From the elements, (a), (b), (c), (d), (e), (f), , 39, 19, , A,, , 28, 14, , B, 16, 8 C and, , 40, 18, , D identify:, , the most electropositive element., a noble gas., a metalloid., an element which will gain 2 electrons to attain nearest noble gas configuration., formula of compound formed between A and C., elements belonging to same period., , VI. Long Answer Type Question, , [CBSE 2020], , (5 Marks), , 1. Name the element which has, (a) the electronic configuration 2, 8, 1, (b) a total of two shells, with 4 electrons in the valence shell., (c) total of three shells, with 3 electrons in valence shell., (d) One shell which is completely filled with electrons., (e) twice as many electrons in the second shell as in the first shell., , [Delhi 2016] [HOTS], , Answers 2.2, I. 1. (b) (i), (ii), (iii) are incorrect statement, only (iv) is correct statement., , 2. (c) It is 18 vertical columns called groups., , 3. (b) B,C,D because they have same number of shells, K, , , 4., 5., 6., 7., , , , L, , A, , 2, , B, , 2, , 1, , C, , 2, , 5, , D, , 2, , 8, , M, , N, , E, 2, 8, 18, 2, (c) Group 18 because they have 8 valence electrons., (b) Mg because its valency is 2 and it forms MgCl2, (b) ‘X’ (2, 3) has 3 valence electrons, so it belongs to group 13 and second period because it has 2 shells., (b) X(2,8,1), Y(2,6), X1 Y 2, X2Y is formula of compound, , Periodic Classification of Elements 31

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8. (d) Group 16 and period 3 is sulphur which is non-metal, will form acidic oxide., 9. (d) It is Al, having 3 valence electrons. Al2O3 is amphoteric oxide. Its valency is 3. The formula for, chloride is AlCl3., II. 1. (c) ‘A’ is true but ‘R’ is false., , 2. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , 3. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , 4. (b) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., III. 1. Properties of elements are a periodic function of their atomic number., 2n2, where ‘n’ represents the number of electronic shell., 17 and 21 respectively., P(11): 2, 8, 1, Q(17): 2, 8, 7, R(19): 2, 8, 8, 1, ‘P’ and ‘R’, because they have the same number of valence electrons., There are 7 horizontal rows. These are called periods., It is because 3rd shell could accommodate a maximum of 18 electrons, but if it is the outermost shell it, could not have more than 8 electrons. Therefore, this period has 8 elements., 7. Aluminium, its valency is equal to 3, because it lose 3 electrons to become stable., 8. P(3): 2, 1; Q(12): 2, 8, 2; R(13): 2, 8, 3; S(20): 2, 8, 8, 2, ‘Q’ and ‘S’ because they have the same number of valence electrons., 9. It belongs to Group 18 and second period of the periodic table., 10. 2nd period has 8 elements, 5th period has 18 elements., 14. B2O3, 11. 3, 12. 8, 13. XCl2, 15. They will be placed in the same slot., 16. No, atomic number cannot be in fractions., 17. XCl4, it has covalent bonding., 18. Its electronic configuration is 2, 8, 7. It belongs to group 17 and 3rd period., 19. Its atomic number is equal to 2 + 8 + 5 = 15., 20. It belongs to group 16 and third (3rd) period., 21. Henry Moseley, 22. There are two metals Lithium (Li) and Beryllium (Be) in second period of periodic table., 23. It is placed in Group 1 and first period., 24. Sodium, Na: 2,8,1, IV. 1. 2 valence electrons are present in the last element ‘Helium’ of 1st period., 2., 3., 4., , 5., 6., , 2. , KLMN, Li(3), 2, 1, K(19), 2, 8, 8, 1, Li and K are placed in Group 1 because both have 1 valence electron., Be(4) and Mg(12) are first two elements of Group 2., 3. (i) Position of isotopes were not justified in Mendeleev’s periodic table but it is justified in the modern, periodic table., (ii) Increasing order of atomic masses could not be followed but increasing order of atomic numbers, has been followed., 4. (a) O, F, Cl will form anions., (b) O2–(10), 2, 8, F–(10), 2, 8, 2, 8, 8., Cl–(18), 5. (a) 2, 8, 2 is the electronic configuration. The number of valence electrons = 2, (b) It is a metal, (c) Magnesium, (d) MgO is the formula of its oxide., 6. (a) It is because they have the same number of valence electrons., (b) It is because they differ in the number of valence electrons., , 32, , Science-10

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7. (a) (i) Atomic number, (ii) No. of valence electrons, (b) It is because hydrogen resembles with Group 1 as well as Group 17 elements, therefore no fixed, position can be assigned to it., 8. (a) Modern Periodic Law: It states that the properties of elements are a periodic function of their, atomic number., (b) ‘B’ with atomic number 8 is an odd element because it has 6 valence electrons whereas others have, 1 valence electron., 9. Position of element in periodic table is decided with the help of electronic configuration e.g. group number, is decided on the basis of valence electrons e.g., elements having valence electrons 1,2,3,4,5,6,7,8,, belong to Group 1, 2, 13, 14, 15, 16, 17 and 18 respectively., Period is equal to number of shells e.g. 2,8,3 belong to third period., 10. (a) It belongs to Group 14, third period., (b) Silicon is the element. It is a metalloid, forms covalent bond. It is a semiconductor., 11. (a) 2, 8, 3, (b) Group 13, (c) Metal, (d) AlBr3, 12. (a) 6C, 8O, 10Ne belong to the same period because all these have 2 shells.,   11Na, 14Si belong to the same period because both of these have 3 shells., (b) 6C and 14Si belong to the same group because they have the same number of valence electrons and, valency., V. 1. They belong to third period because these have 3 shells., A has electronic configuration 2, 8, 1, valence electron 1, valency = 1, D has electronic configuration 2, 8, 7, valence electron 7, valency = 1, , Formula: AD or A+D–, 2. (a) Cl and O will form anions, , Na and Al will form cations, (b) He, Ne are inert., 3. Atomic number of element P = 20, Electronic configuration of element P = 2, 8, 8, 2, Atomic number of element Q = 17, Electronic configuration of element Q = 2, 8, 7, , The position of P in the Modern Periodic Table, Period (Number of shells) = 4, Group (Electrons in outer-most shell) = 2, , The position of Q in the Modern Periodic Table, Period (Number of shells) = 3, Group (Electrons in outer-most shell) = (10 + 7) = 17, When P reacts with Q, it loses the two valence electrons (valency 2)., These two valence electrons are accepted by two Q atoms (valency 1). , Hence, the formula of the compound formed between P and Q is PQ2., 4. (a), (c), (d), , 39, 19, , A is most electropositive element (b), , 28, 14, , B is metalloid, , 16, 8, , C will gain 2 electrons to attain nearest noble gas configuration, , (e) A1, , 40, 18, , D is noble gas, , C2, , A2C, (f), , 28, 14, , B,, , 40, 18, , D belong to same period i.e. 3rd period because they have 3 shells, , VI. 1. (a) Sodium (2, 8, 1), , (b) Carbon (2, 4), , (d) Helium (2), , (e) Carbon (2, 4), , (c) Aluminium (2, 8, 3), , Periodic Classification of Elements 33

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Topic 3. Trends in the Modern Periodic Table, , Valency: Valency increases from left to right till the middle and then decreases in the modern periodic table., Valency remains the same in a group, because valence electrons remains the same., Atomic size: It goes on increasing down the group, because number of shells goes on increasing and effective, nuclear charge decreases., It decreases from left to right in a period due to increase in effective nuclear charge, because one proton and, 1 electron is being added successively, number of shells remains the same, forces of attraction between the, nucleus and valence electrons increases., Metallic and Non-metallic properties: On the right hand side of periodic table, there are non-metals. Metals, are on the left and middle region of periodic table. Metalloids are placed on the borderline of metals and nonmetals, aligned in a zig-zag manner, e.g. B, Si, Ge, As, Sb, Te and Po are metalloids., Tendency to lose electrons: Tendency to lose electrons decreases along a period, because atomic size decreases, and effective nuclear charge increases. Tendency to lose electrons increases down the group, because atomic, size increases and effective nuclear charge decreases. Metallic character decreases along the period, e.g. Na >, Mg > Al. Metallic character increases down the group, e.g. K > Na > Li., Tendency to gain electrons: Tendency to gain electrons increases along a period, ... effective nuclear charge, increases. So as electronegativity increases, non-metallic character increases, e.g. F > O > N > C. Tendency to, gain electrons decreases down the group, ... effective nuclear charge decreases. Therefore, electronegativity, decreases, non-metallic character decreases, e.g. F > Cl > Br > I., Reactivity of metals: It increases down the group, because tendency to lose electrons increases, e.g. Li < Na < K., It decreases along a period due to increase in effective nuclear charge, tendency to lose electrons decreases,, e.g. Al < Mg < Na., Reactivity of Non-metals: It decreases down the group, ... tendency to gain electrons decreases due to increase, in atomic size, e.g. F > Cl > Br > I. Reactivity of non-metals increases along a period due to decrease in atomic, size and increase in tendency to gain electrons, e.g. N < O < F., Basic nature of oxides: It decreases along a period, but increases down the group., Acidic nature of oxides: It decreases down the group, but increases along a period., Stability of noble gases: The atoms of Group 18 elements have a very stable arrangement of electrons in, their outermost valence shell. This makes them unreactive., Cations and anions: Metals lose electrons to form +ve ions (cations), non-metals gain electrons to form –ve, , ions (anions)., • Cations are smaller than neutral atoms due to more effective nuclear charge., • Anions are bigger than neutral atoms due to less effective nuclear charge., • Group 1 and Group 2 elements form ionic compounds with Group 16 and Group 17 elements., • Group 14 elements mostly form covalent compounds., • Metals are mostly solids, except mercury which is a liquid. Non-metals exist as solids, liquids and in gaseous, state, e.g. F2, Cl2, H2, N2, O2 are gases; Br2 is liquid; C, S, P, I2 are solids., • Group 18 elements all are gases. Group 17 and 18 elements are all non-metals. Group 1 and Group 2 elements, are all metals., • Metallic character increases down the group due to increase in tendency to lose electrons., • Metallic character decreases along a period from left to right because tendency to lose electrons decreases., • Non-metallic character decreases down the group as tendency to gain electrons decreases. It increases along, a period due to increase in tendency to gain electrons., , Exercise 2.3, I. Multiple Choice Questions, Choose the correct answer from the given options., 1. Which of the following gives the correct increasing order of the atomic radii of O, F and N?, (a) O < F < N, (b) N < F < O, (c) O < N < F, (d) F < O < N, 2. Which among the following elements has the largest atomic radii?, (a) Na, (b) Mg, (c) K, (d) Ca, , 34, , Science-10, , (1 Mark)

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3. Which of the following elements would lose an electron easily?, (a) Mg, (b) Na, (c) K, (d) Ca, 4. Which of the following elements does not lose an electron easily?, (a) Na, (b) F, (c) Mg, (d) Al, 5. The positions of four elements A, B, C and D in the modern periodic table are shown below. Which, element is most likely to form an acidic oxide?, , A, B, C, D, , (a) A, , (b) B, , (c) C, , (d) D, , [CBSE Sample Paper 2019-2020], 6. Elements P, Q, R and S have atomic numbers 11, 15, 17 and 18 respectively. Which of them are reactive, non-metals?, (a) P and Q, (b) P and R, (c) Q and R, (d) R and S, [CBSE Sample Paper 2019-2020], , II. Assertion-Reason Type Questions, , (1 Mark), For question numbers 1 to 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: X with atomic number 13 is a metal., , Reason: It belongs to group 13 and 3rd period., 2. Assertion: Carbon is a metalloid., , Reason: Carbon forms CO2 which is acidic oxide whereas CO is neutral oxide., , III. Very Short Answer Type Questions, , (1 Mark), , 1. Which is smaller: (i) Na or Na, (ii) Cl or Cl ?, 2. How does metallic character (electropositive character) varies down the group?, 3. Which has smaller size: K(19) or Na(11); B(5) or C(6)?, 4. How does valency vary in a (i) period on going from left to right, (ii) group?, 5. On moving from left to right in the second period, what happens to the number of valence electrons?, 6. How does atomic size vary from left to right in a periodic table?, 7. How does reactivity of metals vary down the group?, 8. Give any one difference in the electronic configuration of Group 1 and Group 2 elements.[Delhi 2014], 9. Out of Li and K, which one have stronger metallic character and why?, [Delhi 2016], 10. “Fluorine is more electronegative than iodine”. Give reason in support of this., 11. List any two properties of the elements belonging to the first group of modern periodic table., [Delhi 2014], 12. The formula of magnesium oxide is MgO. State the formula of barium nitrate and barium sulphate, if, barium belongs to the same group., [Delhi 2012], 13. The electronic configuration of two elements ‘A’ and ‘B’ are 2, 8, 7 and 2, 8, 8, 2, respectively. Write the, atomic number of these elements. What will be the formula of the compound formed and the nature of, bond between them, when these elements chemically combine together?, [Delhi 2012], +, , –, , Periodic Classification of Elements 35

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14. Which has larger atomic radius, K(19) or Ca(20)?, [Delhi 2016], 15. What would be nature of oxides formed by the elements on the right hand side of periodic table?, [Delhi 2014], 16. Arrange the following metals in decreasing order of atomic size:, Ca, Mg, Ba, Be, [Delhi 2014], 17. How does valency of an element vary across a period?, [CBSE Sample Paper 2019-2020], 18. Define electropositivity., [CBSE 2020], 19. The atomic radii of first group elements are given below:, Group-1 element, , Atomic Radii (pm), , Na, K, Rb, Cs, , 86, 231, 244, 282, , State the reason behind the observed trend in the above elements., 20. Write the number of valence electrons present in a nitrogen atom, , (, , [CBSE 2020], , 14, 7, , IV. Short Answer Type Questions-I , , N) .[CBSE 2020], , (2 Marks), , 1. How does the valency of an element be determined, if its electronic configuration is known? What will be, the valency of an element with atomic number 9?, [Delhi 2012, 2011], 2. How does the metallic character of elements changes along a period of the periodic table from left to, right and why?, [Delhi 2011], 3. In the periodic table, how does the tendency of an atom to lose electrons changes on moving from (i) left, to right across a period?, (ii) top to bottom in a group?, [Delhi 2011], 4. What is meant by periodicity of properties of elements? Why are the properties of elements placed in, the same group of periodic table similar? , [Delhi 2011], 5. How does electronegativity of an element change as we go down a group and across a period? Give, reason., 6. Which is bigger (i) O or F, (ii) N or P and why?, 7. Calcium is an element with atomic number 20, (i) Will it be a metal/non-metal?, (ii) What will be its valency?, (iii) What would be formula of its chloride?, (iv) Will it be larger/smaller than K? , [Delhi 2016], 8. Three elements ‘X’, ‘Y’ and ‘Z’ having atomic numbers 11, 7 and 6 respectively react with oxygen to, form their oxides., (a) Arrange these oxides in increasing order of their basic nature., (b) Give reason for your answer., 9. Given below are four elements with their atomic numbers:, Element, A, B, C, D, , Atomic Number, 16, 11, 3, 14, , (a) Identify the element which belong to same group of Modern Periodic Table., (b) Arrange the given elements in decreasing order of atomic size., (c) Write the formula of the oxide of ‘B’., (d) Which of the above element is a metalloid?, [Delhi 2011], 10. Give reasons for the following:, (a) Lithium atom is smaller than sodium atom., (b) Chlorine (Atomic number 17) is more electronegative than sulphur (Atomic number 16).[Delhi 2011], , 36, , Science-10

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11. Two elements ‘M’ and ‘N’ belong to Group I and II respectively and are in the same period of the, periodic table. How do the following properties of M and N vary:, (a) size of their atoms, (b) their metallic characters, (c) their valencies in forming oxides, (d) formulae of their chlorides [Delhi 2012], 12. The following table shows elements represented by the letters A, B, C, D, E, F, G and H:, Group, , 1, , 2, , 13, , 14, , 15, , 16, , 17, , 18, , Element, , A, , B, , C, , D, , E, , F, , G, , H, , (i) Which of the element has the atomic size (a) biggest and (b) smallest?, (ii) Which element has valency (a) 3 and (b) Zero, 13. What is a metalloid? Name any one of them., 14. What is place of metalloid in the periodic table?, , [Delhi 2012], [Delhi 2011], [Delhi 2011], , V. Short Answer Type Questions-II, , (3 Marks), , 1. An element ‘X’ belongs to 3rd period and group 16 of the modern periodic table., (i) Determine the number of valence electrons and valency of ‘X’., (ii) Molecular formula of the compound, when ‘X’ reacts with hydrogen and write its electron dot structure., (iii) Name the element ‘X’ and state whether it is metallic or non-metallic., [Delhi 2016], 2. An element ‘M’ with electronic configuration (2, 8, 2) combines separately with NO3–, SO42– and PO43–, radicals. Write the formulae of three compounds so formed. To which group and period of modern, periodic table, ‘M’ belongs to? Will ‘M’ form covalent or ionic compounds? Give reason to justify your, answer.[HOTS] [Delhi 2016], 3. In the following table, the position of six elements A, B, C, D, E and F are given as they are in the, modern periodic table as follows:, Group Æ, 1, , 2, , 3–12, , 13, , 14, , 15, , 16, , 17, , 18, , Period Ø, 2, , A, , C, , 3, , B, , E, , D, F, , On the basis of above table, answer the following questions:, [HOTS], (i) Name the element which form only covalent compounds., (ii) Name the element which is a metal with the valency of 3., (iii) Name the non-metal with the valency of 3., (iv) Out of B and C, whose atomic size is bigger and why?, (v) Write the common name for the family to which the elements D and F belongs to., 4. Based on the group valency of elements, state the formula of the following, giving justification for each., (i) Oxides of Group 1 elements., (ii) Halides of the elements of Group 13., (iii) Compounds formed when an element of group 2 combines with an element of Group 16., [Delhi 2014] [HOTS], 5. In the following table, are given eight elements A, B, C, D, E, F, G and H (here letters are not the, usual symbols of the elements) of the Modern Periodic Table with atomic numbers of the elements in, parenthesis., , (i), (ii), (iii), (iv), , Period, , Group 1, , Group 2, , 2, 3, 4, 5, , A (3), B (11), C (19), D (37), , E (4), F (12), G (20), H (38), , What is the electronic configuration of F?, What is the number of valence electrons in the atom F?, What is the number of shells in the atom F?, Write the order of size of the atoms of E, F, G and H in decreasing order., , Periodic Classification of Elements 37

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(v) State whether F is a metal or a non-metal., (vi) Out of the three elements B, E and F, which one has the biggest atomic size?, [Delhi 2016] [HOTS], 6. Table given below shows a part of the periodic table:, H, , He, , Li, , Be, , B, , C, , N, , O, , F, , Ne, , Na, , Mg, , Al, , Si, , P, , S, , Cl, , Ar, , Using this table, explain why, (i) Li and Na are considered as active metals?, (ii) Atomic size of Mg is less than that of Na?, (iii) Fluorine is more reactive than chlorine? , [HOTS], 7. What is the position i.e. group number, period number of element, iodine (atomic number 53)? What is, the physical state and nature of this element (metal or non metal)?, [HOTS], 8. Consider the following and answer the questions that follow:, , 9., 10., , 11., , 12., , , 13., , 14., , 38, , Group 1, , Group 2, , Group 3, , A, D, G, , B, E, H, , C, F, I, , (i) Amongst A, D and G, which is not electropositive and why?, (ii) Atomic size of H is bigger than B. Why?, (iii) Write the formula of compound formed by the element E and fluorine., [HOTS], Explain the basic character of oxides of elements down the group and across the period. [Delhi 2016], The atomic number of Na and Mg is 11 and 12 respectively and they belong to same period., (a) Which one would have smaller atomic size?, (b) Which one would be more electropositive?, (c) To which group would each one belongs?, Two elements ‘P’ and ‘Q’ belong to the same period of the modern periodic table and are in Group 1 and, 2 respectively. Compare the following characteristics in tabular form:, (a) The number of valence electrons in their atom., (b) Their metallic character, (c) The size of their atoms, (d) The formulae of their oxides, (e) Their tendency to lose electrons, (f) The formula of their chloride , [Delhi 2015], Given below are some elements of modern periodic table. Atomic number of elements are given in, parenthesis:, A(4), B(9), C(14), D(19), E(20), (a) Select the element that has one electron in outermost shell. Also write the electronic configuration, of this element., (b) Which two elements amongst there belong to the same group? Give reason for your answer., (c) Which two elements amongst there belong to the same period? Which one of the two has bigger, atomic radius? , [Delhi 2015], The elements Be, Mg and Ca are having two electrons in their outermost shells are in periods 2, 3 and, 4, respectively of the modern periodic table. Answer the following questions, giving justification in each, case., (i) Write the group to which these elements belong., (ii) Name the least reactive element., (iii) Name the element having largest radius. , [Delhi 2014, 2015], What is meant by ‘group’ in the modern periodic table? How do the following changes occur on moving, from top to bottom in a group?, (i) Number of valence electrons, (ii) Number of occupied shells, (iii) Size of Atoms, (iv) Metallic character of elements, (v) Effective nuclear charge experienced by valence electrons., , Science-10

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15. Write the number of periods and groups in the Modern Periodic Table. How does the metallic character, of elements vary on moving (i) from left to right in a period, and (ii) down a group? Give reason to, justify your answer., [AI 2017], 16. Na, Mg and Al are the elements of the 3rd period of the Modern Periodic Table having group number, 1, 2 and 13 respectively. Which one of these elements has the (a) highest valency, (b) largest atomic, radius, and (c) maximum chemical reactivity? Justify your answer stating the reason for each., [AI 2017], 17. Two elements X and Y have atomic numbers 12 and 16 respectively. To which period of the modern, periodic table do these two elements belong? What type of bond will be formed between them and why?, Also give the chemical formula of the compound formed., 18. Write the names given to the vertical columns and horizontal rows in the Modern Periodic Table. How, does the metallic character of elements vary on moving down a vertical column? How does the size of, atomic radius vary on moving left to right in a horizontal row? Give reason in support of your answer in, the above two cases. , [Delhi 2017], 19. The electronic configuration of an element ‘X’ is 2,8,6. To which group and period of the modern, periodic table does ‘X’ belong .State it valency and justify your answer in each case., 20. Based on the group valency of elements write the molecular formula of the following compounds giving, justification for each, (i) Oxides of first group elements, (ii) Halides of group 13 and, (iii) Compound formed when an element A of group 2 combines with element B of group 17, [Delhi 2019], 21. How is possible valency of element determined with the help of electronic configuration of its atom?, Determine the valency of ‘X’ whose atomic number is 15., 22. The following table shows the position of five elements A, B, C, D and E in the modern periodic table., , 3, Group→, Period ↓, , 1, , 2, , A, , 2, , 3 to 12, , 13, , 14, , 15, , 16, , 17, , 18, , B, , C, , 3, D, E, Answer the following giving reasons:, (i) Which element is a metal with valency two?, (ii) Which element is least reactive?, (iii) Out of D and E which element has a smaller atomic radius?, , VI. Long Answer Type Questions, , (5 Marks), , 1. Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells, but, different number of electrons in their outermost shell. It was found that elements A and G combine to, form an ionic compound. This compound is added in a small amount to almost all the vegetable dishes, during cooking. Oxides of elements A and B are basic in nature, while those of E and F are acidic. The, oxide of D is almost neutral. Based on the above information, answer the following questions:, (i) To which group or period of the periodic table do the listed elements belongs to?, (ii) What would be the nature of compound formed by the combination of elements B and F?, (iii) Which two of these elements could definitely be metals?, (iv) Which one of the eight elements is most likely to be found in gaseous state, at room temperature?, (v) If the number of electrons in the outermost shell of elements C and G are 3 and 7 respectively,, then write the formula of the compound formed by the combination of C and G., [Delhi 2010] [HOTS], 2. The nucleus of five elements D, E, F, G and H are shown below:, D, 3P, 3N, , E, 9P, 10N, , F, 17P, 18N, , G, 11P, 12N, , H, 19P, 20N, , P = Protons, N = Neutrons, , Periodic Classification of Elements 39

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3., , 4., , 5., , 6., , (i) Identify D and E., (ii) Identify the position of F and H in the periodic table., (iii) What is the cause of similarity among the species D, G, H?, (iv) What will be the formula of compound formed between D and E?, (v) Which is largest in size among D, E, F, G and H?, [HOTS], (i) Which element can lose electrons most easily in 3rd period and why?, (ii) Why does tendency to lose electrons increases down the group?, (iii) What happens to the basic character of oxides down the group and why?, (iv) What happens to the acidic character of oxides along a period and why?, (v) Which group of elements can gain electrons most easily and why?, An element X of group 15 exists as a diatomic molecule and combines with hydrogen at 773 K, in the, presence of a catalyst to form a compound ammonia, which has a characteristic pungent smell., (i) Identify the element X. How many valence electrons does it have?, (ii) Draw the electron dot structure of diatomic molecule of X. What type of bond is formed in it?, (iii) Draw the electron dot structure for ammonia and what type of bond is formed in it?[HOTS], An element X, which is a yellow solid at room temperature shows catenation and allotropy. X forms, two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and, are the major air pollutants., (i) Identify the element X., (ii) Write the electronic configuration of X., (iii) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals., (iv) What would be the nature (acidic/basic) of the oxides formed?, (v) Locate the position of the element in the modern periodic table. , [HOTS], The atomic radius of element of second period are given below:, Second period of elements, , B, , Be, , O, , N, , Li, , F, , C, , Atomic Radius (pm), 88, 111, 66, 74, 152, 64, 77, (i) Arrange these elements in decreasing order of atomic radius., (ii) Are the elements now arranged in the pattern of period in the periodic table?, (iii) Name the element which has (a) largest (b) smallest atomic size., (iv) From the above data, infer how the atomic size or radius of elements changes as we go from left, to right in a period., (v) Name one metal, one non-metal and a metalloid from these elements., (vi) Why does atomic radius decrease as we move from left to right in a period?, 7. (a) How is valency of an element determined if its electronic configuration is known? Determine the, valency of an element of atomic no. 9, (b) Given below are some elements of modern periodic table. Atomic number of elements are given in, parentheses., A (4), B (9), C (14), D (19), E (20), (i) With the help of electronic configuration, find out which ore of the above elements will have one, electron in its outermost shell., (ii) Which two elements belong to the same group? Give reasons for your answer., (iii) Which one of the above element belonging to the fourth period has bigger atomic radius and why?, , [CBSE 2019], 8. Explain giving justification the trends in the following properties of elements, on moving from left to, right in a period, in the Modern Periodic Table., (a) Variation of valency, (b) Change of atomic radius, (c) Metallic to non-metallic character (d) Electronegative character, (e) Nature of oxides, [CBSE 2018(C)], 9. (a) List any three observations which posed a challange to Mendeleev’s periodic table., (b) How does the mettallic character of elements vary on moving from, (i) Left to right in a period., (ii) From top to bottom in a group of the Modern periodic table? Give reason for your answer., , 40, , Science-10

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10. The position of certain elements in the Modern Periodic Table are shown below:, Group, →, , 1, , 2, , 3 to 12, , 13, , 14, , 15, , 16, , 17, , 18, , ↓Period, 1, , G, , 2, , A, , 3, , H, I, D, , B, E, , C, F, , Using the above table answer the following questions giving reasons in each case:, (i) Which element will form only covalent compounds?, (ii) Which element is a non-metal with valency 2?, (iii) Which element is a metal with valency 2?, (iv) Out of H, C and F which has largest atomic size?, (v) To which family does H, C and F belong?, [CBSE 2020], 11. Define atomic size. Give its unit of measurement. In the modern periodic table what trend is observed in, the atomic radius in a group and a period and why is it so?, [CBSE 2020], , Answers 2.3, I. 1. (d) F < O < N  Number of protons and electrons are decreasing, so effective nuclear charge decreases,, and atomic size increases., , 2. (c) K (2,8,8,1) is largest due to least effective nuclear charge as it has 19 protons and 19 electrons and, four shells., , 3. (c) ‘K’ because it has largest atomic size, least effective nuclear charge, therefore, can lose electron easily., , 4. (b) ‘F’ is non-metal, it cannot lose electron easily. It can gain electron easily to become stable., , 5. (c) C is non-metal, it will form acidic oxide, , 6. (c) Q (2, 8, 5) and R (2, 8,7) are reactive non-metals (Phosphorus and Chlorine), II. 1. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , 2. (d) ‘A’ is false but ‘R’ is true., III. 1. (i) Na+, (ii) Cl, 2. It increases down the group., 3. Na(11) is smaller in size than K(19), C(6) is smaller in size than B(5)., 4. (i) In a period, valency first increases till the middle and then it decreases., (ii) In a group, it remains the same., 5. Valence electrons keeps on increasing from left to right in the second period., 6. Atomic size decreases along a period from left to right in the periodic table., 7. It increases down the group., 8. Group 1 elements have 1 valence electron and are more reactive than Group 2 elements which have, two valence electrons., 9. ‘K’, because it can lose electrons easily due to larger size and less effective nuclear charge., 10. ‘F’ is smaller in size than I, therefore the tendency to gain electrons is more due to more effective, nuclear charge., 11. (i) They should have valency equal to 1 and form monovalent positive ions., (ii) They are highly reactive soft metals., 12. Ba(NO3)2, BaSO4, 13. A has atomic number ‘17’, ‘B’ has atomic number ‘20’., BA2 is the formula of the compound. The bond formed between A and B will be ionic bond., 14. K(19) is larger than Ca(20)., 15. Acidic, 16. Ba > Ca > Mg > Be, 17. The valency of an element first increases and then decreases across a period., , Periodic Classification of Elements 41

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18. It is defined as measure of tendency to lose electrons. The greater the tendency to lose electrons, more, will be electropositivity., 19. Atomic radii increases down the group because number of shells go on increasing, effective nuclear, charge decreases, distance between nucleus and valence shell increases., 20. It has 5 valence electrons., IV. 1. Valency is equal to the number of valence electrons when valence electrons are from 1 to 4 or 8 – no. of, valence electrons when valence electrons are from 5 to 8., F(9): 2, 7; It can gain 1 electron to become stable, so its valency = 1., 2. It decreases due to decrease in atomic size and decrease in tendency to lose electrons., 3. (i) It decreases due to increase in effective nuclear charge., (ii) It increases due to decrease in effective nuclear charge., 4. The repetition of similar properties of elements after a certain interval of elements is called periodicity, of properties., Elements of the same group have same number of valence electrons, same valency and therefore posses, similar chemical properties., 5. Electronegativity decreases down the group due to increase in atomic size and decrease in effective, nuclear charge., Electronegativity increases along a period due to decrease in atomic size and increase in effective, nuclear charge., 6. O is bigger in size than F due to less effective nuclear charge., P is bigger in size than N due to more number of shells., 7., (i) It is a metal., (ii) Its valency is equal to 2., (iii) CaCl2 is the formula of its chloride. (iv) It will be smaller than K., , :, , 8. X(11): 2, 8, 1;, Y(7): 2, 5; Z(6): 2, 4, (a) Y < Z < X, (b) ‘X’ is metallic in nature, therefore it will form basic oxide. ‘Y’ and ‘Z’ are non-metals will form acidic, oxides. ‘Y’ will form more acidic oxide than ‘Z’ because it is more non-metallic in nature., 9. (a) ‘B’ and ‘C’ belong to same group., (b) B > D > A > C , (c) B2O, (d) ‘D’ is a metalloid., 10. (a) It is because Li(2, 1) has two shells whereas Na(2, 8, 1) has three shells., (b) Chlorine is smaller in size and has more effective nuclear charge than sulphur, therefore it is more, electronegative., 11. (a) Size of ‘N’ is smaller than ‘M’., (b) ‘M’ is more metallic than ‘N’., (c) Valency of ‘M’ is 1 and valency of ‘N’ is 2., (d) MCl and NCl2 are the formulae of their chlorides., 12. (i) (a) ‘A’ is biggest in size, (b) ‘G’ is smallest in size, (ii) (a) ‘C’ has valency 3., (b) H has zero valency, 13. The element which resembles both with metals and non-metals is called a metalloid, e.g. Boron, Silicon., 14. They are placed between metals and non-metals in a zig-zag manner., V. 1. (i) The element is S(16)—2, 8, 6, The number of valence electrons—6, Valency—2., , :, , (ii) H : S : H, , , H2S, , (iii) Sulphur, non-metallic., 2. Mg(NO3)2, MgSO4, Mg3(PO4)2, It belongs to Group 2, 3rd period of the periodic table., It will form ionic compounds because it can lose 2 electrons easily to form Mg2+ ions., 3. (i) E, (ii) B, (iii) C, (iv) B, ... It has more number of shells, (v) Noble gases, , 4. (i) Group 1 elements can lose one electron to become stable, so its valency is equal to 1, M2O., , 42, , Science-10

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(ii) Group 13 elements have valency equal to 3, MCl3., (iii) Group 2 elements have valency equal to 2, Group 16 elements have 6 valence electrons., M2+, O2–, Thus, formula of oxide:, , MO, , , \ valency = 2, 5. (i) F(12) 2, 8, 2; (ii) 2; (iii) 3;, (iv) H > G > F > E; (v) F is a metal;, (vi) B has biggest atomic size., , 6. (i) Li and Na can lose electrons easily due to their large size and hence are more reactive., (ii) Mg has more effective nuclear charge than Na., (iii) Fluorine can gain electrons more easily than chlorine, due to smaller atomic size., 7. I(53): 2, 8, 18, 18, 7, It belongs to group 17, 5th period., It is a solid. It is a non-metal., 8. (i) ‘A’ is not electropositive because it is hydrogen which is considered as a non-metal., (ii) ‘H’ has more number of shells than ‘B’, therefore it has bigger atomic size., (iii) EF2 is the formula of fluoride of ‘E’., 9. Basic character of oxides increases from top to bottom in a group because metallic character increases, down the group due to increase in tendency to lose electrons., Basic character of oxide decreases along a period from left to right because the atomic size decreases,, tendency to lose electrons decreases, metallic character decreases., 10. (a) Magnesium has smaller size than Na., (b) Na is more electropositive than Mg., (c) Na belongs to Group 1, Mg belongs to Group 2., 11., , Property, (a) Valence electrons, (b) Size, (c) Metallic character, (d) Tendency to lose electrons, (e) Formula of oxide, (f) Formula of Chloride, , P, , Q, , 1, Bigger, More metallic, More, P2O, PCl, , 2, Smaller, Less metallic, Less, QO, QCl2, , 12. (a) D(19) has one valence electron. Its electronic configuration is 2, 8, 8, 1., (b) A(4), E(20) belong to same group because they have same number of valence electrons., (c) A and B belong to same period, A is bigger than ‘B’., , D and E also belong to same period, ‘D’ is bigger than E., 13. (i) They belong to Group 2 because they have 2 valence electrons., (ii) Be is the least reactive element due to smallest size and least tendency to lose electrons., (iii) Ca has largest radius because it has the most, four shells (2, 8, 8, 2)., 14. The vertical columns of periodic table are called Groups., (i) Number of valence electrons remains the same., (ii) Number of occupied shells goes on increasing., (iii) Size of atoms increases down the group., (iv) Metallic character of elements increases down the group., (v) Effective nuclear charge decreases., 15. In the Modern Periodic Table, there are 18 vertical columns known as Groups and 7 horizontal rows, known as Periods. , , Metallic character: It is defined as the tendency of an atom to lose electrons., , Periodic Classification of Elements 43

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Across the period i.e., from left to right: Metallic character decreases., Down the group i.e., from top to bottom: Metallic character increases., , Reason: Across the period, the effective nuclear charge increases, thus decreasing its atomic radius., This favours the increase of electronegativity and therefore the tendency to lose electrons is less. This, accounts for the decrease in the metallic character along the period., But as we move down the group the number of shells keep on increasing and therefore the atomic size, increases. This means that the electronegativity decreases. This enhances the ability to lose electrons, and therefore the metallic character increases down the group., 16. Given are the three elements Na, Mg and Al belonging to group 1 , 2 and 13 respectively., The electronic configurations of the three elements are as follows:, Element Name, , Symbol, , Atomic Number, , Electronic Configuration, , Sodium, , Na, , 11, , 2, 8, 1, , Magnesium, , Mg, , 12, , 2, 8, 2, , Aluminium, , Al, , 13, , 2, 8, 3, , (a) The element having the highest valency signifies the maximum number of electrons present in the, valence shell of an atom. Hence, as per the given electronic configurations, the element having highest, valency is aluminium (Al)., (b) As we move across the period, i.e., from left to right the atomic radius decreases. Therefore the, element having the largest atomic radius will be sodium (Na)., (c) The given three elements are metals. So, the chemical reactivity of a metal is determined by its metallic, character which is the tendency of an atom to lose its electrons. We know that the metallic character, of element decreases across the period, i.e., from left to right. So, the element having highest chemical, reactivity is sodium (Na)., 17. Electronic configuration of X: 2,8,2, Y: 2,8,6, Both X and Y belong to 3rd period because they have 3 shells., Ionic bond will be formed., , Reason: X will lose 2 electrons and Y will gain 2 electrons to complete their octet and become stable., , , , ⋅⋅ , ⋅⋅ : , , Formula is ( X 2 + )  : Y, , , , 2−, , 18. In the Modern Periodic Table, there are 18 vertical columns known as Groups and 7 horizontal rows, known as Periods., As we move down the group, the electrostatic attraction between the nucleus and the outer-most, electron decreases due to increase in the distance between them. This happens because, on moving, down the group, a new shell is added. So the valence electrons can be easily lost by the element. As we, know, metallic character is characterised by the ease of loss of electrons, thereby, metallic character, increases on moving down the group in the Modern Periodic Table., When we move across a period, the number of electrons in the same shell increases. This leads to, greater electrostatic attraction between the nucleus and the outer-most electron. This increased, attraction pulls the outer-most electron closer to the nucleus, thereby decreasing the atomic size., 19. X – 2, 8, 6, (a) Since ‘X’ has three energy shells and period number of an element is equal to the number of energy, shells. So, X belongs to 3rd period., (b) X has 6 valence electrons so, it belongs to group 16., (c) Valency will be 2. To acquire noble gas configuration it will gain 2 electrons., 20. (i) Group 1 elements have valency equal to 1., , Li+ O2–, Li2O, , 44, , Science-10, , Na+, , O2­–, , Na2O

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(ii) Group 13 elements have 3 valence electrons, B3, valency equal to 3, , Cl1, BCl3, , (iii) A2, , Al3 Cl1, AlCl3, , B1, , AB2, , ... A has valency equal to 2 and B has valency equal to 1., 21. Valency is equal to number of valence electrons or 8–valence electrons. X has electronic configuration, 2, 8, 5., Its valency is equal to 3 because it can gain 3 electrons to become stable., , 22. (i) D, As it is on the left side of the table in group 2., (ii) C, as it is in the group 18/ Noble gas., (iii) E, as we move from left to right across a period, atomic radius decreases., VI. 1. (i) They belong to the same period but different groups. ‘G’ belongs to Group 17. A and B belong to Group, 1 and 2, ... their oxides are basic. ‘C’ belongs to Group 13 due to 3 valence electrons. ‘D’ belongs to, Group 14. E and F belong to group 15 and 16, respectively. ‘H’ belongs to group 18., (ii) B and F will form an ionic compound., (iii) A and B are metals., (iv) G, H are gases at room temperature.,  (v) CG3, , 2. (i) ‘D’ is lithium, E is fluorine., (ii) F belongs to group 17, 3rd period., H belongs to group 1, 4th period., (iii) They have the same number of valence electrons, D(3) 2, 1; G(11) 2, 8, 1; H(19) 2, 8, 8, 1., (iv) DE is the formula of the compound., (v) H is largest in size due to the presence of four shells., , 3. (i) Na, it is due to larger atomic size and least effective nuclear charge., (ii) It is due to increase in atomic size and decrease in effective nuclear charge., (iii) Basic character of oxides increases down the group due to increase in metallic character., (iv) Acidic character of oxides increases along a period due to increase in non-metallic character., (v) Group 17 elements, due to smaller atomic size and more effective nuclear charge., , 4. (i) ‘X’ is nitrogen. It has 5 valence electrons., Fe, , , , N2(g) + 3H2(g) , → 2NH3(g), 773 K, , (ii), , : N ::..N :, :, , :N N:, It forms a triple covalent bond., , H : N : H, , , It forms a single covalent bond., , :, , (iii), , H, , 5. (i) ‘X’ is sulphur., , (ii) S(16): 2, 8, 6, , heat, , (iii) 2FeSO4(s) → Fe2O3(s) + SO2(g) + SO3(g), (iv) SO2 and SO3 are acidic oxides and major air pollutants whereas Fe2O3 is a basic oxide., (v) It belongs to group 16 and 3rd period., , 6. (i) Li, Be B, C, N, O, F, , 152 111 88 77 74 66 64, , Periodic Classification of Elements 45

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(ii) Yes, the elements are arranged in the pattern of a period (2nd period in the periodic table)., (iii) (a) Li is largest in size., (b) F is smallest in size., (iv) Atomic radius decreases from left to right in a period., (v) Metal–Li/Be, Non-Metal-C/N/O/F, Metalloid-Boron., (vi) Atomic size decreases as we move from left to right in a period because effective nuclear charge, increases as one electron and one proton is added successively and number of shells remains the, same., , 7. (a) Valency is equal to number of valence electrons or 8— number of valence electrons., F (9): 2,7, Its valency is equal 1 because it will become stable on gaining one electron., (b) (i) A (4): 2,2, D (19): 2,8,8,1, B (9): 2,7, E (20): 2,8,8,2, C (14): 2,8,4, ‘D’ has one valence electron., (ii) ‘A’ and ‘E’ belong to same group because they have same number of valence electrons., (iii) ‘D’ has larger atomic radius than ‘E’ because it has 19 protons which attract 19 electrons which, is there less strongly than 20 protons can attract 20 electrons as in E., , 8. (a) Valency increases from left to right till middle, then decreases because valence electrons goes on, increasing., (b) Atomic radius decreases due to increase in effective nuclear change., (c) Metallic character decreases, non-metallic character increases due to increase in tendency to gain, electrons as atomic size decreases, effective nuclear change increases., (d) Electronegative character increases due to increase in effective nuclear change., (e) Acidic character of oxides increases, basic character of oxides decreases because metallic character, decreases and non-metallic character increases., , 9. (a) (i) Increasing order of atomic mass could not be followed., (ii) Isotopes cannot occupy different positions as they have same chemical properties but different, atomic mass., (iii) Position of hydrogen was not justified., (b) (i) Metallic character decreases from left to right in a period because tendency to lose electrons, decreases as effective nuclear charge increases., (ii) Metallic character increases down the group from top to bottom because tendency to lose, electron increases due to increase in atomic size and decrease in effective nuclear charge., , 10. (i) E will form only covalent compounds., (ii) B is non-metal with valency 2., (iii) D is metal with valency 2., (iv) ‘F’ has largest atomic radius., (v) It belongs to noble gases., 11. Atomic size is the distance between centre of nucleus and valence shell., Its unit of measurement is picometre (10–12­ m) denoted by pm., Atomic radius increases down the group due to increase in number of shells and decrease in effective, nuclear charge., Atomic radius decreases along a period from left to right because effective nuclear charge increases but, number of shells remain the same., , C ase study questions, , 1. Around the year 1800, only 30 elements were known. Dobereiner in 1817 and Newlands in 1866 tried, to arrange the then known elements and framed laws which were rejected by the scientists. Even after, the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the, properties of elements with their atomic masses., The main credit for classifying elements goes to Mendeleev for his most important contribution to the, early development of a Periodic table of elements wherein he arranged the elements on the basis of their, , 46, , Science-10

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fundamental property, the atomic mass and also on the similarity of chemical properties. The formulae, of their hydrides and oxides were treated as basic criteria for the classification of the elements., However, Mendeleev’s classification also had some limitations as it could not assign the position to, isotopes. He also left some gaps in the periodic table., (i) According to Mendeleev’s Periodic Law properties of elements are periodic function of, (a) atomic mass , (b) atomic number, (c) number of protons, (d) number of electrons, (ii) Why did Mendeleev leave some gaps in the Periodic table?, (a) For elements to be discovered, (b) For isotopes, (c) For isobars , (d) None of these, (iii) If the letter ‘R’ was used to represent any of the elements in the group, then the hydride and oxide of, carbon would respectively be represented as, (a) RH4, RO, (b) RH4, RO2, (c) RH2, RO2, (d) RH2, RO, (iv) Isotopes are:, (a) Atoms of an element with similar chemical properties but different atomic masses., (b) Atoms of different elements with similar chemical properties but different atomic masses., (c) Atoms of an element with different chemical properties but same atomic masses., (d) Atoms of different elements with different chemical properties but same atomic masses., (v) How many groups and periods are there in Mandeleev’s periodic table?, (a) 6 group, 8 period , (b) 18 group, 7 period, (c) 7 group, 18 period , (d) 8 group, 6 period, Ans. (i) (a), (ii) (a), (iii) (b), (iv) (a), (v) (d), 2. Modern periodic table has 18 vertical columns known as groups and 7 horizontal rows known as, periods. First period contains 2 elements second and third period contain 8 elements. 4th and 5th period, contains 18 elements and 6th and 7th period contains 32 elements. The graph is plotted between atomic, number and atomic radius of group 17 and group 1 elements., , (i) Which group elements will have largest atomic size?, (a) Group 1, (b) Group 2, (c) Group 3, (d) Group 18, , (ii) Which group elements will gain electrons to form negative ions?, (a) Group 1, (b) Group 2, (c) Group 17, (iii) Which element in group 17 has smallest size?, , (d) Group 18, , (a) Flourine, (b) Bromine, (c) Chlorine, (d) Iodine, (iv) What happens to atomic radii in a group from top to bottom?, (a) Increases , (b) Decreases, (c) First decreases then increases, (d) Number of shells remains the same, , , (v) Atomic size decreases from left to right in a period because, (a) Effective nuclear charge increases, (b) Number of shells remains the same, , Periodic Classification of Elements 47

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(c) Force of attraction between the nucleus and valence electrons increases, (d) All of these, Ans. (i) (a), (ii) (c), (iii) (a), (iv) (a), (v) (d), 3., , Atom (Period II), , Li, , Be, , B, , C, , N, , O, , F, , Electronegativity, , 1.0, , 1.5, , 2.0, , 2.5, , 3.0, , 3.5, , 4.0, , Atom (Period III), , Na, , Mg, , Al, , S., , P, , S, , Cl, , Electronegativity, , 0.9, , 1.2, , 1.5, , 1.8, , 2.1, , 2.5, , 3.0, , Atom Group 1, , Electronegativity, , Atom Group 17, , Electronegativity, , Li, , 1.0, , F, , 4.0, , Na, , 0.9, , Cl, , 3.0, , K, , 0.8, , Br, , 2.8, , Rb, , 0.8, , I, , 2.5, , Cs, , 0.7, , At, , 2.2, , (i) Which element has highest electronegativity?, (a) C, , (b) N, , (c) O, , (d) F, , , (ii) How electronegativity varies in a period?, (a) Increases from left to right, (c) First increases then decreases, , (b) Decreases from left to right, (d) Vary independently, , , (iii) How electronegativity varies in a period?, (a), (b), (c), (d), , Increases down the group, Decreasing down the group, First increases then decreases down the group, Vary independently, , , (iv) Which of the following has least electronegativity?, (a) Li,, , (b) Be,, , (c) O,, , (d) N, , , (v) What happens to tendency to gain electron in a period?, (a) Increases, (b) Decreases, (c) Remaining same, (d) First increases then decreases., Ans. (i) (d), (ii) (a), (iii) (b), (iv) (a), (v) (a), , Quick revision notes, , • Periodic Table: It is a table in which elements are classified on the basis of similarity in properties., • Classification is essential so that the properties of elements can be studied conveniently., • The first attempt of classification was done by Dobereiner in a group of three elements called triads. He could, not classify all the elements discovered at that time., • Newlands arranged elements in the increasing order of their atomic masses. He found that every 8th element, resembles with the first like the notes in music, every 8th note is same as the first. He could not classify all, the elements., • Mendeleev classified all the 63 elements discovered till 1869 in the Mendeleev’s periodic table based on, increasing order of their atomic masses and formulae of their hydrides and oxides., • Mendeleev kept on modifying his periodic table till isotopes were discovered. After the discovery of isotopes,, the basis of his periodic table was rejected., • Modern periodic law was the basis of modern periodic table in which elements were arranged in increasing, order of their atomic number., , 48, , Science-10

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• Modern periodic table (long form of periodic table) could overcome most of the shortcomings of Mendeleev’s, periodic table., • The horizontal rows of periodic table are called periods. There are 7 periods in modern periodic table., • The vertical columns of periodic table are called groups. There are 18 groups in the long form of periodic table., • The elements show periodicity, i.e. repetition of similar properties after a definite interval., • The similar elements are arranged in a group., • A heavy zig-zag line separates metals from non-metals, with non-metals to the right (except for hydrogen), and metals on the left and middle of the periodic table., • Metalloids which resemble metals as well as non-metals are on the border line of metals and non-metals and, arranged in a zig-zag manner., • There are 118 elements discovered so far, which are classified into 18 groups and 7 periods., • First period has 2, second and third period have 8, fourth and fifth period have 18, sixth and 7th period have, 32 elements., • Group 1 elements are called alkali metals, Group 2 elements are called alkaline earth metals, Group 13-Boron, family, Group 14-Carbon family, Group 15-Nitrogen family, Group 16-Oxygen family, Group 17-Halogens, and Group 18 elements are called Noble gases., • Group 3 to Group 12 elements are called transition metals., • Elements with atomic numbers from 58 to 71 are called lanthanoids. It is kept at the bottom of the periodic, table in a separate row., • Elements with atomic numbers from 90 to 103 are called actinoids, kept in the last row in the periodic table,, below lanthanoids., • Atomic size goes on increasing down the group whereas it goes on decreasing along the period from left to right., • Properties of elements depend upon the number of valence electrons., • In a group, all the elements have the same number of valence electrons, i.e. same valency., • Valency is equal to the number of valence electrons or 8-number of valence electrons., • Valency is number of electrons lost or gained or shared by atoms of elements, so as to become stable like, noble gases., • Valency in a period first increases till middle, then decreases., • Tendency to lose electrons increases down the group., • Tendency to lose electrons decreases along a period, from left to right., • Tendency to gain electrons decreases down the group., • Tendency to gain electrons increases along a period, from left to right., • Metallic character increases down the group., • Metallic character decreases along a period, from left to right., • Non-metallic character increases along a period, from left to right., • Non-metallic character decreases down the group., • Group 18 elements have a very stable electronic configuration in their outermost shell. Their valency is zero, because they do not have any tendency to lose/gain or share electrons. This makes them unreactive., • Elements of 1st period have electrons in first shell only, 2nd period has 2 shells (orbits), 3rd period has 3, shells (K, L, M), 4th period has 4 shells (K, L, M, N) and so on., • Over 80% of the elements are metals and remaining are non-metals., • Metals and non-metals differ in their properties., • Hydrogen is a non-metal but kept in Group 1 because it can form H+ ion like alkali metals (Group 1 elements)., • The elements after Uranium (92) are man-made or synthetic elements. Tc(43), Pm(61), At(85) and Fr(87), are also man-made elements., • Across a period, there is a change from metallic to non-metallic character, e.g. in 3rd period, Na, Mg, Al are, metals, Si is metalloid, while P, S, Cl, Ar are non-metals., • Group 1 metals are the most reactive, because they can lose electrons easily to form positive ions., • Group 17 elements (non-metals) are also considered most reactive, because they can gain an electron easily, to become stable and form negative ions., • Metals are good reducing agents, because they can lose electrons., , Periodic Classification of Elements 49

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Important Elements, Electronic Configuration of Elements, H(1), He(2), Li(3), Be(4), B(5), C(6), N(7), O(8), F(9), Ne(10), Na(11), Mg(12), Al(13), Si(14), P(15), S(16), Cl(17), Ar(18), K(19), Ca(20), , K, 1, 2, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, 2,, , L, , M, , N, , 1, 2, 3, 4, 5, 6, 7, 8, 8,, 8,, 8,, 8,, 8,, 8,, 8,, 8,, 8,, 8,, , 1, 2, 3, 4, 5, 6, 7, 8, 8,, 8,, , 1, 2, , Common Errors, Errors, , Corrections, , • Many students get confused and think atomic ☞ Students should learn and understand the definitions of, number of an element is equal to the total number, atomic number and atomic mass properly., of electrons and think that sum of the number of, Atomic number is always equal to the number of protons, electrons and protons is equal to the atomic mass., present in an atom and atomic mass is the sum of mass of, protons and neutrons present in the nucleus of the atom., • Many students get confused among groups and ☞ Although the table itself is called the periodic table, elements, periods., in the same group (or column) are often more similar than, those in the same period (row)., • Many students consider metalloids to show half ☞ Students should properly understand the definition of, of the properties of metals only and none of them, the metalloids. Metalloids are the elements that show, to show any non-metallic character and also get, properties of both metals as well as non-metals. Even, confused with their arrangement in the periodic, though metalloids are also termed as semi metals but some, table., of the properties of metalloids also resemble to that of nonmetals, like the formation of borides, tellurides, etc., Metalloids are located in a zig zag manner in the middle, region of the periodic table., • Many students make mistakes in understanding the ☞ Students should understand the phenomena of effective, trend of atomic size in the periodic table and usually, nuclear charge and the effect of addition of orbits (or shells), consider that non-metals have always bigger atomic, properly and do not confuse with the effect of metallic and, size than metals., non-metallic character for atomic size or radius., • Many students fail to understand why helium is a ☞ Students should properly learn the rules of filling up of, noble element, even when it does not have complete, electrons in orbitals in an atom and should learn that in, octet of electrons., helium only one shell is there which can occupy the electrons, and based on the rule, it can accommodate a maximum of 2, electrons and that is why it is a noble (unreactive) element., , Periodic Classification of Elements 51

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• Students usually make mistakes while listing the ☞ Learn all the rules for deciding the filling up of electrons in, electronic configuration of elements., the orbits of atoms of elements., • Many students get confused in the number of valence ☞ Students should properly understand the arrangement, electrons and valency of halogens., of elements in groups and periods in the modern periodic, Students should properly learn that valency is, table, based on their electronic configuration., necessarily not equal to the number of valence, electrons. For halogens behaving as anions (like in, NaCl), the valency is of Cl– ion is equal to 8–no. of, valence electrons (7), i.e. 1., • Many students do not understand the placement of ☞ Lanthanoids and actinoids are kept separately at the, lanthanoids and actinoids and accidentally neglect, bottom because they resemble with each other but they do, them altogether., not resemble with the other group elements., , Assignment, I. Multiple Choice Questions, , Total Marks : 20, (1 Mark), , Choose the correct answer from the given options., 1. An element ‘X’ with atomic number 12 forms a compound with element ‘Y’ with atomic number 17. The, formula of the compound is, (a) XY, (b) XY2, (c) X2Y, (d) X2Y3, [CBSE 2020], 2. An element ‘X’ is forming acidic oxide. Its most probable position in the modern periodic table is, (a) Group 1 and Period 3, (b) Group 16 and Period 3, (c) Group 17 and Period 3, (d) Group 2 and Period 3, [CBSE 2020], II. Assertion-Reason Type Questions, (1 Mark), , Note: Use instructions as given in topical exercises of the chapter., 1. Assertion: A. ‘X’ has mass no. 35, number of neutrons are 18., , Reason: X belongs to Group 17 and 3rd period, it is non-metal, 2. Assertion: Out of A(4), B(9), C(14), D(19), E(20), D(19) has one valence electron., , Reason: Valency of A(4) and E(20) are equal to 2., , III. Very Short Answer Type Questions, , (1 Mark), , 1. If the atomic mass of ‘Na’ is 23 and ‘K’ is 39, calculate atomic mass of Li, if these elements form, Dobereiners’ triads., 2. An element belongs to Group 15, 2nd period. Write down the formula of its oxide and hydride., , IV. Short Answer Type Questions-I , , (2 Marks), , 1. How does tendency to lose electrons change in a period and why?, 2. How does ionic size vary down the group and along a period from left to right? Why?, 3. What is a metalloid and where are they positioned in the periodic table?, , V. Short Answer Type Question-II , 1. From the elements Li, K, Mg, C, Al and S identity, (a) the case elements belonging to the same group., (b) element which has the tendency to lose two electrons, (c) element which prefers sharing of electrons to complete its octet., (d) most metallic element, (e) element that forms acidic oxide, (f) element that belongs to group 13, , VI. Long Answer Type Question, , (3 Marks), , [CBSE 2020], , (5 Marks), , 1. Answer the following questions based on elements with atomic number 3 to 9., (a) Name the element which has smallest atomic radius., (b) Name the element which shows maximum valency., (c) Name the element which is metalloid., (d) Name the element which is most electropositive., (e) Write the chemical formula of a compound formed when the element with atomic number 6 and 8, react together., , 52, , Science-10

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Unit-II, The World of the Living, , 3, , How do Organism Reproduce?, , Topics Covered, 3.1, 3.2, 3.3, , Do Organisms Create Exact Copies of Themselves?, Modes of Reproduction by Single Organism, Sexual Reproduction, , C hapter map, Reproduction, Asexual, Fission, , Sexual, , Fragmentation, , Binary, , Budding, , Multiple, , Regeneration, , Vegetative, Propagation, , Cutting, , Grafting, , Spore, Formation, , Layering, Humans, , Plants, Pollination, Self-pollination, , Male reproductive system, Female reproductive system, , Cross-pollination, Reproductive Health, , Fertilisation, , Sexually Transmitted Diseases (STDs), Birth Control Methods, , Mechanical barrier, , Chemical method, , Surgical method, , When egg, is fertilised, , 53, , When egg, is not, fertilised

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Topic 1. Do Organisms Create Exact Copies of Themselves?, Reproduction: It is the production of new species from the existing species., Significance of reproduction, , • It ensures continuity of life., • It increases population of species., • It provides variations, which are favourable from one generation to another generation., , Body designs of organisms, , • Organisms look similar because their body designs are similar., • Body designs are similar because blue prints of body designs are similar., • Reproduction involves copies of blue prints of body designs. It is done by creation of DNA (Deoxyribo Nucleic, Acid) copy., • DNA is responsible for the resemblance between parents and children., • DNA in the cell nucleus is the information source of proteins., • If information is changed, different proteins will make different body designs., • Reproduction is a creation of copies of their DNA by cell division., • DNA copying always involve some variations, i.e. copies of DNA will be similar but not identical., • This tendency of variation during reproduction leads to evolution of the species., , Importance of variation in organisms, , Population of organisms fill well defined places in the ecosystem, using reproduction., Organisms with similar design use the same places., If a place suitable for the population is drastically changed, the population may be wiped out completely., If some variations are there in few individual in these populations, there will be some chance for them to, survive., • Variation is useful for the survival of species over time., •, •, •, •, , Exercise 3.1, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. The copying of DNA occur during, (a) cell formation, (b) cell division, (c) protein synthesis, (d) reproduction, 2. The main cause of variations among organisms during sexual reproduction is, (a) Errors in copying DNA, (b) Errors in RNA, (c) Errors in both RNA and DNA, (d) Genetic drift, 3. The reproduction is essential for population of a species, (a) to decrease its number, (b) to increase its number, (c) for its survival, (d) to become extinct, , II. Assertion-Reason Type Questions, , (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: DNA is deoxyribonucleic acid., , Reason: DNA transfers genetic characteristics from parents to offsprings., 2. Assertion: There are three types of RNA, t-RNA, m-RNA and r-RNA., , Reason: RNA does not undergo replication., , 54, , Science-10

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III. Very Short Answer Type Questions, 1., 2., 3., 4., 5., 6., 7., 8., , (1 Mark), , Name the life process of an organism which helps in the growth of its population., [Delhi 2015], Where is DNA found in the cell?, [Delhi 2015], What is DNA? , [Delhi 2015], Name the information source of making proteins in the cell. State two basic events in reproduction., [Delhi 2015] [HOTS], What is the effect of DNA copying which is not perfectly accurate in the reproduction process? [Delhi, 2015] [HOTS], The mode of reproduction depends on which feature of the organism?, Organisms have a varied body design. Name the property which gives the basic difference in body, design. , Explain how do organisms create an exact copy of themselves., [CBSE 2016], , IV. Short Answer Type Questions-I, , (2 Marks), , 1. What is the importance of DNA copying in reproduction?, OR, Why is DNA copying an essential part of the process of reproduction?, [NCERT], [Delhi 2013, 2015], 2. Why is variation beneficial to the species but not necessary for the individual?, [NCERT], 3. How does reproduction help in providing stability to the populations of species?, [NCERT], 4. (a) What is the location of following: (i) DNA in a cell, (ii) Gene, (b) Expand DNA. , [CBSE 2016], 5. When a cell reproduces, what happens to its DNA?, [CBSE 2017], , V. Short Answer Type Question-II, , (3 Marks), , 1. Reproduction is one of the most important characteristics of living beings. Give three reasons in support, of the statement., [CBSE 2017], , VI. Long Answer Type Question, , (5 Marks), , 1. (a) (i) Write full form of DNA., (ii) State the role of DNA in the cell nucleus., (iii) What will be the effect if the information of the DNA is changed?, (b) Explain the importance of DNA copying in reproduction., , [CBSE 2016], , Answers 3.1, I. 1. (b) It takes place during cell division., 2. (a) Errors in copying DNA., 3. (b) It is to increases its number so that it does not became extinct., II. 1. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., 2. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., III. 1. Reproduction, 2. DNA is found in the nucleus., 3. DNA means deoxyribo nucleic acid. It lies in the cell nucleus, which is the source of information for, making proteins and different proteins lead to different body designs., 4. DNA in the nucleus of a cell is the source of information for making proteins. The two basic events in, reproduction are:, (i) creation of copy of DNA, (ii) creation of an additional cellular apparatus by cell then the DNA copies separate, each with its own, cellular apparatus., 5. DNA copying will lead to variation in populations which helps in evolution of the species., , How do Organism Reproduce? 55

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6. The mode of reproduction depends upon the body design of organism. Those with simple body design, may reproduce asexually. Those with complex body design may form gametes and may undergo sexual, reproduction., 7. Errors in DNA copying., 8. The cell uses biochemical reactions to make exact copies of DNA or genetic material., IV. 1. Reproduction involves producing same kind of species from parents. The genetic information is passed, to the offspring by DNA present in each cell. This DNA, which is replicated (copied) is responsible for, the resemblance of parents with offsprings with same traits. New traits are passed on due to difference, in copying, new variations may occur and new species may evolve., 2. If environmental conditions undergo drastic change, some member of a species having variations of, tolerating changed temperature may be able to survive, e.g. suppose population of bacteria is living in, temperate water. If temperature of water increases due to global warming, most of the bacteria will, die. However, if few variants are resistant to heat, then they would survive and grow further. Thus, variation is useful for the survival of species over time, but it is not necessary for the individual., 3. It is because reproduction is a process by which species increase their population. If the rate of birth, is more than death, the size of population will increase and will be more stable., 4. (a) (i) DNA is found in nucleus of cell, (ii) Genes are located on the chromosomes., (b) Deoxyribonucleic acid., 5. During the process of reproduction, transmission of DNA from parents to offspring takes place. Before, reproduction, DNA is replicated, which means two copies of DNA are produced. When the cell divides, into two, these two copies are distributed equally between the two daughter cells so that similar amount, and type of DNA is transferred from the parent cell to the daughter cells. It maintains the consistency, in the amount and type of DNA in the living organism of a particular species., V. 1. Reproduction is an energy consuming process which is not essential for the survival of an individual., But it is the most important characteristic of all living beings, because of the following reasons:, (i) Reproduction helps in increasing the number of members of a population., (ii) By replacing the dead members with the new ones, it minimises the risk of extinction of a species. , (iii) It brings about variations in species, thus leading to their evolution., VI. 1. (b) (i) Deoxy Ribonucleic Acid, (ii) It helps in synthesis of protein and transfer of genetic characteristics., (iii) Proteins will be changed., (b) Body designs are similar due to DNA copying., DNA cell nucleus carry information for synthesis of protein., , If DNA copying will not take place then body design will change., , Topic 2. Modes of Reproduction by Single Organism, , Asexual reproduction: It is the process in which new organism is formed by single parent without involving, sex cells or gametes., • It is simple and fast., • Cell division is amitotic or mitotic., • The new organisms are identical to parents., , Fission: Cell division or fission leads to creation of new individual in unicellular organisms; e.g. Amoeba,, protozoa, bacteria., Binary fission: When a cell splits into two equal halves during cell division, e.g. Amoeba,Bacteria and Protozoa-Paramecium undergo binary fission. This fission or cell division can take place in any plane in Amoeba., In some organisms like Leishmania (which cause kala-azar), binary fission occurs in a definite orientation to, their structure., , 56, , Science-10

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Nucleus lengthening, Cytoplasm, , Nucleus divides, into two parts, , Cytoplasm dividing, , Constriction, , Nucleus Pseudopodia, (a) Parent cell, , Two smaller Amoebae, cells are produced, , (b) Karyokinesis, , (c) Cytokinesis, , (d) Constriction formation, , (e) Two daughter cells, , Binary fission, , Multiple fission: When cell of an organism divides into many daughter cells simultaneously, it is called, multiple fission, e.g. Plasmodium (causing malaria)., , Fragmentation: It is the process in which an organism breaks into two or more pieces or, fragments upon maturation in multicellular organisms like filamentous algae-spirogyra., These fragments grow into new individuals. All cells of body are alike and they all divide, to make new individual., , Regeneration: It is a process in which organisms have the ability to regenerate give rise, to new individual organisms from their body parts. It takes place in fully differentiated, Multiple fission in, Plasmodium, organisms, e.g. Hydra, Planaria. Their cells divide, increase in number and form missing, parts in the body of an individual. Many organisms can regenerate their body parts like house lizard can, regenerate its lost tail. But it is not a way of reproduction in this case., , Budding: A small outgrowth ‘bud’ forms on the body of an organism. It grows in size and develops into a new, individual. It may get detached and lead independent existence like in case of Hydra. In this process, organisms, use regenerative cells for reproduction, e.g. Hydra. Yeast can put out small buds that separate and grow further., , Nucleus, , Daughter, nuclei, , Bud, , Bud formation, , Movement of, nucleus, , Mitosis, , into the bud, , Bud with, nucleus, , Daughter, yeast, Birth scar, Bud scar, , Parent, yeast, , Vacuole, Budding, , Vegetative propagation: It is the method in which vegetative parts like roots, stem and leaves develops into, , new plants under appropriate conditions., Vegetative propagation can be implemented either naturally or artificially., • Natural vegetative propagation: The new plant can be produced by stem, roots or leaves, naturally. E.g., - potato, mint, etc., • Artificial vegetative propagation: The new plant is formed by using techniques like cutting a short piece, of plant and placed in moist soil, layering i.e., branch of plant is buried in soil or grafting i.e., joining a part, of one plant on a different plant., , Advantages:, , • Plants, which do not produce viable seeds or have lost the ability to produce seeds, can be propagated by this, method only., • Plants raised by this method bear flowers and fruits earlier than those produced from seeds., • It maintains the genetic traits in all generations as only one parent is involved, hence conserves characteristics, of specific varieties of plants., , Example: Bryophyllum propagates through a leaf, mint propagates through root, rose propagates through, stem. The commonly used methods are:, • Cutting: e.g. Rose and China rose, • Layering: e.g. Jasmine, • Grafting: e.g. Rose, , How do Organism Reproduce? 57

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Tissue culture: In this process, new plants are grown by removing tissues or separating cells from the growing, tip of the plant, which is placed in an artificial medium. When they divide rapidly to form small group of cells,, it is transferred to another medium containing hormones for growth and differentiation. The small plants, (plantlets) are then placed in soil to grow., , Multiple fission in, Plasmodium, , Spore formation: Some thread-like structures that develop on the bread, , piece placed in a moist dark place for few days. They are ‘hyphae’ of common, bread mould. Some hyphae grow upright, develop a cheb like structure at, its tip–sporangium. The sporangium contain ‘spores’ which are released in, air on bursting of a mature sporangium. Spores of Rhizopus present in air, settle on the bread to form new fungus. The spores are covered by thick walls, that protect them from dryness until they come into contact with another, moist surface and begin to grow., , I. Multiple Choice Questions, , Spore formation in Rhizopus, , Exercise 3.2, , (1 Mark), , Choose the correct answer from the given options., 1. In the list of organisms given below, those that reproduce by the asexual method are, (i) banana, (a) (ii) and (iv), , 58, , Science-10, , (ii) dog, (b) (i), (iii) and (iv), , (iii) yeast, (c) (i) and (iv), , (iv) amoeba, (d) (ii), (iii) and (iv)

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2. In a flower, the parts that produce male and female gametes (germ cells) are, (a) stamen and anther , (b) filament and stigma, (c) anther and ovary , (d) stamen and style, 3. Which of the following is the correct sequence of events of sexual reproduction in a flower?, (a) pollination, fertilisation, seedling, embryo, (b) seedling, embryo, fertilisation, pollination, (c) pollination, fertilisation, embryo, seedling, (d) embryo, seedling, pollination, fertilisation, 4. Offspring formed by asexual method of reproduction have greater similarity among themselves because, (i) asexual reproduction involves only one parent, (ii) asexual reproduction does not involve gametes, (iii) asexual reproduction occurs before sexual reproduction, (iv) asexual reproduction occurs after sexual reproduction, (a) (i) and (ii), (b) (i) and (iii), (c) (ii) and (iv), (d) (iii) and (iv), II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Cell division is a type of reproduction in unicellular organisms., , Reason: It leads to formation of two daughter cells where means is to produce more individuals., 2. Assertion: Spores are formed in sporangia., , Reason: Spores grow into separate individuals in moist conditions., , III. Very Short Answer Type Questions, , (1 Mark), , 1. How does binary fission differ from multiple fission?, [NCERT], 2. Name the part of Bryophyllum where the buds are produced for vegetative propagation. [Delhi 2016], 3. What happens when a Planaria gets cut into two pieces?, [Delhi 2016], 4. What happens when a mature Spirogyra filament attains considerable length?, [Delhi 2016], 5. Name the method by which hydra reproduces. Is this method sexual or asexual?, [Delhi 2016], 6. Name two simple organisms which have ability of regeneration., [Delhi 2015], 7. Name the causative agent of the disease ‘kala-azar’ and its mode of asexual reproduction.[Delhi 2015], 8. Select two plants from the following which are grown by vegetative propagation process:, , Banana, Wheat, Mustard, Jasmine, Gram., 9. Give the respective scientific term used for studying., (i) The mechanism by which variation are created and inherited and, (ii) The development of new type of organism from the existing ones., [CBSE 2015], 10. Name the type of cells which undergo regeneration., [CBSE 2015], 11. Regeneration is not possible in all types of animals. Why?, [CBSE 2012], 12. What is the advantage of reproduction through spores?, [CBSE 2012], OR, How will organism be benefitted if it reproduces through spores?, [NCERT], 13. Name the method by which spirogyra reproduces under favourable conditions. Is this method sexual, or asexual?, [CBSE 2017], 14. How does Planaria reproduce? Is this method sexual or asexual?, [CBSE 2017], 15. How does Plasmodium reproduce? Is this method sexual or asexual?, [CBSE 2017], , IV. Short Answer Type Questions-I, , (2 Marks), , 1. “Cell division is a type of reproduction in unicellular organism”. Justify., [NCERT Exemplar], 2. What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?, , [NCERT Exemplar] [HOTS], , How do Organism Reproduce? 59

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3. Can you think of reasons why more complex organisms cannot give rise to new individuals through, regeneration? , [NCERT], 4. Why is vegetative propagation practised for growing some types of plants?, [NCERT], 5. List two advantages of growing grapes or banana plants through vegetative propagation.[Delhi 2013], 6. List three conditions favourable for spores to germinate and grow., [Delhi 2013], 7. Name the type of asexual reproduction in, (a) Planaria , (b) Rhizopus, (c) Spirogyra , (d) Hydra , [CBSE 2011], 8. Leaves of bryophyllum fallen on the ground produces new plants, why?, [CBSE 2011], 9. Name the type of asexual reproduction in which two individuals are formed from a single parent and, the parental identity is lost. Write the first step from where such a type of reproduction begins. Draw, first two stages of this reproduction., [Delhi 2017], 10. Draw in sequence (showing the four stages), the process of binary fission in Amoeba., [AI 2017], , V. Short Answer Type Questions-II, , (3 Marks), , 1. What is multiple fission? How does it occur in an organism? Explain briefly. Name an organism which, exhibits this type of reproduction., [Delhi 2016], 2. Explain the term ‘Regeneration’ as used in relation to reproduction of organisms. Describe briefly how, regeneration is carried out in multicellular organisms like Hydra., [Delhi 2016], 3. In the context of reproduction of species state the main difference between fission and fragmentation., Also give one example of each., [Delhi 2016], 4. What happens when, (i) Planaria gets cut into two pieces, (ii) A mature spirogyra filament attains considerable length, (iii) On maturation sporangia burst, [Delhi 2016], 5. Explain budding in hydra with the help of labelled diagrams only., [Delhi 2015], 6. What happens when:, (a) Accidently, Planaria gets cut into many pieces?, (b) Bryophyllum leaf falls on the wet soil?, (c) On maturation sporangia of Rhizopus bursts?, [Delhi 2017], 7. What is vegetative propagation? State two advantages and two disadvantages of this method., [CBSE 2017], 8. Define the term pollination. Differentiate between self pollination and cross pollination. What is the, significance of pollination?, [CBSE 2020], 9. (a) List in tabular form two differences between binary fission and multiple fission., (b) What happens when a mature spirogyra filament attains considerable length., [CBSE 2020], , VI. Long Answer Type Questions, , (5 Marks), , 1. What is binary fission in organisms? With the help of suitable diagrams, describe the mode of, reproduction in amoeba., [Delhi 2011], 2. Identify the following methods and give one example of each:, (a) Process in which reproduction takes place by breaking up of parent into several fragments., (b) Process of dividing of organisms into many cells simultaneously., (c) Process of reproduction by formation of bud on the parent body., (d) Process of reproduction by formation of spores., (e) Process used by multi-cellular organisms to reproduce by cutting into many pieces and each piece, forms a new individual., [CBSE 2016], 3. (a) Identify the organism A, B and mode of asexual reproduction exhibited by them., (b) How will an organism be benefitted if it reproduces through, spores?, (c) Mention the two asexual methods by which hydra can, reproduce. Explain briefly any one such method.[CBSE 2013], 4. What is vegetative propagation? Give examples of plants which, can be propagated by their:, (a) Stem, (b) Roots, (c) Leaves, , 60, , Science-10

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5. (i) Describe the various steps involved in the process of binary fission with the help of a diagram., (ii) Why do multicellular organisms use complex way of reproduction? [CBSE Sample Paper 2019-2020], , Answers 3.2, I. 1. (b) Banana, Yeast and Amoeba reproduce by asexual reproduction., 2. (c) anther and ovary, 3. (c) pollination, fertilisation, embryo, seedling, (a) (i) and (ii) statement are correct., (a) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (a) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., In binary fission cell divides into two cells whereas in multiple fission a cell divide into many daughter, cells., 2. Buds arise from the notches in the leaf margins of Bryophyllum., 3. Each piece regenerates into new organism, planaria., 4. A mature spirogyra filament breaks into smaller fragments and each fragment grows into a new plant., This process of reproduction is called fragmentation., 5. Hydra reproduces by budding. It is an asexual mode of reproduction., 6. Planaria and Hydra, 7. Leishmania causes ‘kala-azar’. It reproduces by binary fission in a definite orientation., 8. Banana and jasmine are grown by vegetative propagation, because they do not produce seeds., 9. (i) Heredity, (ii) Evolution., 10. Specialised cells called regenerative cells which can make large number of new cells., 11. Regeneration is carried out by specialised cells which are present in few animals which can reproduce, by regeneration., 12. Spore with a cell wall can survive even in adverse conditions. Large number of spores are produced in, one sporangium. It is easily dispersed through wind as they are large in number and light in weight., 13. Under favourable conditions, spirogyra reproduces by a process known as fragmentation. This is an, asexual method of reproduction. , 14. Planaria reproduces by a process known as regeneration. It is a type of asexual reproduction in which, if Planaria can be cut into any number of pieces, each piece grows into a new individual organism., 15. Plasmodium is a single celled organism which reproduces by the process of multiple fission. Multiple, fission (i.e. breaking up of a single cell into many daughter cells) is an asexual mode of reproduction., IV. 1. Cell division in a unicellular organism results in the formation of two or more daughter cells which, means it produces more individual., 2. Clones are organisms which are exact genetics copies of their parents. Their DNA is exactly identical, to their parents, which is the cause of remarkable similarity., 3. Those organisms which reproduce by regeneration have similar and non-differentiated cells throughout, the body, therefore body parts of organism grows into new organism., In multicellular complex organisms, the cells get differentiated and perform different functions. In, such organisms, body parts like skin, muscles, i.e. tissues can be regenerated, but the whole organism, cannot be reproduced by regeneration., 4. (i) Vegetative propagation is used to grow plants in which seeds are not formed or very few seeds are, formed, e.g. banana, pineapple, orange., (ii) It helps to grow plants in conditions where seed germination fails due to change in environment., (iii) It is a faster, easier and cheaper process., (iv) The plants produced are genetically similar and good quality or variety can be preserved easily., 5. (i) Characteristics of parent plants are preserved., (ii) Since these plants do not have viable seeds, therefore vegetative propagation is advantageous., 6. (i) Availability of nutrition (food), (ii) moist place, (iii) warmth, (iv) dark place. (Any three), 4., II. 1., 2., III. 1., , How do Organism Reproduce? 61

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7. (a) Regeneration (b) Spore formation, (c) Fragmentation , (d) Budding, 8. Leaves of bryophyllum has adventitious buds or plantlets in the notches along the leaf margin. When, buds fall on the soil, they develop into new plant under favourable conditions., 9. Binary fission, e.g. Fission in Amoeba, , Elongation of cell and its nucleus is the first step., , I, , II, , III, , IV, , 10. Sequence (showing the four stages), the process of binary fission in Amoeba., (Refer to ans. 9 for diagram), V. 1. The process in which parent cell divides into several small and equal sized daughter cells, which grows, into a new organism is called multiple fission., The nucleus of a cell divides into large number of nuclei and cytoplasm separates, forming a membrane, around it. All this occurs within a protective covering. Plasmodium exhibits multiple fission., 2. Regeneration is the ability to produce an organism from their body parts. Many fully differentiated, organisms show ability to reproduce by regeneration. In hydra, if the body is cut into two or three, pieces, the lower part will develop head while the upper part will develop rest of the body. If its cells, are separated, hydra will reform its structure by regeneration., 3., , Fission, , Fragmentation, , It takes place in unicellular organisms., , It takes place in multicellular organisms., , The cell splits into two or more cells, giving rise, to daughter cells, e.g. amoeba, paramecium., , The body of the organism simply breaks into, smaller pieces, which upon maturation grow into, new individual, e.g. spirogyra., , (i) Each piece will regenerate into complete organism. Cells at the location of the site of cut or wound,, forms a small ball of cells that will differentiate into new tissues and regenerate the missing parts, of the cut piece of the planaria., (ii) When spirogyra attains considerable length, it breaks into smaller fragments and each fragment, grows into a new plant., (iii) On maturation, sporangial wall breaks and spores are dispersed to grow into new individual. These, spores are very light and easily dispersed by wind., 5. A bud is an outgrowth from the body part of parent due to repeated cell division at a specific site. These, buds develop into new individuals, which detach from the parent body on maturation., In hydra, the cells divide very fast at a specific site as an outgrowth called bud. These bud develops, into a small individual, while remaining attached to the parent. When it matures, it detaches from the, parent body to exist as an independent organism., 4., , Budding in Hydra, , 6. (a) When Planaria gets cut into many pieces, it will undergo a process known as regeneration due to, which each piece will grow into a new planaria organism., (b) When bryophyllum leaf falls on the wet soil, the buds that are produced in the notches along the, leaf will develop into new plants by the process known as vegetative propagation., , 62, , Science-10

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7., , , , , , 8., , (c) When the sporangia of Rhizopus bursts upon maturation, the spores present inside it spread in the, open environment. Then, with the help of different agents, they are carried to different places and, when they land on a favourable surface, they start growing and produce new organism., Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from, vegetative parts of the plants. It does not involve the production of seeds or spores for the propagation, of new plants., Two advantages of vegetative propagation are:, (i) Plants which do not produce seeds are propagated by this method, for example sugarcane, potato,, etc., (ii) Vegetative propagation is a cheaper, easier, rapid method of propagation in plants than growing, plants from their seeds. For example, lilies grow very slowly and take 4 to 7 years to develop, flowers when grown through their seeds, but flowers are produced only after a year or two when, grown vegetatively., Two disadvantages of vegetative propagation are:, (i) As there is no genetic variation, there is no chance of development of new and better varieties., (ii) The vegetatively propagated plants are more prone to diseases that are specific to the species. This, can result in the destruction of an entire crop., Pollination: The process in which pollen is transferred from stamen to the stigma is called pollination., Self pollination, , Cross pollination, , If the transfer of pollen occurs in the same If the transfer of pollen occurs from one flower to, flower, it is called self pollination., another, it is called cross pollination., , Significance: After the pollen lands on suitable stigma, it needs to reach the female germ cells in the, ovary where fertilisation takes place, zygot is formed. Zygot divides several times to form embryo with, in ovule which develops a tough coat around it called seed coat and seed is formed. The ovary grows, rapidly and ripens to form fruit., Binary fission, , 9. (a), , Multiple fission, , Nucleus divides into two parts., , Nucleus divides into more than two parts., , It occurs in normal conditions., , It occurs in abnormal conditions., , It give rise to two new individuals., , It give rise to many new individuals., , Cytoplasm divides after each division e.g. in Cytoplasm does not divide after every nuclear, Amoeba, division e.g. in plasmodium., (b) A mature spirogyra filament breaks into smaller fragments and each fragment grows into a new, plant. This process of reproduction is called fragmentation., VI. 1. Binary fission is a fission in which two daughter cells are formed of nearly equal size after replicating, the genetic material of a single cell. Single-celled organisms like amoeba undergoes binary fission., Nucleus lengthening, Cytoplasm, , Nucleus divides, into two parts, , Two smaller Amoebae, cells are produced, , Constriction, , Nucleus Pseudopodia, (a) Parent cell, , Cytoplasm dividing, , (b) Karyokinesis, , (c) Cytokinesis, , (d) Constriction formation, , (e) Two daughter cells, , Binary fission in Amoeba, , 2. (a), (c), (e), 3. (a), (b), , Fragmentation, Spirogyra, (b) Multiple fission, Plasmodium, Budding, Yeast/Hydra, (d) Spore formation, Rhizopus, Regeneration, Planaria, ‘A’ is Bryophyllum–Vegetative propagation; ‘B’ is Plasmodium–Multiple fission, Spores are covered with thick walls which protect them until they come into contact with a moist, surface., (c) Budding and regeneration, , How do Organism Reproduce? 63

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Budding: In this process hydra (or any other organism like yeast) use regenerative cells for, reproduction. A bud develops as an outgrowth due to repeated cell division which develop into new, individuals., (a) Stem—Potato, Onion, Ginger, (b) Roots—Banana, Asparagus, (c) Leaves—Bryophyllum, 5. (i), , (ii) Multicellular organisms cannot reproduce by cell because they are not simple random collection of, cells., They have specialised cells, organised as tissues which are organised into organs., Cell-by-cell division would be impractical (not practical)., Multicellular organisms require to use more complex ways of reproduction., , Topic 3. Sexual Reproduction, Sexual Reproduction: It involves two individuals, male and female to generate a new organism. It is necessary, , because in a sexual reproduction usually DNA is copied., • The DNA copying mechanism cannot be absolute accurate, the errors are source of variations in population, of organism which are useful., • Sexual reproduction mode allows more and more variations to be generated., • If the DNA copying mechanism is less accurate, many resultant DNA copies will not be able to work with, the cellular apparatus and cell would die., • Combining variations from two or more individuals would create new combination of variants. Each, combination will be new and unique., , Difficulty: If each new generation is to be the combination of the DNA copies of existing individual, then new, generation will have twice the amount of DNA than previous generation. This is likely to mess up the control, of the cellular apparatus by DNA., Solution: Special lineages of cells in specialised organs which have only half the number, , of chromosomes and half the amount of DNA as compared to the non-reproductive body, cells. When these germ cells from two individuals combine during sexual reproduction to, form new individual, it results in formation of same number of chromosomes and the DNA, content in new generation., Chromosomes: These are the linear sequence of genes composed of nucleic acids and, proteins, carrying hereditary information. There are 46 chromosomes in the human body,, i.e. 23 pairs., Male gamete: It is a germ cell which is smaller and likely to be motile. These are produced, in the bodies of male organism., , Chromosome, , Female gamete: It is the germ cell which is large and contains food storage. These are produced in the body, of female organism., , 64, , Science-10

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Sexual reproduction in flowering plant, • The reproductive parts of angiosperms are located in, the flower., • Different parts of flower are sepals, petals, stamen and, carpel., • Stamen and carpels are the reproductive parts of flower, which contain germ cells., , Unisexual flower: The flower which contains either, , Parts of flower, , stamen or carpels, e.g. papaya, watermelon., , Bisexual flower: The flower which contains both stamen and carpels, e.g. hibiscus, mustard., Sepal: It is the green leaf like structures which form the outermost layer of a flower. It protects the bud., Petals: It is the part of flower that are found inner to sepal and collectively called corolla. Insect pollinated, flowers which are brightly coloured and often scented (have nice fragrance), like rose., Stamen: It is the male reproductive organ of a plant. It consists of anther and filament. They are yellowish in, colour, which sticks to our hand if we touch the stamen of a flower., Anther: It is the part of male organ of the flower (stamen) that produces, and contains pollens., Carpel: It is the female reproductive organ of flowering plants present in, the centre of the flower. It consists of ovary, containing one or more ovules, and stigma, a receptive surface for pollen grains. Stigma is present at the, apex of the stalk and the style. It is made up of three parts— ovary, style, and stigma., Ovules: Grain like structure growing inside the ovary. Contain female, gamete or egg. They become seeds after fertilisation., Ovary: The swollen bottom part of the carpel in a flower. It contains ovules, and each ovule has an egg cell., Reproductive System in Plants, Style: It is the middle, elongated part of carpel in a flower., Stigma: The terminal part of carpel, which may be sticky is called stigma., Self Pollination: If the transfer of pollen grains is from the stamen to stigma of the same flower, it is called, self pollination., Cross-pollination: If the pollen is transferred from one flower to another, it is called cross pollination. This, transfer of pollen from one flower to another is achieved by agents like wind, water or animals (insects)., ,    , , Cross-pollination, , Growth of pollen tube and Fertilisation: When the pollen of same species lands on suitable stigma it has to, , reach the female germ cell, which are present in ovary. For this, a tube grows out of pollen grains and travels, through the style to ovary due to chemotropism. Pollen tube releases male gamete inside ovule. The male, gamete and the female gamete fuse inside ovule and make a zygote., , Zygote: It is formed by fusion of male germ cell produced by pollen grains with female gamete present in ovule., , This fusion of the germ cells is called fertilisation which gives zygote, capable of growing into a new plant., , Embryo: The zygote divides several times to form an embryo with the ovule after fertilisation., Plumule (future shoot): The part of plant embryo that develops into shoot system. It contains stem apex, and first leaf., , How do Organism Reproduce? 65

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Radicle: The part of plant embryo that develops into primary root., Seed: The ovule develops a tough coat and is gradually converted into seed. Seed contains the future plant or, embryo, which develops into seedling, under suitable conditions., , Cotyledon (seed leaf): A leaf forming part of a seed embryo that contains starch and is a source of food for, the germinating seed., , Plumule, , Epicotyl, Point of attachment, , Seed coat, Hypocotyl, Hilium, Micropyle, , Embryo, , Radicle, Testa, Tegmen, Cotyledon, , External Structure of a Dicot Seed, (Bean Seed), , Internal Structure of a Dicot Seed, (Bean Seed), , Fruit: The ovary grows rapidly and ripens to form fruit., Germination: The process of converting seed into seedling under appropriate conditions is called germination., Secondary sexual Characteristics, Most of the higher animals like humans, birds, reptiles are unisexual. Some invertebrates like earthworms,, leech, star-fish, hydra are bisexual or hermaphrodite., In humans, sex organs or primary sexual characteristics are those by which a young one is born and can, be distinguished from secondary sex characteristics, which develop later in life, usually during puberty., The development of both is controlled by sex hormones produced by the body hormones that express sexual, differentiation in humans include:, • oestrogens • progesterone • androgens such as testosterone, Pubic hair, underarm hair appear in both males and females but females have larger breasts, menstrual cycle,, development of wider hips. On the other hand males develop facial and body hair, development of wider chest, and broad shoulders, etc., , Reproduction in Human Beings, Puberty: The period during adolescence in which lot of bodily changes take place in males as well as in females., , The rate of general body growth begins to slow down, reproductive tissues begin to mature. Many changes, during puberty, such as new hair growth patterns are signals that sexual maturation is taking place., Gonad: An organ of our body in which gametes are produced, e.g. ovary in female or testis in a male., Gametes: A sexual reproduction cell containing a set of dissimilar chromosomes and dissimilar chromosomes, and assisting in fertilisation., Male reproductive system: It consists of parts which, produce the germ-cells and transfer them to the reproductive, passage for fertilisation. Some parts produce nourishing, liquid for sperms., 1. Testis: These are located outside the abdominal cavity, in scrotum, because sperm formation requires 1-3°C lower, temperature than normal body temperature. It secretes, testosterone which brings changes in boys at the time of, puberty. It is also responsible for male fertility., 2. Vas deferens: One of the pair of ducts carrying sperms, from testis to the urethra., 3. Seminal vesicle: It is one of the pair of glands in, males that secretes a liquid component of semen into vas, deferens. This secretion is alkaline, which neutralises acidic, conditions in female genital tract and contains fructose,, used by sperms as a source of energy., 4. Prostate gland: A gland in male mammals that surrounds and opens into the urethra, where it leaves the, bladder. During ejaculation it secretes slightly alkaline fluids into semen that activate the sperms and prevents, them from sticking together., , 66, , Science-10

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Semen: A slightly alkaline fluid (pH-7.2 to 7.6) containing sperms and various secretions of prostate and seminal, vesicle produced during copulation and introduced in the body of female by ejaculation., Sperms: These are male germ cells that consist of mainly genetic material and a long tail that helps them to move, towards the female germ cell., 5. Penis: The male reproductive organ of mammals (and also of some birds and reptiles), used to introduce, sperms into the female reproductive tract to ensure internal fertilisation. It contains a duct (urethra) through, which sperms can pass. The penis becomes erect during precopulatory activity by filling with blood or by action, of muscles and can be inserted into the vagina., 6. Urethra: It becomes common passage for urine and sperms., , Female Reproductive System, Ovaries: The female germ cells are made in ovaries. They are also, , responsible for the production of some hormones. When a girl is born,, the ovaries already contain thousands of immature eggs., Fallopian tube (oviduct): The egg starts maturing at puberty. The, egg is carried from the ovary to the womb through a thin oviduct or, fallopian tube. Fertilisation also takes place in fallopian tube in case, live sperms are present in it when egg reaches here., Uterus: The two oviducts unite into a elastic bag like structure known, as uterus. Uterus opens into vagina through the cervix., The uterus prepares itself every month to receive and nurture the, growing embryo. The lining thickens and is richly supplied with blood, to nourish the growing embryo., Female Reproductive System, Vagina: The tube leading from the uterus to the outside. Sperms are, deposited in the vagina during copulation and fully developed foetus is born through it (birth canal)., Fertilisation: The sperms enter through the vaginal passage during sexual intercourse. They travel upwards, and reach the oviduct, where they encounter the egg and may get fertilised., If the egg is fertilised, a child may be conceived., Zygote: The fertilised egg is called zygote, which starts dividing and gets implanted in the lining of uterus., The mother’s body is designed to undertake the development of the child., Embryo: A development stage which is nurtured in uterus. In mammals it is called foetus., Placenta: It is a disc like tissue which is embedded in the uterine wall. It contains villi on the embryo’s side of, the tissue. The embryo gets nutrition from mother’s blood with the help of this special tissue called placenta., On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose, and oxygen to pass from mother to the embryo., The developing embryo will also generate waste substances which can be removed by transferring them into, the mother’s blood through the placenta., Gestation period or Pregnancy: The development of child inside the mother’s body takes approximately, nine months. The child is born as a result of rhythmic contraction of the muscles in the uterus (labour)., Epidymis, Ductus vas, deferens, , Uterine, tube, , Ovary, , Testis, , Gonad,   , Umbilical cord: The connection between the foetus and placenta. It is usually cut through at the time of, child’s birth., Gamete, , What Happens When the Egg is Not Fertilised?, • If the egg is not fertilised, it lives for one to few days., • The ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised, egg., , How do Organism Reproduce? 67

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• The lining of uterus becomes thick and spongy so as to nourish the embryo, if fertilisation has taken place., • If the egg is not fertilised, the lining of uterus slowly breaks and comes out through the vagina as blood, and mucous. (Menses or menstrual flow), Menstruation: The release of blood and mucous occurs every month (28 days). It usually lasts for about 2 to, 8 days. Girls should use good sanitary napkin during this period and maintain proper hygiene. It starts from, puberty as ‘menarche’. Its beginning marks the fertile life of a female., The menstrual cycle is the series of changes a woman’s body goes through to prepare itself for a pregnancy., About once a month, the uterus grows a new lining (endometrium) to get ready for a fertilised egg. When there, is no fertilised egg to start a pregnancy, the uterus sheds its lining. This is the monthly menstrual bleeding, (also called menstrual period) that women have from their early teen age until menopause, age around 50 years., The menstrual cycle starts from day 1 of bleeding to day 1 of the next cycle of bleeding. Although the average, cycle is 28 days, it is normal to have a cycle that is shorter or longer., Girls usually start having menstrual periods between the age of 11 to 14 years., The hormones oestrogen and progesterone play the biggest roles in how the uterus changes during each cycle., • Oestrogen builds up the lining of the uterus., • Progesterone increases after an ovary releases an egg (ovulation) at the middle of the cycle. This helps the, oestrogen keep the lining thick and ready for a fertilised egg. A drop in progesterone (along with oestrogen), causes the lining to break down. This is when menstrual period starts., , Reproductive health, , • We must consider the possible health consequences of having sex before marriage or at early age. Our body, and mind may not be ready for the birth of a child and to take responsibility of the child., • STDs (Sexually Transmitted Diseases): Since the sexual act is very intimate connection between, the bodies, it is possible that many diseases can be sexually transmitted, like bacterial infection such as, gonorrhoea and syphlis and viral infections such as warts and HIV-AIDS., • We can protect ourselves from these diseases and unwanted pregnancy by using a latex covering called, condom for the penis during sex, it also helps to prevent transmission of many of these infections to some, extent. If condom gets torn during sexual act then danger of unwanted pregnancy and infection will exist., These days, emergency pill is being used by females to prevent unwanted pregnancy in case of unprotected, sex within 72 hours of unprotected intercourse, but it should not be taken regularly or frequently or without, consulting the doctor because chances of infections are still being there., • Pregnancy demands a lot from the body, mind and health of would be parents and it has a big responsibility., Contraceptive methods: The methods to prevent pregnancy are called contraceptive methods. They are also, used by married couples to avoid early pregnancy or to create a gap between two children., (i) Condoms: They are used as a covering on the penis by males. Females can also use a similar covering worn, in the vagina, which can serve the same purpose., (ii) Oral pills: These pills change the hormonal balance of the body so that egg is not released and fertilisation, cannot occur. These can also cause side effects, and should not be taken without consulting doctor., (iii) Intra Uterine Contraceptive devices (IUCD) : For example, loop or Copper-T is placed in the uterus by, doctors to prevent pregnancy. It may also cause side effects due to irritation in uterus., Surgical Methods: Surgical methods can be used to block vas deferens in males. These methods are safe, but, sometimes may cause infections if not performed properly. This process is called vasectomy. In females, small, portion of oviducts is removed surgically and the cut ends are ligated or tied. It prevents the ovum (or eggs), from entering into oviducts. It is called tubectomy., , Abortion, , • Surgery can be used for the medical termination of pregnancy (MTP) before first 3 months are over. Some, people may misuse this method for female foeticide., • Pre-natal sex determination is illegal in India., • Abortion after 20-24 weeks or around six months after pregnancy is risky and not allowed legally., • Sex ratio is abnormal in many states of India due to female foeticide, which needs to be prevented., • The size of human population is a cause of great concern, therefore population needs to be controlled and, also standard of living of poor people must be improved., Infertility problems: If vas deferens in males is blocked, sperm transfer may not take place. It can be treated, surgically, but sperm count can be less or quality and mobility of sperms may not be proper. Females fallopian, tubes may also get blocked which can be opened by surgery. These are natural problems which can be treated, easily by doctors., , 68, , Science-10

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Exercise 3.3, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. During adolescence, several changes occur in the human body. Mark one change associated with sexual, maturation in boys., (a) loss of milk teeth , (b) increase in height, (c) cracking of voice , (d) weight gain, 2. In human females, an event that reflects onset of reproductive phase is, (a) growth of body , (b) changes in hair pattern, (c) change in voice , (d) menstruation, 3. In human males, the testes lie in the scrotum, because it helps in the, (a) process of mating , (b) formation of sperm, (c) easy transfer of gametes, (d) all the above, 4. Which among the following is not the function of testes at puberty?, (i) formation of germ cells, (ii) secretion of testosterone, (iii) development of placenta, (iv) secretion of estrogen, (a) (i) and (ii) , (b) (ii) and (iii), (c) (iii) and (iv) , (d) (i) and (iv), 5. Fertilisation is the process of, (a) transfer of male gamete to female gamete., (b) fusion of nuclei of male and female gamete., (c) adhesion of male and female reproductive organs., (d) the formation of gametes by a reproductive organ., [CBSE 2020], II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Pollination is different from fertilisation., , Reason: The process of transfer of pollens from anther to stigma is called pollination which takes, place in plants., 2. Assertion: Pistil is male reproductive part of flower., , Reason: Pollen grain land on stigma and germinate., , III. Very Short Answer Type Questions, , (1 Mark), , 1. If a women is using copper-T, will it help in protecting against sexually transmitted diseases?, [NCERT], 2. What are those organisms called which bear both the sex organs in the same individual? Give one example of such organisms. , [Delhi 2016], 3. List two functions of ovary of human female reproductive system., [NCERT], 4. Why is fertilisation not possible without pollination in plants?, [Delhi 2016], 5. List two unisexual flowers., [Delhi 2016], 6. List two reasons for the appearance of variations among the progeny formed by sexual reproduction., [Delhi 2016], 7. List two functions performed by testis in human beings., [Delhi 2015], 8. Name the parts of a bisexual flower that are not directly involved in reproduction., [Delhi 2015], 9. What is the role of scrotum?, [HOTS], 10. How can the chromosomes be identified? , [CBSE 2014], 11. Why is temperature of scrotal sac 2°C less than the body temperature?, [CBSE 2012, 2014], 12. Differentiate between pollen grain and ovule., [CBSE 2011], 13. Differentiate between germination and fertilisation., [CBSE 2011], , How do Organism Reproduce? 69

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14. What are sexually transmitted diseases? Name a STDs which damages the immune system of human, body. , [CBSE 2015], 15. What happens when egg is not fertilised? , [CBSE 2012], 16. Why does the lining of uterus becomes thick and spongy during every month?, [CBSE 2013], 17. Give one difference between zygote and embryo., 18. Write the expanded form of AIDS., 19. Give an example of a flower which contains both stamens and carpels.[CBSE Sample Paper 2017-18], , IV. Short Answer Type Questions-I, , (2 Marks), , 1. How is the process of pollination different from fertilisation?, [NCERT], 2. What is the role of seminal vesicles and prostate gland?, [NCERT], OR, Write the functions of secretions of prostate gland and seminal vesicles in humans.[CBSE 2016], 3. List two preparations shown every month by the uterus in anticipation of pregnancy in the humans., [Delhi 2015], 4. Write the number of immature eggs present in the ovaries of newly born baby girl. Mention what, happens to these immature eggs when the girl attains maturity., [Delhi 2013], 5. Trace the path of sperms from where they are produced in human body to the exterior. [Delhi 2015], 6. What is the main difference between sperms and eggs of humans? Write the importance of this, difference. , [CBSE 2014], 7. The chromosomal number of the sexually producing parents and their offspring is the same. Justify, this statement., 8. Differentiate between plumule and radicle., [CBSE 2011], 9. Why do we need to adopt contraceptive measures?, [CBSE 2019] [CBSE 2012, 2013], 10. Give two differences between male gametes and female gametes., [CBSE 2012], 11. State one function each performed by following organs in human beings., (a) Testes, (b) Prostate gland. , [CBSE 2013], 12. Differentiate between the following:, (i) Role of placenta and uterus in pregnancy, (ii) Unisexual and bisexual flowers, , V. Short Answer Type Questions-II, , (3 Marks), , 1. What are the two roles of testosterone?, [CBSE 2015], 2. What are changes seen in girls at the time of puberty?, [NCERT], 3. List three techniques that have been developed to prevent pregnancy. Which one of these is not meant, for males? How does the use of these techniques have a direct impact on health and prosperity of a, family?[AI 2017], 4. Foetus derives its nutrition from the mother., (i) Identify the tissue used for above purpose. Explain its structure., (ii) Explain how wastes generated by developing embryo are removed., (iii) How does the birth of child take place?, 5. Draw the diagram of a female reproductive system and label the part which:, (i) Produces egg in female germ cell, (ii) Part where zygote is implanted., (iii) Path for entry of sperms., 6. Name the parts A, B and C shown in the following diagram and state one function of each. [Delhi 2016], , A, B, C, , 7. Name the reproductive parts of an angiosperm. Where are these parts located? Explain in brief the, structure of female reproductive parts., [Delhi 2016], , 70, , Science-10

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8. Suggest three contraceptive methods for birth control, which is essential for the health and prosperity, of a country. State the basic principle involved in each., [Delhi 2016], 9. List three distinguishing features between sexual and asexual types of reproduction in tabular form., [Delhi 2015], 10. Describe the structure and function of placenta., [Delhi 2014][AI 2017], 11. Differentiate between self pollination and cross pollination., [CBSE 2011], 12. Why are testes located outside the abdominal cavity? Mention the endocrine and exocrine functions of, the testes., [CBSE 2016], 13. List six specific characteristics of sexual reproduction., [CBSE 2016], 14. (a) State in brief the functions of following female reproductive system, (i) Ovary, (ii) Fallopian tube, (iii) Uterus, [CBSE 2017], (b) State in brief the functions of following male reproductive system, (i) Scrotum, (ii) Testes, (iii) Vas deferens , [CBSE 2011], 15. Why must pollination occur before fertilisation? How is pollination different from fertilisation? What does a, pollen contain inside?, 16. Mention the changes observed in flower after fertilisation., 17. How do sperms reach the female genital tract? Where fertilisation and implantation of the embryo, does take place? For how long does the embryo remain attached to uterine walls?, 18. Draw a labelled diagram of longitudinal section of pistil of flower showing germination of pollen grains, on the stigma. , [CBSE 2004], 19. State the basic requirements for sexual reproduction. Write the importance of such reproduction in, nature.[Delhi 2017], 20. State the changes that take place in the uterus when:, (a) Implantation of embryo has occurred., (b) Female gamete/egg is not fertilised., [Delhi 2017], 21. List any four steps involved in sexual reproduction and write its two advantages., [CBSE 2017], 22. Write one main difference between asexual and sexual mode of reproduction. Which species is likely to, have comparatively better chances of survival – the one reproducing asexually or the one reproducing, sexually? Give reason to justify your answer., , VI. Long Answer Type Questions, 1., , 4., , 3., , 4., , 5., 6., , (5 Marks), , (i) Identify A, B, C and D in the given figure. Write their names., A, (ii) What is pollination? Explain its significance., B, (iii) Explain the processes of fertilisation in flowers. Name the parts of the flower, that develop after fertilisation into (a) seed (b) fruit.[Delhi 2015], (i) Draw a sectional view of human female reproductive system and label the, C, part where (a) Egg develops, (b) fertilisation takes place, (c) fertilised egg gets, implanted.[Delhi 2013], (ii) Describe in brief the changes that uterus undergoes (a) to receive the zygote (b), if zygote is not formed., [Delhi 2014], D, List four points of significance of reproductive health in society. Name any two, areas related to reproductive health which have improved over the past 50 years., [CBSE 2016], Explain what happens when:, (a) Testosterone is released in males., (b) Pollen grains falls on the stigma of flowers., (c) Egg fuses with sperm cell., (d) Planaria is cut into many pieces., (e) Buds are formed on notches of the bryophyllum leaf. , [CBSE 2014, 2015], Write two causes of human population explosion. Explain with the help of a suitable examples how this, explosion can be checked. , [CBSE 2013], (a) Name the organ that produces sperms as well as secretes a hormone in human males. Name the, hormone it secretes and write its functions., (b) Name the parts of the human female reproductive system where fertilisation occurs., (c) Explain how the developing embryo gets nourishment inside the mother’s body.[Delhi 2017], , How do Organism Reproduce? 71

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7. (a) Draw the diagram of female reproductive system and match and mark the part (s):, (i) Where block is created surgically to prevent fertilisation., (ii) Where CuT is inserted., (iii) Inside which condom can be placed., (b) Why do more and more people prefer to use condoms? What is the principle behind use of condoms?, [CBSE Sample Paper 2018-19], 8. (i) Describe the role of prostate gland, seminal vesicle and testes in the human male reproductive, system., (ii) How is the surgical removal of unwanted pregnancies misused?, (iii) Explain the role of oral contraceptive pills in preventing conception., [CBSE Sample Paper 2019], 9. (a) List three different categories of contraception methods., (b) Why has Government of India prohibited prenatal sex determination by law? State its benefits in, the long run., (c) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused, due to unsafe sex., [CBSE 2020], 10. Trace the changes that take place in a flower from gamete formation to fruit formation., , Answers 3.3, I. 1. (c) cracking of voice, , 3. (b) formation of sperm, , 5. , II. 1., 2., III. 1., , 2. (d) menstruation, 4. (c) (iii) and (iv), , (b) fusion of nuclei of male and female gamete., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (d) ‘A’ is false but ‘R’ is true., No, it can only prevent unwanted pregnancy. It will not be able to prevent contact of body fluids., , 2. These are called hermaphrodites, e.g. earthworm and leech., 3. (i) Ovary produces eggs for fertilisation., (ii) They also produces hormones oestrogen and progestrone., 4. Fertilisation is the process in which pollen grain and egg fuse to form zygote. Pollination is the process, of transfer of pollen grains from stamen to the stigma of carpel. It means that fertilisation is not, possible without pollination., 5. Watermelon, Cucumber and Willows (Any two), 6. (i) Special cell division involved in the process of gametes formation is the cause of variations., (ii) Genetic material comes from two parents, which brings variations in offsprings., 7. (i) Testis produces sperms., (ii) It produces testosterone hormone., 8. Sepals and petals are not directly involved in reproduction., 9. Scrotum regulates the temperature of testes and maintains it at 35°C, two degree below the body, temperature, so as to protect sperms from high temperature., 10. Chromosomes can be seen as thread like structure having specific shape when cell is dividing by which, they can be identified., 11. Scrotal sac temperature is less by 2° because sperms are safe at a little lower temperature than body, temperature. It is outside the body that is why it has lower temperature than body., 12. Pollen grains contain male gametes in plants and ovules contain female gametes., 13. Germination: Involves development of embryo into a seedling., , Fertilisation: It involves fusion of male with female gametes., 14. Diseases that spread through the sexual contact are called STDs, AIDS damages the body’s immune system., 15. When egg is not fertilised, blood and mucus comes out through vagina. This process is called, menstruation., 16. The lining of uterus becomes thick and spongy by the action of progesterone to receive and nurture the, development of embryo., 17. Zygote is a single celled fusion product of sperm and ovum whereas embryo is a multicellular, product produced by mitotic divisions from zygote., , 72, , Science-10

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18. Acquired Immuno Deficiency Syndrome., 19. Hibiscus, Mustard (Any one), IV. 1. The process of transfer of pollens from anther to stigma is called pollination, which takes place only in, plants., Fertilisation is a process in which male sex cell and female sex cell join or fuse together to form zygote. It, happens in all living organisms, in sexual reproduction., 2. Seminal vesicle: It holds the liquid that mixes with sperm to form semen., , Prostate gland: It secretes fluid adding upto the semen and contains enzymes and other substances., It also provides nutrition to the sperms, in the form of fructose and calcium. It protects sperms., 3. (i) The inner uterine wall becomes thick., (ii) More blood vessels develop in its lining., 4. Ovaries contain thousands of immature eggs at the time of birth. Some of these eggs start maturing, when girls attain puberty. One egg is produced every month by one of the ovaries., 5. Testes Æ vas deferens Æ urethra Æ penis and then opens to outside., 6. Sperms are motile (movable) and have X or Y chromosomes whereas eggs are non-motile and have X, chromosome only., The sperms can reach to egg for fertilisation because these are motile. Chromosomes in them help in, determination of sex of a new born child., 7. (i) In sexual reproduction, fusion of male and female gametes takes place, each of their germ cells or, gametes contain half the number of chromosomes., (ii) When male and female gametes fuse at the time of fertilisation it restores the original number of, chromosomes of parent., Plumule, , 8., , Radicle, , It is part of growing embryo which gets converted The part of growing embryo which later forms the, into shoot of young plant., root of plant., It shows positive photoropism and negative It shows negative phototropism and positive, geotropism., geotropism., 9. (i) To prevent unwanted pregnancies., (ii) To prevent STD (Sexually Transmitted Diseases)., (iii) To have proper gap between two children., (iv) To control population., (v) To have sound health., Male gamete, , 10., , Female gamete, , It is smaller in size., , It is bigger in size., , It is motile., , It is non-motile., , , 11. (a) Formation of sperms takes place in testes., (b) Prostate gland contributes fluid to the semen., 12. (i) Placenta: The embryo gets nutrition from the mother’s blood with the help of a special tissue called, placenta., , Uterus: After fertilisation, embryo gets attached to the walls of uterus., (ii) Unisexual flowers: Flowers which contain either stamens or carpels., Bisexual flowers: Flowers which contain both stamens and carpels., V. 1., , (i) Testosterone regulates formation of sperms., (ii) The appearance of secondary sexual characteristics at puberty like beard, genital hair, change in, voice is due to testosterone., , 2. (i) Change in voice., (ii) Increase in size of breasts., (iii) Appearance of hair in armpit and genital hair (pubic hair)., , How do Organism Reproduce? 73

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(iv) Widening of hips., (v) Rapid physical growth., (vi) Onset of menstruation., 3. The three techniques which prevent pregnancy are:, (i) Barrier method, (ii) Chemical method (iii) Surgical method, Chemical methods are not for males., The use of contraceptive have a direct effect on the health and prosperity of the family., (i) To avoid unwanted pregnancy–if the woman is not physically or mentally prepared to bear a child, her health gets adversely affected., (ii) Contraception allows the parents to space the birth of two children and helps in family planning., (iii) This way they can decide how many children to have and allows them to bring them up properly, especially in case of limited resources. (or any other), 4. (i) Placenta is a disc like special tissue connection between embryo and uterine wall. It acts as an, endocrine gland. It possesses villi that increases the surface area for absorption of nutrients., Facilitates passage of nutrition and oxygen to embryo from mother through blood., (ii) Waste substances produced by embryo are removed through placenta into mother’s blood., (iii) Birth of child takes place after the gestation period (9 months inside the womb of mother). When, the contractions in muscles of the uterine walls is at highest then the birth of child takes place by, the birth canal., 5. (i) Ovary produces eggs, (ii) Zygote is implanted in womb or uterus, , (iii) Entry of sperms through vagina., , ‘A’ is anther. It contains pollen grains., ‘B’ is style. It allows growth in pollen tube up to the ovary from the stigma., ‘C’ is ovary. It contains ovules., The male reproductive part of an angiosperm is stamen. The female reproductive part is pistil/carpel,, which consist of stigma, style and ovary., , Stigma: It is the site for deposition of pollen grains after pollination., , Style: It is a tube that allows growth of pollen tube to reach the ovary., , Ovary: It contains ovules that develops into seeds., 8. (i) Barrier method: Condom is placed on the erect penis of male before sexual intercourse. In female,, a thin rubber disc is placed in the vagina, which covers the opening of cervix., (ii) Oral pills: Birth control pills can be taken to prevent pregnancy., (iii) Surgical methods: Use of copper-T in females, surgically implanted at the opening of the cervix,, prevents entry of sperms., Vasectomy in males, tubectomy in females can also help in population control. In vasectomy, sperm, ducts are cut. In tubectomy, oviducts are tied, blocked or cut. Sperms cannot reach the ova and, thus pregnancy is avoided., 6., , , 7., , 74, , Science-10

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9., , Asexual reproduction, , Sexual reproduction, , Only single parent is needed., , Two parents are involved., , Gametes are not produced., , Male and female gametes are produced., , Offsprings produced are identical to parent., , Offsprings are different from parent., , No mixing of genetic material., , Mixing of genetic material from both the parents., , It is not useful for natural selection in the evolution of It helps in natural selection in the evolution of species., species., It is a rapid process, under proper conditions., , It is a slow process., , 10. Structure of placenta: It is a special disc like tissue embedded in mother’s uterine wall, and connected to the foetus/embryo., , Functions of placenta: It provides a large surface area for glucose and oxygen/nutrients to pass from, mother’s body to the developing/developed embryo/foetus and also helps in passing the waste from the, foetus/embryo to the mother’s body., 11., , Self pollination, , Cross pollination, , (i) It involves transfer of pollen grains from, anther to stigma within the same flower., , (i) Cross pollination is the transfer of pollen, grains from anther to stigma in another flower, of another plants., , (ii) It occurs in same flower or in two flowers of (ii) It occurs between two flowers of different, same plant., plants but of same species., (iii) Flowers should be genetically same., , (iii) It occurs between flowers which are genetically, different., , 12. Sperm formation takes place at a lower temperature than body temperature therefore testes are, located outside the body and its temperature is 2°C below the body temperature., , Functions of Testes:, Endocrine Function: The production of testosterone hormone., , Exocrine Function: The production of sperms., , 13. (i) Two parents are involved, (ii) Two dissimilar gametes are formed, (iii) Variations are produced, (iv) Occurs in higher and some of lower organisms, (v) Fertilisation is needed for zygote formation, (vi) It is a slow process., , 14. (a) (i) Ovary: It produces ova and female sex hormones., (ii) Fallopian tube: It is the site of fertilisation and transfer of female gamete from the ovary., (iii) Uterus: Implantation of zygote and it keeps foetus till complete development., (b) (i) Scrotum: It protects testes., (ii) Testes: It produces sperms., (iii) Vas deferens: It delivers sperms from testes to urethra., 15. Pollination must occur before fertilisation as it has to reach the male gametes present in pollen grain, which will germinate to form a pollen tube and carry the male gametes to the ovum. Pollination, is different from fertilisation because here the pollen grain with its male gametes just reaches the, stigma, whereas fertilisation of male gamete to ovum results in formation of diploid zygote which is, the foundation of new generation., , 16. (i) Ovary ripens and developed into fruit., (ii) Ovules develop into seed., , How do Organism Reproduce? 75

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(iii) Petals and sepals wither and drop., (iv) Stigma, style and stamens dry up and fall off., 17. Sperms travel upwards through uterus to oviduct where they may meet an ovum and, hence fertilise it. Fertilisation takes place in oviduct to give rise to single celled zygote. The zygote, divides to become multicellular embryo which gets fixed in uterus. The embryo remains attached to, uterine walls throughout gestation period which is about 40 weeks in humans., 18., , 19. The basic requirements for sexual reproduction to take place are involvement of two parents and, fusion of their haploid gametes. In the sexual reproduction, a new individual is formed by the fusion of, two haploid gametes, one from the male parent and the other from the female parent. Since the new, individual formed is diploid in nature, the gametes must be formed by meiosis, so that chromosome, number can be reduced to half. When fusion of gametes occurs, the two nuclei of these two gametes, fuse and the chromosome number is restored to normal. The zygote, thus formed is diploid in nature., Importance of sexual reproduction:, Sexual reproduction involves fusion of male and female gametes coming from both the parents. The, fusion of these gametes results in genetic variations in the offsprings. This way sexual reproduction, promotes diversity of characters in offsprings by providing genetic variations. These genetic variations,, thus lead to evolution of species as well as allow the organisms to become better adapted in the changing, environment., 20. (a) When the implantation has occurred in uterus of the mother, the inner lining of the uterus, thickens and is richly supplied with the blood vessels to provide nourishment to the growing, embryo., (b) If the egg is not fertilised, it lives for about one day. Since, the thickened uterus lining is no more, required, it will slowly break down and come out through the vagina as blood and mucus known, as menstruation which lasts for about two to eight days., 21. The four main steps involved in sexual reproduction are:, (i) In the first stage of sexual reproduction, meiosis process occurs and the number of chromosomes, reduces from diploid (2n = 46) to haploid (n = 23) for each gamete., (ii) In the second stage, there is transfer of male gametes into the female body., (iii) In the third stage, the two gametes will fuse together after fertilisation, a single male gamete will, fuse with a female gamete. i.e. fertilisation process takes place., (iv) After fusion of male and female gametes, they form a zygote, in which the number of chromosomes, is restored to diploid (2n = 46)., The two main advantages of sexual reproduction are:, (i) There are more variations, which leads to better adaptability of the offsprings in the environment., (ii) Promotes the diversity in the characteristics of offspring, because it results by fusion of gametes., 22. Any one of the following differences:, (i) In sexual reproduction two opposite sexes are involved whereas in asexual reproduction only one, individual is involved., (ii) In sexual reproduction male and female gametes formation take place whereas in asexual reproduction, no gamete formation occurs., , 76, , Science-10

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• Sexually reproducing organisms have better chances of survival., , • This is because more variations are generated., VI. 1. (i) ‘A’ is stigma, ‘B’ is pollen tube, ‘C’ is ovary and ‘D’ is egg cell (female germ cell)., (ii) Pollination is a process of transfer of pollen grains from the anther of stamen to the, stigma of carpel. It is necessary for fertilisation by sexual reproduction., (iii) When male gamete and egg fuse together to form zygote, it is called fertilisation., It takes place in ovule. After that the ovule develops a tough coat and is gradually, converted into seed., Fruit: The ovary grows rapidly and ripens to form a fruit after ovule has been, fertilised., 2. (i) (a) Egg develops in ovary., (b) Fertilisation takes place in fallopian tube., (c) The fertilised egg gets implanted in uterus., , A, B, , C, , D, , (ii) (a) The inner uterus lining becomes thick to receive the zygote and is supplied with blood and, nutrients to nourish the embryo., (b) T,  he inner uterus lining breaks and released in the form of blood and mucus through vagina., 3. Significance of reproductive health in society are:, (i) Prevent STD (Sexually Transmitted Disease), (ii) Advantages of small family, (iii) Less mortality among new borns, (iv) Reduces cases of maternal mortality, , Two areas of Improvement are:, (i) Family planning. , (ii) Decrease in STD cases., 4. (a) (i) Formation of sperms and change in appearance., (ii) Thick hair growth on face stet and pubic region and change in voice., (b) A tube grows out of the pollen grain and travels through the style to the ovary., (c) Zygote is formed i.e. fertilisation takes place., (d) Each piece grows into new organism., (e) Buds may fall on the soil and change into new organism., 5. Two causes of human population explosion are:, (i) Reduced mortality rate due to better medical facilities., (ii) Desire for male child., (iii) Less awareness of birth control methods., (iv) Illiteracy and poverty., (Any two), Methods to check population explosion are:, (i) By using contraception methods., (ii) Awareness among people of the advantage of small family., 6. (a) The organ that produces sperms as well as secretes male hormone is testis. The hormone secreted, by it is testosterone. Its important functions are as follows:, It stimulates sperm production., It stimulates the development of secondary sexual characters in males like growth of beard hairs,, low pitch voice, etc. It involves in the development, maturation and functioning of the male, accessory sex organs like vas deferens and seminal vesicles, , How do Organism Reproduce? 77

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7., , (b) In human female reproductive system, the process of fertilisation takes place in one of the fallopian, tubes., (c) The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta., Placenta is a vascular membranous organ that connects the developing foetus to the uterine wall, of the mother. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood, spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass, from the mother to the embryo. The placenta draws nutrients and oxygen, which it supplies to the, foetus, from the maternal circulation. In turn, the placenta receives carbon dioxide and wastes of, foetal metabolism and discharges them into the maternal circulation for disposal., (a) (i) Fallopian Tube/Oviduct, (ii) Uterus, (iii) Vagina, , (b) People prefer use of condoms as it prevents STDs/gives privacy to the user. Condoms help create a, mechanical barrier preventing meeting of sperms and ovum., 8. (i) Prostate glands and seminal vesicle add their secretions so that the sperms are in a fluid state and, it makes their transport easier and also provides nutrition to sperms. Testes secrete testosterone, hormone which brings about changes in the appearance in the boys at the time of puberty., (ii) Female foeticides/illegal sex selected abortion of female child., (iii) Interfere in release of egg and eggs are not released., 9. (a) (i) Barrier method, (ii) Oral pills, (iii) Use of copper-T, (iv) Vasectomy in males, tubectomy in, females., (b) • It is because female foeticide is increasing., • It leads to unbalanced sex ratio i.e., more males, less females., On long run, it will help in maintaining healthier (equal) sex ratio., It will save mothers from illegal medical termination of pregnancy and health issues., (c) Gonorrhoea and syphilis are bacterial infections., Warts and HIV-AIDS are viral infections., 10. [Diagram drawn and annotated with the following points will also be considered], , – Stamen is the male reproductive part and it produces pollen, grains., • The ovary contains ovules and each ovule has an egg cell., • The pollen needs to be transferred from the stamen to the, stigma., • If this transfer of pollen occurs in the same flower, it is referred, to as self-pollination./ On the other hand, if the pollen is, transferred from one flower to another, it is known as crosspollination., , After the pollen lands on a suitable stigma, it has to reach the, female germ-cells which are in the ovary. For this, a tube grows, out of the pollen grain and travels through the style to reach, Germination of pollen on stigma, the ovary/Figure, • The male germ-cell produced by pollen grain fuses with the, female gamete present in the ovule., • This fusion of the germ-cells or fertilisation gives the zygote., • After fertilisation, the zygote divides several times to form an embryo within the ovule., , 78, , Science-10

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• The ovule develops a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens, to form a fruit., • Meanwhile, the petals, sepals, stamens, style and stigma may shrivel and fall off., , C ase study questions, , 1. The male reproductive system consist of portions which, produce the germ-cells and other portions that deliver the, germ-cells to the site of fertilisation. Testes are located, outside the abdominal cavity in scrotum because sperm, formation requires a lower temperature than normal, body temperature. It also has a role of secretion of male, sex hormone which brings changes in appearance seen, in boys at the time of puberty. Vas deferens unites wih a, tube coming from urinary bladder. Urethra is a common, passage for sperms and urine. Prostate gland and seminal, vesicles add their secretions so that sperms are now in, fluid., , (i) Name the sex hormone associated with males., (a) Testosterone (b) Progesterone, , (c) Oestrogen, , Seminal vesicle, Ureter, Bladder, Prostate gland, Penis, Urethra, , Vas deferens, , Testis, Scrotum, Human-male reproductive system, , (d) None of these, , (ii) Which of the following statements is incorrect ?, (a) Sperms are present in a fluid, (b) Fluid provides nutrition to sperms, (c) Fluid makes easier transportation of sperms, (d) Fluid helps to bind the sperms together, , (iii) Testes are located outside the abdominal cavity in scrotum because, (a) sperms formation requires higher temperature than body temperature, (b) sperms formation requires lower temperature than body temperature, (c) it is easier to transport sperms from the scrotum, (d) None of these, , (iv) Which of the following statement is incorrect?, (a) Sperms and urine has a common passage from urethra., (b) Sperms have long tail that helps them to move forward., (c) Sperms contain genetic material., (d) Sperms formation requires 1–3°C higher temperature than normal body temperature., , (v) What is the nature of semen?, (a) slightly acidic (b) Neutral, (c) Slightly basic, (d) Strongly basic, Ans. (i) (a), (ii) (d), (iii) (b), (iv) (d), (v) (c), 2. Study the table related to sex ratio of females/1000 males in different states and answer the questions, that follow:, State, , 2013-15, , 2012-14, , Andhra Pradesh, , 918, , 919, , Assam, , 900, , 918, , Bihar, , 916, , 907, , Chhatisgarh, , 961, , 973, , Delhi, , 869, , 876, , Gujarat, , 854, , 907, , How do Organism Reproduce? 79

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Haryana, , 831, , 866, , Himachal Pradesh, , 924, , 938, , Jammu & Kashmir, , 899, , 899, , Jharkhand, , 902, , 910, , Karnataka, , 939, , 950, , Kerala, , 967, , 974, , Madhya Pradesh, , 919, , 927, , Maharashtra, , 878, , 896, , Odisha, , 950, , 953, , Punjab, , 889, , 870, , Rajasthan, , 861, , 893, , Tamil Nadu, , 911, , 921, , Uttar Pradesh, , 879, , 869, , Uttrakhand, , 844, , 871, , West Bengal, , 951, , 952, , India, , 903, , 914, , , (i) Name the state which has males to female ratio to maximum extent in 2013-15., , (a) Haryana, , (b) Kerala, , (c) West Bengal, , (d) Uttar Pradesh, , (ii) What is major cause of less females than males in India?, , (a) Male Foeticide, , (b) Female Foeticide (c) Natural, , (d) None of these, , , (iii) Which test is responsible for female foeticide?, , (a) UV-Spectroscopy (b) Ultrasound, , (c) MRI, , (d) X-Ray, , , (iv) Which state of India has lowest sex ratio in 2013-15?, , (a) Punjab, , (b) Odisha, , (c) Haryana, , (d) Delhi, , , (v) Which of the following state improves sex ratio in 2013-15 from 2012-14?, , (a) Delhi, Ans. (i) (b), , (b) Karnataka, (ii) (b), , Quick revision notes, , (iii) (b), , (c) Bihar, (iv) (c), , (d) Kerala, (v) (c), , • Reproduction is not essential to maintain the life of an individual organism, unlike respiration, nutrition or, excretion. But it is essential to maintain the continuity of race., • Those organisms which may look similar to each other and can breed with each other to produce a fertile, offspring belong to the same species., • Reproducing organisms create new individuals that look very much like themselves., • Reproduction is linked to the stability of population of species., • The chromosomes in the nucleus of a cell contain information for the inheritance of features from parents, to their offsprings in the form of DNA (Deoxyribo Nucleic Acid) molecules. DNA makes genes hence express, themselves by regulating production of proteins in the cell. Offspring look similar to parents as they inherit, genes from their parents., • Before dividing a cell uses chemical reactions to build copies of their DNA (replication of DNA). Cell divides, to give rise to two new cells and both daughter cells receive one copy of DNA., , 80, , Science-10

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• DNA copies generated will be similar but may not be identical to the original due to errors during copying., • Division of cell is equivalent to cell reproduction. Organisms reproduce due to division in cells. Reproduction, can be of two types:, (a) Asexual: The cells divide to make identical cells keeping the chromosome number constant., (b) Sexual: It involves formation of gametes. They fuse to form zygote. Zygote once again multiplies keeping, the chromosome number constant., • During sexual reproduction gametes form due to a special cell division which not only reduces the, chromosome number to half but also brings minor changes in DNA. This results in genetic variations among, the offsprings., • Variations are useful for the survival of species over time., • The inbuilt tendency for variation during reproduction is the basis for evolution., • In asexual reproduction, the offspring arises from a single parent without the involvement of sex cells (or, gametes)., • Binary fission in Amoeba, budding in Hydra, spore formation in Rhizopus fungus (or bread mould),, regeneration in Planaria (flatworm), fragmentation in Spirogyra and vegetative propagation in flowering, plants like Rose plant are examples of asexual mode of reproduction., • Fission can be binary fission (divide into two), or multiple fission (splits into many new organisms)., • Artificial propagation of plants can be done by cutting, layering, grafting and tissue culture., • Sexual reproduction involves two parents by making use of gametes., • Human, fishes like shark, cats, dogs, horses, deer, rabbits, lions and most of the flowering plants reproduce, by sexual reproduction., • Sexual reproduction in flowering plants take place by pollination and fertilisation., • Sexual reproduction in animals involves the formation of sperms and egg, joining together to form zygote, and then form zygote to form the baby animal., • The male reproductive system involves testis, penis, seminal vesicle, prostate gland, vas deferens (sperm, duct), urethra., • Female reproductive system involves ovary, uterus, oviduct (fallopian tube), cervix, vagina. Fertilisation of, egg occurs in fallopian tube., • In human females, the ovaries start releasing ovum or egg (female gamete) once every 28 days from the age, of puberty. The first occurrence of this process (menstruation or periods cycle) at puberty is called menarche., • The permanent stoppage of periods cycle after attaining the age of 45 to 50 years is called menopause., • Birth control methods like barrier method (using condoms and diaphragm pills, IUCD (Intra-Uterine, Contraceptive Device), surgical methods (Vasectomy in males and Tubectomy in females) are essential to, control population and for gap between the birth of children., • STDs are sexually transmitted diseases like Gonorrhoea, Syphilis and AIDS., • By educating adoloscents and youth about reproductive issues, it could be possible to keep society healthy, and avoid problems like female foeticide., , Common Errors, Errors, , Corrections, , • Students do not make diagrams correctly, neatly ☞ Students must do practice of all diagrams in this, and do not label it properly., chapter and label them properly with pencil., • Students write wrong examples of asexual, reproduction., , ☞ Students should remember:, spirogyra–, fragmentation, planaria and hydra–regeneration,, Amoeba–binary fission, Plasmodium–multiple, fission, Rhizopus–spore, Hydra and Yeastbudding., , How do Organism Reproduce? 81

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• Students forget examples of unisexual flowers., , ☞ Papaya, watermelon have unisexual flowers., , • Students write function(s) of particular organ ☞ Understand and learn function(s) of each organ,, wrongly., then only you will be able to remember it., • Full form of abbreviations like STD, IUCD, MTP ☞ STD is sexually transmitted diseases, IUCD is, is not known to some students., intra uterine contraceptive devices, MTP stands, for medical termination of pregnancy (Abortion)., • Students interchange vasectomy with tubectomy., , ☞ Vasectomy is surgical method for males, and, tubectomy for females to prevent the unwanted, birth of children., , • Students write wrong spelling of biological terms ☞ Do practice of writing names of biological terms, and organs., and names of organs., • Students get confused between abortion and, miscarriage., , ☞ Abortion is decision taken by patient or doctor, whereas miscarriage takes place naturally due to, medical problems., , Assignment, , Total Marks : 20, , I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. A feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that, (a) they reproduce asexually, (b) they are all unicellular, (c) they reproduce only sexually, (d) they are all multicellular, 2. In Spirogyra, asexual reproduction takes place by, (a) breaking up of filaments into smaller bits, (b) division of a cell into two cells, (c) division of a cell into many cells, (d) formation of young cells from older cells., , II. Assertion-Reason Type Questions, , (1 Mark), , , Note: Use instructions as given in exercises of the chapter., 1. Assertion: STD are sexually transmitted diseases., , Reason: AIDS is STD., 2. Assertion: Gonorrhea and Syphilis are bacterial infections., , Reason: Health of women will not be affected if she adopts contraceptive measures., , III. Very Short Answer Type Questions, , (1 Mark), , 1. Which type of vegetative propagation is grafting?, 2. Mention the information source of making proteins in the cell. What is the basic event in the, reproduction?, , IV. Short Answer Type Questions-I, , (2 Marks), , 1. Why should a woman take oral pills after consulting doctors?, 2. List any two differences between pollination and fertilisation., 3. How is the process of pollination of different from fertilisation?, , V. Short Answer Type Question-II, , (3 Marks), , 1. What is reproduction? Mention the importance of DNA copying in reproduction., , VI. Long Answer Type Question, , (5 Marks), , 1. Define pollination. Explain the different type of pollination. List two agents of pollination? How does, suitable pollination lead to fertilization? , [Delhi 2019], , 82, , Science-10

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4, , Heredity and Evolution, , Topics Covered, 4.1 Accumulation of Variation during Reproduction and Heredity, , C hapter map, , Heredity, Accumulation of Variations, Heredity, Traits, Acquired, , Inherited, , Mendel’s experiments and, formulation of laws of genetics, How traits get expressed, Sex-determination, , Chromosomes, , Male, , Female, , Topic 1. Accumulation of Variation During Reproduction and Heredity, , Genetics: Branch of science that deals with heredity and variation., Heredity: It means the transmission of features/ characters/ traits from one generation to the next generation., Variation: The differences among the individuals of a species/ population are called variations., • There are two types of variations, , Somatic variation, , Gametic variation, , Takes place in the body, , Takes place in the gametes/cells., (Reproductive cells)., , Neither inherited nor transmitted, , Inherited as well as transmitted., , Also known as acquired traits., , Also known as inherited traits., , Example: boring of pinna, cutting of tails in dogs, , Example: human height, skin colour., , 83

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Accumulation of Variation during Reproduction, • Variations appear during reproduction whether organisms multiply asexually or sexually., Asexual Reproduction, Sexual Reproduction, Variations are fewer., , Variations are large., , Occurs due to small, inaccuracies in DNA copying Occurs due to crossing over and separation of, (mutation), chromosomes, (mutation)., , Importance of Variation, • Depending upon the nature of variations different individuals would have different kinds of advantage. For, example, bacteria that can withstand heat will survive better in a heat wave., • It increases the chances of its survival in a changing environment. Free ear lobes and attached ear lobes are, two variants found in human populations., • If one bacterium divides and again the resultant two bacteria divide, the four individual bacteria generated, will be highly similar, due to asexual reproduction., • There will be only minor differences between them, generated due to small inaccuracy in copying of DNA., • If sexual reproduction is involved, greater diversity will be generated., • All these variations in the species do not have equal chances of survival., • Different individuals would have different kind of advantages., • Evolution involves selection of variants by environmental factors., , Gene: It is a section of DNA that provides information for one protein in a cell., • If proteins works better and efficiently, the traits get expressed in better way. If protein helps in growth of, plant, it will be taller. If protein does not work properly, plant will be shorter. It means gene will control the, trait. It is a unit of inheritance., , Chromosome: Each gene set is present as separate independent pieces called chromosomes. Each cell will, , have two copies of each chromosome, one from each parent. The total number of chromosomes in the offspring, will be 46, 23 from mother and 23 from father., , Mendel and His Work on Inheritance, Gregor Johann Mendel (1822-1884): Started his experiments on plant breeding and hybridization, • Mendel was known as the Father of Genetics, , Plant selected by Mendel: Pisum Sativum (garden pea). Mendel used a number of contrasting characters, for garden pea., , Table of Contrasting Characters (Seven Parts), , Character, , Dominant Trait [capital letter], , Recessive Trait [small letter], , Flower colour, , Violet, , V, , White, , v, , Flower position, , Axial, , A, , Terminal, , a, , Seed colour, , Yellow, , Y, , Green, , y, , Seed shape, , Round, , R, , Wrinkled, , r, , Pod shape, , Inflated, , I, , Constricted, , i, , Pod colour, , Green, , G, , Yellow, , g, , Height of plant, , Tall, , T, , Dwarf, , t, , • Seven pairs of contrasting characters in garden pea and total 14 varieties of plant were studied by Mendel., , Genetic Terminology, Gene: Mendel used the term factor for a gene. A gene is the unit of DNA responsible for the inheritance of, character., , 84, , Science-10

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Allele: A pair of genes that control the two alternatives of the same character e.g., TT/tt., Heterozygous: The organism in which both the genes of a character are unlike e.g., Tt., Homozygous: The organism in which both the genes of a character are similar e.g., TT, tt., Dominant: The gene which expresses itself in F1 generation is known as dominant gene., Recessive: The gene which is unable to express itself in presence of the dominant gene., Genotype: It is the genetic constitution (genetic makeup) of an organism which determines the characters., Phenotype: It is the physical appearance of an individual. (Tall or short), Mendel’s Experiments: Mendel conducted a series of experiments in which he crossed the pollinated plants, to study one character (at a time), TT, tt, -----Pure or homozygous condition, Tt, -----Heterozygous condition or Hybrid, , Phenotypic ratio: Ratio among numbers of individuals with different external features, e.g., 3:1, Genotype → Genetic makeup [TT, Tt or tt], , Genotypic ratio: Ratio among numbers of individuals with different genetic make up, e.g., 1:2:1, , Monohybrid Cross:, • Cross between two pea plants with one pair (monohybrid cross) contrasting characters,, Example: Tall or Short Plants., Parent Generation , Tall plant, ×, Dwarf plant, , TT ×, tt, Gametes , T, T , t, t, (Ovules) (pollen), F1 Generation T T, (first filial generation) , t, T t , Tt, t, Tt Tt, Genotypic and phenotypic ratio , All hybrid tall plants Tt, , Self Pollination (F1), ×, (F1), Gametes , T, F2 Generation, (Second Filial Generation) , , T, , , t, , , t , T , TT , Tall , Tt , Tall , , T, , t, , t, Tt, Tall, tt, Short, , , Phenotypic ratio, , = 3:1, Genotypic ratio, = 1:2:1, Both dominant gene TT : One dominant, one recessive gene Tt : Both recessive gene tt., , Observations:, • All F1 progeny were tall. , • F2 progeny ¼ were short and, ¾ were tall., • Phenotypic ratio: F2, , –, , 3:1, , • Genotypic ratio: F2, , –, , 1:2:1, , Conclusions:, TT and Tt both are tall plants while tt is a short plant., • A single copy of T is enough to make the plant tall, while both copies have to be t for the plant to be short., • Character/ Trait like ‘T’ is called dominant trait (because it expresses itself) and ‘t’ is recessive trait (because, it remains suppressed)., , Heredity and Evolution 85

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Law of independent assortment, • Genes for different traits can segregate independently during the formation of gametes., , Mechanism of Heredity: Most of the characters or traits of an organism are controlled by the genes. Genes, , are actually segments of DNA guiding the formation of proteins by the cellular organelles. These proteins may, be enzymes, hormones, antibodies, and structural components of different types of tissues. In other words,, DNA/ genes are responsible for structure and functions of a living body. Genotype of an individual controls its, phenotype., , • Since we inherit half of our chromosomes[genes] from each of our two parents, hence we resemble both of, them or their side of family members. For the same reasons, siblings resemble each other too. But if there are, errors during DNA copying, genes may get altered and variation may appear in the form of a defect, disease, or simply changed phenotype. Sexual reproduction is also a source of variation., , Sex Determination, , • Phenomenon of decision or determination of sex of an offspring., , Factors Responsible for Sex Determination, Environmental: In some animals the temperature at which the fertilised eggs are kept decides the gender., e.g. in snails, some lizards and turtle., In some animals like humans gender of individual is determined by a pair of chromosomes called sex, chromosomes., , Sex Chromosomes: In human beings there are 23 pairs of chromosomes. Out of these 22 pairs of chromosomes, are called autosomes and the last pair of chromosomes that help in deciding gender of that individual are called, sex chromosomes. XX – female; XY – male., , Sex determination in Human beings, , • Male produces two genetic types of sperms, half with X and other half with Y chromosome. The female, produces only one genetic type of ova, all carrying X chromosome., • This shows that, • All children will inherit an X chromosome from their mother regardless whether they are boys or girls., • Thus sex of children will be determined by what they inherit from their father, and not from their mother., , Heredity and Evolution 87

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Exercise 4.1, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. Exchange of genetic material takes place in, (a) vegetative reproduction, (b) asexual reproduction, (c) sexual reproduction , (d) budding, 2. Sugarcane field has little variation because of, (a) sexual reproduction , (b) asexual reproduction, (c) Both (a) and (b) , (d) None of these, 3. When two parents are crossed, the offsprings are referred to, (a) F1 generation , (b) F2 generation, (c) Either F1 or F2 , (d) None of these, 4. A cross between two individuals result are in ratio of 9:3:3:1. The cross is, (a) Monohybrid cross , (b) Dihybrid cross, (c) Cross-pollination , (d) Self pollination, 5. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea, plants bearing white flowers. In the progeny, all bore violet flowers, but almost half of them were short., This suggests that the genetic makeup of tall plant can be depicted as, (a) TTWW, (b) TTww, (c) TtWW, (d) TtWw, [NCERT], 6. Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds, produce F1 progeny that have round, yellow (RrYy) seeds. When F1 plants are selfed, the F2 progeny, will have new combination of characters. Choose the new combination from the following., (i) Round, yellow , (ii) Round, green, (iii) Wrinkled, yellow , (iv) Wrinkled, green, (a) (i) and (ii), (b) (i) and (iv), (c) (ii) and (iii), (d) (i) and (iii), 7. Select the statements that describe characteristics of genes, (i) genes are specific sequence of bases in a DNA molecule, (ii) a gene does not code for proteins, (iii) in individuals of a given species, a specific gene is located on a particular chromosome, (iv) each chromosome has only one gene, (a) (i) and (ii), (b) (i) and (iii), (c) (i) and (iv), (d) (ii) and (iv), II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 to 4 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given ahead:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: If one bacterium divides then two resultant bacteria divide again to generate four individual, bacteria which will be highly identical., , Reason: It is due to asexual reproduction., 2. Assertion: Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny., , Reason: It is due to double fertilisation., 3. Assertion: The sex of a child in human beings will be determined by the type of chromosome he/she, inherits from the father., , Reason: A child who inherits ‘X’ chromosome from his father would be a girl (XX), while a child who, inherits a ‘Y’ chromosome from the father would be a boy (XY)., [CBSE 2020], 4. Assertion: Dominant traits express itself with or without the presence of recessive trait., , Reason: Recessive trait can express itself only in absence of dominant trait., 5. Assertion: A geneticist crossed a pea plant having violet flowers with a pea plant with white, , flowers, he got all violet flowers in first generation., , , Reason:, , 88, , White colour gene is not passed on to next generation., , Science-10

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III. Very Short Answer Type Questions, , (1 Mark), , 1. If a trait ‘A’ exists in 10% of the population of asexually reproducing species and trait ‘B’ exists in 60%, of the same population, which trait is likely to have arisen earlier?, [NCERT], 2. How does the creation of variations in a species promote survival?, [NCERT], 3. What is DNA?, [Delhi 2016], 4. Where is DNA found in the cell?, [Delhi 2015], 5. Give the respective scientific names used for studying:, (i) the mechanism by which variations are created and inherited by organism from the previous, generation., (ii) the development of new type of organisms from the existing ones., [Delhi 2014], 6. What is a gene?, [Delhi 2014], 7. Name the information source for making proteins in the cells., [Delhi 2014], 8. What is heredity?, [Delhi 2014], 9. No two individuals are absolutely alike in a population. Why?, 10. All the variations in the species do not have equal chances of survival. Why?, [Delhi 2014], 11. Why do mice whose tails were surgically removed, continue to produce mice with tails?, 12. A tall plant is crossed with a dwarf plant. What will be the ratio of homozygous tall and heterozygous, dwarf plant in F2 generation?, 13. Name the genetic material that is responsible for the inheritance of traits., [Delhi 2014], 14. Do genetic combination of mothers play a significant role in determining the sex of a new born?, [HOTS], 15. A man with blood group ‘A’ marries a woman with blood group ‘O’ and their daughter has blood group, O. Is this information enough to tell you which of the traits-blood group A or O is dominant? Why or, why not?, [NCERT] [HOTS], 16. What type of traits are phenotype?, [HOTS], 17. What is genotype?, [HOTS], 18. State Mendel’s first law of inheritance., [HOTS], 19. State Mendel’s second law of inheritance., [HOTS], 20. What is variation?, 21. Name the human traits which show variations., [HOTS], 22. What is monohybrid cross?, [HOTS], 23. What is the scientific name of man and garden pea?, 24. What are sex chromosomes?, [HOTS], 25. What are chromosomes? Where are they located?, [HOTS], 26. What indication do we get by appearance of dwarf plant in F2 generation?, 27. Why is it that asexual reproduction produces exact copies but sometimes minor variations are seen in, next progeny?, 28. Name the term used for traits that are exhibited externally., [CBSE 2014], 29. Give an example where sex determination is regulated by environmental factors., [CBSE 2014], 30. Name the plant on which Mendel performed his experiments., [CBSE 2013, 14], 31. Mendel observed a contrasting trait in relation to position of flowers. Mention that trait., 32. In order to ensure than Mendel gets pure breeding plants in his experiments, what did he do?, 33. A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing, white flowers. What will be the result in F1 progeny?, [CBSE 2018], 34. How can chromosomes be identified?, [CBSE 2015], 35. What is sex of the baby that inherits Y-chromosome from the father?, [CBSE 2014], , IV. Short Answer Type Questions-I, , (2 Marks), , 1. The chromosomal number of the sexually producing parents and their offspring is the same. Justify, this statement., [Delhi 2014], 2. How do Mendel’s experiments show that traits may be dominant or recessive?, [NCERT], 3. List two differences in tabular form between dominant traits and recessive traits., 4. Why are small number of surviving tigers a cause of worry from genetics point of view?, [NCERT], , Heredity and Evolution 89

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5. A study found that children with light-coloured eyes are likely to have parents with light-coloured, eyes. On this basis, can we say anything whether the light eye colour trait is dominant or recessive?, Why or why not?, [NCERT] [HOTS], 6. (a) On what rules inheritance is based? , [CBSE 2016], (b) Is each trait influenced by both parental and maternal DNA?, 7. What is F2 generation? , [CBSE 2015], 8. If YYRR is round yellow, what do the following represent?, [CBSE 2015], yyrr, yyRR, 9. In a monohybird cross between tall pea plants denoted by TT and short pea plant by tt, Sehaj Anant, obtained only tall plants denoted by Tt in F1 generation. However in F2 generation she obtained both, tall and short plants. Using the above information explain the law of dominance., [CBSE 2013, 14], 10. How can we say that change in genes can be brought by the change in DNA?, [CBSE 2014], 11. Where are genes located? What is the chemical nature of genes?, [CBSE 2014], 12. Sex determination in man depends upon 23rd pair of chromosomes, called the sex chromosomes. If, it were a homologous pair-XX, it would be a female. If it were a heterologous pair – XY, it would be a, male. Based on this statement, answer these questions:, (i) How many types of eggs/ova and how many type of sperms female and male human being will, produce respectively ?, (ii) Which parent’s contribution of sex chromosomes determines sex of the child?, 13. (a) What is genetic constitution of human sperm?, (b) Mention the chromosome pair present in zygote determining the sex of male child., , V. Short Answer Type Questions-II, , (3 Marks), , 1. Study the following cross showing self pollination in F1, fill in the blank and answer the question that, follow:, Parents, RRYY, ×, rryy, , Round, yellow , Wrinkled, green, , F1, Rr Yy, ×, .........................., What are the combinations of character in the F2 progeny? What are their ratios?[NCERT Exemplar], 2. Explain the Mendel’s concept of heredity, by giving three points., [CBSE 2016], 3. An angiosperm plant having red flowers when crossed with the other having same colour flower, produced 40 progenies, out of which 30 were red coloured flowers, 10 plants were with white flowers., Find out:, (i) What is the possible genotype of parent plants?, (ii) Which trait is dominant and recessive?, (iii) What is the cross called and what is phenotype ratio?, [CBSE 2016], 4. In a pea plant, find the contrasting trait if, (i) The position of flower is terminal., (ii) The flower is white in colour, (iii) Shape of pod is constricted., 5. A cross was carried out between pure breed tall pea plant with pure dwarf pea plant and F1 progeny, was obtained. Later, F1, progeny was selfed to obtain F2 progeny. Answer the following questions:, [CBSE 2013, 2014], (a) What is the phenotype of the F1 progeny and why?, (b) Give the phenotypic ratio of the F2 progeny., (c) Why is F2 progeny different from the F1 progeny?, 6. ‘DNA is the carrier of the genetic information’. Justify., 7. ‘‘It is a matter of chance whether a couple will have a male or a female child.’’ Justify this statement, by drawing a flow chart., [Foreign 2015], OR, In humans, there is a 50% probability of the birth of a boy and 50 % probability that a girl will be born., Justify the statement on the basis of the mechanism of sex-determination in human beings., [CBSE Sample Paper 2021], , 90, , Science-10

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8. What do you understand by the following terms:, (i) Phenotype , (ii) Genotype, (iii) Dominant trait , (iv) Recessive trait, (v) Factors or Genes, 9. Mention the total number of chromosomes along with the sex chromosomes that are present in a human, female and a human male. Explain how in sexually producing organisms the number of chromosomes, in the progeny remains the same as that of the parents., [Delhi 2017], OR, What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes, in the progeny is maintained.[CBSE 2020], 10. How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism?, [CBSE 2017], OR, ‘‘It is possible that a trait is inherited but may not be expressed.’’ Give a suitable example to justify this, statement. , [Foreign 2015], 11. In a pea plant, the trait of flowers bearing purple colour (PP) is dominant over white colour (pp)., Explain the inheritance pattern of F1 and F2 generations with the help of a cross following the rules of, inheritance of traits. State the visible characters of F1 and F2 progenies., 12. After self-pollination in pea plants with round, yellow seeds, following types of seeds were obtained by, Mendel:, , Seeds, , Number, , Round, yellow, , 630, , Round, green, , 216, , Wrinkled, yellow, , 202, , Wrinkled, green, , 64, , Analyse the result and describe the mechanism of inheritance which explains these results., , [CBSE Sample Paper 2021], , VI. Long Answer Type Questions, , (5 Marks), , 1. How do Mendel’s experiments show that traits are inherited independently?, [AI 2016], 2. How do Mendel’s experiments show that, (a) traits may be dominant or recessive?, (b) inheritance of two traits is independent of each other?, [Delhi 2017], 3. (a) What is the law of dominance of traits? Explain with an example., (b) Why are the traits acquired during the life time of an individual not inherited? Explain., [CBSE 2020], , Answers 4.1, I. 1. (c) sexual reproduction, , 3. (a) F1 generation, , 5. (c) TtWW, , 7., II. 1., , 2., , 3., , 4., , 5., III. 1., , 2. (b) asexual reproduction, 4. (b) Dihybrid cross., 6. (b) (i) and (iv), , (b) (i) and (iii), (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false because it is due to self pollination., (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., Trait ‘B’ is likely to have arisen earlier, because it has higher percentage in the population. In asexual, reproduction, the traits which are present in parent generation are carried over to next generation, with minimum variation., , Heredity and Evolution 91

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2. Variations lead to adaptation of an organism, which is then able to survive in difficult and unfavourable, environmental conditions. It means variations promote survival., 3. DNA stands for deoxyribonucleic acid. It is self replicative, molecule present in all living organisms as, the main constituent of chromosomes. It passes on genetic characteristics to offsprings., 4. DNA is found in the nucleus of the eukaryotic cells and cytoplasm of prokaryotic cells. It is also present, in plastids and mitochondria., 5. (i) Heredity (ii) Evolution, 6. Gene is the unit of heredity present in chromosomes, DNA which directs specific protein synthesis,, when it is passed from the parent to the offspring., 7. DNA, 8. Heredity is a process in which traits are passed onto the offspring from parents., 9. Sexual reproduction involves combination of genes from two parents, the genetic material gets, exchanged between pairs of chromosomes before formation of their gametes which cause changes., 10. All variations will not be able to survive in the environmental changes, which is an essential requirement, for survival., 11. It is because cutting of tail is done surgically and it is not inherited., 12. The ratio of homozygous tall and heterozygous dwarf plant in F2 generation is 3 : 1., 13. Gene or DNA, 14. No, mother does not play an important role because mother has only ‘X’ chromosomes whereas father, has both X and Y chromosomes. When offspring takes ‘X’ from mother and ‘Y’ from father, then baby, boy is born., If offspring takes ‘X’ chromosomes from mother as well as father, girl child is born. The probability of, getting boy or girl is 50 : 50., 15. The information is not sufficient because information is confined upto two generation. We need, information about third generations to predict the dominant trait., 16. The traits which are visible to us are called phenotype, e.g. tall or dwarf (short) are phenotype traits of, the plants., 17. Genotype shows the genetic constituent of an organism, i.e. it is the description of genes present in, an organism. For example, TT, Tt or tt where T and t are the different forms of the same gene. The, genotype of tall plant is TT and that of dwarf plant is ‘tt’., 18. Mendel’s first law, also known as the law of segregation states that ‘during gamete formation, the, alleles of the character segregate in such a way that each gamete carries only one allele for each gene’., 19. Mendel’s second law, also known as the law of independent assortment states ‘that for different traits, genes segregate independently during the formation of gametes’., 20. Variation is the difference in characteristics or traits among the individuals in a particular species., 21. (i) Colour of eye, (ii) Height, (iii) Colour of skin, 22. Monohybrid cross is the cross between two individuals with one pair of different traits., 23. Man — Homo sapiens, Garden pea — Pisum sativum, 24. Those chromosomes which decide whether the offspring will be male or female are called sex, chromosomes. Many animals have two types of chromosomes. Human beings have ‘X’ and ‘Y’ sex, chromosomes., 25. Chromosomes are long thread like structures which contain genetic information of an individual., These are located in the nucleus of a cell., 26. After obtaining F2 progeny from F1 generation in the dihybrid cross, Mendel concluded that when two, pairs of traits are combined in a hybrid, one pair of character segregates independently from the other, pair of character., 27. Bio-chemical reactions are not fully reliable, therefore, it may cause slight difference which causes, these variations., 28. Phenotype., 29. In snail, sex is determined by temperature i.e., environmental factor., 30. Garden pea (Pisum Sativum), 31. Terminal flowers have recessive trait whereas axial flowers have dominant trait., , 92, , Science-10

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32. Mendel allowed each variety to self fertilise for several generations., 33. Violet flowers, 34. Individual chromosomes can be identified by their lengths, position of centromere and binding pattern, of staining and shape., 35. Male, IV. 1. Offspring always takes 23 chromosomes from father and 23 chromosomes from mother and in total has, 46 chromosomes. It means that total number of chromosomes remain constant., 2. • Mendel selected pure breed of tall (TT) and short (tt) pea plants., • He crossed these plants and carefully produced seeds. This is called F1 generation., • All the plants in F1 generation were tall, showing that tallness is dominant trait., • Now these plants were self pollinated., • In the F2 generation, 3 out of 4 plants, i.e. 75% were tall and one out of four, i.e. 25% were short, plants. It shows that shortness is the recessive trait., 3., , Dominant traits, , Recessive traits, , I t expresses itself with or without the presence of, recessive trait., , I t is able to express itself only in the absence, of dominant trait., ,  or example: tall plant, round seed, violet flower, F, etc. are dominant traits in a pea plant., ,  warf plant, wrinkled seed, white flower, etc., D, are recessive traits in a pea plant., , (i) Tigers may get extinct in near future due to natural calamities, lack of available food and due to, their small number., (ii) Cross breeding may be less possible. Variations will not occur, which is essential for the survival., (iii) Adaptation due to changing environment, like cutting of forests, global warming becomes difficult., (iv) Protection from enemies is easy if they are more in number., 5. We cannot predict because information is not sufficient. We can decide dominant or recessive trait if, we have the data for at least three generations. More information is required., 6. (a) (i) Law of dominance. (ii) Law of segregation (iii) Law of independent assortment, (b) Yes, each trait is influenced by DNA of both parents., 7. The generation produced by the offsprings of F1 generation is called F2 or second generation., 8. yyrr – wrinkled, green seeds, yyRR – Round, green seeds., 9. According to law of dominance, dominant trait is expressed in F1 generation although dominant as, well as recessive traits are inherited. Single copy of dominant trait is sufficient for expression of tall, dominant trait in F1 generation., 10. A gene is present on a segment of DNA chromosome., (i) It provides information of one protein to another and is responsible for its change., (ii) It ensures stability of DNA., It means change in gene segment of DNA will bring change in DNA., 11. Genes are located on chromosomes at fixed positions. They are made of nucleic acid (DNA) therefore, acidic in nature., 12. (i) Male produces two genetic types of sperms, half with X and other half with Y chromosome. The, female produces only one genetic type of ova, all carrying X chromosome., (ii) Sex of children will be determined by what they inherit from their father, and not from their, mother., 13. (a) 22 + Y chromosome or 22 + X chromosomes., (b) (22 + X + 22 + Y) = (44 + X + Y) chromosomes., V. 1. F1 progeny is Rr Yy-Round, Yellow, Combinations of character in the F2 progeny are:, (i) Round yellow — 9 (Both dominant traits), (ii) Round green — 3 (One recessive, one dominant), 4., , Heredity and Evolution 93

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(iii) Wrinkled yellow — 3 (One dominant, one recessive), (iv) Wrinkled green — 1 (both recessive traits), The ratio is 9 : 3 : 3 : 1, 2. (i) Mendel worked on pea plant., (ii) He found that traits are controlled by genes which come in pairs., (iii) Genes are inherited as separate units, one from each parent., 3. (i) Rr and Rr, (ii) Red colour of flower is dominant trait while white colour is the recessive trait., (iii) Monohybrid cross, phenotype ratio is 3 : 1., 4. (a) Axial position of flower., (b) The flower is violet in colour., (c) Shape of pod is inflated., 5. (a) Tall because it is a dominant trait whereas dwarf is a recessive trait., (b) 3 : 1 is ratio between tall to dwarf., (c) In F2 generation, recessive genes are also expressed in homozygous condition., 6. Most of the characters or traits of an organism are controlled by the genes. Genes are actually segments, of DNA guiding the formation of proteins by the cellular organelles. These proteins may be enzymes,, hormones, antibodies, and structural components of different types of, tissues. In other words, DNA (genes) is responsible for structure and, functioning of a living body. Genotype of an individual controls its, phenotype., In human beings there are 23 pairs of chromosome. We inherit half, of our chromosomes (genes) from our two parents. This means half, of DNA in each cell has been inherited from each parent, hence we, resemble both of them or their side of family members., 7. Justification: Women produce only one type of ovum (carrying X, chromosome) and males produce two types of sperms (carrying either X, or Y chromosome) in equal proportions. So the sex of a child is a matter, of chance depending upon the type of sperm fertilising the ovum., 8. (i) Phenotype: The set of characteristics observed in an individual as, a result of interaction of its genotype with the environment., (ii) Genotype: The genetic make up of the cell which determines the, characteristics (phenotype) of an organism., (iii) Dominant trait: The trait of the parent that expresses itself in the, offspring., (iv) Recessive trait: The trait of the parent appearing in the offspring, which cannot express itself in the presence of dominant trait., (v) Factors or Genes: The units of inheritance responsible for a trait in an individual., 9. Chromosomes are long thread like structures which contain heriditary information of individual and, are carrier of genes., The total number of chromosomes present in both human male and female is 46. Out of these, two, chromosomes are the sex chromosomes. In human males, the two sex chromosomes present are X and Y,, while in human female, both sex chromosomes are X., During sexual reproduction, the new individual is formed by the fusion of gametes from both the parents., These gametes are haploid in nature, i.e. they contain only one set of the chromosomes. They are formed, by the meiosis, a type of cell division which reduces chromosome number to half. When these haploid, gametes fuse during fertilisation, the two nuclei of these gametes fuse and the chromosome number is, then restored to normal. Hence, the progeny formed has the same number of chromosomes as that of the, parents., 10. Some traits that are inherited may not express themselves. Such hidden traits are known as recessive, traits. Mendel explained this phenomenon with the help of monohybrid cross. In a monohybrid cross, performed by Mendel, a tall plant was crossed with a dwarf plant which produced all tall plants in Fl, progeny., , 94, , Science-10

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However, when these F1 tall plants were crossed with each other, ‘dwarf’ trait, which was not observed, in the Fl generation, reappeared in the F2 progeny., , Parents, X, , Pure tall plant, (TT), , Pure dwarf plant, (tt), , P1 generation, (Tt), , Selfing of F1 plants, , (Tt), , X, (Tt), , (Tt), , F2 generation, , (Tt), , (Tt), , (Tt), , (tt), , By this, it is concluded that dwarfness is a trait of parent pea plant that was not lost. It was suppressed, in the F1 generation by the tallness trait and reappeared in the F2 generation. So, we can say that a, trait that is inherited may not be always expressed in an organism., 11. Let purple trait be represented by: PP, White trait be : pp, , parents: PP X pp, , ↓, F1 Pp X Pp (Selfing), , ↓, Gametes, , P, , p, , P, , PP, , Pp, , p, Pp, pp, Visible characters of F1 progeny has all flowers purple coloured and in F2 progeny 3 are purple coloured, and 1 is white coloured flower., 12. The ratio obtained is 9:3:3:1 in which parental as well as new combinations are observed. This indicates, that progeny plants have not inherited a single whole gene set from each parent. Every germ cell takes, one chromosome from the pair of maternal and paternal chromosomes. When two germ cells combine,, segregation of one pair of characters is independent of other pair of characters., VI. 1. Mendel carried out dihybrid crosses by crossing two pea plants differing in contrasting traits of two, characters. For example, he crossed a pea plant having yellow colour and round seed characters with, another pea plant bearing green colour and wrinkled seed characters. In the F2 generation, he obtained, pea plants with two parental and two recombinant phenotypes as yellow round and green wrinkled, (parental) and yellow wrinkled and green round (recombinant). This indicated that traits separated, from their original parental combinations and got inherited independently., , Heredity and Evolution 95

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2. (a) Mendel demonstrated that traits can be either dominant or recessive through his monohybrid cross., He crossed true-breeding tall (TT) and dwarf (tt) pea plants. The seeds formed after fertilisation, were grown and the plants that were formed represent the first filial or F1 generation. All the F1, plants obtained were tall., Then, Mendel self-pollinated the F1 plants and observed that all plants obtained in the F2 generation, were not tall. Instead, one-fourth of the F2 plants were short., (For diagram refer to Ans. 10, Short Answer Type Questions-II), RRyy, From this experiment, Mendel concluded that the F1 tall, plants were not true breeding; they were carrying traits Parents Round green, of both short height and tall height. They appeared tall, only because the tallness trait was dominant over the, Ry, dwarfness trait. This shows that traits may be dominant Gametes, or recessive., , (b) Mendel demonstrated that traits are inherited, independently through his dihybrid cross. He considered, two traits at a time, seed colour and seed shape in F1 generation, which yellow colour (YY ) and round shape (RR) are, dominant over green colour (yy) and wrinkled shape, (rr), respectively., , rrYY, Wrinkled yellow, , rY, , RrYy, Round and Yellow, , Mendel cross bred the plants and observed that the F2 progeny of dihybrid cross had a phenotypic, ratio of 9 : 3 : 3 : 1 and produced nine plants with round yellow seeds, three plants with round green, seeds, three plants with wrinkled yellow seeds and one plant with wrinkled green seeds., RY, , Ry, , rY, , ry, , RY, , RRYY, Round yellow, , RRYy, Round yellow, , RrYY, Round yellow, , RrYy, Round yellow, , Ry, , RRYy, Round yellow, , RRyy, Round green, , RrYy, Round yellow, , Rryy, Round green, , rY, , RrYY, Round yellow, , RrYy, Round yellow, , rrYY, Wrinkled yellow, , rrYy, Wrinkled yellow, , ry, , RrYy, Round yellow, , Rryy, Round green, , rrYy, Wrinkled yellow, , rryy, Wrinkled green, , In this experiment, he found that round yellow and wrinkled green are parental combinations whereas, round green and wrinkled yellow are the new combinations. In a dihybrid cross between two plants, having round yellow (RRYY) and wrinkled green seeds (rryy), four types of gametes (RY, Ry, rY, ry ), are produced. Each of these gametes segregate independently of each other and each has a frequency, of 50% of the total gametes produced., From this experiment, he concluded that when two pairs of traits are combined together in a hybrid,, one pair of character segregates independently of the other in terms of character. This is known as the, law of independent assortment., 3. (a) Law of dominance: Some alleles are dominant while others are recessive. An organism with at least, one dominant allele will display the effect of dominant trait e.g. If we carry out a cross between pure, breed tall pea plant with pure dwarf pea plant then F1 progeny will be tall plant because it is dominant, trait whereas dwarf is a recessive trait., (b) Acquired traits even if cause genetic changes in non-reproductive tissues, can not be passed on to, next generation., Genetic changes in reproductive tissues can only be passed on to next generation., , 96, , Science-10

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C ase study question, , 1. In some animals, the temperature at which fertilised eggs are kept determines whether the animal, developing in the egg will be male or female. In other animals, such as snails, individuals can change, sex, that is sex is not genetically determined. In human beings, sex of individuals is largely genetically, determined. All chromosomes in human beings are not paired. We have 22 pairs and one pair of sex, chromosomes which is odd and not always a perfect pair., , (i) Which pair of chromosomes are present in Male, , (a) XX, (b) YY, (c) XY, (d) XXY, , (ii) Which pair of chromosomes are present in female?, , (a) XX, (b) YY, (c) XY, (d) XXY, (iii) Who is responsible for birth of male child?, , (a) Father, (b) Mother, (c) Father only in first pregnancy., (d) Mother only in first pregnancy, , (iv) How many pairs of chromosomes are called autosomes?, , (a) 23, (b) 22, (c) 21, (d) 20, (iv) Which of the following statement is true?, , (a) Men have short sized X chromosome, (b) Men have one long sized Y chromosome, (c) Men have normal sized Y chromosome, (d) Men have one short sized Y chromosome, Ans. (i) (c), (ii) (a), (iii) (a), (iv) (b), (v) (d), , Quick revision notes, , • The difference in traits among the individuals is called variation., • Inheritance from the previous generation provides both common body design as well as changes in it (variations) in the next generation at genetic level., • The second generation will have differences that they inherit from the first generation as well as newly created differences., • Some of these variations may lead to increased survival of individuals., • Sexually reproducing individuals have two copies of genes for the same character. If the copies are not, identical, the form of character that gets expressed is called the dominant trait and the other is called the, recessive trait., • The rules of heredity determines the process by which traits and characteristics are reliably inherited., • Traits in one individual may be inherited separately, giving rise to new combinations of traits in offspring, of sexual reproduction., • The rules for the inheritance of traits in human beings are related to the fact that mother and father equally, contribute the genetic material to the child., • Each trait can be influenced by the maternal and paternal DNA., • Mendel worked out the main rules of inheritance through hybridisation experiments on Garden pea., • Traits are controlled by DNA. A portion of DNA that provides information for one protein in a cell is called gene., • Gene is the unit of inheritance., • DNA is a chemical substance in the chromosomes which carries hereditary characteristics., • In human beings, sex is determined by chromosomes. If parental chromosomes are XX from both the parents,, it is a girl. If ‘X’ chromosome from mother combines with ‘Y’ chromosome of father, then it is a boy., , Heredity and Evolution 97

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Common Errors, Errors, , Corrections, , • Students are not able to differentiate between ☞ Somatic variation takes place within the body, somatic and genetic variations., cells, not inherited, leads to acquired traits., Genetic variations takes place in gamete cells,, inherited and leads to inherited traits., • Students are not able to distinguish between ☞ Children should remember dominant as well as, dominant and recessive traits., recessive traits, e.g. violet flower, yellow seed,, round shaped seed are dominant traits whereas, white flower, green wrinkled seed are recessive, traits., • Students are confused in writing symbols for tall ☞ Dominant traits are written in capital letters, ‘T’,, and dwarf, i.e. dominant and recessive traits., recessive traits are written in small letters ‘t’., • In monohybrid cross, Students write wrong F1 ☞ Gametes, Tall, progeny., TT, T, , Dwarf, tt, , ×, , T, , t, , t, , F1 progeny, , Tt, , , • In Tt, F1 generation, Students do not conclude ☞ ‘T’ decides the traits, i.e. All tall plants., traits properly., progeny, Tt, ×, Tt,, Tt, • In, selfing, F1, in gametes of F2 generation students make wrong, combination., ☞ Gametes T, F2 generation, (progeny), , Tt, , ×, t, , T, , t, , TT-Tall, , Tt-Tall, , Tt-Tall, , tt-Small, , • Where two traits are involved in dihybrid cross, ☞ Think of all possible combinations carefully. Total, total number of combinations are wrongly, no. will be 16. Teacher can teach them ways to, calculated and written., check the answers by using angle triangle method., • In a hurry, students write similar alphabets for V ☞ They should write them carefully., and v, W and w., • Students do not show the factors segregating in ☞ They also do not write genotype of a dihybrid in, gamete formation., individual in correct way and order., , 98, , Science-10

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Assignment, , Total Marks : 20, , I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. Colour of eyes is, (a) Acquired trait, (b) Inherited trait, (c) Due to changes in non-reproductive tissue, (d) Can’t be passed on to offspring, 2. A cross between two individuals result are in ratio of 9:3:3:1. The cross is, (a) Monohybrid cross , (b) Dihybrid cross, (c) Cross-pollination , (d) Self pollination, , II. Assertion-Reason Type Questions, , (1 Mark), , , Note: Use instructions as given in topical exercises of the chapter., 1. Assertion: A sperm carrying Y-chromosome fertilise an egg with X-chromosome to develop a male, zygote XY., , Reason: A sperm carrying X-chromosome fertilise an egg to develop a female zygote., 2. Assertion: Change in genetic composition results in variation., , Reason: All variations in a species have equal chance of survival., , III. Very Short Answer Type Questions, , (1 Mark), , 1. What are alleles? Give example., 2. Mendel took tall pea plants and short pea plants and produced F1 progeny through cross fertilization., What did Mendel observe in F1 progeny?, [CBSE 2018(C)], , IV. Short Answer Type Questions-I, , (2 Marks), , 1. Give two differences between somatic variation and genetic variation., 2. A man with blood group A marries a woman with blood group O and their daughter has blood group O., Is this information enough to tell you which of the traits- blood group A or O is dominant? Why?, 3. How do Mandel’s experiments show that traits may be dominant or recessive?, , V. Short Answer Type Question-II, , (3 Marks), , 1. Define the term variation. Why is variation beneficial to a species? List two reasons for the appearance, of variations among the progeny formed by sexual reproduction, [CBSE 2020], , VI. Long Answer Type Question, , (5 Marks), , 1. Name the plant Mendel use for his experiment. What type of progeny was obtained by Mendel in, F1 and F2 generation when he crossed the tall and short plants? Write the ratio he obtained in F2, generation plants., [Delhi, 2015, 2019], , Heredity and Evolution 99

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Unit-III, Effects of Current, , 5, , Electricity, , Topics Covered, 5.1, 5.2, 5.3, , Circuit Diagram, Ohm’s Law, Factors on which Resistance Depends, Resistance of a System of Resistors, Heating Effect of Current, , C hapter map, Electric Current, (I) and its unit, , Ohm’s Law, , Resistance, Factors, affecting, resistance, , Resistivity, Factors affecting, resistivity, , Advantage, Disadvantage, , Electric, Power, Safety Devices, , Combination of Resistances, In series, RS = R1 + R2 + R3, , Heating, Effect, , In parallel, , Electric, Fuse, , Earth, Wire, , 1= 1, 1, 1, + +, RP R1 R2 R3, Advantage, Disadvantage, , Topic 1. Circuit Diagram, Ohm’s Law, Factors on which Resistance Depends, , Circuit diagram: The schematic diagram in which different components of the circuit are represented by the, symbols conveniently used., Sl. No., Components, 1., Electric cell, 2., , A battery, , 3., , Plug key (switch open), , 4., , Plug key (switch closed), , 5., , A wire joint, , Symbols, , 100

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6., , Wire crossing without joining, , 7., , Electric bulb, , 8., , A resistor of resistance R, , 9., , Variable resistor or Rheostat, , 10., , Ammeter, , 11., , Voltmeter, , R, , Ohm’s law: It states ‘the potential difference across the given metallic wire in an electric circuit is directly, proportional to the electric current flowing through it, if the temperature remains constant’., V ∝I, V, V, = R ⇒ V = IR, = constant ⇒, I,                 I, ‘R’ is a constant for a given metallic wire at a given temperature and is called resistance., Resistance: It is the property of a conductor to resist the flow of charges through it. Its S.I. unit is Ω (ohm)., Ohm: The resistance of a conductor is 1 ohm if 1 ampere current is passed across the two ends of conductor, having a potential difference of 1 V., 1 volt, V, 1 ohm =, R=, 1 ampere   , I, •, , I=, , V, , The current through a resistor is inversely proportional to its resistance., R, , • If resistance is doubled, current gets halved if ‘V’ remains the same., Variable resistance (Rheostat): It is a device which is used to change the resistance in the circuit due to, which current flowing through the circuit will change., • Different components of an electric circuit, ammeter, voltmeter, torch bulb, Nichrome wire have different, resistance, therefore flow of current will be different in different components., • Motion of electrons in an electric circuit constitutes an electric current. The electrons are not completely, free to move within a conductor. They are held by attractive forces of the atoms in which they move., • Motion of electrons is retarted by resistance., • A good conductor offers low resistance., • A component of electricity that offers high resistance is a poor conductor., • An insulator offers maximum resistance and does not allow the current to flow., Factors on which resistance of a conductor depend:, (i) Length: Resistance of a wire is directly proportional to its length. If length of the wire is doubled,, resistance will also become double., (ii) Area of cross-section: Resistance is inversely proportional to the area of cross section of a conductor., A thin wire will have more resistance than a thick wire., (iii) Temperature: When we increase the temperature, resistance of metallic conductor will increase., (iv) Nature of material: A material may be a conductor with low resistance, semiconductor with medium, resistance, or an insulator having high resistance., R ∝l R∝, , l, l, 1, ⇒ ⇒ R = ρ., A, A, A, , , r(rho) is a constant of proportionality called resistivity of the material of conductor., Resistivity (r): Resistivity is defined as the resistance of a metallic wire whose area of cross section is 1 m2, and of length 1 m, , Electricity 101

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If A = 1 m2,, , , l = 1 m,, , then r = R, , ρ=R×, , A, l, , 2,    ρ = ohm × m = ohm m, m, Its S.I. unit is Ω m (Ohm –metre)., Resistivity is a characteristic property of a material., Metals have low resistivity (10–8 to 10–6 Ω m), therefore they are good conductors., Insulators like rubber and glass have high resistivity, 1012 to 1017 Ω m., Resistance and resistivity of a material vary with temperature., Resistivity of an alloy is generally higher than the constituent metals. Alloys do not oxidise (burn) readily at, high temperature, therefore these are used in making heating devices like electric iron, toaster, immersion, rod, heaters, etc., Tungsten is used for filaments of electrical bulbs due to their high resistivity and high melting points., Copper and aluminium are used for electrical transmission lines due to their low resistance and high, conductance., , , •, •, •, •, •, •, •, •, , I. Multiple Choice Questions, , Exercise 5.1, , (1 Mark), , Choose the correct answer from the given options., 1. Electrical resistivity of a given metallic wire depends upon, (a) its length , (b) its thickness, (c) its shape , (d) nature of the material, 2. Identify the circuit (Fig) in which the electrical components have been properly connected., +, , –, , +, , –, , –, , V, , R, , A, , +, –, , +, , R, , (iii), , 3., 4., 5., , 6., , A, , +, , +, –, , V, –, , (iv), , (a) (i), (b) (ii), (c) (iii), (d) (iv), Electric current flows from ‘A’ to ‘B’ in metallic conductor. The point is at higher potential is, (a) A , (b) B, (c) Both have equal potential, (d) Both have lower potential, If electrons flow from A to B, current will flow from, (a) A to B, (b) B to A, (c) It will not flow (d) None of these, When a 4V battery is connected across an unknown resistor there is a current of 100 mA in the circuit., The value of the resistance of the resister is:, (a) 4 Ω, (b) 40 Ω, (c) 400 Ω, (d) 0.4 Ω, [CBSE Sample Paper 2019-2020], A cell, a resistor, a key and ammeter are arranged as shown in the circuit given below. The current, recorded in the ammeter will be, K – +, R, R, –, + –, + –, A+, K, –, K, R, A, –, +, A+, (i), (ii), (iii), (a) maximum in (i) , (c) maximum in (iii) , , II. Assertion-Reason Type Questions, , (b) maximum in (ii), (d) the same in all the cases, , (1 Mark), , For question numbers 1 and 2 two statements are given-one labeled as Assertion (a) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., , 102, , Science-10

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(c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Resistance depends on length and area of cross-section of material and temperature., , Reason: Resistivity is a characteristic property of material., 2. Assertion: Fuse wire is thin and has high resistance., , Reason: Alloys do not oxidise readily at high temperature., , III. Very Short Answer Type Questions, , (1 Mark), , 1. Let the resistance of an electrical component remain constant, while the potential difference across the, two ends of the component decreases to half of its former value. What change will occur in the current, through it?, [NCERT] [HOTS], 2. Which among iron and mercury is a better conductor?, , (Given: rFe = 10.0 × 10–8 W – m, rHg = 95 × 10–8 W – m, 3. Write the S.I. unit of resistivity., [Delhi 2015, 16], 4. Mention two reasons why tungsten is used for making filaments of electric lamps., [Delhi 2016], 5. How does resistivity of alloys compared with those of pure metals from which they have been, formed? , [CBSE 2014], 6. State the difference between a wire used in the element of electric heater and in fuse wire., [Delhi 2013] [CBSE 2014], 7. Name a device which helps to maintain the potential difference across a conductor., [CBSE 2014], 8. Draw a circuit diagram having the following components:, (a) Bulb (b) A two cell battery (c) Ammeter (d) A closed key, 9. Name the factors on which the resistance of a conductor depend?, [NCERT], OR, List the factors on which the resistance of a conductor in terms of shape of a wire depends., 10. What happens to the resistance of a conductor when its temperature is increased?, [CBSE 2010], 11. Nichrome is used to make the element of an electric heater, why?, [CBSE 2010], 12. Mention two special features of the material to be used as an element of an electric iron.[CBSE 2014], 13. What happens to resistance of a conductor when its area of cross section is increased?, [Delhi 2011], 14. What does electric circuit mean?, [NCERT], 15. List two factors on which resistance depends., [CBSE 2015], 16. In an electric circuit, state the relationship between the direction of conventional current and the, direction of flow of electrons., [CBSE 2014], 17. A given length of wire is doubled on itself and the process is repeated once again. By what factor does, the resistance of wire will change? , [CBSE 2011], , IV. Short Answer Type Question-I, , (2 Marks), , 1. Out of the two wires ‘X’ and ‘Y’ of the same material as shown below, which one has greater resistance?, Justify your answer., [Delhi 2012], , V. Short Answer Type Questions-II, , (3 Marks), , 1. Resistance of a metal wire of length 1 m is 26 Ω at 20°C. If the diameter of the wire is 0.3 mm, what will, be the resistivity of the metal at that temperature?, [NCERT] [HOTS], 2. The figure below shows three cylindrical copper conductors along their face areas and lengths. Discuss, in which geometrical shape the resistance will be the highest., [Delhi 2013], , Electricity 103

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3. Calculate the resistance of 1 km long wire of copper of radius 1 mm. (Resistivity of copper is, 1.72 × 10–8 Ω m.)[Delhi 2013], 4. The resistance of a wire of 0.01 cm radius is 10 Ω. If resistivity of the material of wire is 50 × 10–8 ohm, metre, find the length of the wire. , [Delhi 2016], 5. The resistance of a wire of length 250 m is 1 ohm. If the resistivity of the material of wire is, 1.6 × 10–8 ohm metre, find the area of cross-section of the wire. How much does the resistance change, if the diameter of the wire is doubled?, [Delhi 2016], 6. The electrical resistivity of three materials A, B, C are given below:, ‘A’ = 2.3 × 103 ohm metre   ‘B’ = 2.63 × 10–8 ohm metre   ‘C’ = 1.0 × 1015 ohm metre, Which material will you use for making (i) electric wires, (ii) handles for soldering iron and (iii) solar, cells? Give reason to support your answer., 7. Suppose the ammeter or voltmeter you are using in Ohm’s law experiment do not have +ve and –ve, terminal markings, how will you use such an ammeter or voltmeter in the circuit?, [Delhi 2015], 8. Study the V–I graph for a resistor as shown in the figure and prepare, a table showing the values of I (in amperes) corresponding to four, different values of V (in volts). Find the value of current for V = 10, volts. How can we determine the resistance of the resistor from this, graph?, 9. Name and define SI unit of resistance. Calculate the resistance of a, resistor if current flowing through it is 200 mA, when the applied, [CBSE 2014], potential difference is 0.8 V., 10. V–I graph for two wires A and B are shown in the figure. If both the wires are of same, length and same thickness, which of the two is made of a material of high resistivity?, Give justification for your answer., 11. The figure below shows three cylindrical copper conductors along with their face, areas and lengths. Compare the resistance and the resistivity of the three conductors. Justify your, answer., , , 12. The potential difference between the terminals of an electric heater is 60 V when it draws a current of, 4 A from the source. What current will the heater draw if the potential difference is increased upto 120, V?[NCERT], 13. (i) How much current will an electric bulb draw from a 220 V source, if resistance of the filament of a, bulb is 1200 Ω?, , (ii) How much current will an electric heater coil draw from a 220 V source, if the resistance of the, heater coil is 100 Ω? , [NCERT] [Delhi 2012], 14. A wire of given material having length l and area of cross-section A has a resistance of 4 Ω. What would, be the resistance of another wire of the same material having length l/2 and area of cross-section 2A?, [NCERT] [HOTS], 15. A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10–8 Ω m. What will be the length of this, wire to make its resistance 10 Ω? How much does the resistance change if the diameter of the wire is, doubled?[NCERT], , 104, , Science-10

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16. The values of current I flowing in a given resistor for the corresponding values of potential difference, V across the resistor are given below :, I (amperes), , 0.5, , 1.0, , 2.0, , 3.0, , 4.0, , V (volts), , 1.6, , 3.4, , 6.7, , 10.2, , 13.2, , Plot a graph between V and I and calculate the resistance of that resistor. [NCERT] [HOTS], 17. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the, circuit. Find the value of the resistance of the resistor., [NCERT], 18. A piece of wire of resistance 20 Ω is drawn out of a material so that its length, B, is increased to twice of its original length. Calculate the resistance in the, new situation., [HOTS], A, 19. V-I graph for two wires ‘A’ and ‘B’ are shown in the figure. If both the wires, are of same length and are of same thickness, which of these two is made of, the material of higher resistivity? Give justification for your answer., 20. (i) What are the values of mA and mA in amperes?, , (ii) Draw the symbols of battery and rheostat?, [CBSE 2014], , VI. Long Answer Type Questions, , (5 Marks), , 1. (i) Write an expression for the resistivity of a substance., , (ii) State the SI unit of resistivity., , (iii) Distinguish between resistance and resistivity., , (iv) Name two factors on which the resistivity of a substance depends and two factors on which it does, not depend. , [Delhi 2015], 2. List two distinguishing features between the resistance and resistivity of a conductor. A wire is, stretched so that its length becomes 6/5 times of its original length. If its original resistance is 25 W,, find its new resistance and resistivity. Give justification for your answer in each case. [Delhi 2016], 3. State Ohm’s law. Draw a labelled circuit diagram to verify this law in the laboratory. If you draw a, graph between the potential difference and current flowing through a metallic conductor, what kind of, curve will you get? Explain how would you use this graph to determine the resistance of the conductor., [Delhi 2016], 4. You have been assigned a duty to create awareness in your school, about saving electricity., , (i) Write any two ways by which you will create awareness, among your schoolmates about saving electricity., , (ii) Explain how saving electricity is important at individual level, as well as at national level.             [Delhi 2015], 5. (i) Draw a closed circuit diagram consisting of a 0.5 m long, nichrome wire XY, and ammeter, a voltmeter, four cells of 1.5, V each and a plug key., , (ii) Following graph was plotted between V and I values:, What would be the values of V/I ratios when the potential, difference is 0.8 V, 1.2 V and 1.6 V respectively? What, conclusion do you draw from these values?, , Answers 5.1, I. 1. (d) It depends only upon nature of the material. Resistance depends on the length of wire and area of, cross section., , 2. (b) It is correct because Ammeter should be connected in series and voltmeter should be connected in, parallel., , 3. (a) ‘A’ because current flow from higher to lower potential., , 4. (b) Current flows in opposite direction to the direction of flow of electrons, B to A., , 5. (b) V = IR, V = 4V, I = 100 mA = 0.1 A; Hence, R = V/I = 4/0.1 = 40., , 6. (d) It will be same in all cases, II. 1. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , 2. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , Electricity 105

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The current flowing through the electrical component will get halved., Iron, Ω m (ohm metre), (i) High resistivity, (ii) High melting point, Alloys have higher resistivity as compared to pure metals., The wire used in the elements of an electric heater has high melting point whereas a fuse wire has low, melting point., 7. Cell or battery eliminator., 8., , III. 1., 2., 3., 4., 5., 6., , 9. (i) Nature of material, (ii) Length of conductor [or R µ l], , (iii) Area of cross section of the conductor [or R µ 1/A], (iv) Temperature, 10. Its resistance increases., 11. It is an alloy with high resistivity and high melting point., 12. The material should have (i) high resistivity, (ii) high melting point., l, , Resistance is directly proportional to length but inversely proportional, 13. Resistance decreases, ... R ∝, A, to area of cross-section., 14. It is a continuous and closed path in which current flows with the help of conducting wires. It consists, of a cell, an ammeter, voltmeter, plug key, bulb, etc., 15. (i) Length, (ii) Area of cross section, It is directly proportional to the length and inversely proportional to the area of cross section of a, resistor., 16. The direction of conventional current is opposite to the direction of flow of electrons., 1, 17. Length becomes 4 times whereas area becomes, times of the original value. Since,, 4, L, 4L, 16 L, L, R=ρ =ρ, =ρ, = 16 ρ, where r (rho) is resistivity, L is length and ‘A’ is area of cross section., , A, A, A, A, 4, , \ Resistance will become 16 times of the original value., IV. 1. ‘Y’ has more resistance because resistance is directly proportional to the length of the wire., V. 1. R = 26 Ω, l = 1 m, d = 0.3 mm = 3 × 10–4 m, d 3 × 10 −4, r= =, = 1.5 × 10 −4 m, 2, 2, 22, A = pr2 ⇒ A =, × (1.5 × 10–4)2, 7, R × A 26 × 22 × 2.25 × 10 −8, = 1.84 × 10–6 W m, , ρ=, =, l, 7 × 1m, L, A, 2L, L, R2 = ρ ×, = 4ρ × = 4 R 1, A/2, A, L/2 1, L 1, R3 = ρ ×, = × ρ × = R1, 2A 4, A 4, , 2. R1 = ρ ×, , (i), (ii), (iii), , Thus in figure (b) the resistance is maximum., So, from equations (i), (ii) and (iii), we get R2 > R1 > R3., , 106, , Science-10

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Hence, the cylinder having length (2L) and area of cross-section (A/2) has the highest resistance, followed by the cylinder having length (L) and area of cross section (a), while cylinder with length, (L/2) and area of cross-section (2A) has the least resistance. This is because resistance of a substance, is directly proportional to the length and is inversely proportional to the area of cross-section., 3. R = ρ ×, , l, A, , 22, × 1 × 10–6, , r = 1.72 × 10–8 Ω m; r = 1 mm = 1 × 10–3 m; A = pr2 =, 7, l = 1 km = 1000 m, ⇒ R=, , 4. R = r ×, , 1.72 × 10 −8 × 1000 × 7 12.04, 120.4, =, × 10 −8 + 3 + 6 =, = 5.473 Ω, −6, 22 × 1 × 10, 22, 22, l, A, , R = 10 W,, r = 50 × 10–8 W m, , \ l=, 5. R = r, , r = 0.01 × 10–2 m = 1 × 10–4 m, A = pr2 =, , 22, × 1 × 10–8, 7, , R × A 10 × 22 × 10 −8 220, = 0.628 m = 62.8 cm, =, =, ρ, 50 × 10 −8 × 7, 350, , ρl, l, ⇒ A=, R, A, , 1.6 × 10 −8 Ω m × 250 m, = 4 × 10–6 m2, 1Ω, If diameter is doubled then area of cross-section becomes four times and the resistance will become one, fourth, i.e., 0.25 W., 6. (i) ‘B’ will be used for electric wires because it has lowest resistivity, therefore current can flow easily., , (ii) ‘C’ will be an insulator, so it can be used for handles of soldering iron. Since its resistivity is very, high, therefore current cannot pass through it., , (iii) ‘A’ will be used in solar cells because it is a semiconductor which can convert solar energy into, electric energy., 7. (i) Connect the device in the circuit with battery., , (ii) Close the circuit and notice the deflection of the pointer., , (iii) If the deflection is in the opposite direction i.e. below zero, then interchange the terminals., , A =, , 8., , I (in amp), , 2, , 4, , 6, , 8, , V (in Volt), , 1, , 2, , 3, , 4, , When V = 10 Volts, I = 5 amperes, then, , R=, , V 10 V, =, =2Ω, I, 5A, , 9. (i) The SI unit of resistance is Ohm (W)., , (ii) If the current of 1 ampere flows through a wire on applying a potential difference of one volt across, it, then the resistance of the wire is said to be 1 W., , (iii) I = 200 mA = 200 × 10–3 A, V, 0 .8, =, = 4 ohms, I, 0 .2, 10. Greater the slope of V–I graph, greater will be the resistance of the given metallic wire. In the given, graph, wire A has greater slope than B. Hence, wire A has greater resistance., For the wires of same length and same thickness, resistance depends on the nature of the material of, wire, i.e., R1, ρ, l, l, , R1 = ρ1 and R 2 = ρ2, ⇒, = 1 or R ∝ ρ, A, A, R2, ρ2, , R =, , Since, R1 > R2. Hence, wire ‘A’ is made of a material of high resistivity., , Electricity 107

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11. For the geometrical shapes shown in figure:, , l, ρL,  L / 3  1 ρL 1,  3L , Ra = ρ A ; Rb = ρ  A / 3  = 9 A = 9R a ; Rc = ρ  3 A  = 9 A = 9 R a, , , Hence Rb > Ra > Rc, ρ = ρb = ρc because all the three conductors are of same material., a, , , 12. V = 60 V, I = 4 A, V 60, =, = 15 Ω [ By Ohm’s Law: V = IR], R=, , I, 4, Now, V = 120 V, I = ? R = 15 Ω, V 120, I=, =, =8A, R, 15, , 13. (i) V = 220 V, R = 1200 Ω, V, 220, I=, =, = 0.18 A [ By Ohm’s Law: V = IR], , R 1200, , (ii) Now, V = 220 V, R = 100 Ω, 220, I=, = 2 .2 A, ,    , 100, 14. R1 = ρ ×, , l, = 4 Ω, A, , Also, R 2 = ρ ×, , l/2, 1 l, = ρ× ×, 2A, 4 A, , 1, 1, R1 = × 4 = 1 Ω, 4, 4, 15. ρ = 1.6 × 10 −8Ω m ; R = 10 Ω, d = 0.5 mm = 5 × 10–4 m [ 1 mm = 10–3 m], , R 2 =, , 22, 5, × 10–4 m = 2.5 × 10–4 m; A = pr2 =, × (2.5 × 10–4)2 m2, 7, 2, A, , ρ=R×, l, 22 6.25 × 10 −8, 10 × 22 × 6.25 × 10 −8 1375, ×, 1.6 × 10–8 = 10 ×, ⇒ l=, =, = 122.77 m, 7, l, 7 × 1.6 × 10 −8, 11.2, r =, , 16. The slope of the graph is equal to the resistance., Change in V ∆V 13.2 − 1.6 ,, , =, =, R=, Change in I, ∆I, 4 .0 − 0 .5, 11.6, , R=, = 3.314 Ω, 3 .5, 17. V = 12 V, I = 2.5 mA = 2.5 × 10–3 A, , (1 mA = 10–3 A), 12, 12000, V, R=, =, =, = 4800 Ω = 4.8 k Ω, , −3, I 2.5 × 10, 2 .5, , ( By Ohm’s Law: V = IR), l, 2l, 18. R1 = r ×, ; R2 = r ×, A, A, 2l, ρ×, R2, A, , \, =, l, R1, ρ×, A, , 108, , ⇒ R2 = 2R1 = 2 × 20 = 40 W, , Science-10, , A, , ∵ R = ρ × l , , 

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19. ‘A’ has greater resistivity than ‘B’. It depends upon the nature of material. High resistivity means, lower value of electric current flowing through the wire., 20. (i) 1mA = 10–3A, 1mA = 10–6A., , (ii), , is the symbol of battery, and, , or, , is the symbol of rheostat., , RA, , (ii) Its SI unit is W m., l, (iii) Resistivity is a characteristic property of a material that does not depend upon the dimensions, of the material whereas resistance depends upon the dimensions of the material., VI. 1. (i) Resistivity (r) =, , , (iv) Resistivity does not depend on the:, , (a) length of conductor,, Resistivity depends on the:, , (a) nature of material of conductor, 2., , (b) area of cross section of conductor, (b) temperature of conductor, , Resistance, , Resistivity, , (i) It is the ratio of voltage over current at a, particular temperature., , (i) It is the resistance of a wire of length 1 m and, area of cross section 1 m2., , (ii) Its S.I. unit is ohm., , (ii) Its S.I. unit is ohm metre., , (iii) It is the property of a conductor., , (iii) It is the property of the material of the conductor., , , (Any two), Since resistance is directly proportional to the length and is inversely proportional to the area of cross, section., 6, 25, 150, 216, \ New Resistance: R = ×, × 36 =, = 43.20 ohms, 2 =, 5  5, 5 × 25, 5,  6 , When the wire is stretched, its length becomes 6/5 times of its original length, and area of cross-section, will become 5/6. Resistivity will remain the same because it does not depend upon the length and area, of cross section. It depends on the nature of material of the substance and the temperature., 3. Ohm’s Law: It states that ratio of potential difference and current is constant and is equal to the, resistance of the conductor at a particular temperature. In other words, the current flowing through a, conductor is directly proportional to the potential difference at a constant temperature., The graph between V and I will be a straight line., Slope = tan θ = ‘R’, BC, Slope =, =R, AC, 4. (i) Speaking over it in the morning assembly in school., , • Putting posters over it on the school notice board., , (ii) If we save electricity, it can be used by those villages which do not have electricity., , • It can be used in industries, agriculture and for other useful purposes., , • It improves the national economy because high speed trains, industries, development in villages, depends upon electricity., 5. (i), , Electricity 109

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(ii) The V/I ratio for, 0.8, V, V, 1 .2, = 2.67 ; • V = 1.2 V,, is, =, • V = 0.8 V,, = 2.67, 0.3, I, I, 0.45, V 1 .6, • V = 1.6 V,, =, = 2.67, I, 0 .6, It shows that V a I or, , V, = constant., I, , Topic 2. Resistance of a System of Resistors, There are two methods of joining the resistors together., , Resistors in Series, When resistors are joined end to end, it is called that resistors are connected in series., (i) The value of current in the ammeter remains the same, independent of its position in the electric circuit., It means that in a series combination of resistors, the current remains the same in every part of the circuit, or same current flows through every resistor., , (ii) In the above circuit in V is equal to the sum of V1, V2, V3, that is total potential differences (V) across a, combination of resistors in series is equal to sum of potential difference across the individual combinations,, i.e.,                  , V = V 1 + V2 + V 3, (iii) The current through each resistor and all the three resistors is I.,               V = IR, , \    , V1 = IR1, V2 = IR2 and V3 = IR3,         So,, V = V1 + V2 + V3 ⇒ IR = IR1 + IR2 + IR3,        or      R = R1 + R2 + R3, Thus we can conclude that when several resistors are joined in series combination, then equivalent, resistance of the combination is equal to the sum of their individual resistances and is thus greater than, any of the individual resistance.,               RS = R1 + R2 + R3, , Resistors in Parallel, (i) Suppose we connect three resistances R1, R2, R3 in parallel combination as shown in the diagram., (ii) Let us connect it with the battery, a plug key, an ammeter as shown in the diagram., (iii) Also connect voltmeter in parallel combination with the resistors as shown., , 110, , Science-10

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By applying a potential difference V, the current flowing in the, circuit be I. This circuit is distributed in different branches., Suppose I1, I2, I3 be the current in each resistor., Then we observe, I = I1 + I2 + I3, According to Ohm’s Law, ,            , ∵,        , , I=, , V, Rp, , I1 =, , V, ;, R1, , I2 =, , V, ;, R2, , I3 =, , V, R3, , V, V, V, V, =, +, +, R p R1 R 2 R 3, , I = I1 + I2 + I3 ⇒, , 1, 1, 1, 1, =, +, +,              R p R1 R 2 R 3, , Circuit in series vs Circuit in parallel (Disadvantages of series circuit), , (i) We have observed in series circuit, the current is constant throughout the electric circuit. Thus, it is not, practical to connect an electric bulb and electrical heater in series, because they need current of widely, different values to operate properly. Total resistance increases in a series connection., , (ii) Another disadvantage of series circuit is that when one component fails, the entire circuit is broken and, current stops flowing in the circuit. You must have seen in ‘fairy lights’ used in diwali, if one bulb fuses,, the circuit is broken, none of the small bulbs work or light up., , Parallel Circuit Advantages, , (i) It divides the current through the electric gadgets., , (ii) The total resistance in a parallel circuit decreases. It is helpful when gadgets have different resistances, and they require different current to operate., , Exercise 5.2, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. When the current passing through each resistor is same, the circuit is called, (a) series circuit, (b) parallel circuit, (b) Both (a) and (b) (c) None of these, 2. In parallel circuit, which of the following is same across resistors, (a) Current , (b) Potential difference, (c) Resistance , (d) Resistivity, 3. When resistance is doubled at constant voltage, current will become., 1, 1, (b) 2 times, (c), (d) 4 times, (a), 2, 4, 4. Resistance in a circuit if current flowing is doubled will become, (a) double, (b) half, (c) four times, (d) remains same, 5. A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel., If the equivalent resistance of this combination is R′, then the ratio R/R′ is, (a) 1/25, (b) 1/5, (c) 5, (d) 25, [CBSE 2020, NCERT], 6. Two conducting wires of the same material and of equal lengths and equal diameter are first connected, in series and then in parallel in a circuit across the same potential difference. The ratio of heat produced, in series and parallel combinations would be, (a) 1:2, (b) 2:1, (c) 1:4, (d) 4:1, [NCERT], , II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (a) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given ahead:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., , Electricity 111

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(c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: In parallel circuit, the current is divided into electrical gadgets, therefore, used in domestic, circuit., , Reason: The resistance in parallel circuit decreases, therefore, useful., 2. Assertion: Fairy lights circuit is connected in series connection., , Reason: In series combination, if one component fails then complete circuit is broken., , III. Very Short Answer Type Questions, , (1 Mark), , 1. Draw a schematic diagram of a circuit consisting of a battery of three cells of 6 V each, a, 5 W resistor, an 8 W resistor and a 12 W resistor and a plug key, all connected in series., [NCERT], 2. Judge the equivalent resistance when the following are connected in parallel:, (i) 1 W and 106 W, (ii) 1W, 103 W and 106 W[NCERT], 3. What are the advantages of connecting electrical devices in parallel with the battery instead of, connecting them in series?, [NCERT], 4. Two unequal resistances are connected in parallel. If you are not provided with any other parameters, (eg. numerical values of I and R), what can be said about the voltage drop across the two resistors?, [CBSE Sample Paper 2020-21], , IV. Short Answer Type Questions-I, , (2 Marks), , 1. If you connect three resistors having values 2 W, 3 W and 5 W in parallel, calculate the equivalent, resistance., 2. B1, B2, B3 are three identical bulbs connected as shown in the figure., When all the three bulbs glow, a current of 3 A is recorded by the, ammeter A., , (i) What happens to the glow of the other two bulbs when bulb B1 gets, fused?, , (ii) What happens to the reading of A1, A2, A3 and A when bulb B2 gets, fused.                 [CBSE 2010], 3. Redraw the circuit in the above question, putting an ammeter to, measure the current through the resistors and a voltmeter to measure, I, →, the voltage across the 12 W resistor. What would be reading in the, A, ammeter and the voltmeter?, [NCERT] [HOTS], 4. A student has two resistors- 2 W and 3 W. She has to put one of them, R1 = 4W, 12V, R2, in place of R2 as shown in the circuit. The current that she needs in, the entire circuit is exactly 9A. Show by calculation which of the two, B, resistors she should choose., , V. Short Answer Type Questions-II, , (3 Marks), , 1. What is (a) the highest, (b) the lowest total resistance that can be secured by combination of four coils, of resistances 4 W, 8 W, 12 W, 24 W?, [NCERT], 2. Show how you would connect three resistors, each of resistance 6 W, so that the combination has a, resistance of (i) 9 W, (ii) 4 W., [HOTS], 3. (i) What are the disadvantages of resistances connected in a series circuit?, , (ii) Find the resistance between A and B in the following network., [Delhi 2014], , 112, , Science-10

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4. What are the advantages of connecting electrical devices in parallel combination with the battery, rather than in series combination?, 5. Find the current drawn from the battery by the network of four resistors as shown in the figure., , 6. Show how would you join three resistors, each of resistance 9 Ω so that the equivalent resistance of the, combination is (i) 13.5 Ω, (ii) 6 Ω?[CBSE 2018], 7. If three resistors of 6 Ω, 9 Ω and 21 Ω are connected in series to a 12 V battery, find:, , (a) The total resistance of the circuit., , (b) The current flowing through the circuit., , (c) The potential difference across the 21 Ω resistor., 8. An electric lamp of 100 W, a toaster of resistance 50 W, and a water filter of resistance 500 W are, connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same, source that takes as much current as all the three appliances, and what is the current flowing through, it?[NCERT], 9. Study the following electric circuit and find the, , (i) current flowing through the circuit and, , (ii) the potential difference across 10 W resistor., , [Delhi 2016], , 10. Figure shows a 2 W resistor and a 6 W resistor connected in series, 2, with a 4 V battery. Calculate:, , (a) the combined resistance of the resistors., , (b) the current in the battery., , (c) the current in 2 W resistor., 11. How can three resistors of resistances 2 W, 3 W, and 6 W be, connected to give a total resistance of (a) 4 W, (b) 1 W?[NCERT], 12. The parallel combination of two 10 W resistors are placed across, 4V, the terminals of a 24 V battery., , (a) What is the effective resistance of the parallel combination of resistances in the circuit?, , (b) What is the current through the entire circuit?, , (c) What is the current through each branch of the circuit?, 13. How many 176 W resistors (in parallel) are required to carry 5 A current on a 220 V line?, 14. A hot plate of an electric oven connected to a 220 V line has two coils A and B, each of 24 W, resistance, which may be used separately, in series, or in parallel. What are the values of current in, the these cases?, [NCERT], , Electricity 113

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VI. Long Answer Type Questions, , (5 Marks), , 1. (i) , What is meant by series combination and parallel combination of, resistances?, , (ii) In the circuit diagram given below five resistances of 5W, 20W, 15W, 20W, and 10 W are connected as given in the figure to a 6 V battery., Calculate: (a) Total resistance in the circuit., , (b) Total current flowing in the circuit.     [Delhi 2016], 2. Study the following electric circuit and find (i) the current flowing in the, circuit and (ii) the potential difference across the 10 W resistor., , 20 Ω, 15 Ω, 20 Ω, 5Ω, 6V, , , 3. Find the net current flowing through the following electric circuit:, , , 4. (a) , With the help of suitable circuit diagram prove that the, reciprocal of the equivalent resistance of a group of resistances, joined in parallel is equal to the sum of the reciprocal of the, individual resistances., , (b) In an electric circuit two resistors of 12 W each are joined in, parallel to a 6V battery. Find the current drawn from the, battery., 5. Figure shows a 3 W resistor and a 6 W resistor connected in parallel, across a 1.5 V cell., Calculate the current across: (i) 3 W resistor, (ii) 6 W resistor, (iii), the cell, (iv) calculate the resistance of the parallel combination of, 3 W and 6 W resistors., , Answers 5.2, I. 1. (a) The circuit is called series circuit., , 2. (b) Potential difference is same., V, 1,     I =, R, 2, 4. (d) Resistance does not depend upon current., , 3. (a) It will became, , 5. (d), , , , 114, , 1, R, , ′, , =, , R′ =, , 1, 1, 1, 1, 1 25, +, +, +, +, =, R R R R R, R, 5, 5, 5, 5, 5, R, Ω, 25, , ⇒, , Science-10, , R, = 25 . So option (d) is correct., R′, , 1.5 V, , 10 Ω

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6. (c) Resistances of identical conducting wires are equal. Let R be the resistance of each resistor in series, combination.,     \ Rs = R + R = 2R, V2, 2R, 1, 1 1, 2,     When resistances are connected in parallel,, =, +, =, RP R R R, V2, H =,     P R / 2, ,    Hs = Heat produced in series. Hence Hs =, , RP =, , R, , 2, , HS V 2, 1, R, =, ×, = . So option (c) is correct., 2, 4, HP 2R 2V, II. 1. (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., ,    , , 2. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., III. 1., , 2. Equivalent resistance in parallel combination of resistances is always less than the lowest individual, resistance i.e. less than 1 Ω in both the cases (i) and (ii)., 3. Parallel circuit advantages:, , (a) Voltage is same across all the components when connected in parallel., , (b) Parallel combination of resistances helps us to obtain an overall lower potential than the resistances, used., , (c) In household circuit, parallel connection is useful because each appliance has its own ON/OFF, switch., , (d) A fault in one appliance will not affect the working of other appliances., (Any two), 4. Voltage-drop is same across both resistors., 1, 1, 1, 1, 1 1 1, 15 + 10 + 6 31, +, +, = + + =, =, IV. 1., =, R, R1 R 2 R 3 2 3 5, 30, 30, 30, = 0.967 Ω, 31, 2. (i) The glow of bulbs B2 and B3 will remain same because they are in parallel connection with bulb B1., , (ii) A 1 shows 1 ampere reading, A 2 shows zero and A 3 show 1 ampere reading. ‘A’ will show, 2 A reading., 3. RS = R1 + R2 + R3 = 5 + 8 + 12 = 25 Ω; V = 6 V, , , , R=, , V, 6V, =, = 0.24 A, , I=, R 25 Ω, In series combination current in all resistances is same., Here, I = 0.24 A across 12 Ω resistance, , \ Voltmeter reading, V = IR = 0.24 × 12 = 2.88 V, , \, I = 0.24 A,, V = 2.88 V, 4. The overall current needed = 9A. The voltage is 12V, Hence by Ohm’s law V=IR,, 4, 12, =, Ω. = R, The resistance for the entire circuit =, 3, 9, R1 and R2 are in parallel., (R1R 2 ) = 4R 2 = 4 , Hence, R =, (R1+R 2 ) (4 + R 2 ) 3, R2 = 2Ω, , Electricity 115

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V. 1. (a) The highest resistance can be obtained by connecting all resistances in series, i.e., Rs = R1 + R2 + R3 + R4 = 4 Ω + 8 Ω + 12 Ω + 24 Ω = 48 Ω, (b) The lowest resistance can be obtained by parallel combination:, 1, 1, 1, 1, 1, 1, 1, 6 + 3 + 2 + 1 12, 1 1, =, =, +, +, +, = + +, +, =, R p R1 R 2 R 3 R 4 4 8 12 24, 24, 24, , Rp = 2 Ω, (i) When two 6 Ω resistances are connected in parallel and connected to another 6 Ω in series, we get, 9 Ω resistance., 1, 1 1 2 1, = + = = ⇒ R p = 3 Ω ⇒ RNet = R3 + RP = 6 + 3 = 9 Ω, Rp 6 6 6 3, , (ii) When two resistors are connected in series and third one is in parallel, we get 4 Ω resistance., Rs = R1+ R2 = 6 + 6 = 12 Ω, 2., , 1, 1, 1, 1, 1 1+2, 3, , =, +, =, + =, =, 12, 12, R p R s R 3 12 6, , fi Rp = 4 Ω, , 3. (i) Circuit in series vs Circuit in Parallel (Disadvantages of series circuit):, , (a) If one electrical appliance stops working due to some factor, then all the other appliances also stop, working., , (b) All the electrical appliances have only one switch due to which they can’t turned on or off individually., , (c) The appliances do not get the same voltage as of the input power supply., , (d) Overall resistance increases due to which the current from the input power supply becomes low., , (ii) Two resistances of 2 Ω are in series \ Rs = R1 + R2 = 2 + 2 = 4 Ω, , The third resistance of 4 Ω is parallel to Rs \, , 1, 1, 1, 1 1 2, =, +, = + =, Rp Rs R3 4 4 4, , , ⇒ RP = 2 Ω, 4. (1) The current required by each device is different which is possible only in parallel combination., , (2) If one device fails others can still work., , (3) Total resistance in the circuit is decreased., 5. R1, R2, R3 are in series combination and R4 is in parallel combination to these combination of resistors., Equivalent resistance of the given network is given as:, 1, 1, 1, 1, 1, 1, 1, 3+1, 4, +, +, =, +, =, =, =, =, R, R 4 R1 + R 2 + R 3, 10 10 + 10 + 10 10 30, 30, 30, , , , 30, = 7 .5 Ω, 4, V, 30 2, 3, =, =, =, Current drawn from the battery I =, R 7.5 75 5, , \R=, , 6., , (i) , , ⇒ I = 0.4 A, , , , Two 9 ohm resistors in parallel combination are connected to one 9 ohm resistor in series;, 1, 1 1 2, 9,   , = + =    \     R p = Ω, Rp 9 9 9, 2, R = 9 Ω +, , 9, Ω = 13.5 Ω, 2, , , (ii) Two 9 ohm resistors in series connected are connected to one 9 ohm resistor, in parallel;, , 116, , Science-10

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Rs = 9 Ω + 9 Ω = 18 Ω,    , , 1, 1 1, 3, =, + =, R 18 9 18, (b) I =, , 7. (a) 36 W, , \    , , R=6Ω, , V 12 V, =, = 0.33 A, R 36 Ω, , (c) V = R × I ⇒ V = 21 × 0.33 = 6.93 V, , 8. R1 = 100 Ω, R2 = 50 Ω, R3 = 500 Ω, V = 220 V, , , 1, 1, 1, 1, 1, 1, 1, 5 + 10 + 1, 16, =, =, +, +, +, +, =, =, R p R1 R 2 R 3, 100 50 500, 500, 500, , RP =, , 500 125, =, Ω = 31.25 Ω, 16, 4, , V 220 × 4 880, =, =, = 7.04 A, R, 125, 125, Current will remain the same if the electric iron is connected with the same source, i.e., , I = 7.04 A, 125, = 31.25 Ω across the electric iron., R =, 4, 9. (i) Rs = R1 + R2 = 10 Ω + 20 Ω = 30 Ω, , Current through all appliances =, , I =, , V, 3V, =, = 0 .1 A, R 30 Ω, , , (ii) V = I × R = 0.1 × 10 = 1 V, 10. (a) Rs = R1 + R2 = 2 W + 6 W = 8 W, V 4, = = 0 .5 A, R 8, (c) Current across the 2 W resistor = 0.5 A, 11. (a) In order to get 4 W resistance, 2 W resistance should be, connected in series with a combination of 3 W and 6 W, resistances connected in parallel with each other., , , (b) I =, , 1, 1, 1, 1 1 3, =, +, = + = ⇒ Rp = 2 Ω, , R p R1 R 2 3 6 6, ,  Rs = R3 + Rp = 2 W + 2 W = 4 W, , (b) In order to get 1 W resistance all the three resistors should be, connected in parallel., 1, 1, 1, 1, =, +, +, R p R1 R 2 R 3, =, , 1 1 1 3+2+1 6, + + =, = =1, 2 3 6, 6, 6, , ,  Rp = 1 W, 12. (a), , 1, 1, 1, 1, 1, 2 1, +, =, +, =, =, ⇒ RP = 5 Ω, =, RP, R1 R 2 10 10 10 5, , , (b) From Ohm’s law, I =, , (c) I1 =, , V 24, =, = 2 .4 A, R 10, , V 24, =, = 4 .8 A, R, 5, V 24, = 2 .4 A, I2 = =, R 10, , 13. When ‘N’ resistors each of resistance ‘R’ are connected in parallel, then R p =, , R, N, , Electricity 117

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Current drawn from the cell, I =, , , ⇒, , V, V V×N, =, =, R, Rp, R, N, 220 × N, 5A =, 176 Ω, , , 14. I =, , N=, , 5 × 176 880, =, =4, 220, 220, , V 220, =, = 9.17 A, R, 24, , When coils are used in series, Rs = R1 + R2 = 24 + 24 = 48 W ⇒ I =, , V 220, =, = 4.58 W, R, 48, , When coils are used in parallel,, 1, 1, 1, 1, 1, 2, +, =, +, =, =, ⇒ Rp = 12 W, R p R1 R 2 24 24 24, , ⇒, , I=, , V 220, =, = 18.3 A, R, 12, , VI. 1. (i) Resistors in Series: When resistors are joined end to end, it is called, series combination of resistances., In series combination of resistors, the current remains the same through, each resistor. Therefore the value of current in the ammeter remains the, same, independent of its position in the electric circuit., In the above circuit, V is equal to the sum of V1, V2, V3, that is the total, potential difference (V) across a combination of resistors in series is equal, to the sum of potential differences across the individual resistors., V = V1 + V2 + V3, The current through each resistor is I., V = IR, V1 = IR1 V2 = IR2 V3 = IR3, As V = V1 + V2 + V3 ⇒ \ IR = IR1 + IR2 + IR3 ⇒, , RS = R1 + R2 + R3, , \ We can conclude that when several resistors are joined, in series, then equivalent resistance of the combination, is equal to the sum of their individual resistances and, is thus greater than any of the individual resistance., ,  Resistors in Parallel:, When the resistances, says, R1, R2, R3 are connected, in in parallel combination as shown in the diagram,, then the potential difference remains the same, across each resistor in parallel combination of, resistors. In parallel combination the current is, distributed in different resistances in different, branches., As, I = I1 + I2 + I3, V, V, V, V, , I2 =, , I3 =, According to Ohm’s Law, I =, ⇒ I1 =, R1, R2, R3, Rp, , \ I = I1 + I2 + I3, 1, 1, 1, 1, V, V, V V, =, +, +, +, +, Or, ⇒, =, , R p R1 R 2 R 3, Rp, R1 R 2 R 3, (ii) (a) Resistance across parallel combination,, 1, 1, 1, 1, 1 + 1, , +, +, =, +, R3 R4 R5, R p R1 R 2, , Resultant resistance of 5 Ω, 20 Ω, 15 Ω, 10 Ω, and 20 Ω resistances is given as:, , 118, , Science-10, , 20 Ω, 15 Ω, 20 Ω, 5Ω, 6V, , 10 Ω

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1, 1 1, 1, 1, 1, = +, +, +, +, R p 5 20 15 10 20, 1, 28, =, R p 60, , ⇒, , Rp =, , , (b) V= 6 V, Resistance =, , ⇒, , 1 12 + 3 + 4 + 6 + 3, =, Rp, 60, , 60, Ω ⇒ R p = 2.14 Ω, 28, 60, Ω, 28, , V 6 × 28, =, ⇒ I = 2.8 A, R, 60, 2. 10 W and 20 W resistances are connected in series, therefore their equivalent resistance is given by: R1, = R1 + R2 = 10 + 20 = 30 W, V, 3, 1, , (i) Current flowing in the circuit, I =, =, =, = 0 .1 A, R S 30 10, , , \I=, , 1, × 10 = 1 volt, 10, 3. Series combination of 1 W and 3 W resistance is in parallel combination with 6 W resistor. Their, equivalent resistance is, , , (iii) Potential difference across the 10 W resistor, V = IR =, , 1, 1, 1, 1 1 2+3, = + =, = +, RP, 6 3+1 6 4, 12, , ⇒ RP =, , 12, = 2 .4 Ω, 5, , Now, 3.6 W, 2.4 W and 3 W resistors are connected in series, therefore their equivalent resistance be, given by: RS =R1 + R2 + R3 = 3.6 + 2.4 + 3 = 9 W, V 4.5 45 1, =, =, = = 0 .5 A, Hence, the current flowing through the circuit is, I =, R, 9, 90 2, 4. (a) Refer to Answer 1(i) — Long Answer Type Questions., 1, 1, 1, 1, 1, 1+1, 2, =, ⇒ R p = 6 Ohms, , (b) R = R – R = 12 + 12 =, 12, 12, p, 1, 2, , , I=, 5., , V, 6V, =, = 1 Ampere, R 6 ohm, , (i) I1 =, , V, 1 .5, ⇒ I1 =, = 0 .5 A ,, R, 3, , (ii) I2 =, , , (iii) ITotal = I1 + I2 = 0.50 + 0.25 = 0.75 A (iv), , V, 1 .5, ⇒ I2 =, = 0.25 A, R, 6, , 1, 1, 1, 1 1 3 1, =, +, = + = =, R p R1 R 2 3 6 6 2, , ⇒ R p = 2Ω, , Topic 3. Heating Effect of Current, , • Battery or cell is a source of electrical energy in any electric circuit., • The chemical energy is converted into electrical energy in a cell or a battery., • Chemical reaction generates the potential difference that sets, the motion of electrons, current flow through the resistors, connected to the battery., • The source keeps on expending its energy in maintaining the, current., • A part of energy is converted into useful work, e.g. rotation of, motor of fan or mixer and grinder or juicer., • When electric current is passed through a conductor, generated, by it heat due to the resistance it offers to the current flow. The, work done in overcoming the resistance is generated as heat. This is called the heating effect of current., , Electricity 119

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Heat produced by a heating element (resistor) is directly proportional to the (i) Square of the current (I2), passing through the conductor, (ii) Resistance R of the conductor, (iii) Time it for which the current is, passed through the conductor., • Heating effect of current has its application in appliances like electric iron, microwave, immersion rod,, induction cooker, heater as these are based on heating effect of current., • Let there be a current I flowing through the resistor of resistance (R). Let the potential difference be ‘V’., • Let ‘t’ be the time during which charge ‘Q’ flows. , (W) Work done = Charge (Q) × Potential difference (V), Power is defined as the energy consumed or work done per unit time.,                P =, , QV, t, , ⇒, , P=, , I×t×V, = V ×I, t, , Amount of heat produced in time ‘t’, H = V × I × t, , ⇒, , H = I2 R t , , ( Q = It), ( V = IR), , Joule’s Law of Heating: It states heat produced in a resistor is, , (i) directly proportional to the square of current for a given resistor., (ii) directly proportional to the resistance for a given resistor., , (iii) directly proportional to the time for which the current flows through a resistor., Practical Applications of Heating Effect of Current, , • The unavoidable heating can increase the temperature of electrical appliances and can alter their properties,, or they may be damaged due to excessive heat., • The electric laundry iron, electric toaster, oven, electric kettle, electric heater, all are based on heating, effect of current., • Heating effect of current in filament produces light in a bulb. It does not melt at high temperature due to, its high resistance. Tungsten has melting point 3380°C. So it is used as a filament in an electric bulb., • Electric bulbs are filled with inert gas like Argon to prevent its oxidation or burning of filament., • Fuse in an electric circuit is most important and is based on heating effect of current. It protect electric, circuits from overvoltage and high current., • The fuse is placed in series combination with the electric device. It is a thin wire of an alloy of copper,, aluminium, iron, etc., • If high current flows in a fuse wire, as the temperature of fuse wire increases, it melts and circuit is, broken., • In domestic circuits different type of fuse wires are used, depending upon the load of the circuit., , Electric Power, The rate of consumption of electric energy in a electric circuit is called electric power, e.g. a 100 watt bulb has, power 100 watt or 100 J s–1. The S.I. unit of power is Watt (W)., , P=V×I, R=, , , , \     , , V, I, , fi, , I=, , V, R, , V V2, V2, =, ∴ P=, R, R, R, 2, P = V × I ⇒ P = R × I × I = I × R, P=V×, ,     , , ( V = R × I), , P = I2 R, , , fi     , , Watt: It is the power consumed by a device that carries 1 A of current when operated at a potential difference, of 1 V.,                1 W = 1 volt × 1 ampere = 1 V A, The unit of electric energy is kilowatt hour (kW h). 1 kilowatt (kW) = 1000 watt, 1 kW h = 1000 watt × 3600 seconds = 3.6 × 106 Watt seconds = 3.6 × 106 J, Important Note: Electrons are not consumed in an electric current, only electrical energy is consumed., Direct current (D.C.): The current which flows only in one direction is called direct current (DC)., • It is produced by a cell or battery., • Circuits in which direct current flow are called D.C. circuits. Both AC and DC can give electric shock., , 120, , Science-10

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AC circuit: The current that flows in two directions alternatively is called alternating current., • It is supplied by electricity department., • Voltage is 220 V to 250 Volt for domestic supply, current is 5 A, frequency is 50 cycles per second or 50, Hertz., • Power is transmitted by AC current., • It gives electric shock if live wire is touched., , Earth wire: It is connected to the metal case of an electrical appliance. In case of leakage of electricity, we may, get shock if live wire is connected to the metal case., • The earth wire allows the current to flow through it to the ground. It can protect us from fatal electric, shock., • In a three pin plug, blue is neutral wire, red is live wire. Earth wire is green or yellow. The earth pin is, longer and thicker than live and neutral pins. The sockets are mechanically protected. The earth pin must, enter in the top hole and other two pins in the bottom holes., , Exercise 5.3, I. Multiple Choice Questions, (1 Mark), Choose the correct answer from the given options., 1. In an electrical circuit three incandescent bulbs A, B and C of rating 40 W, 60 W and 100 W respectively, are connected in parallel to an electric source. Which of the following is likely to happen regarding, their brightness?, (a) Brightness of all the bulbs will be the same, (b) Brightness of bulb A will be the maximum, (c) Brightness of bulb B will be more than that of A, (d) Brightness of bulb C will be less than that of B, 2. In an electrical circuit two resistors of 2 Ω and 4 Ω respectively are connected in series to a 6 V battery., The heat dissipated by the 4 Ω resistor in 5 s will be, (a) 5 J      (b) 10 J, (c) 20 J       (d) 30 J, 3. An electric kettle consumes 1 kW of electric power when operated at 220 V. A fuse wire of what rating, must be used for it?, (a) 0.454A    (b) 2 A, (c) 4 A       (d) 5 A, 4. The type of current supplied by cell or battery is, (a) A.C     (b) D.C, (c) Both (a) and (b) (d) None of these, 5. Unit of electric power may also be expressed as:, (a) volt-ampere (b) kilowatt-hour, (c) watt-second   (d) joule-second, [CBSE Sample Paper 2019-2020], II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 to 3 two statements are given-one labeled as Assertion (a) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given ahead:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Electric toasters are made up of alloys., , Reason: Alloys have high resistivity and do not get oxidised at high temperature., 2. Assertion: The commercial unit of electrical energy is 1 kWs, , Reason: 1 kWh = 3.6 × 106 J., 3. Assertion: A fuse wire is always connected in parallel with the mainline., , Reason: If a current larger than the specified value flows through the circuit, fuse wire melts., , [CBSE Sample Paper 2019-2020], III. Very Short Answer Type Questions, , (1 Mark), , 1. What determines the rate at which energy is delivered by a current?, 2. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?, 3. Name the type of current used in household supply., , [NCERT], [Delhi 2016], , Electricity 121

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4. Write the relationship between heat energy produced in a conductor when potential difference V, is applied across its terminals and a current, I flows through it for the time ‘t’. , [Delhi 2016], 5. Why does the cord of an electric heater not glow while the heating element does?, [NCERT], 6. Why heat is produced when current is passed through a conductor?, 7. Explain the role of fuse wire connected in series with any electrical appliance in an electric circuit., Why should a fuse with a defined rating for an electric circuit not be replaced by the one with a larger, rating?, 8. Why are heating elements made of alloys rather than metals?, OR, Why are alloys commonly used in electrical heating devices like toasters and electric iron? Give reason., [CBSE 2019 AI], 9. A bulb gets dimmer when an electric iron or geyser is switched on, why?, , IV. Short Answer Type Questions-I, , (2 Marks), , 1. Compute the heat generated while transferring 96000 coulomb of charge in one hour through a, potential difference of 50 V., [NCERT], 2. An electric iron of resistance 20 W takes a current of 5 A. Calculate the heat developed in 30 s., [NCERT], 3. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy, consumed in 2 hours., [NCERT], 4. Several electric bulbs designed to be used on a 220 V electric supply line are rated 10 W. How many, lamps can be connected in parallel with each other across the two wires of 220 V line, if the maximum, allowable current is 5 A? , [NCERT], 5. Find the resistance of bulb rated as 100 W at 250 V., [CBSE 2014], 6. Name the commercial unit of energy. Convert it into Joules. What is other name of commercial unit of, energy?, 7. Find the minimum rating of fuse that can be safely used on a line on which two 1.1 kW rating electric, geysers are to be run simultaneously. The supply voltage is 220 V., [Delhi 2016], , V. Short Answer Type Questions-II, , (3 Marks), , 1. An electric heater of resistance 8 W draws 15 A current from the supply mains for 2 hours. Calculate, the rate at which heat is developed in the heater., 2. A potential difference of 4 V derive a current of 3 A through a resistor. How much electrical energy will, be converted into heat during 10 seconds?, 3. An electric fan has a rating of 460 W on the 230 V mains line. What fuse should be fitted in the plug?, 4. What is the cost of running an AC with average power of 1000 W for 8 hours for 30 days. The cost of, electric energy is `4.70 per kW h., 5. Why do we get electric shock in damp conditions?, 6. Compare the power used in the 2 W resistor in each of the following circuits: (i) a 6 V battery in, series with the 1 W and 2 W resistors, and (ii) a 4 V battery in parallel with 12 W and 2 W resistors., [NCERT], 7. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to, electrical mains supply. What current is drawn from the line if the supply voltage is 220 V?, [Delhi 2018] [NCERT], 8. (i) Explain what is the difference between direct current and alternating current. Write one important, advantage of using alternating current., , (ii) An air conditioner of 2 kW is used in an electric circuit having a fuse rating of 10 A. If the potential, difference of the supply is 220 V, will the fuse be able to withstand when the air conditioner is, switched on? Justify your answer., [Delhi 2016], 9. What is meant by ‘electrical resistance’ of a conductor? State how resistance of a conductor is effected, when, , (i) Low current passes through it for a short duration., , (ii) A heavy current passes through it for 30 seconds. , [Delhi 2015], 10. An electric kettle of 2 kW works for 2 hours daily. Calculate the, , (a) Energy consumed in SI unit and commercial unit., , (b) Cost of running it in the month of June at a rate of ` 3.00 per unit., [Delhi 2014], 11. An electric bulb is rated 220 V and 100 W, when it is operated at 110 V. What will be the power, consumed? , [Delhi 2010], , 122, , Science-10

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12. An electric iron has a rating of 750 W, 220 V. Calculate the, , (i) Current flowing through it and (ii) Its resistance when it is in use., 13. Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 4 W, in series with a combination of two resistors (8 W each) in parallel and a voltmeter across parallel, combination. Each of them dissipate maximum energy and can withstand a maximum power of 16 W, without melting. Find the maximum current that can flow through the three resistors., , , [CBSE Sample Paper 2017-2018], , 14. Two lamps, one rated 100 W at 220 V and the other 200 W at 220V are connected (i) in series and, (ii) in parallel to electric main supply of 220V. Find the current drawn in each case., 15. How many 40 W; 220 V rating lamps can be safely connected to a 220 V, 5 A line? Justify your answer., [Delhi 2015], , VI. Long Answer Type Questions, , (5 Marks), , 1. An electric circuit two resistors of 20 W and a conductor of resistance, 4W are connected to a 6 V vattery as shown in the figure. Calculate:, , (a) The total resistance of the circuit,, , (b) the current through the circuit,, , (c) the potential difference across the (i) electric lamp and (ii) conductor,, and, , (d) power of the lamp., 2. Explain the following:, , (i) Why is tungsten used almost exclusively for filament of electric lamps?, , (ii) Why are the conductors of electric heating devices, such as bread-toaster and electric iron, made of, an alloy rather than a pure metal?, , (iii) Why is series arrangement not used for domestic circuits?, , (iv) How does the resistance of a wire vary with its area of cross-section?, , (v) Why are copper and aluminium wires usually used for the transmission of electric current?, [NCERT], 3. (a) Define electric power. Express it in terms of potential difference, V and resistance, R., , (b) An electrical fuse is rated at 2 A. What is meant by this statement?, , (c) An electric iron of 1 kW is operated at 220 V. Find which of the following fuse that are respectively, rated at 1 A, 3 A and 5 A can be used for it., 4. (a) Write two points of differences between electric energy and electric power., , (b) Out of 60 W and 40 W lamps, which one has higher electrical resistance when in use., , (c) What is the commercial unit of electric energy? Convert it into the units of Joule., 5. Two identical wires, one of nichrome and other of copper are connected in series and a current (i) is, passed through them. State the change observed in the temperature of the two wires. Justify your, answer. State the law which explains the above observations., 6. (a) State Ohm’s law. Derive the relation and give graphical representation for it., , (b) An electric oven rated at 500 W is connected to a 220 V line and used for 2 hours daily. Calculate, the cost of electric energy per month at the rate of ` 5 per kW h., 7. In the given circuit, A, B, C and D are four lamps connected with a battery of 60V., , 60 V, , 3A, , A, , 4A, , B, , 5A, , C, , 3A, , D, , Analyse the circuit to answer the following questions., , Electricity 123

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(i) What kind of combination are the lamps arranged in (series or parallel)?, , (ii) Explain with reference to your above answer, what are the advantages (any two) of this combination, of lamps?, , (iii) Explain with proper calculations which lamp glows the brightest?, , (iv) Find out the total resistance of the circuit., [CBSE Sample Paper 2020-21], 8. (a) What is the function of fuse wire in an electric circuit?, , (b) What would be the rating of the fuse for an electric kettle which is operated at 220 V and consumes, 500 W power?, , (c) How is the SI unit of electric energy related to its commercial unit?, 9. (i) Consider a conductor of resistance ‘R’, length ‘L’, thickness ‘d’ and resistivity ‘ρ’., Now this conductor is cut into four equal parts. What will be the new resistivity of each of these, parts? Why?, , (ii) Find the resistance if all of these parts are connected in: (a) Parallel (b) Series, , (iii) Out of the combinations of resistors mentioned above in the previous part, for a given voltage which, combination will consume more power and why? [CBSE Sample Paper 2019-2020], , Answers 5.3, I. 1. (c) Higher the wattage (power), more will be brightness, 2. (c) H = I2× R × t = 1 × 4 × 5 = 20 J. I = V = 6 V = 1A, R 6Ω, P 1000 W, =, 3. (a) I =, = 0.454 A, V, 220 V, 4. (b) D.C (Direct current) which flows only in one direction., , 5. (a) volt-ampere,  Power = Voltage × Current., II. 1. (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., , 2. (d) ‘A’ is false and ‘R’ is true because commercial unit is kW h and not kW s., , 3. (d) ‘A’ is false and ‘R’ is true., III. 1. Electric power is the rate at which energy is delivered by a current., 2. Energy consumed by 250 W TV in 1 h = 250 × 1 = 250 W h, Energy consumed by 1200 W toaster in 10 minutes = 1200 × 10 = 200 W h, 60, Here total energy consumed by the TV is more than toaster., 3. Alternate current, 4. H = VIt, 5. The cord of the electric heater is made up of copper or aluminium which has lower resistance and, higher conductance, therefore very less heat energy is produced., Heating element is made up of alloys which have high resistance and lot of heat is produced, and only, a little amount of electric energy makes it to glow., 6. The electrons collide with each other while moving and loses some kinetic energy which is converted, into heat energy., 7. Fuse wire is a safety device connected in series with the live wire of the circuit, since it has high, resistivity and low melting point. It melts when a sudden urge of large current passes through it and, disconnects the entire circuit from the electrical supply. But in case if we use a larger rating fuse wire, instead of a defined rating fuse wire then it will not protect the circuit as high current will easily pass, through it and it will not melt., 8. Alloys have high resistivity/high melting point/alloys do not oxidise (or burn readily at high, temperatures)., 9. It is because electric iron or geyser draws heavy current from the circuit, takes heavy power and, therefore bulb becomes dimmer due to decrease in voltage., IV. 1. Q = 96000 C, t = 1 hr = 3600 s, V = 50 volt, H = V × I × t = V × Q = 50 × 96000 C =, , 124, , Science-10, , 50 × 96000, kJ = 4800 kJ, 1000

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2., , 3., , , 4., , R = 20 Ω, I = 5 A, t = 30 s, H = I2 × R × t = 5 × 5 × 20 × 30 = 15000 J = 15 kJ, I = 5 A, V = 220 V, P = ?, E = ?, t = 2 hours, P = V × I = 220 V × 5 A = 1100 W, E = P × t = 1100 W × 2 h = 2200 W h = 2.2 kW h, Total power = N × P where ‘N’ is the number of bulbs, ‘P’ power of each bulb., , , I=, 5. P =, , N×P, V, , V2, R, , ⇒ 5=, , ⇒ R=, , N × 10, 220, , ⇒ N=, , 5 × 220, = 110, 10, , 250 × 250, V2, =, = 625 Ω, 100, P, , 6. The commercial unit of electrical energy is kW h. (Kilowatt hour), 1 kW h =1 kW × 1 hour = 1000 W × 3600 s = 3.6 × 106 J, P 1.1 × 1000 1100, =, =, =5A, V, 220, 220, The rating of fuse that can be used is more than 5 A., It is also called Board of Trade Unit (BOTU), V. 1. R = 8 Ω, I = 15 A, t = 2 hours, H I2 × R × t, =, = I2 × R, Rate of heat developed =, t, t, 7. I =, , , = 152 × 8 = 1800 J s–1 = 1800 Watt = 1.8 kW, V 4, 2. R =, = = 1.33 Ω, I, 3, 4, H = I2 × R × t = 3 × 3 × × 10 = 120 J, 3, 3. P = V × I ⇒ 460 = 230 × I ⇒ I = 2 Ampere, A 3A fuse should be fitted (It should be slightly more than 2A)., 4. E = P × t = 1000 W × 8 × 30 = 240000 W h = 240 kW h, Cost of electric energy = 240 × 4.70 = ` 1128., 5. Water provides conducting path for a current to flow through the human body in damp conditions like, bathroom. We get electric shock if we are bare footed. Wet body has low resistance, high current can, easily pass through, leading to electric shock., 6. (i) Rs = R1 + R2 = 1 Ω + 2 Ω = 3 Ω, V = 6 V, I = V = 6 = 2 A, R 3, , P = I2 × R (Since same current flows through each resistor) = 2 × 2 × 2 = 8 W, , (Q R = 2 Ω), , 1, 1, 1 1+6, 7, 1, 1, 1, 12, =, + =, =, =, +, , (ii), ⇒, ⇒ Rp =, Ω, R, 12, 2, 12, 12, R p R1 R 2, 7, p, , Resistance will change, voltage remains the same., , V2 4 × 4, =, =8W, R, 2, Power used are in the ratio 1 : 1., , Power across 2 W resistor, P =, , 7. R100 W =, I =, , V 2 220 × 220, V 2 220 × 220, =, ; R60 W =, =, P, 100, P, 60, , V, 220 × 100 100, V, 220 × 60, 6, =, =, = 0.45 A ; I =, =, =, = 0.27 A, R100 220 × 220 220, R 60 220 × 220 22, , , \ Total current = 0.45 A + 0.27 A = 0.72 A, 8. (i) The current whose direction gets reversed after every half cycle is called alternating current or A.C., There is no change in the direction of D.C. D.C. is a uni directional current., , Electricity 125

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The most important advantage of using A.C. over D.C. is that in the A.C. mode electric power can, be transmitted over long distances at a high voltage and low current with very little loss of power., , (ii) Here P = 2 kW = 2000 W, V = 220 Volt, P 2000, = 9.09 A, , P = VI, so the current, I =, =, V, 220, As the current is 9.09 A below the rating of fuse, therefore the fuse will withstand, i.e. it will not, blow off when A.C. is on., 9. It is in opposite direction offered to the flow of electric current., , (i) No effect on resistance, low current, hence no appreciable rise in temperature so there no change, in resistance., , (ii) Heavy current for 30 seconds may increase the temperature so resistance will increase., 10. (a) P = 2 kW, t = 2 h, E =P × t = 2 × 2 h = 4 kW h, , (b) Total energy consumed per month = 4 kW h × 30 = 120 kW h, Total cost = 120 × 3 = ` 360., 11. R =, P =, 12., , V2, 220 V × 220 V, = 484 Ω, =, P, 100 W, V2, 110 × 110, =, = 25 W, R, 484, , (i) P = 750 W, V = 220 V, , P = V × I ⇒ 750 = 220 × I ⇒ I =, , (ii) P =, , V2, R, , ⇒, , R=, , V 2 220 × 220, =, P, 750, , 750, = 3.409 A, 220, ⇒ R = 64.53 Ω, , 13., , , , Maximum current through 4 W resistor =, , , , Maximum current through each 8 W resistor =, , 14. R1 =, , 2 = 1.414 A, , In series: Rs= R1 + R2 = 484 + 242 = 726 W, ∴ Is =, , , In parallel:, , 126, , P, 16 W, =, =, R, 8Ω, , V 2 220  220, V 2 220  220, ,  242 , ,  484  ; R2 =, P2, 200, P1, 100, , , , , , P, 16 W, =2A, =, R, 4Ω, , V 220 10, =, = A = 0.30A, R s 726 33, , 484, 1, 1, 1, 1, 1, Ω, , , =, ⇒ Rp =, +, 3, R p R1 R 2, 484 242, V 220  3 30, , , A  1.36A, Ip =, RP, 484, 22, , Science-10

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N × 40 W, 220 V × 5 A 110, N×P, ⇒ 5A =, ⇒N=, =, = 27 lamps, 220 V, 40 W, 4, V, VI. 1. (a) Rs = R1 + R2 = 20 Ω + 4 Ω = 24 Ω, 15. I =, , V, 6V, , (b) I = R = 24 Ω = 0.25A, , (c) (i) V = I × R = 0.25 A × 20 Ω = 5 V, , (ii) V = I × R = 0.25 A × 4 = 1V, 2, , 1,  1, × 20 = 1.25 W, , (d) (i) P = I × R =   × 20 =,  4, 16, 2. (i) It has high resistance and high melting point. So it does not melt when current is passed through, it., , (ii) Alloys have more resistivity and higher melting point., , (iii) It increases the resistance and current decreases. Also if one component fails to work, others will, also not work, , (iv) Resistance is inversely proportional to the area of cross section., , (v) It is because Cu and Al have low resistivity and it allows current to flow., 3. (a) Electric power is the rate of doing work by an energy source or the rate, at which the electrical energy dissipated or consumed per unit time in the, electric circuit., 2, , So,, , , , Power (P) =, =, , Work done (W), Time (t), , Electrical energy dissipated, Time (t), , ⇒ VI or P =, , 3, V (Volt) 2, 1, , V2, R, , 1, 0.5, 1.5, I (Ampere), , , (b) It means the maximum current will flow through it is only 2 A. Fuse wire will melt if the current, flowing through it exceeds 2 A value., , (c) Given:, P = 1 kW = 1000 W, V = 220 V, P, 1000, 50, =, =, = 4.54 A, V, 220, 11, To run electric iron of 1 kW efficiently, rated fuse of 5 A should be used., , Current drawn, I =, , , 4. (a) Difference between electric energy and electric power:, Electric Energy, , Electric Power, , (i) The work done or energy supplied by the (i) The time rate at which electric energy is, consumed or dissipated by an electrical device, source in maintaining the flow of electric, is called electric power and is given by:, current is called electrical energy. It, appears in the form of heat and is given, V2, P, =, VI, =, = I2 R, , by:, R, V2t, H = VIt =, = I 2 Rt, , R, (ii) It is also equal to the product of power and (ii) It is also equal to the rate of doing work by an, time taken:, energy source and is given by:, , E=P×t, W, P=, , t, (iii) Its SI unit is Joule (J), (iii) Its SI unit is Watt (W), , 1J=1W×1s,       1 W = 1 J s–1      (Any two), , Electricity 127

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1, ,, R, i.e. smaller the power of electrical device, higher is its electrical resistance., So a 40 W lamp has higher electrical resistance than a 60 W lamp., , (c) Kilowatt hour – Commercial unit of electrical energy., 1 kW h = 1000 W h = 1000 J/s × 3600 s = 3600000 J = 3.6 × 106 J, 5. The resistivity of nichrome is more than that of copper, so its resistance is also high. Therefore large, amount of heat is produced in the nichrome wire for the same current passed as compared to that of, the copper wire. Accordingly greater change in temperature is observed in case of nichrome wire. This, can be explained by Joule’s law of heating., Joule’s law of heating states that the amount of heat produced in a conductor is:, , (i) Directly proportional to the square of current flowing through it, i.e., , H ∝ I2, , (ii) Directly proportional to the resistance offered by the conductor to the flow current, i.e., H ∝ R, , (iii) Directly proportional to the time for which current is flowing through the conductor, i.e., H ∝ t, Combining these, we get, H ∝ I2Rt, or H = KI2Rt, where K is a proportionality constant and in SI units, it is equal to unity., , (b) For the same applied voltage, P ∝, , 6. (a) Linear equation, hence a straight line passing through the origin, is obtained as follows:, Ohm’s law states that potential difference across the given metallic, wire in an electric circuit is directly proportional to the electric, current flowing through it, if the temperature remains constant., Mathematically, V ∝ I., or, or, , V, = Constant, I, V = IR (where R is a constant known as the, constant of proportionality)., , , (b) Energy consumed per day = 1 kW h., , , P = V × I, E = P × t  E = V × I × t = 220 × 2.27 × 2 = 1 kWh, 500 , P, 500, , =, = 2.27 A, ∵ P = V × I ∴ I = 220 , V, 220, Cost of electric energy for 30 days = 1 × 5 × 30 = ` 150.00, 7. (i) The lamps are in parallel., , (ii) Advantages:, If one lamp is faulty, it will not affect the working of the other lamps., They will also be using the full potential of the battery as they are connected in parallel., , (iii) The lamp with the highest power will glow the brightest., , P = VI, In this case, all the bulbs have the same voltage. But lamp C has the highest current., Hence, for lamp C, P = 5 × 60 Watt = 300 W. (the maximum)., , (iv) The total current in the circuit = (3 + 4 + 5 + 3) A = 15A, , The Voltage = 60V, , V = IR and hence R = V/I, , R = 60/15 W = 4 W, 8. (a) Fuse wire protects the electrical circuits from over voltage and high current., , (b) 2.2 A flows through the circuit, fuse should be rated 3 A., , (c) 1 kW h = 3.6 × 106 J, 9. (i) Resistivity will not change as it depends on the nature of the material of the conductor., , (ii) The length of each part becomes L/4. While ρ, A remain constant.  R = ρL/A., Resistance of each part = Rpart = (ρL/4)/A = R/4., So, I =, , 128, , Science-10

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(a) In parallel connection,, , 1, 1, 1, 1, 1, 4, 16, R, =, +, +, +, =, =, ⇒ R eqv =, Ω, R eqv R part R part R part R part R part R, 16, , , (b) In series connection, Reqv =, , R R R R, + + +, = R Ω (ohms), 4 4 4 4, , , (iii) P = V2/R., If Reqv is less, power consumed will be more., In the given case, Reqv is lesser in the parallel connection and the power consumed will be more., , C ase study questions, , 1. Ohm’s law gives the relationship between current flowing, , through a conductor with potential difference across it, provided the physical conditions and temperature remains, constant. The electric current flowing in a circuit can be, measured by an ammeter., Potential difference is measured by voltmeter connected, in parallel to the battery or cell. Resistances can reduce, current in the circuit. A variable resistor or rheostat is used, to vary the current in the circuit., , (i) What type of conductor is represented by the following, graph?, , Current, , I, , V, Voltage, , , (a) Non-ohmic conductor like thermistor, (b) Non-ohmic conductor like metal filament, , (c) Ohmic conductor like copper, (d) None of these, , (ii) What type of conductors are represented by the following graph?, , Current, , I, , V, Voltage, I, , Current, , , (a) Non-ohmic conductor like thermistor, , (b) Non-ohmic conductor like metal filament, , (c) Ohmic conductor like copper, , (d) None of these, , (iii) Which type of conductor is represented by the graph given alongside?, , (a) Non-ohmic conductor like thermistor, , (b) Non-ohmic conductor like metal filament, , (c) Ohmic conductor like copper, , (d) None of these, , V, Voltage, , Electricity 129

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(iv) What is the slope of graph in (i) equal to?, , (a) V, , (b) I, , (c) R, , (d) VI, , , (v) Which of the following is the factor on which resistance of a conductor does not depend?, , (a) Length, (b) Area, (c) Temperature, (d) Pressure, Ans. (i) (c)  (ii) (b)  (iii) (a)  (iv) (c)  (v) (d), 2. Study this table related to material and their resistivity and answer the questions that follow., Material, , Resistivity (W m), , Conductors, , Silver, Copper, Sluminium, Tungsten, Nickel, Iron, Chromium, Mercury, Manganese, , 1.60 × 10–8, 1.62 × 10–8, 2.63 × 10–8, 5.20 × 10–8, 6.84 × 10–8, 10.0 × 10–8, 12.9 × 10–8, 94.0 × 10–8, 1.84 × 10–6, , Alloys, , Constantan (alloy of Cu and Ni), Manganin (alloy of Cu, Mn and Ni), Nichrome (alloy of Ni, Cr, Mn and Fe), , 49 × 10–6, 44 × 10–6, 100 × 10–6, , Insulators, , Glass, Hard rubber, Ebonite, Diamond, Paper (dry), , 1010 – 1014, 1013 – 1016, 1015 – 1017, 1012 – 1013, 1012, , , (i) What is the range of resistivity in metals, good conductors of electricity?, (b) 10–6 to 10–4 Ωm (c), (a) 10–8 to 10–6 Ωm , 10, 14, (d) 1012 to 1014 Ωm, 10 to 10 Ωm , , (ii) Which property of the alloy makes it useful in heating devices like electric iron, toasters,, immersion rods, etc.?, (a) Higher resistivity, (b) Do not oxidise at low temperature, (c) Do not reduce at high temperature, (d) Oxidise at high temperature, , (iii) Which of the following is used in transmission wires?, (a) Cr (b) Al, (c) Zn, (d) Fe, , (iv) Which is the best conducting metal?, (a) Cu (b) Ag, (c) Au, (d) Hg, , (v) Which of the following is used as a filament in electric bulbs?, (a) Nichrome (b) Tungsten (c) Manganese, (d) Silver, Ans. (i) (a)  (ii) (a)  (iii) (b)  (iv) (b)  (v) (b), , Quick revision notes, , • Resistance is the property of a conductor that resists or opposes the flow of current through it. It controls the, magnitude of current passing through the substance., • Higher resistance reduce the current in a circuit., • The S.I. unit of resistance is Ohm (W)., , 130, , Science-10

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• Rheostat is used to provide variable resistance, e.g. speed of fan can be decreased by increasing the resistance, and can be increased by decreasing the resistance., • Ohm’s law gives the relationship between potential difference (V) and current (i):, V ∝ I or V = RI, where R is a constant called resistance of the conductor., • The resistance of a wire is directly proportional to the length of wire and is inversely proportional to its area, of cross section., • Thinner the wire, more will be resistance, that is why a thin wire is used in electric fuse which can resist, high voltage only to some extent and prevent electric circuit from damage., • Longer the wire, more will be resistance., • Resistance also depends upon the material of conductor, e.g. copper is a good conductor of electricity due to, its low resistance., • Temperature also affects the resistance, e.g. resistance of metals increases with increase in temperature and, decreases with decrease in temperature., • That is why some metals become superconductors at very low temperature because practically they offer no, resistance in the path of flow of current., • The equivalent resistance of many resistors connected in series is equal to the sum of the resistances of, individual resistors: RS = R1 + R2 + R3 + …, • The equivalent resistance of resistors connected in parallel is given by:, 1, 1, 1, 1, =, +, +, +…, RP, R1, R2, R3, • A cell can supply energy but not charge. Its function is to drive the free electrons in a circuit to flow., • The electrical energy dissipated (lost) in a resistor is given by:, W=V×I×t, where ‘V’ is voltage, ‘I’ is current, ‘t’ is time for which current flows., • Electric kettles, cookers, electric iron and heaters make use of electric energy which is converted into heat, energy. The heating element is made up of a material having high resistance., • When electrons pass through the metal wire, they give some of their energy to the particles of wire and make, them vibrate more randomly, and that is why wire gets hotter., • For the same current flowing in the circuit, greater the resistance, the hotter it becomes. That is why electric, iron, immersion rod becomes red hot but electric transmission wires remain cool due to low resistance., • Energy is measured in Joules., • Electric power is the rate of using electrical energy. It is measured in joules per second J s –1 or, in a unit called Watt (W)., • One watt power is consumed when 1 Ampere (a) current flows at a potential difference of 1 Volt., • The commercial unit of electrical energy is kilowatt hour (kW h)., , 1 W = 1 J s–1,  , 1 kW = 1000 W, , 1 hour = 3600 seconds, , \ , 1 kW h = 1 × 1000 × 60 × 60 J = 36 × 105 = 3.6 × 106 J, • Power (P) = V × I, where ‘V’ is voltage (potential difference) and I is current in Ampere., V, V, \ I=,      , Ohm’s law, R =, I, R, P=V × I =V×, ,             , , V, V2, =, R, R, , ⇒, , P=, , V2, or P = I 2 R, R, , • Electric energy (E) = V × I × t, E=, , V2t, R, , E = I2 Rt, , V, , , ∵ I = R by Ohm’s law , , [∵, , V = I × R by Ohm’s law ], , Electricity 131

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important Formulae, 1. Ohm’s law: V = IR , where R is resistance., l, 2. R = ρ, where, ‘l’ is length of conductor, ‘A’ is, A, area of cross section, rho (r) is resistivity., 3. R S = R1 + R 2 + R3, , where,, , RS, , is, , total, , resistance connected in series combination, In series combination, current across each, resistor remains same, 1, 1, 1, 1, =, +, +, 4., where RP is equivalent, R P R1 R 2 R 3, resistance in parallel combination; R1, R2, R3, are resistors connected in parallel., , In parallel combination potential difference across, each resistor remains same., 5. H = VIt ; H = P × t, ‘H’ is heat produced in a conductor, I is current, t, is time, ‘V’ is voltage (Potential difference), ‘P’ is, power., 6. Joule’s Law: H = I 2Rt, 7. P = I2 × R, , 13. P =, , V2, R, , 6, 8. 1 kW h = 3.6 × 10 J, , Common Errors, Errors, ●, ●, , ●, , ●, , ●, , ●, , ●, , Students do not write the correct SI units., , Corrections, , ☞ Always write the correct SI unit., , Students do not show arrowhead in circuit ☞ Direction of current should be shown by arrowhead, diagrams., in circuit diagram., Students connect Ammeter in parallel and ☞ Ammeter is always connected is series, Voltmeter, Voltmeter in series., in parallel., Students do not write formulae in numericals., , ☞ Formula must be written before starting a, numerical., , Students interchange or write incorrect formulae ☞ Rs = R1 + R2 + R3: for series combination;, for series and parallel combination of resistances., For parallel combination:, 1, 1, 1, 1, and not, =, +, +, RP, R1, R2, R3, 1, 1, 1, +, +, RP =, R1, R2, R3, Students get confused between resistance and ☞ ‘R’ (resistance) depends upon length, area,, resistivity., temperature; while resistivity only depends upon, temperature and nature of material., Circuit diagrams and other diagrams are not ☞ Circuit diagrams and other diagrams must be, drawn and properly labeled., made with pencil with proper labeling., , 132, , Science-10

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Assignment, I. Multiple Choice Questions, , Total Marks : 20, (1 Mark), , Choose the correct answer from the given options., 1. Which of the following does not represent electric power?, (a) I2R, (b) IR2, (c) VI, (d) V2/R, [CBSE 2020], 1, 2. If a person has five resistors each of value Ω , then the maximum resistance he can obtain by, 5, connecting them is, (a) 1 W, (b) 5 W, (c) 10 W, (d) 25 W , [CBSE 2020], II. Assertion-Reason Type Questions, (1 Mark), , Note: Use instructions as given in topical exercises of the chapter., 1. Assertion: The graph between V and I is a straight line., , Reason: V is directly proportional to ‘R’ and the slope gives value of ‘R’., 2. Assertion: At high temperature, metal wires have greater chances of short circuiting., , Reason: Both resistance and resistivity of metallic wires varies with temperature., , III. Very Short Answer Type Questions, , (1 Mark), , 1. What is the function of rheostat?, 2. List two factors on which resistance depends., , IV. Short Answer Type Questions-I, , (2 Marks), , 1. Which has more resistance, ammeter or voltmeter? Give reason., 2. How are voltmeter and ammeter connected in an electric circuit?, 3. If you connect three resistors having values 2 W, 6 W and 8 W in parallel, calculate the equivalent, resistance., , V. Short Answer Type Question-II, , (3 Marks), , 1. (a) Write mathematical expression for Joule’s Law of heating., , (b) Compare the heat generated while transferring 96500 coloumb of charge in two hours through a, potential difference of 40 V., [CBSE 2020], , VI. Long Answer Type Question, , (5 Marks), , 1. (a) Two lamps rated 100 W, 200 V and 10 W, 220 V are connected in parallel to 220 V supply. Calculate, the total current through the circuit., , (b) Two resistors X and Y of resistance 2 W and 3 W respectively are first joined in parallel and then in, series. In each case the voltage is 5 V., (i) Draw circuit diagram to show the combination of resistors in each case., (ii) Calculate the voltage across the 3 W resistor in the series combination of resistors., [CBSE 2020], , Electricity 133

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6, , Magnetic Effects of Current, , Topics Covered, 6.1 Magnetic field and Field lines, 6.2 Magnetic field due to Current carrying conductors in Magnetic Field., 6.3 Electric Motor, Electromagnetic Induction, , C hapter map, Magnetic effects of Current, , Magnetic, field, , Straight, conductor, Direction by, Right hand, Thumb Rule, , Electricity and Magnetism, , Electric effect of moving magnet, , Magnetic effect of moving charges, , Induced Current, , Magnetic field lines, , Direction, , Solenoid, , Force on, current-carrying, conductor in, magnetic field, , Current, through, circular loop, , Direction of Magnetic field, Clock face rule, , Fleming’s Right, hand Rule, , Fleming left hand Rule, Electric motor, , Topic 1. Magnetic field and field lines, , Magnet: It is a substance which has the property to attract certain substances like iron, cobalt, nickel, steel,, etc. These are known as magnetic substances., , Poles of magnet: One end of the magnet points towards the north pole of the earth and it is called North, , pole, the other end which points towards the south pole of the earth is called the South pole of the magnet., Induced magnet (Artificial magnet): It is a temporary magnet made up of iron or steel or a magnetic material, when it is near to or in contact with the magnet., Magnetic substances: Those substances which are attracted by magnets, e.g. Fe, Co, Ni, Alnico (alloy of Al,, Co, Ni, Fe)., Non-magnetic substances: Those substances which are not attracted by magnet, e.g. Copper, Zinc,, Aluminium, Brass, Wood, Glass, Rubber, Plastic, etc., Uses of Magnet: Magnets are used in Fridge doors so that they close automatically., , 134

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• Electric motor, fan, electric generators, etc., • MRI (Magnetic Resonance Imaging) scan uses magnetic field to create a picture of internal organs., • Hard discs, audio-video tapes etc. use magnetic substances., Characteristics of Magnets:, • Like poles repel and unlike poles attract each other., • Magnet attracts magnetic substances., • Freely suspended magnet aligns itself to the north-south direction as the geographic north-south direction., • Magnetic poles cannot be separated. Every magnet has two poles, i.e. monopoles does not exist., Magnetic compass: It has a freely suspended magnet enclosed in a small glass case. It rests in north-south, direction. It is used to find Earth’s north and south direction. It is used in navigation of ships, aeroplanes., Magnetic needle is a permanent magnet., Magnets can be made by stroking or electric method., Oersted Experiment: He showed that a current carrying conductor behaves like a magnet., Magnetic field: The region around a magnet where its magnetic effect can be observed is called magnetic field., The strength of magnetic field depends on the closeness of magnetic field lines of force. Its unit is Weber per, m2 or Tesla. It is a vector quantity, i.e. it has magnitude as well as direction. The direction of magnetic field is, the direction in which a north pole of a compass needle moves when it is kept in the magnetic field., Magnetic lines of Force (Magnetic field lines): It is the closed path traced by the unit north pole, in a, magnetic field. These can be drawn on the paper using a bar magnet and a compass needle., , Properties of magnetic field lines:, , N, , S, , S, , N, N, , Iron filings near the bar magnet, align themselves along the field lines., , •, •, •, •, •, •, , N, , S, , S, , Drawing a magnetic field line with, the help of a compass needle, , These lines start from N-pole and goes to to S-pole outside the magnet., These lines never intersect with each other., These lines tend to shorten themselves due to magnetic force., These lines repel each other sideways., Higher the density of the magnetic field lines of force, greater is the magnetic field strength., Magnetic field lines are closed curves., , Magnetic field due to a current carrying conductor:, N, E, W, , North, , North, , S, East, K, , K, N, , West, N, S, , S, +, , –, , (a), (b), A simple electric circuit in which a straight copper wire is placed parallel to and over a compass needle., The deflection in the needle becomes opposite when the direction of the current is reversed., , • An electric current through a conductor produces a magnetic field. It causes deflection in the magnetic, compass needle when placed near it., • If the current flows from north to south, the north pole of the compass needle would move towards the east, direction., • If the direction of current is reversed, the needle will move in the opposite direction., , Magnetic Effects of Current 135

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Magnetic field due to current through a straight conductor:, , • A pattern of concentric circles indicates the field lines of the, • magnetic field around a straight conducting wire as shown in the Fig. (a) above. Magnetic, These circles become larger and larger as we move away from it., Field, • The magnetic field strength at any point is inversely proportional to the distance, of that point from the current carrying wire., Current, Fleming’s Right hand thumb rule: It states that if we hold a current carrying, Right-hand thumb rule, conductor in the right hand in such a way that the thumb is stretched along the, direction of the current, then fingers will wrap around the conductor in the direction of the field lines of the, magnetic field., , Exercise 6.1, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. Choose the incorrect statement from the following regarding magnetic lines of force, (a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a, magnetic compass needle will point, (b) Magnetic field lines are closed curves, (c) If magnetic field lines are parallel and equidistant, they represent zero field strength, (d) Relative strength of magnetic field is shown by the degree of closeness of the field lines, 2. If the key in the arrangement is taken out (the circuit, Variable resistance, is made open) and magnetic field lines are drawn over, R, A, the horizontal plane ABCD, the lines are, A, Long straight, (a) concentric circles, conductor, (b) elliptical in shape, B, O, (c) straight lines parallel to each other, D, (d) concentric circles near the point O but of elliptical, shapes as we go away from it, C, 3. A circular loop placed in a plane perpendicular to the, plane of paper carries a current when the key is ON., K, The current as seen from points A and B (in the plane, of paper and on the axis of the coil) is anti clockwise and clockwise respectively. The magnetic field, lines point from B to A. The N-pole of the resultant magnet is on the face close to, (a) A, (b) B, (c) A if the current is small, and B if the current is large, (d) B if the current is small and A if the current is large, 4. Two organs where magnetic field is produced are, (a) Heart and lungs , (b) Heart and brain, (c) Brain and lungs , (d) Heart and Liver, II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 and 2, two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., , 136, , Science-10

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(c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Magnetic field lines do not intersect., , Reason: Magnetic field lines are closed curves., 2. Assertion: A compass needle gets defected when electric current is passed through the nearly metallic, wire., , Reason: The S.I unit of magnetic field strength is Oersted., , III. Very Short Answer Type Questions, , (1 Mark), , 1. Why does a compass needle get deflected when brought near a bar magnet?, [NCERT], 2. Why don’t two magnetic lines of force intersect each other?, [NCERT] [Delhi 2014], 3. A current through a horizontal power line flows from east to west direction. What is the direction of, magnetic field at a point directly below it and at a point directly above it?, [NCERT], 4. If in a straight wire ‘A’, current is flowing in vertically downward direction whereas in the straight, wire ‘B’ current is flowing in vertically upward direction. What is the direction of magnetic field (a) in, wire ‘A’, (b) in wire ‘B’.?, 5. A bar magnet is placed between two iron bars. Draw a diagram to show the induced poles., 6. Identify the poles of the magnet as shown in the given figure:, [CBSE 2014], , A1, , B1, , 7. State the direction of magnetic field inside a bar magnet., [CBSE 2014], 8. Mention the special feature regarding the shape of magnetic field lines., [CBSE 2014], 9. If magnetic field lines are crossed at a point, what does it indicate?, [CBSE 2014], , OR, Explain why two magnetic lines of force do not intersect., 10. Draw a diagram to represent the uniform magnetic field in the region around the magnet., [CBSE 2014], 11. What type of core is used in electromagnets?, [CBSE 2014], 12. Draw the magnetic field lines around a straight current carrying conduction., , IV. Short Answer Type Questions-I, , (2 Marks), , 1. Draw magnetic field lines around a bar magnet., [NCERT], 2. What are magnetic field lines? Explain why magnetic field lines are closed curves?, [Delhi 2014], 3. The given magnet is divided into three parts A, B and C as:, A, B, C, Name the part when the strength of magnetic field is (i) maximum, (ii) minimum. How will the density, of magnetic field lines differ at these parts?, [Delhi 2012], 4. A compass needle is placed near a current-carrying wire. State your observation for the following, cases, and give reason for the same in each case., [Delhi 2012], (a) Magnitude of electric current in the wire is increased., (b) The compass needle is displaced away from the wire., 5. (a) Two magnets are lying side by side as shown below. Draw magnetic field lines between the poles P, and Q:, S, , N, , S, , N, , P, Q, (b) What does the degree of closeness of magnetic field lines near the poles signify?, 6. Magnetic field lines of two magnets are shown in figure A and figure B., , (A), , (B), , Select the figure that represents the correct pattern of field lines. Give reasons for your answer. Also, name the poles of the magnets facing each other., [Delhi 2012], , Magnetic Effects of Current 137

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7. Identify the poles of the magnet in the given figure (1) and (2)., ,                   , , [Delhi 2011], ,      (1)            (2), , 8. The magnetic field associated with a current carrying straight conductor is in anticlockwise direction., If the conductor was held along the east-west direction, what will be the direction of current through, it? Name and state the rule applied to determine the direction of current., [Delhi 2011], 9. (a) In a pattern of magnetic field lines due to bar magnet, how can the regions of relative strength be, identified?, (b) Compare the strength of magnetic field near the poles and the middle of a bar magnet.[CBSE 2014], , V. Short Answer Type Questions-II, , (3 Marks), , 1. What are magnetic field lines? How is the direction of magnetic field at a point deter- mined?, 2. Describe an activity to determine the direction of magnetic field produced by a current carrying straight, conductor. Also show that the direction if the magnetic field is reversed on reversing the direction of, the current., [Delhi 2015], , VI. Long Answer Type Question, 1. PQ is a current carrying conductor in the plane of the paper as shown in the figure, below., , (i) Find the directions of the magnetic fields produced by it at points R and S?, , (ii) Given r1> r2, where will the strength of the magnetic field be larger? Give reasons., , (iii) If the polarity of the battery connected to the wire is reversed, how would the, direction of the magnetic field be changed?, , (iv) Explain the rule that is used to find the direction of the magnetic field for a straight, current carrying conductor., , (5 Marks), P, r1 R, S, , r2, Q, , Answers 6.1, I. 1., , 2., , 3., , 4., II. 1., , 2., III. 1., 2., 3., 4., 5., 6., 7., 8., 9., , (c) If magnetic field lines are parallel and equidistant, they represent zero field strength, (c) It is because only earth’s magnetic field will be present, (a) Magnetic field lines emerge out from North pole and enter into south pole., (b) In heart and brain magnetic field is produced., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., (c) ‘A’ is true but ‘R’ is false., A compass needle behaves like a small bar magnet when it is brought near a bar magnet. Its magnetic, field lines interact with that of bar magnet. Hence compass needle gets deflected., No two magnetic field lines intersect each other because if they did, it would mean that at the point of, intersection, the compass needle would point towards two direction, which is not possible., At a point below it, the direction is from North to South and at a point above it, the direction is from, South to North., (a) Anticlockwise, (b) Clockwise, N  S, N  S, N  S, Both the iron bars get magnetised as shown in the figure, Iron bar 1, Bar Magnet, Iron bar 2, A1 represents North pole and B1 represents South pole., It is from South pole to North pole., Magnetic field lines are closed curves., The magnetic lines of force do not intersect with each another due to the fact that resultant force on, the north pole at any point can only be in one direction. But if the two magnetic lines of force intersect, one another, then the resultant force on the north pole placed at the point of intersection will be along, two directions, which is not possible., 11. Soft iron core., , 10., , 138, , Science-10

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IV. 1., , 2. The closed path traced by the unit North pole (imaginary) in a magnetic field are called magnetic field, lines., They are continuous closed curves because they diverge from the north pole of a bar magnet and, converge to its south pole., 3. (i) Maximum of magnetic field strength is at ‘A’ and ‘C’, (ii) Minimum of magnetic field strength is at ‘B’., At ‘A’ and ‘C’ magnetic field lines are crowded whereas these are spread out at ‘B’., 4. (a) Observation: The compass needle is deflected more., Reason: Current carrying wire produces magnetic field, (B µ I)., (b) Observation: The deflection of magnetic needle decreases., , Reason: The strength of magnetic field decreases with increase in distance from, 1, the wire.  B ∝ , , d, 5. (a) Magnetic field lines are shown below:, , P, , Q, , (b) It shows that magnetic field is stronger near the poles, i.e. the pole of another magnet when placed, in the magnetic field of a magnet will experience greater force. That is why field lines are crowded., 6. Figure ‘B’ represents correct pattern of magnetic field lines because magnetic field lines never, intersect each other. If these intersect there will be two directions of the magnetic field at the point of, intersection, which is not possible. In figure B. field lines are emerging (going away) from the magnet,, so both the poles are north poles., 7. Field lines emerge from North pole and merge at South pole (S). So, X represents North pole and Y, represents South pole., , 8. When the observer observes the direction of magnetic field from west then the direction of current is, from east to west and if observer is at east side then the direction of current is from west to east., , Right hand thumb rule: If we hold a current carrying conductor in our right hand in a such a way, that stretched thumb is along the direction of the current, then curls of fingers around the conductor, represents the direction of magnetic field lines., 9. (a) The closeness of lines measures the relative strength of magnetic field., (b) The strength of magnetic field is highest near the poles whereas minimum in the middle of bar, magnet., V. 1. (i) The magnetic field lines produced is into the plane of the paper at R and out of it at S., 1, (ii) Field at S > Field at P, , Magnetic Effects of Current 139

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Magnetic field strength for a straight current carrying conductor is inversely proportional to the, distance from the wire., 2, (iii) The current will be going from top to bottom in the wire shown and the magnetic field lines are now, in the clockwise direction on the plane which is perpendicular to the wire carrying current., 1, (iv) Right hand thumb rule. The thumb is aligned to the direction of the current and the direction in, which the fingers are wrapped around the wire will give the direction of the magnetic field., 1, , 2. (i) Take a straight vertical wire AB passing through a horizontal cardboard ‘C’., B, (ii) The ends of wires are connected to a battery and a switch., (iii) When the current is passed through the wire AB, it produces a, magnetic field around it, which can be shown by sprinkling iron, ‘C’, filings on the cardboard ‘C’., (iv) The iron filings get magnetised and arrange themselves in, concentric circles around the wire., ‘C’, (v) It shows that magnetic field of lines are circular in nature., A, (vi) When current passed in the wire it flows in upward direction, the, lines of force are in anticlockwise direction., (vii) Now pass current from B to A, i.e. in downward direction, the magnetic lines of force will be, clockwise., VI. 1. (i) The Magnetic field lines produced is into the plane of the paper at R and out of it at S., (ii) Field at S > Field at P, Magnetic field strength for a straight current carrying conductor is inversely proportional to the, distance from the wire., (iii) The current will be going from top to bottom in the wire shown and the magnetic field lines are now, in the clockwise direction on the plane which is perpendicular to the wire carrying current., (iv) Right hand thumb rule. The thumb is aligned to the direction of the current and the direction in, which the fingers are wrapped around in wire will give the direction of the magnetic field., , Field due to Current Carrying Conductors in Magnetic, Topic 2. Magnetic, Field, Magnetic field due to current in circular loop and circular coil, , • The magnitude of magnetic field is directly proportional to the current passing through the circular loop or wire., • It is inversely proportional to the radius of circular loop or wire., Maxwell Cork Screw Rule: If we consider ourselves driving a corkscrew in the direction of the current, then, the direction of the advancement of corkscrew is the direction of magnetic field. This is Right Hand Thumb, Rule, it is also called Maxwell’s cork screw rule., • At every point of current carrying circular loop, the concentric circles of magnetic field become larger and, larger as we move away from the wire., • Near the center of loop, magnetic field appears as straight lines., , N, , S, , –, +, Magnetic field lines of the field produced, by a current-carrying circular loop., , 140, , Science-10

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• In a circular coil, if there are ‘n’ turns, the field produced will be ‘n’ times as large as produced by the single, turn because the current in each circular turn has the same direction and the field due to each turn that will, just add up., If the direction of current in a loop appears to be flowing in the anticlockwise, direction then that end of the loop will be or behave as north pole or and if, the direction of the current in the loop appears to be flowing in the clockwise, direction then it will be the south pole or behaves like south pole., , Solenoid: The solenoid is a long coil containing large number of turns of an, , insulated copper wire wrapped around a soft iron or steel core in the shape of a cylinder., • The pattern of magnetic field lines due to a solenoid are shown in the figure depicted below:, , Field lines of the magnetic field through and, around a current carrying solenoid., , A current-carrying solenoid coil is used to magnetise, a steel rod inside it – an electromagnet., , • These magnetic field lines are similar to the magnetic field lines produced by a bar magnet., • One end of the solenoid behaves like north pole and other behaves as the south pole., • The field lines inside the solenoid are in the form of parallel straight lines, which shows that magnetic field, is same at all the points in solenoid and the magnetic field is uniform inside., • When soft iron is placed inside the solenoid, it can also be magnetised., , Elecro-magnet: The magnet formed with the help of electric current is called Electro-magnet. It works on, magnetic effect of current., • Larger the number of turns in the solenoid, greater will be the magnetism, produced in the soft iron core, • The magnetic field produced is directly proportional to the current passed, through the solenoid., • The use of soft iron rod as core of solenoid produces strong magnetism., , Force on a current carrying conductor in magnetic field:, , S, , B, , A, N, , – +, • When a current carrying conducter is placed in a magnetic field it experiences, K, a force., • When the direction of current is reversed, the direction of force is also A current-carrying rod AB, experiences, a force perpendicular to its length, reversed., and the magnetic field, • If the direction of magnetic field is reversed by interchanging the poles of, magnet, the direction of force is also reversed., • The force is maximum when the direction of current is at 90° to the direction of magnetic field. The direction, of force is given by Fleming’s left hand rule., , Fleming’s left hand rule: According to this rule, stretch the thumb, fore, , finger and middle finger perpendicular to each other. If the force finger, points in the direction of magnetic field, middle finger in the direction of, current, then the thumb will point in the direction of force or motion of, the conductor., • Electric motors, electric generators, loudspeakers, microphones are, based on the use of conductor carrying current and magnetic field, produced by them., , Magnetic Effects of Current 141

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Exercise 6.2, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. The magnetic field inside a long straight solenoid-carrying current, (a) is zero. (b) decreases as we move towards its end., (c) increases as we move towards its end. (d) is the same at all points., [NCERT], 2. Which of the following property of a proton can change while it enters freely in a magnetic field? (There, may be more than one correct answer.), (a) mass (b) speed, (c) velocity (d) momentum, [NCERT], 3. For the current in a long straight solenoid N- and S-poles are created at the two ends. Among the, following statements, the incorrect statement is, (a) The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic, field is the same at all points inside the solenoid, (b) The strong magnetic field produced inside the solenoid can be used to magnetise a piece of magnetic, material like soft iron core, when placed inside the coil, (c) The pattern of magnetic field associated with the solenoid is different from the pattern of the, magnetic field around a bar magnet, (d) The N- and S-poles exchange positions when the direction of current through the solenoid is, reversed, II. Assertion-Reason Type Questions, (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Compass is a small magnet and gives direction of magnetic field lines., , Reason: It gets deflected when brought near a bar magnet., 2. Assertion: A current carrying solenoid behaves like a bar magnet., , Reason: When soft iron is placed inside the solenoid it can also be magnetised., , III. Very Short Answer Type Questions, , (1 Mark), , 1. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop, clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside, the loop., [NCERT], 2. What type of core is used to make electromagnets?, [CBSE 2014], , OR, What type of core should be put inside a current-carrying solenoid to make an electromagnet?, 3. Give the factors on which magnetic field produced by a current carrying solenoid will depend., 4. Name the factors on which force acting on a current carrying conductor will depend., 5. State the direction of magnetic field in the following case:, [CBSE 2014], Force on the conductor, , Current, , 6. A beam of alpha particles enters a chamber moving along the magnetic field. What is the magnetic, force experienced by the beam?, 7. When is the force experienced by a current carrying conductor placed in a magnetic field greatest?, [CBSE 2012], 8. What is the pattern of field lines inside a solenoid? What do they indicate?, [CBSE 2010], 9. How is magnetic field produced in a solenoid used?, [CBSE 2010], 10. What does the direction of thumb indicate in the right hand thumb rule?, [CBSE 2010], 11. Suggest one way to distinguish a wire carrying current from a wire carrying no current.[CBSE 2012], 12. Why are magnetic field lines form closed curves?, [CBSE 2012], , 142, , Science-10

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13. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving, horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your, right side. What is the direction of the magnetic field?, , IV. Short Answer Type Questions-I, , (2 Marks), , 1. (a) Draw magnetic field lines of a current carrying circular loop. Identify the region where field is, strongest and why?, (b) List two properties of magnetic field lines., [Delhi 2016], 2. Why and when does a current carrying conductor kept in magnetic field experiences force? List the, factors on which direction of force will depend., [Delhi 2014] [HOTS], 3. How is the strength of magnetic field near a straight current-carrying conductor, (i) related to the strength of current in the conductor?, (ii) is affected when the direction of flow of current is reversed?, 4. State two ways by which the strength of an electromagnet is increased.[CBSE 2014], 5. An alpha particle (positively charged) enters a magnetic field at right, +, angle to it as shown in figure. Explain with the help of relevant rule,, the direction of force acting on the alpha particle., [CBSE 2014], Alpha particle, 6. (i) A compass needle gets deflected when brought near a current, carrying conductor. Why?, (ii) What happens to the deflection of needle when current in the conductor is increased? [CBSE 2014], 7. Identify the type of magnetic field represented by the magnetic field lines, given below and name the type of conductors which can produce them., [CBSE 2014], 8. Define a solenoid. Compare the magnetic field produced by a solenoid with, that of a bar magnet., [CBSE 2019], (a), (b), 9. Distinguish between a bar magnet and an electromagnet., 10. Can a freely suspended current carrying solenoid stay in any direction? Justify your answer. What will, happen when the direction of current in the solenoid is reversed? Explain., [CBSE 2015], 11. A uniform magnetic field is directed vertically upwards. In which direction in this field forces an, particle (+ve charged) be projected to that it is deflected southward? Name and state the rule you have, to use to find the direction in this force., [CBSE 2015], , V. Short Answer Type Questions-II, , (3 Marks), , 1. For the circular coil carrying current shown below draw magnetic, field lines. Decide which of its face behaves as north pole and which, face behaves as south pole. Give reason to justify your answer., [Delhi 2016], 2. You are given three identical looking bars one of which is a magnet,, the other made of a magnetic material and the third made of a non, magnetic material. Using just these three bars how will you find out, which is which?, [Delhi 2016], 3. Describe an activity to show magnetic field lines are produced when, current is passed through circular coil., [Delhi 2015], 4. What is meant of solenoid? How does a current carrying solenoid behave? Give its main use., [Delhi 2015], 5. With the help of diagram of experimental set up describe an activity to show that the force acting on a, current carrying conductor placed on magnetic field increases with increase in field strength., [Delhi 2015], 6. Write one application for each of the following:, (a) Right-hand Thumb Rule,, (b) Fleming’s left Hand Rule,, (c) Fleming’s Right Hand Rule., 7. How will the magnetic field produced at a point due to a current carrying circular coil change if we:, (i) increase the current flowing through the coil, (ii) reverse direction of current through coil,, (iii) increase the number of turns in the coil?, [Delhi 2011], 8. (a) Mention the factors on which the direction of force experienced by a current carrying conductor, placed in a magnetic field will depend., , Magnetic Effects of Current 143

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(b) Under what conditions is the force experienced by a current carrying conductor placed in a magnetic, field maximum?, (c) A proton beam is moving along the direction of a magnetic field. What force is acting on proton, beam?[Delhi 2011], 9. List three sources of magnetic field., [CBSE 2014], , VI. Long Answer Type Questions, , (5 Mark), , 1. (a) Draw the pattern of magnetic field lines through a bar-magnet and around a current carrying, solenoid., (b) What is the pattern of magnetic field lines inside the solenoid and what does these indicate?, (c) How can a solenoid be utilised to make an electromagnet?, [Delhi 2015], (d) State two ways by which the strength of this electromagnet can be increased., 2. With the help of a labelled circuit diagram describe an activity to illustrate the pattern of the magnetic, field lines around a straight current carrying long conducting wire., (i) Name the rule that is used to find the direction of magnetic field associated with a current carrying, conductor., (ii) Is there a similar magnetic field produced around a thin beam of moving:, (a) alpha particles and (b) neutrons? Justify your answer., 3. What is meant by magnetic force? Name and explain the rule to determine the direction of force, experienced by a current carrying conductor in a magnetic field. How does this force gets affected on:, (i)doubling the magnitude of current, (ii) reversing the direction of flow of current, (iii) reversing the, direction of magnetic field., [Delhi 2015], , Answers 6.2, I. 1. (d) It is same at all points, , 2. (b) The velocity and momentum are changing when a charged particle enters a magnetic field, and it, moves in a circular path so that its velocity will change at every point, so also its momentum., , 3. (c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the, magnetic field around a bar magnet, II. 1. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , 2. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., III. 1. The direction of magnetic field will be perpendicular to the plane of paper inwards inside the loop and, perpendicular to the plane of paper outwards from inside., 2. Soft Iron, 3. (i) The current through the solenoid. (ii)The number of turns in the solenoid, (iii) Nature of core on which wires are wound in solenoid., 4. (i) The current through the conductor. (ii)The strength of magnetic field., (iii) The length of the conductor., 5. Direction is out of the page., Force on the conductor, , Current, , Magnetic field, , 6. Zero, it is because beam is moving parallel to the magnetic field., 7. When the current in the conductor flows perpendicular (90°) to the direction of the magnetic field,, maximum force is generated., 8. The magnetic field is in the form of parallel lines. It indicates a uniform magnetic field because, magnetic field lines are parallel., 9. It is used to magnetise a soft iron bar to form an electromagnet., 10. The thumb indicates the direction of current in the straight conductor held by curved fingers of our, hand., 11. The magnetic compass needle will get deflected near the wire current carrying but not near the wire, with no current., , 144, , Science-10

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12. It is because outside the magnet, magnetic field lines start from north pole and merge at south pole, whereas inside the magnet they start from south pole and merge at, north pole, therefore these lines from closed curves., 13. The direction is vertically downwards., IV. 1. (a) On observing the field lines, it shows that magnetic field due to, the current carrying circular loop is maximum and normal to, the current carrying loop at its center because magnetic field, due to each part of loop adds up., (b) (i) No two magnetic field lines intersect with each other at any, point., (ii) More crowded field lines means a stronger magnetic field., 2. The movement of electrons takes place in the conductor in a particular direction when current is, passed through it. These charged particles are moving in the magnetic field which experiences force., The current carrying conductor has its own magnetic field, when it superimpose the magnetic field, of magnet. Due to this, current carrying conducter experiences a force. Thus conductor experiences a, force when placed in a uniform magnetic field., , Factors on which direction of force depends:, (i) The direction of force depends upon the direction of magnetic field., (ii) It also depends upon the direction of current flowing through the conductor., 3. (i) The strength of magnetic field is directly proportional to the strength of current., (ii) If we reverse the direction of current, the direction of magnetic field will also be reversed., 4. (i) Increase in number of turns in the solenoid., (ii) Increase in the strength of current flowing in the solenoid., 5. The force will act in upward direction given by thumb, if forefinger points in the direction of magnetic, field and the middle finger points in the direction of current, according to Fleming’s left hand rule., 6. (i) It is because current carrying conductor produces a magnetic field which superimposes with magnetic, field of compass needle due to which needle of compass gets deflected., (ii) The deflection in the magnetic needle will increase as the strength of current increases., 7. (a) These magnetic field lines are produced by a current carrying loop., (b) These are magnetic field lines produced by solenoid., 8. A coil of many circular turns of copper wire wrapped in the shape of a cylinder, is called a solenoid., The magnetic field lines in a solenoid, through which current is passed, is very similar to that of a bar, magnet. One end of the coil acts like the magnetic north pole, while the other acts like the magnetic, south pole. The magnetic field produced by a long solenoid has all the properties of the field produced, by a bar magnet., 9., , S.No., , Bar Magnet, , Electromagnet, , 1., , The bar magnet is a permanent magnet., , 2., , It produces a comparatively weak magnetic It produces a very strong magnetic force., force., The strength of a bar magnet cannot be The strength of an electromagnet can be, changed., changed by changing the number of turns in, its coil or by changing the current passing, through it., , 3., , 4., , An electromagnet is a temporary magnet., , The polarity of a bar magnet is fixed and The polarity of an electromagnet can be, cannot be changed., changed by changing the direction of current, in its coil., , 10. A current carrying solenoid behaves like a bar magnet. When it is suspended freely it will stay in, north–south direction. On reversing the direction current, it will turn to 180�° because its polarity will, be reversed., 11. The direction of motion of particles is from west to east. Fleming’s left hand rule is used to find the, direction of force., , Magnetic Effects of Current 145

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V. 1. Front face behaves like a north pole as field emerges out of it. Rear face behaves as south pole as field, enters into this face., , 2. Bring one bar close to the other two one by one: if the bar attracts one of these and does not attract the, other one, the bar which is not attracted is made of non-magnetic material and the bar in our hand is, a magnet or a bar of magnetic material. Keep one bar on the table and move other bar along its length, from one end to the other, if uniform attraction is felt the bar in our hand is a magnet and vice versa., 3. (i) Take a rectangular cardboard having two holes., (ii) Insert a circular coil through these holes, normal to the plane of, paper., (iii) Connect the ends of coil in series with a battery, and key., (iv) Sprinkle iron filings uniformly on the cardboard., (v) Plug the key., (vi) Tap the cardboard gently a few times. Note the pattern of the, iron filings., (vii) The pattern of magnetic field lines will be same as the pattern of, iron filings., 4. The long coil containing large number of close turns of insulated, copper wires wrapped around, is called a solenoid., Insulated, Current carrying solenoid behaves like a bar magnet. It is called, Cardboard ring, an electromagnet., conducting, It is used for making electromagnets., copper wires, 5. (i) Take an aluminium rod, AB of size 3 inches., (ii) Suspend it horizontally using connecting wires, (iii) Place a horse-shoe magnet in such a way that the rod lies between, the two poles with magnetic field directed upwards., (iv) Put north pole of the magnet vertically below and south pole, B, S, vertically above the rod., A, (v) Connect aluminium rod in series with the battery and key., N, (vi) Now pass the current in the rod from B to A., – +, (vii) Aluminium rod will be displaced towards the left., K, (viii) , Now bring a stronger horse-shoe magnet and observe the, A current-carrying rod AB, experiences, displacement of rod., a force perpendicular to its length, and the magnetic field, (ix) The displacement of rod will increase with the increase in strength of, the magnetic field., 6. (a) It is used to find the direction of magnetic field in a coil of wire and electric current in a straight, conductor., (b) It is used to find the direction of force exerted on a current carrying conductor in a magnetic field., (c) It is used to find the direction of induced current in a closed circuit placed in a changing magnetic, field, e.g. in an electric generator., 7. (i) The strength of magnetic field will increase. ( B µ I), (ii) The direction of magnetic field will be reversed., (iii) The magnetic field produced will increase because magnetic field produced is directly proportional, to the number of turns in the coil., 8. (a) (i) direction of current, (ii) direction of magnetic field., (b) When direction of current is perpendicular to the direction of magnetic field, the force experienced, will be maximum., (c) No, force is exerted by a proton beam because proton beam is moving along the direction of magnetic, field., , 146, , Science-10

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10. (i) Magnetic field is associated with bar magnet, (ii) A current carrying conductor produces magnetic field., (iii) A current carrying curricular loop also produces magnetic field., VI. 1. (a), ,    , (b) These are parallel straight lines indicating that magnetic field is uniform inside the solenoid., (c) By inserting a soft iron rod into the middle part of solenoid it is used to make an electromagnet, (d) (i) By increasing the number of turns., (ii) By increasing the strength of current., 2. (i) Take a battery (12 V), a variable resistor (rheostat),, Variable resistance, an Ammeter (0.5 A), a plug key, a long thick straight, – A +, copper conducting wire., (ii) Insert the thick wire through the centre normal to the, plane of rectangular cardboard., +, (iii) Take care that cardboard is fixed and does not slide up, P, –, or down., (iv) Connect the copper wire vertically between points X, and Y as shown in diagram in series with battery, plug, and a key., (v) Sprinkle some iron flings unformly on the cardboard., Pattern of Magnetic field lines, (vi) Keep the variable resistance in fixed position., (vii) Close the key so that current flows through the wire., (viii) Ensure the copper wires placed remains vertically straight., (ix) Gently tap the iron filings., Observation:, Iron filings align themselves showing a pattern of concentric circles around the copper wire which, represents magnetic lines of force., (i) Right hand rule., (ii) (a) Yes, alpha particle being positively charged constitutes a current in the direction of motion., , (b) No, neutrons being electrically neutral constitute no current., 3. The force experienced by a current carrying conductor when placed in a magnetic field or the force, experienced by a charged particles moving in a magnetic field is called magnetic force., , Fleming left hand rule: According to this rule, on stretching the thumb, forefinger and the middle, finger of your left hand such that these are perpendicular to each other, if the force finger points, in the direction of magnetic field and middle finger in the direction of current, then the thumb will, point in the direction of motion of force acting on the conductor., (i) If magnitude of current is doubled, then force is doubled., (ii) If direction of flow of current is reversed, the direction of force is also reversed., (iii) If direction of magnetic field is reversed, the direction of force is also reversed., , Topic 3. Electric Motor, Electromagnetic Induction, , Electric Motor: It is a rotating device which converts electrical energy into mechanical energy. It is based on, magnetic effect of current., • It is used in electric fans, refrigerators, mixer and grinder, juicer, washing machine, computers, submersible, pump, flour mill, etc., Commercial Motors:, • An electromagnet is used instead of a permanent magnet in commercial motors., • Large number of turns of conducting wires are used in current carrying coils., , Magnetic Effects of Current 147

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• An electric motor consists of a soft iron core on which coil is wounded which is called the armature. It, increases the power of motor., Electromagnetic induction: It is the phenomena of production of induced current and potential difference, in a conductor by changing the magnetic flux associated with the conductor., Galvanometer: It is an instrument used to detect the presence of current in, a circuit. A pointer in it deflects to the left or right depending on the direction, of the current., Fleming’s Right hand rule for the direction of Induced current: Hold, the thumb, the forefinger and central finger of your right hand perpendicular, to each other in such a way that forefinger represents the direction of magnetic, field, the thumb points in the direction of motion of conductor, then the central, finger will give the direction of induced current in the conductor., Faraday’s Law of Electromagnetic Induction: The strength of induced, current and potential difference are directly proportional to the magnetic flux., Faraday and Henry made the following observations on the basis of experiments about electromagnetic induction., (i) A current and potential difference are produced in the coil when there is relative motion between the coil, and magnet., (ii) A current and potential difference is also induced in the fixed coil when either the magnet or coil is rotated., We can keep the magnet at rest and move the coil or vice versa., (iii) No current flows if both coil and magnet are stationary. No potential difference and current are induced if, magnet and solenoid are moving at same speed, or if there is no relative motion between them., (iv) When the direction of movement of coil is reversed, the direction of current induced is also reversed., (v) The magnitude of induced current and potential difference can be increased by:, (a) wounding coils on soft iron core, (b) increasing number of turns on the coil, (c) increasing the speed of rotation of magnet or coil, (d) increasing the strength of magnet, (vi) The direction of induced e.m.f. (electromotive force) and induced current is reversed when the magnet is, moved out of the solenoid., E.M.F. (electromotive force): It is equal to the maximum potential difference when no current is drawn, from the cell., , Variation in which the moving magnet is replaced by current carrying coil and the current in the, coil is varied:, I, II, • As soon as coil I reaches either a steady value or zero, the galvanometer, in coil shows no deflection., • When current in coil I is changing, potential difference in coil II is, induced., • Take the two coils, coil I as primary coil and coil II as secondary coil., • As the current in the first coil changes, magnetic field associated with, the first coil also changes., • The change in magnetic field in coil I is the cause of induced potential, difference in coil II., • The induced current is maximum when direction of motion of coil is at right angle to the magnetic field., , Exercise 6.3, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. When the speed of rotation of coil is doubled, the frequency of current will be, (a) same, (b) doubled, (c) half, (d) qudrapled times, 2. If a rectangular copper wired coil is rotated in magnetic field, in how many revolutions, the direction, of induced current will be change?, (a) one, (b) two, (c) half, (d) three, , 148, , Science-10

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II. Assertion-Reason Type Questions, , (1 Mark), For question numbers 1 and 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Galvanometer is used to detect current., , Reason: Ammeter is used measure current generated in A.C. generator, 2. Assertion: When the direction of movement of coil is reversed, the direction of induced current is also, reversed., , Reason: Fleming’s right hand thumb rule detects the direction of induced current., , III. Very Short Answer Type Questions, , (1 Mark), , 1. When a magnet is moved into the coil of wire as shown in the figure, there, is small reading in the ammeter. How can we increase the reading?, 2. What is the principle of an electric motor?, [NCERT], 3. Meena draws magnetic field lines of field close to the axis of a current, carrying circular loop. As she moves away from the centre of the circular loop, she observes that the, lines keep on diverging. How will you explain her observation?, [NCERT Exemplar], 4. What does the divergence of magnetic field lines near the ends of a current carrying straight solenoid, indicate?[NCERT Exemplar], 5. What is the role of the two conducting stationary brushes in a simple electric motor?, 6. State Faraday’s first law of electromagnetic induction., 7. A square coil moves in a plane with uniform velocity ‘V’ parallel to its sides and magnetic field acts at, 90�° into the loop. What is the induced current in the coil?, 8. How is induced current in a secondary coil related to the current flowing in the primary coil?, [CBSE 2009], 9. Name any one method to induce current in a coil., [CBSE 2013], 10. State Faraday’s second law of electromagnetic induction., 11. In the arrangement shown in figure there are two coils wound on a nonconducting cylindrical rod., Initially the key is not inserted in the circuit. Later the key is inserted and then removed shortly after., I, , II, , What are the two observations that can be noted from the galvanometer reading?, [CBSE Sample Paper 2020-21], , IV. Short Answer Type Questions-I, , (2 Marks), , 1. When a magnet was pushed towards a solenoid, the galvanometer connected to the solenoid showed, a deflection in right direction. When the same magnet was pulled away from the solenoid at a faster, speed, what was the deflection in the galvanometer?, , Magnetic Effects of Current 149

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2. What is the role of split rings in an electric motor?, [NCERT], 3. Explain different ways to induce current in a coil., [NCERT], 4. Imagine that you are sitting in a chamber with your back to one wall. An electron beam moves, horizontally from back wall towards the front wall and by a strong magnetic field to your right side., What is the direction of magnetic field?, [NCERT], 5. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will, the same current be induced in the coil B? Give reason., [NCERT], 6. It is established that an electric current through a metallic conductor produces a magnetic field, around it. Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles,, (ii) neutrons? Justify your answer. , [NCERT Exemplar], 7. State Fleming’s right Hand Rule., , V. Short Answer Type Questions-II, , (3 Marks), , 1. Figure shows equipments used to demonstrate, electromagnetic induction., Two pieces of soft iron core ‘A’ and ‘B’ each, having a coil of insulated wire wrapped around, them. The coil around ‘A’ is connected to a switch, and a cell. The coil around ‘B’ is connected to a, galvanometer. When the switch is closed, the galvanometer shows a rapid deflection to the left before, returning to zero., (i) Explain why the galvanometer shows a rapid deflection to the left before returning to zero?, (ii) Explain what, if anything, would be observed on the galvanometer as the switch is opened?, 2. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (a), pushed into the coil, (b) withdrawn from inside the coil, (c) held stationary inside the coil?, [NCERT] [CBSE 2020], 3. A magnetic compass needle is placed in the plane of paper near point A as shown in the figure. In, which plane should a straight current carrying conductor be placed so that it passes through A and, there is no change in the deflection of the compass? Under what conditions is the deflection maximum, and why?, [NCERT Exemplar], , 4. Under what conditions a permanent electromagnet is obtained if a current carrying solenoid is used?, Support your answer with the help of a labeled circuit diagram., [NCERT Exemplar] [CBSE 2020], , 5. What is meant by electromagnetic induction? State the rule which helps to determine the direction of, induced current., [CBSE 2015], 6. State the condition for electromagnetic induction to take place. A cylindrical bar magnet is kept along, the axis of circular coil as shown in the figure. Will there be a current induced in the coil, if the magnet, is rotated about its axis? Discuss. , [CBSE 2014], S, , , , VI. Long Answer Type Questions, , N, , (5 Marks), , 1. Explain the principle and working of an electric motor with the help of a labelled diagram. What is the, function of a split ring commutator?, , 150, , Science-10

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(i) With the help of an activity, explain the method of inducing electric current in a coil with a moving, magnet. State the rule used to find the direction of electric current thus generated in the coil., (ii) Two circular coil-1 and coil-2 are kept close to each other as, I, II, shown in the diagram.Coil-1 is connected to a battery and, key and coil-2 with a galvanometer. State your observation, in the galvanometer:, (a) When key K closed;, (b) when key K is opened;, Give reason for your observations., [CBSE Sample paper 2018-19], 3. (a) State Fleming’s left hand rule., (b) Write the principle of working of an electric motor., (c) Explain the function of the following parts of an electric motor., (i) Armature, (ii) Brushes, (iii) Split ring, 2., , Answers 6.3, I. 1. (b) Frequency is directly proportional to speed of rotation of coil., , 2. (c) If rectangular copper wire coil is related in magnetic field, the direction of induced current will be, change every half revolution., II. 1. (b) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., , 2. (c) ‘A’ is true but ‘R’ is false., III. 1. It can be done by pushing the magnet or coil faster towards, respectively the magnet or coil., 2. It is based on the principle that a force is experienced by the current carrying conductor in a magnetic, field. The two forces on the opposite sides of current carrying rectangular coil in a magnetic field will, act in different lines, thus bringing the rotational motion., 3. Strength of magnetic field decreases with increase in distance from the from the magnetic substance., That is why magnetic lines keep on diverging due to decrease in magnetic field., 4. It indicates that strength of magnetic field decreases near the end of the solenoid., 5. They make the contact between the two halves of the split rings and the battery. Current from the, battery enters a conducting brush and flows back to the battery through the brush., 6. When magnetic field in around a conducting coil is changed, induced emf is produced., 7. Zero, it is because there is no change in magnetic flux., 8. It may be greater than or less than primary coil., 9. It can be done by moving a magnet towards the coil., 10. The induced e.m.f depends directly upon the relative speed between the coil and the magnet., 11. There are momentary galvanometer deflections that die out shortly; the deflections are in opposite, directions., IV. 1. Deflection in galvanometer will be towards the left, because when the direction of movement of magnet, is reversed, the direction of induced current is also reversed. The induced current is increased but it is, flowing in opposite direction when the magnet is moving faster and in opposite direction., 2. It act as a commutator in D.C (direct current) motor. The direction of current through the coil is, reversed with the help of split rings after every half rotation of the coil, direction of current in the, rotating coil remains the same and the coil continues to rotate in the same direction, thus producing, direct current., 3. (i) By changing the direction of current in the conductor., (ii) By changing the magnetic field in around the coil., current, , electrons, 4. BackWall electron beam, , Front wall, , (Right side), , Magnetic field, Current will move in the opposite direction to the flow of electrons. The direction of magnetic field will, be downwards as shown in the figure., , Magnetic Effects of Current 151

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152, , Science-10, , n, , mo, tio, , on, , ele, ctr, , ele, , ctr, , on, m, , oti, , on, , 5. No, the induced current in coil ‘B’ will change. It is because magnetic field produced in coil ‘A’ will, change, therefore magnetic field induced in coil ‘B’ will also change. Hence induced current in the coil, will also change., 6. (i) Yes, similar magnetic fields are produced. α-particles are positively charged particles, so current, will be in the direction of motion of beam of particles., (ii) No, in neutrons no current will be produced, as these are neutral particles., 7. According to Fleming’s right hand rule, when the thumb, fore finger and the central finger of our, right hand are kept perpendicular to each other when the thumb shows the direction of motion of the, conductor, the forefinger shows the direction of magnetic field when current induced is in the direction, of central finger as shown in the figure., V. 1. (i) When the switch is closed, a changing magnetic field is produced in A which produces a, change in magnetic field in ‘B’ resulting in induced current. However, the magnetic field in A, becomes steady after sometime. Therefore, there is no more induced current in B as there is, no change in the magnetic flux and the reading is zero., (ii) When the switch is opened, there is deflection in the galvanometer but in the opposite direction., The decreasing magnetic field in A produces an induced current in B. Since the change is reversed,, the direction of induced current is also reversed., 2. (a) It will show deflection., (b) The deflection will be in the opposite direction., (c) The galvanometer will not show any deflection., 3. Straight current carrying conductor should be placed in the plane of paper. The magnetic field produced, will be at 90° to the plane of paper and parallel to the vertical axis of magnetic needle. The deflection, will be maximum when current carrying conductor is at 90�°to the plane of paper and magnetic field, will be in the direction parallel to the plane of paper., 4. (i) Direct current should be used., (ii) Magnitude of current should be large., (iii) The number of turns in solenoid are more and close to each other, like windings in an electric motor., (iv) The soft core inside the solenoid should be made up of steel., 5. It is the phenomena of production of induced current and potential, difference in a conductor by moving a magnet or if there is a change in, magnetic field or flux., , Fleming’s right hand rule for determining the direction of induced current: Hold the thumb,, the forefinger and central finger of your right hand perpendicular to each other in such a way that, forefinger represents the direction of magnetic field, the thumb points in the direction of motion of, conductor, then the central finger will give the direction of induced current in the conductor., 6. • Either the coil or the magnet should be in motion, • If there is relative motion between a coil carrying current and coil not carrying current, there will, be induced current in the second coil., • No current will be induced because there is no change in magnetic field which is essential to, produce induced current., VI. 1. An electric motor converts electrical energy into, mechanical energy. It works on the principle that a, current carrying conductor placed in a magnetic field, experiences a force., N, S, Following are the essential parts of an electric motor., (i) Coil: It is a rectangular coil of insulated copper wire, having large number of turns., (ii) A large permanent magnet provides strong magnetic, field between its pole pieces. The coil rotates between brush, brush, these pole pieces., (iii) Split rings: The two ends of coil are connected to two, split rings, which are two halves of slip rings., , Working, split ring commutator, When a current is passed through the coil, the direction, of current in AB and CD is in opposite direction but, both are perpendicular to magnetic field. Therefore, by, Fleming’s left hand rule, arm AB of the coil experiences, DC power supply

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an upward force and arm CD experiences a downward force. These two forces being equal and opposite, to each other form a couple which rotates the coil. Arms BC and DA are parallel to the field and the, force between them is zero. The forces on AB and CD turns the coil in clockwise direction. After half, revolution, the split rings change their position. So the direction of current in the coil reverses. The, couple now acting on the coil again moves it in clockwise direction. Due to the function of split ring, commutator and brushes, coil continues to turn in clockwise direction., Split ring commutator changes direction after every half rotation, so that the direction of current going, in the coil also reverses. As a result, the coil continues to rotate in one direction. So, the electrical, energy given to the coil changes into mechanical energy., 2. (i) • Take a coil of wire AB having a large number of turns., • Connect the ends of the coil to a galvanometer as shown in, figure., • Take a strong bar magnet and move its north pole towards the, end B of the coil., • There is a momentary deflection in the needle of the, galvanometer, say to the right. This indicates the presence of a, current in the coil AB. The deflection becomes zero the moment, the motion of the magnet stops., • Now withdraw the north pole of the magnet away from the coil., Now the galvanometer is deflected toward the left, showing that the current is now set up in the, direction opposite to the first., Fleming’s right hand rule is used find the direction of electric current generated in the coil., (ii) (a) The galvanometer needle deflects momentary in one direction because when the key, is closed, magnetic field lines around coil-2 increases momentarily that causes induced current, in coil-2., (b) The galvanometer needle deflects momentarily but in opposite direction because when the, key is opened, magnetic field lines around coil-2 decreases momentarily that causes induced, current in coil-2., 3. (a) Fleming’s left-hand rule: Stretch the forefinger, middle finger and thumb of left hand in such a, way that they are mutually perpendicular to each other. If the forefinger points in the direction of, magnetic field, middle finger points in the direction of current then the thumb shows the direction, of force or motion of the current carrying conductor., (b) Principle of working of electric motor: A coil carrying electric current placed in an external magnetic, field experiences a force or torque., (c) (i) Function of armature: Enhances the power of the motor/induces motion., (ii) Function of brushes: Helps easy transfer of charge between the coil and the external circuit., (iii) Function of split rings: Reverses the direction of current after every half rotation of the coil, so, that coil can keep rotating continuously., , C ase study questions, , 1. Study this table related to wattage of home appliances and answer the questions that follow., Home Appliance, , Wattage, , Home, Appliance, Bulb, , Wattage, , LED, , CFL, , 100 Watt, , 12 Watt, , 23 Watt, , 1. Air conditioner, , 3517 per ton, , 2. Blender, , 350 Watt, , Bulb, , 75 Watt, , 11 Watt, , 3. Washing machine, , 500 Watt, , Bulb, , 60 Watt, , 8 Watt, , 15 Watt, , 4. Dish washer, , 1200–1500 Watt, , Bulb, , 40 Watt, , 6 Watt, , 11 Watt, , 5. Geyser, , 1000–2000 Watt, , 6. Iron, , 500–750 Watt, , 7. Coffee maker, , 800 Watt, , 8. Fridge, , 475–540 Watt, , 9. Laptop, , 20–75 Watt, , Magnetic Effects of Current 153

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10. Desktop, , 80–200 Watt, , 11. Ceiling fan, , 10–50 Watt, , 12. Blow dryer, , 1000–1500 Watt, , 13. Vacuum cleaner, , 200–700 Watt, , 14. Microwave, 600–1500 Watt, , (i) Which of the following home applicance is not based on magnetic effect of current?, , (a) Ceiling fan, (b) Blender, (c) Geyser, (d) Washing Machine, , (ii) Which of the following lighting device is best to use in terms of power consumption?, , (a) Bulb, (b) CFL, (c) Tube light, (d) LED, (iii) Which of the following will to consume least power?, , (a) Laptop, (b) Desktop, (c) Printer, (d) Blender, , (iv) Which of the following will consume maximum power?, , (a) Fridge, (b) Iron, (c) Air conditioner, (d) Coffee maker, , (v) Many appliance works on the principle of electromagnetic induction. The role which depicts the, direction of induced current is as, , (a) Faraday’s rule , (b) Henery’s rule, , (c) Fleming’s rule , (d) Maxwell’s rule, Ans. (i) (c), (ii) (d), (iii) (a), (iv) (c), (v) (c), 2. A magnetic stripe card, also referred to as a swipe card or magstripe, is a plastic card with a magnetic, strip attached on its surface. This stripe is made of tiny iron-based components whose magnetism can, be modified and can therefore be used to store information. A magstripe is quite similar to a magnetic, recording tape, which you might find in videotape or a music cassette. The magnetic strip on a card can, be ‘written’ or encoded with information because the tiny iron-based particles that make up the strip can, be magnetised in different directions by a device that produces a strong magnetic field. This device is a, ‘solenoid’, which is basically a coil wound into a tightly packed helix. The wire is wound around a highpermeable, metallic core that produces a strong magnetic field when a current is passed through it. This, device encodes the required information onto the stripe, which is then pasted on a plastic card. When a, card with a magnetic strip is moved back and forth over the ‘reader head’ , a voltage is induced in the, coils of the card reader device. A card reader consists of solenoid too – the same component that is used, to write information in the magnetic strip., This voltage can be amplified and recorded electronically, which is finally read by a computer (or a processor, installed within the reader) to authenticate a user (in the case of identity cards) or a transaction (in the, case of credit/debit cards)., , (i) Which of the following are the devices that uses magnetic theory to record data, (a) The hotel key cards, (b) Audio tapes, (c) CD’s , (d) All of the above, , (ii) Name the scientist who gave the principle of electromagnetic field, (a) Oersted, (b) Faraday, (c) Bohr, (d) Ampere, (iii) The force on a wire inside a magnetic field increase when, (a) The current is increased, (b) Strength of magnetic field increases, (c) Length of wire is increased, (d) All of above, (iv) The information of users which are read by the ATM machines are stored on, (a) Magnetic box on card, (b) Magnetic strip on card, (c) Inside ATM machine, (d) None of above, (v) The factors on which one magnetic field strength produced by current carrying solenoids depends are, (a) Magnitude of current, (b) Number of turns, (c) Heat produced , (d) Both (a) and (b), Ans. (i) (d), (ii) (a), (iii) (d), (iv) (b), (v) (d), 3. A solenoid is a long helical coil of wire through which a current is run in order to create a magnetic field., The magnetic field of the solenoid is the superposition of the fields due to the current through each coil. It, is nearly uniform inside the solenoid and close to zero outside and is similar to the field of a bar magnet, having a north pole at one end and a south pole at the other depending upon the direction of current flow., The magnetic field produced in the solenoid is dependent on a few factors such as, the current in the coil,, number of turns per unit length etc., , 154, , Science-10

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The following graph is obtained by a researcher while doing an experiment to see the variation of the, magnetic field with respect to the current in the solenoid., The unit of magnetic field as given in the graph attached is in milli-Tesla (mT) and the current is given, in Ampere., 18, 16, , Magnetic field B (mT), , 14, 12, 10, 8, 6, 4, 2, 0, 0.0, , 0.2, , 0.4, , 0.6, , 0.8, , 1.0, , 1.2, , Current (A), , , (i) What type of energy conversion is observed in a linear solenoid?, (a) Mechanical to Magnetic, (b) Electrical to Magnetic, (c) Electrical to Mechanical, (d) Magnetic to Mechanical, , (ii) What will happen if a soft iron bar is placed inside the solenoid?, (a) The bar will be electrocuted resulting in short-circuit., (b) The bar will be magnetised as long as there is current in the circuit., (c) The bar will be magnetised permanently., (d) The bar will not be affected by any means., , (iii) The magnetic field lines produced inside the solenoid are similar to that of …, (a) a bar magnet , (b) a straight current carrying conductor, (c) a circular current carrying loop, (d) electromagnet of any shape, , (iv) After analysing the graph a student writes the following statements., I. The magnetic field produced by the solenoid is inversely proportional to the current., II. The magnetic field produced by the solenoid is directly proportional to the current., III. The magnetic field produced by the solenoid is directly proportional to square of the current., IV. The magnetic field produced by the solenoid is independent of the current., Choose from the following which of the following would be the correct statement(s)., (a) Only IV, (b) I and III and IV (c) I and II, (d) Only II, , (v) From the graph deduce which of the following statements is correct., (a) For a current of 0.8A the magnetic field is 13 mT, (b) For larger currents, the magnetic field increases non-linearly., (c) For a current of 0.8A the magnetic field is 1.3 mT, (d) There is not enough information to find the magnetic field corresponding to 0.8A current., , Quick revision notes, , • An electric current carrying wire behaves like a magnet., • A magnetic field is produced near a current carrying conductor. This is called magnetic effect of current., • When a magnetic compass is placed near the conductor through which current is passed there is a deflection, in the compass., , Magnetic Effects of Current 155

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• Electric motors, fans, generators are based on magnetic effect of current., • A magnet attracts magnetic materials like iron, cobalt, nickel and some alloys like steel., • Each magnet has two poles. One end of the magnet points towards the north end of the Earth, which itself, is a huge magnet. It is called north pole, the other end of the magnet points towards the south end of the, Earth & is called the south pole of the Earth., • Law of magnetic poles: Like poles repel, unlike poles attract each other., • The region around a magnet in which its effect can be observed is called magnetic field. It is a vector quantity,, it has magnitude as well as direction., • Magnetic field lines can be drawn around a magnet with the help of compass needle., • The relative strength of magnetic field is shown by the degree of closeness of magnetic field lines., • A compass needle is a small magnet. Its one end which point towards the north direction is called north pole,, and the other end pointing towards the south direction is called the south pole., • Magnetic field lines are used to represent magnetic field., • A magnetic field is associated with a current carrying conductor., • The direction of magnetic field lines about the wire consist of concentric circles whose direction is given by, Anpere’s right hand thumb rule., • The pattern of magnetic field around a conductor depends on the shape of the conductor., • A current carrying solenoid behaves like a bar magnet, • The magnetic field of a solenoid carrying current is similar to that of a bar magnet., • An electromagnet is a type of magnet in which the magnetic field is produced by current., • If the direction of magnetic field and the current in the conductor are perpendicular to each other, the force, acting on the conductor will be perpendicular to both, current as well as magnetic field. It is Fleming’s left, hand rule., • An electric motor works on Fleming’s left hand rule. It converts electrical energy into mechanical energy., • The production of emf (voltage) in a conductor when there is a change in magnetic flux linked with the conductor, is called electromagnetic induction. The emf so produced is called induced emf., • The strength of the induced emf (electromotive force) is directly proportional to the rate of change of the, magnetic flux. It is Faraday’s law of electromagnetic induction., • The magnitude of induced emf increases when the magnet is (i) moved quickly, (ii) number of turns in the, solenoid increases, (iii) the strength of magnet is increased, (iv) change the angle between coil and magnetic, field., • The direction of the induced current in a conductor is given by Fleming’s right hand rule., , Common Errors, Errors, , Corrections, , • Students write the SI unit of magnetic field ☞ Tesla (T) is the SI unit of magnetic field., , wrongly., , • Students do not show magnetic field lines correctly ☞ Magnetic field lines start from North to South, , with proper arrowhead., , and must be shown by using proper arrow head, (→)., , • Students get confused between Fleming’s left hand ☞ Right hand thumb rule gives the direction of, , rule, right hand thumb rule and Fleming’s right, hand rule., , magnetic field, Fleming left hand rule gives, the direction of force or motion, Fleming, right hand rule gives the direction of induced, current., , • Students, , do not know the relationship ☞ Direction of force is reversed if the direction of, between direction of current and direction of force., current is reversed., , • Students do not know the full form of MRI, MCB., , ☞ MRI is magnetic resonance imaging, MCB is, , miniature circuit breaker., , • Students write lengthy answers for short answer ☞ Answer should be given according to the marks., , type questions and short answers for long answer, type questions., , 156, , Science-10, , All parts should be answered carefully, especially, 3 marks and 5 marks questions have many parts.

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Assignment, , Total Marks : 20, , I. Multiple Choice Questions, , (1 mark), , Choose the correct answer from the given options. , 1. Fleming’s Right-hand rule gives, (a) magnitude of the induced current, (b) magnitude of magnetic field, (c) direction of induced current, (d) both direction and magnitude of induced current, [CBSE 2020], 2. If a rectangular copper wired coil is rotated in magnetic field, in how many revolutions, the direction, of induced current will be change?, (a) one, , (b) two, , (c) half, , (d) three, , II. Assertion-Reason Type Questions, , (1 mark), , , Note: Use instructions as given in topical exercises of the chapter., 1. Assertion: The energy of charged particles moving at right angles to a uniform magnetic field does not, change., , Reason: No work is done by the magnetic field on the charged particles., 2. Assertion: Magnetic field lines do not intersect., , Reason: Magnetic field lines are closed curves., , III. Very Short Answer Type Questions, , (1 Mark), , 1. Define the term induced electric current., [CBSE 2020], 2. The change in magnetic field lines in a coil is the cause of induced current in it. Name the underlying, phenomenon.[CBSE 2020], , IV. Short Answer Type Questions-I, , (2 Marks), , 1. Give four differences between electromagnet and permanent magnet., 2. How can we demagnetise a magnet?, 3. Define trophic level. Name the first trophic level., , [Delhi 2011] [CBSE 2020], , V. Short Answer Type Question-II, , (3 Marks), , 1. (a) A coil of insulated wire is connected to a galvanometer. Explain what happens if a bar magnet with, its pole towards one face of the coil is (i) moved quickly towards the coil, (ii) kept stationary inside, the coil and (iii) moved quickly away from the coil., (b) Name the phenomenon involved., (c) State the conclusion based on the observation in (i), (ii) and (iii)[CBSE 2020], , VI. Long Answer Type Questions, 1. (a), (b), (c), (d), , (5 Marks), , State Fleming’s Left Hand rule., List three characteristic features of the electric current used in our homes., What is a fuse? Why is it called a safety device., Why is it necessary to earth metallic electrical appliances., , [CBSE 2020], , Magnetic Effects of Current 157

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Unit-V, Nature Resource, , 7, , Our Environment, , Topics Covered, 7.1 What happens when we add waste to the environment? Ecosystem — what are its components?, 7.2 How do our activities affect the environment?, , C hapter map, , Our environment, Ecosystem, , Producer, Plants, , Biodegradable, , Primary, Herbivores, , Non-biodegradable, , Management, of garbage, we produce, , Ozone layer, depletion, , Food web, , Biotic components, (Plants and Animals), , Abiotic components, (Air, water, soil), , Waste in our, environment, , Food chain, , Consumer, Animals, Secondary, Eat small, animals, , Tertiary, Eat secondary, consumers, , Ecological, Pyramids, , Decomposers, Microorganisms, Parasites, Food from host, , 5 R’s, Approach, Recycle, , Reuse, , Reduce, , Repurpose, , Refuse, , Happens When We Add Waste to the Environment?, Topic 1. What, Ecosystem – What are its Components?, Human beings generate a lot of waste materials. These are classified as biodegradable and non-biodegradable, substances., Biodegradable substances: These substances can be decomposed by the action of micro-organisms such, as bacteria into harmless substances. They do not persist in environment and can be converted into compost., Cattle dung, wool, paper, vegetables and fruit peels, agricultural waste are few examples., Non-biodegradable substances: These substances do not break into simpler substances by the action, of micro-organisms. They persist in the environment, therefore, they should be recycled or reused. Plastic,, polythene bags, DDT (pesticide), metal articles, glass objects are all called non-biodegradable substances., , 158

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Ecosystem: It is formed by the interaction of all living organisms (biotic components) with the non-living, , constituents (abiotic components) like air, water, temperature of the environment together. Living organisms, interact with each other and their environment for reproduction, growth, survival, and other activities., Ecosystem can be natural or man made/ artificial., • Natural ecosystem: These are formed in nature e.g. ponds, deserts, mountains, oceans, forests., • Artificial ecosystem: These are man-made ecosystems e.g. garden, crop field, aquarium., Producers: Those living organisms which produce their own food are called producers e.g. all green plants, and certain blue-green algae which can produce their own food by photosynthesis are called producers. They, produce food for consumers. They link non-living world to living world., Consumers: Those organisms which depend directly or indirectly on producers for their food are called, consumers. These are of four types, herbivore, carnivore, omnivore, parasites as per their feeding habits but, as per the level in food chain, they are categorised as: primary, secondary, tertiary consumers and so on., • Primary Consumer or Herbivores: Those organisms which eat plants are called herbivores e.g. deer,, rabbit, horse, cow, elephant, goat, sheep, grasshopper, seed eating birds, butterfly etc., • Secondary Consumer or Primary Carnivores: Those animals which eat flesh of the herbivores e.g. lion,, tiger, lizard, frog, crocodile etc., • Small Carnivores: They come at 3rd trophic level because they get their food by eating herbivorous animals., They are also called secondary consumers., • Big Carnivores: They are at 4th trophic level as they eat, small carnivores. They are also called tertiary consumers., Omnivores: Those animals which eat plants as well as, animals are omnivores e.g. Cat, human., Parasites: Those organisms which live on the body of, host and take food from it e.g. lice, cuscuta, virus., Decomposers: Those micro-organisms which decompose, the dead plants and animals to simpler substances, e.g. bacteria, fungi. They help in the replenishment of, natural reserviors and for cleaning environment. They, increase the fertility of soil., , Food Chain, • It is a series of organisms taking part at various biotic, levels to form a chain of who eats whom e.g. Grass →, Deer → Lion., , Trophic level: Each level of the food chain is called trophic, level. There is transfer of energy between each trophic, level, which is unidirectional and keeps on decreasing by, 90%, just 10% is available., [CBSE 2020], , Different Food chain in nature, , Autotrophs: Those organisms which prepare their own food from inorganic nutrients are called autotrophs., , They are called producers. They form the first trophic level. They fix up or use sunlight and make it available, for heterotrophs or consumers., , Heterotrophs: They need organic nutrients from other organisms. They derive energy from sun indirectly., These are also called consumers., , 10 percent law: Green plants capture 1% of total incident sunlight and convert it into food energy. Only, 10% of this energy is transferred to the next trophic level. The remaining 90% of energy is consumed in, life processes like digestion, respiration, growth, reproduction by each trophic level. The energy left beyond, 3-5 trophic level is so less that none of the food chains could go beyond. Flow of energy in an ecosystem is, unidirectional. As energy flows from lower to higher trophic level, no energy is available for previous level. It, flows from producer into consumer and not vice versa. Sun is the universal source of energy for all., [CBSE 2020], , Our Environment 159

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[Delhi 2019], ,       Flow of energy in an ecosystem, , Biological Magnification, , The concentration of some toxic substances like pestmicides, insecticides increases with every trophic level, in food chain if it is not metabolised by the body of organism. It is called biological magnification. Humans, occupy top position in food chain, so maximumh amount of toxic substances are present in human bodies., • Food web: In an ecosystem, there are more than one food chain. One species may occupy different trophic, levels in different food chains. Large number of food chains are interconnected to form a food web in an, ecosystem., , Tertiary, consumers, Tertiary, consumers, Secondary, consumers, Secondary, consumers, , Primary, consumers, Primary, consumers, , Producers, , Producers, , Pond food, chain, , Grass land, food chain, , Forest food, chain, , Exercise 7.1, I. Multiple Choice Questions, Choose the correct answer from the given options., 1. Which one of the following is an artificial ecosystem?, (a) Pond, (b) Crop field, (c) Lake, 2. In a food chain, the third trophic level is always occupied by, (a) carnivores, (b) herbivores, (c) decomposers, , 160, , Science-10, , (1 Mark), , (d) Forest, (d) producers

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3. An ecosystem includes, (a) all living organisms , (b) non-living objects, (c) both living organisms and non-living objects, (d) sometimes living organisms and sometimes non-living objects, 4. In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the, energy available at the producer level?, Grass → Grasshopper → Frog → Snake → Hawk, (a) 5 kJ, (b) 50 kJ, (c) 500 kJ, (d) 5000 kJ, 5. In an ecosystem, 10% of energy available for transfer from one trophic level to the next is in the form, of:, (a) heat energy , (b) chemical energy, (c) mechanical energy , (d) light energy, [Delhi 2020], 6. Which of the following are water intensive crops?, (a) Wheat are rice , (b) Wheat and sugarcane, (c) Sugarcane and rice , (d) Wheat and gram, [Delhi 2020], 7. The most poisonous product formed by incomplete combustion of fossil fuels is, (a) Carbon dioxide , (b) Nitrogen dioxide, (c) Carbon monoxide , (d) Sulphur dioxide, [Delhi 2020], 8. Food web is constituted by, (a) relationship between the organisms and the environment., (b) relationship between plants and animals., (c) various interlinked food chains in an ecosystem., (d) relationship between animals and environment., [CBSE 2020], 9. How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?, (a) 100%, (b) 10%, (c) 1%, (d) 0.1%, [CBSE 2020], 10. The decomposers in an ecosystem, (a) convert inorganic material, to simpler forms, (b) convert organic material to inorganic forms, (c) convert inorganic materials into organic compounds, (d) do not breakdown organic compounds, II. Assertion-Reason Type Questions, (1 Mark), For question numbers 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Aquarium needs regular cleaning, , Reason: There are no microbes to clean water in aquarium, therefore, it needs to be regularly cleaned., 2. Assertion: The concentration of harmful chemicals is least in human beings., , Reason: Man is at the apex of the food chain., , III. Very Short Answer Type Questions, , (1 Mark), , 1. In the following food chain, 20,000 J of energy was available to the plants. How much energy will be, available to man in this chain?, , Plants → Sheep → Man, 2. Which will get more energy, secondary consumers or tertiary consumers?, [DOE], 3. List two natural ecosystems., [Delhi 2016], 4. List two biotic components of environment., [Delhi 2016] [CBSE 2020], 5. Why are green plants called producers?, [Delhi 2016], 6. Why do producers always occupy first trophic level of food chain?, [Delhi 2016], Or, The first trophic level in a food chain are always occupied by green plants, why?, 7. Which of the following are always at second trophic level of food chains?, Carnivores, Autotrophs, Herbivores., [Delhi 2015], , Our Environment 161

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8. What will be the amount of energy available to the organisms of secondary consumer trophic level of, food chain, if the energy available to producer level is 10000 Joules., [Delhi 2012], 9. The following organisms form a food chain. Which of these will have the highest concentration of nonbiodegradable chemicals? Name the phenomenon., Insects, Hawk, Grass, Snake, Frog., [Delhi 2015] [CBSE 2020], 10. Select two non-biodegradable substances from the following waste generated in the kitchen:, Spoil food, Paper bags, Milk, Tea bags, vegetable peels, tin cans, used tea leaves.[Delhi 2012], 11. What are various steps in the food chain called?, [Delhi 2011], 12. Why are bacteria and fungi called decomposer?, [Delhi 2011], 13. Consider the following food chain which occurs in forest: Grass → Deer → Lion, If 10000 J of solar energy is available to grass, how much energy would be available to deer to transfer, to lion., [Delhi 2012], 14. In a food chain of frog, grass, insect and snake, assign trophic level to frog. , [AI 2016], 15. Give one protective function of forests. , [CBSE 2016], 16. What will be the amount of energy available to the organisms of 2nd trophic level of food chain if energy, available at the first trophic level is 1000 J., [CBSE 2016], 17. Write the appropriate names of trophic level ‘Z’ and ‘X’ in the figure given below., [CBSE 2015], Z, Secondary, Consumer, X, Producer, , 18. State a way to prevent accumulation of harmful chemicals in our bodies., [CBSE 2014], 19. During heavy rain in a village the rain water carried excessive fertilizer to a pond. How will it affect, the fish production in pond in the long run? , [CBSE 2014], 20. “Flow of energy is unidirectional”. Name the first two components of the environment involved in flow, of energy from the Sun. , [CBSE 2014, 2020], 21. Define ecosystem., , OR, What is an ecosystem? , [CBSE 2014, Delhi 2017], 22. Draw a food chain which operates in forest ecosystem., [CBSE 2012, 13], 23. What is depicted in the below mentioned scheme?, [CBSE 2012], , Sun, , Photoplankton, 400 kJ, , Zooplankton, , Smaller fishes, , Big fish, , 40 kJ, , 4 kJ, , 0.4 kJ, , 24. List two man-made ecosystem. , [CBSE 2012], 25. “Save the Tiger” campaign is being over emphasised these days by our government. What may be, possible reason?, 26. Why are plastics non-biodegradable substances?, [CBSE 2012], 27. Consider a food chain consisting of wheat, rat, snakes, peacock. What will happen if all snakes are, killed?[CBSE 2012], 28. Change one consumer each that belongs to the second and third trophic levels from the following, organisms : Eagle, frog, tiger, rabbit, fox, [CBSE 2012], 29. In the following food chain, 100 J of energy is available to the lion. How much energy was available to, the producer? Plants → Deer → Lion, [AI 2017], , 162, , Science-10

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30. In the following food chain, 10 J is energy available to the hawks. How much energy would have been, present for the rats? Plants → Rats → Snakes → Hawks, [CBSE 2019(C)], 31. List two steps that should be taken for the maintenance of healthy environment., [CBSE 2019(C) for Blind], 32. What is the functional unit of environment?, [DOE], 33. Crop fields are called artificial ecosystem, Justify., , IV. Short Answer Type Questions-I , , (2 Marks), , Why are some substances biodegradable and some are non-biodegradable?, [Delhi 2011], Define trophic level. Name the first trophic level., [Delhi 2011] [CBSE 2020], Give an example of food chain and state the different trophic levels in it., [Delhi 2011], What is the role of decomposers in the ecosystem?, [NCERT] [Delhi 2014, 2011], Study the following food chain: Grass → Sheep or Goat → Man; Algae → Fish → Man, Who is the ultimate sufferer of using pesticides like DDT on land and in water? Give reason., Why do most food chains have 3-5 steps only?, Compare the advantages of cloth bags over polythene bags., [CBSE 2016], Pesticides like DDT which are sprayed to kill pests on crops are found to be present in soil, ground, water, water bodies etc. Explain how do they reach these places., 9. Accumulation of harmful chemicals in our body can be avoided. Explain how this can be achieved., [CBSE 2015], 10. What would happen if number of carnivores decreases in the ecosystem?, 11. Will the impact of removing all the organisms in a trophic level be different for different trophic levels?, Can the organisms of any trophic level be removed without causing any damage to the ecosystem?, 12. Construct an aquatic food chain showing four trophic levels., [Delhi 2010], 13. Energy flow is unidirectional in food chain? Explain., [Delhi 2013] [CBSE 2020], 14. Name the organisms which belong to first and third trophic level in food chain comprising of the, following: Insects, birds, frog and grass., 15. (a) What is an ecosystem? List its two main components., [CBSE 2020], (b) We do not clean ponds or lakes, but an aquarium needs to be clean regularly, explain., 16. Arrange the following in food chain:, [CBSE 2019], (a) Frogs, Insects, Birds, grass., (b) Fish, algae, small animal, big animal., 1., 2., 3., 4., 5., , 6., 7., 8., , V. Short Answer Type Questions-II, , (3 Marks), , 1. What will happen if we kill all the organisms in one trophic level?, [Delhi 2011, 2020], 2. What is biological magnification? Will the levels of this magnification be different at different levels of, the ecosystem?, [NCERT], 3. What is meant by food chain? ‘The number of trophic levels in food chain is limited.’ Give reason to, justify the statement., [Delhi 2014], 4. Differentiate between autotrophs, heterotrophs and decomposers and give one example of each., 5. What term do you use for trophic levels comprising of, (a) the organisms which make their own food, (b) animals feeding on plant matter only, (c) organisms breaking down dead plants and animals, 6. List three characteristics of energy flow in an ecosystem., 7. (i) Create a terrestrial food chain depicting four trophic levels., [CBSE 2020], (ii) Why do we not find food chains of more than four trophic levels in nature?, [CBSE Sample Paper 2019-2020], 8. How will you create an artificial aquatic ecosystem, which is self-sustainable?, [CBSE Sample Paper 2019-2020], 9. (a) Construct a terrestrial food chain comprising four trophic levels., (b) What will happen if we kill all the organisms in one trophic level?, (c) Calculate the amount of energy available to the organisms at the fourth trophic level if the energy, available to the organisms at the second trophic level is 2000 J. , [Delhi 2020], , Our Environment 163

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10. Your mother always thought that fruit juices are very healthy for everyone. One day, she read in the, newspaper that some brands to fruit juices in the market have been found to contain certain level of, pesticides in them. She got worried as pesticides are injurious to health., (a) How would you explain to your mother about fruit juices getting contaminated with pesticides?, (b) It is said that the harmful pesticides enter our body as well as the bodies of other organisms, they, get accumulated and beyond a limit causes harm and damage to our organs. Name the phenomenon, and write about it., , Answers 7.1, (a) Crop field is artificial ecosystem., (a) carnivores are always at the third tropic level, (c) It includes both living organisms as well as non-living objects., (d) 5000 kJ because 10% of energy is available from one level to another., (b) It is in form of chemical energy., (a) Wheat and rice, (c) The most poisonous product is Carbon monoxide., (c) various interlinked food chains in an ecosystem., (b) 10%, (b) convert organic material to inorganic forms, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the assertion., (d) ‘A’ is false but ‘R’ is true., Plants have 20,000 J of energy available to them. Sheep will get 10% of 20000 J, 10, = 2000 J, 20000 ×, 100, , I. 1., , 2., 3., , 4., , 5., , 6., 7., 8., 9., , 10., II. 1., , 2., III. 1., , Humans will get 10% of 2000 J., 10, = 200 J, 2000 ×, 100, 2. Secondary consumers will get more energy., 3. (i) Oceans, (ii) forests are two natural ecosystems., 4. Plants, animals, micro-organisms (any two) are biotic components., 5. Green plants prepare their own food by photosynthesis with the help of CO2, H2O, sunlight and, chlorophyll., 6. They prepare their own food from CO2, H2O and sunlight from environment. They are consumed by, herbivores, therefore they always occupy first trophic level., 7. Herbivores will always be at second trophic level., 10, 8. Energy available to primary consumers level is 10000 ×, = 1000 J, 100, 10, Energy available to secondary consumer trophic level = 1000 ×, = 100 J, 100, 9. Hawk is a decomposer and have maximum concentration of non-biodegradable chemicals., The phenomenon is called Biomagnification., 10. Tea bags and tin cans., 11. Trophic level., 12. Bacteria and fungi are called decomposer because they breakdown complex organic matter as remains, of plants and animals into CO2, methane and other simple molecules which go into atmosphere and as, nutrients to soil., 1, 13. Grass will absorb 1% solar energy i.e. 10000 ×, = 100 J, 100, 10, = 10 J, 100, Out of this 10 J of energy, only 1 J of energy can be transferred to lion., 14. Grass → Insect → Frog → Snake, Frog is a secondary consumer and belongs to 3rd trophic level., , Dear will get 10% of 100 J = 100 ×, , 164, , Science-10

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15. Forests help to reduce air pollution., 1, = 100 J., 10, 17. ‘X’ is primary consumer, ‘Z’ is tertiary consumer in the given figure., 18. Minimum use of fertilizers, insecticides and pesticides, can prevent the accumulation of harmful, chemicals in our body., 19. Fish production will decrease due to formation of excess of algae., 20. Producers and primary consumers are first two components in the flow of energy., 21. All living organisms and abiotic components of surroundings forms an ecosystem., 22. Grass → Deer → Tiger., 23. It depicts 10% law in food chain for energy transfer from one trophic level to another., 24. Aquarium, crop land, park. (Any two), 25. It helps to maintain ecological balance in nature and also to preserve gene pool of a particular species., 26. It is because plastics are not decomposed by micro-organisms. (Note: Now, plastic eating enzymes has, been discovered)., 27. The peacock will also die. The population of rats will increase., 28. (i) Second trophic level → Rabbit, (ii) Third trophic level → Frog and fox., 29. Plants → Deer → Lion, It is given that 100 J of energy is available to lion., Let the amount of energy available to deer be x Joules., According to 10% law, 10% energy from deer must have been transfered to lion. So, energy available to, 10, × x = 100 J, Therefore, x = 1,000 J, deer can be calculated as,, 100, Now, let the amount of energy available to plants be y Joules., According to 10% law, 10% energy from plants must have been transfered to deer. So, energy available, to plant can be calculated as,, 10, × y = 1,000 J, 100, 16. 1000 ×, , Therefore, y = 10,000 J, So, we have found that energy available to the producer is 10,000 J., 30. 1000 J., 31. (i) Controlling pollution (ii) Afforestation (iii) Proper Waste Disposal, (Any two), 32. Ecosystem is the functional unit of environment., 33. Crop field ecosystem is created by man and needs care like watering, supply of manure, protection, from diseases. Therefore, it is an artificial ecosystem., IV. 1. Biodegradable substances are those which are broken by micro-organisms and get decomposed. They, do not persist in environment for a very long time e.g., paper., Non-biodegradable substances are those which are not broken by micro-organisms. They persist in, environment for long time. e.g. plastic, DDT., 2. Each level in a food chain is called trophic level. First trophic level is producers., 3. An example of food chain is grassland food chain. Its different trophic levels are shown in the given, figures., , Snake, Frog, Grass hopper, Grass, , OR, , Tertiary, Consumer, Secondary, Consumer, Primary Consumer, Producer, , Our Environment 165

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4. (i) Decomposers decompose the remains of plants and animals., (ii) They clean the environment., (iii) They bring back the raw materials to environment. (Any two), 5. Man is the ultimate sufferer. Food chain in given cases ends on man i.e. last trophic level., 6. Following 10% rule of energy flow, very little energy is left at the trophic levels beyond 3-5 levels that, may not be enough to sustain life of a big carnivore, hence most food chains are short and have 3-5, steps only. Longer ones will have very small carnivores at the top., 7. (i) Cloth is biodegradable, does not pollute environment., (ii) It can be used again like plastic bag and moreover it is ecofriendly., 8. (i) Soil. Pesticides get settled on soil when sprayed over plants., (ii) Groundwater. Pesticides present in soil reach lower layers of soil during irrigation and get mixed, with ground water., (iii) Waterbodies: When agricultural waste as well as waste water get mixed up with water bodies,, pesticides enter waterbodies because these are non-biodegradable., 9. (i) Wash vegetables and fruits with saline water and vinegar., (ii) Shock the vegetables in salt water for few minutes before cooking., (iii) Boil the vegetables., (iv) Organic manure and organic ecofriendly pesticides should be used., 10. If number of carnivores decreases in the ecosystem, then it will lead to increase in number of herbiores., As a result number of plants will decrease and consequently amount of O2 will also decrease in the, ecosystem., 11. The impact of removing all the organisms in a trophic level will be different for different trophic, levels. It is not possible to remove organisms of any trophic level without causing damage to ecosystem, because organisms of each level are interdependent., 12., Hawk, or, Sea gull, (Top carnivore), Fish (carnivore), Crustacean (carnivore), Zooplankton (herbivore), Phytoplankton (producer), , Aquatic food chain, 13. The energy of sun is taken by plants and cannot be given back. Herbivore eat plants and cannot give, back energy to plants. Carnivores eat herbivores and cannot give back energy to herbivores. It means, flow of energy is unidirectional from lower trophic level to higher trophic level., 14. First trophic level – Grass, Third trophic level – Frog, 15. (a) Ecosystem is composed of different organisms interdependent upon each other. Biotic and abiotic, components are its two main components., (b) Pond or lake is a natural ecosystem, several organisms present in it maintain a balance in the, ecosystem. Aquarium is an artificial ecosystem in which bacteria convert fish food into ammonia, which is harmful for fish. Water needs to be changed regularly. Chlorine water should be, dechlorinated otherwise fish will not survive. Air pump is needed to provide oxygen. Artificial, ecosystem need utmost care to remain stable., 16. (a) Grass → Insects → Frog → Birds, (b) Algae → Small animal → Fish → Big animal, V. 1. If we kill the organisms in one trophic level., (i) The population of organisms in previous trophic level will increase., (ii) The population of organisms in next trophic level may decrease., (iii) It will cause an ecological imbalance in the food chain., , 166, , Science-10

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2. The process in which harmful chemicals like pesticides enter the food chain and get accumulated, in each trophic level is called biomagnification. The level of biomagnification will be different from, different trophic level. Primary consumers will have higher concentration of pesticides than producers, and secondary consumers will get pesticides by eating primary consumers and will have even higher, concentration., 3. Food chain is a sequence in which nutrients, food and energy is transferred in systematic way. Lower, trophic level have maximum population because energy is available in more extent., Primary consumers get 10% of energy of producers., Secondary consumers get 10% of energy of primary consumers., Tertiary consumers get 10% of energy of secondary consumers i.e. very less energy is available, that, is why the trophic levels are limited. Tiger population is decreasing day by day as food is not easily, available for them and forests are decreasing due to cutting of trees., 4. (i) Autotrophs. Those organisms which prepare their own food with the help of CO2, H2O and sunlight, in presence of chlorophyll e.g. green plants., (ii) Heterotrophs. Those organisms which do not prepare their own food but dependent on the other, food. e.g. animals and human beings., (iii) Decomposers. Those organisms which decompose the complex molecules present in the dead, remains of plants and animals e.g. bacteria, fungi, earthworm., 5. (a) Producers, (b) Herbivores, (c) Decomposers, 6. (i) The sun is the main source of energy on earth. About 1% of incident solar energy is utilized by, plants during photosynthesis., (ii) Producers [plants] convert solar energy to chemical energy of food, and then it is passed on to, the consumers and to decomposers back to soil. This is in accordance with law of conservation of, energy., (iii) The energy flow is unidirectional, that is, it flows from producers through herbivores to carnivores;, it cannot be transferred in the reverse direction., (iv) The amount of energy flow decreases with successive trophic levels. , [Any three], 7., , (i) A terrestrial food chain depicting four tropic levels is, shown in diagram., ½, (ii) According to the 10% law, the amount of energy available, will not be sufficient for the survival of the organisms in, the 5th trophic level., ½+½+½, (A flow chart or a diagrammatic representation showing, all the four tropic levels would also be accepted)., , Tertiary consumer, , Red tailed hawk, , Secondary consumer, , Spotted Frog, , Primary consumer, , Grass Hopper, , Primary producer, , Bunch grass, , According to the 10% law, the amount of energy available will not be sufficient for the survival of, the organism in the 5th trophic level., 8. • Take a large jar filled with water, oxygen, food and aquatic plants and animals., • Oxygen/oxygen pump., • Fish food., • Aquatic plants/Producers provide O2 during photosynthesis., • Aquatic animals/Consumers release CO2 for the process of photosynthesis., • Decomposers are also important for natural cleaning of the aquarium., 9. (a) Level 1 Plants and algae, Level 2 Herbivores like goat, cow, Level 3 Carnivores like fox, wild cat, mongoose, Level 4 large carnivores, lion, tiger, (b) If we kill all organisms in one trophic level, then transfer of energy as well as matter to next higher, level will stop, it will lead to overpopulation at one particular level, disturb the food chain and, cause collapse of ecosystem., (c) Energy available at second trophic level of 2000 J, 1, = 200 J, 10, 1, Energy available at fourth trophic level is 200 ×, =2J, 10, Energy available at third trophic level is 2000 ×, , Our Environment 167

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10. (a) Farmers spread pesticides on fruits and it get mixed up with fruits and enter fruit juices., (b) The process is called bio-magnification. The concentration of toxic substances like pesticides,, insecticides increase with each trophic level in food chain., , Topic 2. How do our Activities affect the Environment?, , Ozone: It is formed in upper atmosphere by action of UV light on molecules of oxygen (gas)., UV, , →O + O, , , , O2, , , , O + O2 → O3 (ozone), , • Ozone is deadly poisonous. Ozone protects us from harmful UV radiations of the Sun., • UV radiations are highly harmful for living organisms, it can cause skin cancer, blood cancer, cataract in, humans., , Ozone depletion: Ozone layer is getting thinner and thinner day by day., • I t is due to use of CFCs (Chlorofluorocarbons) in refrigerators, in fire extinguishers and air conditioners., • UNEP has succeeded in reaching in agreement to freeze CFCs production to save environment and stop, its production. It is called Kyoto Protocol., , Waste Management, • Biodegradable waste and non-biodegradable wastes should be put in separate blue and green bins, respectively., • Biogas plant is excellent way of disposal of waste in rural areas., • Sewage treatment plants are must in urban areas to detox water before releasing into river., • Land fillings can be decomposed in a pit that changes waste into manure and sold to farmers, home makers, for kitchen gardens., • Recycling of non-biodegradable waste is essential to clean environment., • Newspapers can be recycled very easily and used for making envelopes, eco-friendly carry bags., • Used bottles, cans, boxes, clothes, envelopes can also be reused., • 5R’s approach, Reuse, Recycle, Refuse, Reduce and Repurpose is best to save environment., , Exercise 7.2, I. Multiple Choice Questions, , (1 Mark), , Choose the correct answer from the given options., 1. Depletion of ozone is mainly due to, (a) chlorofluorocarbons , (b) carbon monoxide, (c) methane , (d) pesticides, 2. Excessive exposure of humans to UV-rays results in, (i) damage to immune system, (ii) damage to lungs, (iii) skin cancer , (iv) peptic ulcers, (a) (i) and (ii), (b) (ii) and (iv), (c) (i) and (iii), (d) (iii) and (iv), 3. In the following groups of materials, which group(s) contains only non-biodegradable items?, (i) Wood, paper, leather, (ii) Polythene, detergent, PVC, (iii) Plastic, detergent, grass, (iv) Plastic, bakelite, DDT, (a) (iii), (b) (iv), (c) (i) and (iii), (d) (ii) and (iv), 4. Which one of the following greenhouse gases is a contributor due to incomplete combustion of coal and, petroleum?, (a) Oxides of nitrogen , (b) Methane, (c) Carbon monoxide , (d) Carbon dioxide[CBSE Sample Paper 2019-2020], 5. Choose the incorrect statement from the following:, (a) Ozone is a molecule formed by three atoms of oxygen., (b) Ozone shields the surface of the Earth from ultraviolet radiations., (c) Ozone is deadly poisonous., (d) Ozone gets decomposed by UV radiations., [CBSE 2020], , 168, , Science-10

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II. Assertion-Reason Type Questions, , (1 Mark), For question numbers 2 two statements are given-one labeled as Assertion (A) and the other labeled, Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:, (a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion., (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion., (c) ‘A’ is true but ‘R’ is false., (d) ‘A’ is false but ‘R’ is true., 1. Assertion: Ozone is formed in upper atmosphere by O2 in presence of UV radiations., , Reason: Ozone depletion will lead to UV rays reaching earth which may cause skin cancer., 2. Assertion: Polythene bags and plastic containers are non-biodegradable substances., , Reason: They can be broken down by microorganisms in natural simple harmless substances., , III. Very Short Answer Type Questions, , (1 Mark), , Which of the following are not biodegradable: Wool, glass, silver foil, leather?, [DOE], What is full form of CFC and UNEP?, [DOE] [Delhi 2015], Name the radiations that are absorbed by ozone layer?, [DOE], Why is excessive use of CFC a cause of concern?, [Delhi 2016], Name the gases which have replaced CFCs., [CBSE 2014], Ozone is deadly poisonous, still it performs an essential function. How?, [CBSE 2012], What happens during first step of ozone formation in the the atmosphere?, Why should bio-degradable and non-biodegradable wastes discarded into separate dust bins?, [Delhi 2015], 9. Name any two items which can be easily recycled but are generally thrown in the dust-bin by us., [Delhi 2013], , 1., 2., 3., 4., 5., 6., 7., 8., , IV. Short Answer Type Questions-I , , (2 Marks), , What is ozone and how does it affect any ecosystem?, [NCERT], If all the waste we generate is biodegradable, will this have no impact on the environment?, Mention three methods to reduce amount of wastes produced., List two causes of depletion of ozone layer. Mention any two harmful effects of depletion of this layer., , [CBSE 2019 AI], 5. Which compounds are responsible for the depletion of ozone layer? [CBSE 2012, 13, AI], 1., 2., 3., 4., , V. Short Answer Type Questions-II, , (3 Marks), , 1. When the government banned the use of polybags in Delhi, the vegetable grocers found it difficult as, it affected their sales. The market committee held a meeting and decided to spread awareness about, harmful effect of polybags., [Delhi 2016], (i) How will you convince people that plastics are harmful to the environment?, (ii) What alternatives of polythene bags do we have, which are environment friendly?, (iii) Not many people in Delhi have stopped using polythene bags even though they are officially, banned. How can schools enaculate environmental values in students?, 2. (a) Why is it necessary to conserve our environment?, (b) State the importance of green and blue dustbins in the safe disposal of the household waste., 3. (i) What is the height of ozone from the equator?, (ii) Name the rays against which ozone layer provides protection., (iii) Name one effect of depletion of ozone layer., [CBSE 2016], 4. You have been selected to talk on “ozone layer and its protection” in the school assembly on ‘Environment, Day’., (a) Why should ozone layer be protected to save the environment?, (b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow, friends that would also help in protection of ozone layer as well as the environment., 5. (a) Water is an elixir of life, a very important natural resource. Your Science teacher wants you to, prepare a plan for a formative assessment activity, “How to save water, the vital natural resource”., Write any two ways that you will suggest to bring awareness in your neighbourhood, on ‘how to, save water’., (b) Name and explain any one way by which underground water table does not go down further., [AI 2017], , Our Environment 169

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6. How is ozone both beneficial and damaging? How can we prevent the damaging effect of ozone? List, one way., 7. (a) Complete the following table:, Oxygen, Formula, Benefits, to, component, , Ozone, , (i) ________________________, , (ii) ________________________, , biotic (iii) ________________________, , (iv) ________________________, ________________________, ________________________, , (b) How is ozone formed at the higher levels of atmosphere?, [CBSE 2020], 8. (a) Improvement in our lifestyle has resulted in greater amount of waste generation. Suggest one, change we can incorporate in our lifestyle in order to reduce non-biodegradable waste., (b) The following organisms form a food chain:, Insect, Hawk, Grass, Snake, Frog, Which of these will have highest concentration of non-biodegradable chemicals? Name the, phenomenon.[CBSE Sample Paper 2017-18] [CBSE 2020], , VI. Long Answer Type Questions, , (5 Marks), , 1. Differentiate between biodegradable and non-biodegradable substances with the help of one example, each. List two changes in habit that people must adopt to dispose of non-biodegradable waste for, saving the environment., [AI 2015], 2. What is ozone? How and where is it formed in the atmosphere? Explain how it affects an ecosystem., [Foreign 2015], OR, What is ozone and how does it affect any ecosystem?, 3. Mention the negative effect of our lifestyle on the environment., [Delhi 2013, 2016], 4. (a) What do you understand by ‘watershed management’? List any two advantages of watershed, management., (b) Human beings occupy the top level in any food chain. What are the consequences of this on our, body?[CBSE Sample paper 2017-2018], , Answers 7.2, I. 1. (a) chlorofluorocarbons deplete ozone layer., , 2. (c) (i) and (iii),, (iii) (d) (ii) and (iv),, (iv) (c) Carbon monoxide, 3. (d) Ozone gets decomposed by UV radiations., II. 1. (b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the assertion., , 2. (c) ‘A’ is true but ‘R’ is false., III. 1. Glass, silver foil., 2. CFC stands for Chloroflurocarbon, UNEP stands for United Nations Environment Programme., 3. UV radiations (Ultra-Violet radiations) are absorbed by ozone layer., 4. CFC will deplete ozone layer which prevents UV radiation to reach earth. It causes skin cancer., 5. (i) HFCs (Hydrofluorocarbons), (ii) Perfluorocarbons (PFCs) have replaced CFCs., 6. It protects earth from harmful UV radiations., UV, , →O + O, 7. O2  , 8. It saves time and energy by separating them and waste disposal can be done in right way in minimum, time., 9. (i) Bits of paper (ii) Plastic bottles of water or cold drinks., IV. 1. Ozone is a triatomic (O3) gas formed in upper atmosphere by action of UV light on oxygen. It protects, earth from harmful UV radiations., 2. If all waste we generate is biodegradable, the adverse effect on environment will be minimum. They, will produce CO2, methane which is released in atmosphere., Nutrients will be mixed in soil to increase the fertility of soil., 3. (i) Recycling of non-biodegradable waste., (ii) Reuse of waste such as newspapers can be used for making carry bags and envelopes., 170, , Science-10

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(iii) Biodegradable domestic waste should be disposed in pits to form manure., , (iv) Biogas plants should be used for disposal of waste in rural areas., 4. Two causes of depletion of ozone layer are: (i) CFCs (ii) Aerosols, Two harmful effects of depletion of this layer are:, , (i) UV radiations can reach the earth and causes skin cancer, harmful to eyes and immune system will, be disturbed., (ii) It may lead to variations in rainfall, ecological disturbance., 5. (i) CFC, (ii) NO, (iii) Free radicals of chlorine (iv) Aerosols, V. 1. (a) They need to be told that cows and other animals eat polythene which is fatal for them. Coloured, polythene is also very harmful for vegetables and fruits., (ii) Paper bags, jute bags, bags of biodegradable materials are ecofriendly and carrying your own, shopping bag is also more convenient., (iii) Schools must teach students to protect environment. They should make paper bags and distribute, to small shopkeepers regularly so that gradually their habits will change., 2. (a) It is necessary to conserve our environment because, , (i) It helps in protecting the ozone layer., (ii) It helps in maintaining animal and human food chains., (iii) It provides us with many useful products such as medicines and wood., (b) Disposal of household waste is carried out in green and blue bins, respectively. It will be very useful, in the separate disposal of biodegradable and non-biodegradable wastes. This will also ensure the, application of 3 R’s— Reduce, Reuse and Recycle., 3. (i) 10 to 16 km, (ii) UV rays, (iii) Global warming., 4. (a) Ozone layer is a rich zone of ozone found in upper atmosphere. It helps in shielding the Earth from the, harmful UV radiations coming from the Sun. If ozone layer gets depleted, UV radiations can directly, reach the Earth’s surface and drastically affect the life on Earth. For instance, UV radiations coming, from the Sun causes skin cancer. So, it is very important to protect the ozone layer so as to save our, environment and the planet Earth., (b) Some of the ways to help protect and stop the depletion of the ozone layer include: Not buying, products in aerosol cans, maintaining air-conditioning filters and units., In order to halt the depletion of the ozone layer, countries around the world have banned the use of, chlorofluorocarbons and other ozone-depleting substances. These compounds produce chlorine and, bromine atoms high in the atmosphere, and these atoms react with ozone, destroying it., By reducing the use of fluorescent lights., , By minimising the use of vehicles to limit the emission of harmful gases that cause damage to the, ozone layer, we can contribute to its protection., 5. (a) Water is one of the most precious natural resources that has vital importance in our lives. It is an, essential component of the human body and is used almost everywhere in our day-to-day activities,, such as cooking, washing, in agriculture and industries. It is an indispensable part of our life,, without which the life on earth is not possible. However, the amount of fresh water available for, sustaining life is very less. So, it is very important to conserve water. For creating awareness, among people, we can adopt the following two ways., (i) Door to door campaigning., (ii) Nukkad Nataks, (b) Underground water table can be recharged through rainwater harvesting. Rainwater harvesting, is a process by which rain water is collected and stored for the purpose of recharging the ground, water or for future use like for irrigation and agriculture, for livestock, etc. In India, rainwater, harvesting is an old tradition, which is followed till now in many parts of India. For example,, bawris are traditional architectural rainwater harvesters that were built for collecting water, in, the state of Rajasthan., There are two ways of rainwater harvesting:, , (i) Surface runoff harvesting: In urban areas, rain water that flows away from the surface can, be collected and used for various purposes., (ii) Rooftop rainwater harvesting: The rainwater on the roofs of the buildings is collected, through canals that drains the water into ground water reservoirs. This stored water can later, be utilised., 6. Damaging as it is a deadly poison., Beneficial as it shields the surface of the earth from UV radiations of the Sun., By not using synthetic chemicals like CFCs, that depletes O3 layer., , Our Environment 171

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Oxygen, , 7. (a), Formula, , Ozone, , (i) O2, , (ii) O3, , Benefits to biotic (iii) e ssential for, component, breathing and, to survive, , (iv) • prevents UV rays to reach earth, • disinfectant, • strong oxidant, , UV, , , (b) It is formed by action of UV light on oxygen. 3O2(g) , ,  2O3 (g), 8. (a) (i) More use of disposable items like paper plates, plastic and polythene which are recyclable., (ii) Change in packaging Suggestion. Reuse of plastic containers, (b) Hawk will have highest concentration of non-biodegradable chemicals. This process is called, biomagnification., , VI. 1., , Biodegradable substances, , Non-biodegradable substances, , Can be broken down into simpler substances Can’t be broken down into simpler substances by, by nature / decomposers/ bacteria/ saprophytes. nature / decomposers., Eg. – Human Excreta/ Vegetable peels, etc. Eg. – Plastic/ glass (any one), (any one), Two habits to dispose of non-biodegradable wastes are:, (i) Use of separate dustbins for biodegradable and non-biodegradable wastes,, (ii) Reuse of things such as polybags, etc.,, (iii) Recycling of wastes, (iv) Use of cotton /jute bags for carrying vegetables etc. (Any two), 2. Ozone is a molecule containing three atoms of oxygen (O3). It is a highly poisonous gas present in the, upper layers of the atmosphere., Formation of ozone: The UV radiations from Sun split some molecules of oxygen (O2) apart into free, oxygen atoms (O + O). These atoms then combine with oxygen molecules to form ozone., UV, O2 , → O+O, , ;, , O + O 2 , → O3, , (Ozone), , Ozone layer shields the surface of the earth against damaging UV radiations of the Sun., 3. (i) Global warming occurs due to increase in number of vehicles and over use of fossil fuels., (ii) Due to excessive use of deodrants, perfumes, CFCs, etc. ozone layer is getting depleted., (iii) Air pollution occurs due to industralisation., (iv) Wastes causes pollution due to release of sewage in water bodies., (v) Pollution of soil occurs due to overuse of chemicals is agriculture., 4. (a) Soil and water conservation in a scientific way is called ‘watershed management’., , Advantages: (i) Increase in production and income of watershed communities,, (ii) Mitigate draughts and floods, (iii) Increase the life of downstream dam reservoir., (b) Maximum level of biomagnification occurs in human beings because of progressive accumulation., We get very small amount of energy as only 10% of previous energy gets transferred to each trophic, level., , C ase study questions, , 1. Food chains are very important for the survival of most species., , 172, , Science-10

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(i) If 10,000 J solar energy falls on green plants in a terrestrial ecosystem, what percentage of solar, energy will be converted into food energy?, (a) 10,000 J, (b) 100 J, (c) 1000 J , (d) It will depend on the type of the terrestrial plant., , (ii) If Ravi is consuming curd/yogurt for lunch , which trophic level in a food chain he should be considered, as occupying ?, (a) First trophic level , (b) Second trophic level, (c) Third trophic level, (d) Fourth trophic level, (iii) The decomposers are not included in the food chain.The correct reason for the same is because, decomposers:, (a) Act at every trophic level of the food chain, (b) Do not breakdown organic compounds, (c) Convert organic material to inorganic forms, (d) Release enzymes outside their body to convert organic material to inorganic forms, (iv) Matter and energy are two fundamental inputs of an ecosystem. Movement of, (a) Energy is bidirectional and matter is repeatedly circulating., (b) Energy is repeatedly circulation and matter is unidirectional., (c) Energy is unidirectional and matter is repeatedly circulating., (d) Energy is multidirectional and matter is bidirectional., (v) Which of the following limits the number of trophic levels in a food chain?, (a) Decrease in energy at higher trophic levels, (b) Less availability of food, (c) Polluted air, (d) Water, Ans. (i) (b), (ii) (c), (iii) (a), (iv) (c), (v) (a), 2. Observe the following diagram and answer the questions any four from (i) and (v), , , (i) Choose the waste management strategy that is matched with correct example., (a) Refuse Choose products that use less packaging , (b) Reduce Give unwanted toys and books to hospitals or schools, (c) Reuse Not using single use plastic, (d) Repurpose Making flower pot from used plastic bottle, , (ii) Recycling of paper is a good practice but recycled paper should not be used as food packaging because, (a) recycled papers may release color /dyes on food items, (b) recycled papers are not absorbent, (c) recycled papers can cause infection due to release of methane, (d) recycled papers are costly, , Our Environment 173

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(iii) According to the ‘Solid Waste Management Rule 2016’, the waste should be segregated into three, categories. Observe the table below and select the row that has correct information, Waste Water, , Dry Water, , Hazardous Water, , (a) Cooked food, vegetable, peels, , Used bulbs, fluorescent, lamps, , (b) Coffee and tea powder,, garden waste, , Plastic carry bags, bottles, Expired medicines, razors, paint cans, newspaper, cardboard, , (c) Leftover food, vegetable, peels, , Coffee and tea powder,, garden waste, , (d) Uncooked food, tea leaves Old crockery, frying pans, , Plastic carry bags, bottles, newspaper,, cardboard, , Insect repellents, cleaning solutions, Coffee and tea powder, garden waste, , (iv) Effective segregation of wastes at the point of generation is very important. Select the appropriate, statements giving the importance of waste segregation., I. less waste goes to the landfills, II. better for public health and the environment, III. help in reducing the waste, IV. resulting in deterioration of a waste picker’s health, (a) both I and II, (b) both I and III, (c) both II and III, (d) both I and IV, (v) The given graph shows the amount of waste generated, dumped and treated in percentage. Identify, the reason of low success rate of waste management process., , (a), (b), (c), (d), Ans. (i) (d), , only 15% of urban India’s waste is processed, less than 60% of waste is collected from households, more than 60% of waste is collected from households, both (a) and (b), (ii) (c), (iii) (b), (iv) (a)    (v) (a), , 3. Biosphere is a global ecosystem composed of living organisms and abiotic factors from which they derive, energy and nutrients. And ecosystem is defined as structural and functional unit of the biosphere, comprising of living and non-living environment that interact by means of food chains and chemical cycles, resulting in energy flow, biotic diversity and material cycling to form a stable, self-supporting system, BIOTIC vs. ABIOTIC FACTORS, Living Examples, , Non-Living Examples, , • Plants, , • Water, , • Animals, , • Sunlight, , • Fungi, , • Soil, , • Bacteria, , • Air, • Temperature, , 174, , Science-10

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(i) Which trophic level is incorrectly defined?, (a) Carnivores – secondary or tertiary consumers, (b) Decomposers – microbial heterotrophs, (c) Herbivores – primary consumers, (d) Omnivores – molds, yeast and mushrooms, , (ii) The diagram below shows a food web from the sea shore, , The mussel can be described as, (a) Producer , (c) Secondary consumer, (iii) The given figure best represents:, , (b) Primary consumer, (d) Decomposer, , (a) Grassland food chain, (b) Parasitic food chain, (c) Forest food chain , (d) Aquatic food chain, (iv) Consider the following statements concerning food chains:, (i) Removal of 80% tigers from an area resulted in greatly increased growth of vegetation, (ii) Removal of most of the carnivores resulted in an increased population of herbivores., (iii) The length of the food chains is generally limited to 3 – 4 trophic levels due to energy loss, (iv) The length of the food chains may vary from 2 to 8 trophic levels, , Which two of the above statements are correct?, (a) (i), (iv), (b) (i), (ii), (c) (ii), (iii), (d) (ii), (iv), (v) Which of the following group of organisms are not included in ecological food chain?, (a) Carnivores, (b) Saprophytes, (c) Herbivores, (d) Predators, Ans. (i) (d), (ii) (c), (iii) (a), (iv) (c), (v) (b), , Common Errors, Errors, , Corrections, , • Students get confused between biotic and abiotic ☞ Biotic components are living and abiotic components, components of environment., are non-living., • Students arrange organisms in food chain wrongly., , ☞ Producers are always at the bottom, decomposers at, the top. Small Carnivores will be secondary consumers., Big carnivorous will be tertiary consumers., , • Students get confused in food web., , ☞ Basics of food chain is applicable to food web., , • Students are not able to differentiate ate between ☞ Vegetable, dead plants, animals are biodegradable, biodegradable and non-biodegradable wastes., whereas metals, glass, plastic are non-biodegradable., • Cause of ozone layer depletion may not be known to ☞ CFCs, NO2 are major causes of ozone depletion., students., , Our Environment 175

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Assignment, , Total Marks : 20, , I. Multiple Choice Questions, , (8 × 1 = 8 ), , Choose the correct answer from the given options., 1. In the given figure the various trophic levels are shown in a pyramid. At which trophic level is maximum, energy available?, , T4, T3, T2, T1, , , (a) T4, , (b) T2, , (c) T1, , (d) T3, , 2. What will happen if deer is missing in the food chain given below?, Grass → Deer → Tiger, (a) The population of tiger increases, (b) The population of grass decreases, (c) Tiger will start eating grass, (d) The population of tiger decreases and the population of grass increases, , II. Assertion-Reason Type Questions, , (2 × 1 = 2 ), , , Note: Use instructions as given in topical exercises of the chapter., 1. Assertion: CFCs (Chloro fluorocarbons) deplete ozone layer., , Reason:, , NO also depletes ozone layer which is generated by jet aeroplanes in stratosphere., , 2. Assertion: Aquarium needs regular cleaning, , Reason:, , There are no microbes to clean water in aquarium, therefore, it needs to be regularly cleaned., , III. Very Short Answer Type Questions, , (1 Mark), , 1. If producer have 1000 J of energy, how much energy will reach to tertiary consumer?, 2. Why should biodegradable and non-biodegradable waste be discarded in two separate dust-bins?, , IV. Short Answer Type Questions-I, , (2 Marks), , 1. Draw an energy pyramid showing different trophic levels., 2. Distinguish between producers and decomposers., , V. Short Answer Type Question-II, , (3 Marks), , 1. How can we help in reducing the problem of waste disposal? Suggest any three methods.[Delhi 2019], , VI. Long Answer Type Question, , (5 Marks), , 1. (i) What is food web? Illustrate with the help of example., (ii) (a) What is an ecosystem? List its two main components., (b) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly, explain., , 176, , Science-10

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This chapter to be assessed in the Periodic Tests/Portfolio Only, , 8, , Management of Natural Resources, , Topics Covered, 8.1 Why do we need to manage our resources?, 8.2 Forests and wild life, Water for all, Coal and hpetroleum., , C hapter map, , Natural Resources, , Water, , Forest and wild life, , Conservation of Water, , • Rain Water Harvesting, • Dams, • Watershed Management, • Traditional Method for, Water Conservation, , Biodiversity, , Air pollution, , • Afforestation, • Social forestry, • Agro forestry, • Urban forestry, , Stakeholders, , Amrita Devi Bishnoi Award, , Fossil fuel, , Coal, , Conservation of Forests, , Petroleum, , CNG, LPG, , Chipko Movement and, recoverer of Arabari forests, , Conservation of, Fossil fuels, , Management, of Natural Resources, , Pollution, , Sustainable Management, , Water pollution, , Coliform Bacteria, , Soil pollution, , Ganga Action Plan, , 177, , 3R-Approach, • Reduce, • Reuse, • Recycle

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Quick Revision Notes, • Those substances which can be used and occur in nature are called natural resources, e.g. soil, air, water,, forest, oceans, wildlife, coal, petroleum, minerals., • There are two types of natural resources (i) Exhaustible (ii) Inexhaustible., • We must avoid wastage and conserve natural resources for future., • Ganga Action plan project was launched to clean Ganga., • Reduce, Recycle and Reuse is the best way to save environment., • Reuse is better than recycle because it saves energy., • Wise management of natural resources not only meet current basic needs but also conserve them for future, generation., • Forest and wildlife must be conserved so as to protect the natural environment and prevent global warming, and climate change., • Biodiversity must be maintained which helps in forest and wildlife conservation., • People play an important role in conservation of forests., • Water for all is most important for the progress of the country., • Dams are build to regulate the flow of water, prevent floods and generate electricity., • There are disadvantages of dams also but these cannot be avoided., • Rainwater harvesting must be used in urban areas to increase the level of underground water., • Coal and petroleum are non-renewable natural resource which are limited in nature. These must be used, carefully., • Fossils fuels create air pollution, respiratory diseases and global warming., • Vehicles must be Euro IV norms which controls emission of harmful products., • Local resources available must be used, e.g. Uttrakhand Government has decided that the trees which catch, fire during summer should be used to produce electricity., • Hot water springs can be used to heat rooms of villages in winters and also to produce electricity., • Medicinal trees of Himalayan region must be protected and used for the treatment of various diseases., , Topic 1., , Why do we need to manage our resources?, , Natural resource: The substances present in nature which can be used are called natural resources, e.g. sun,, wind, soil, air, water, coal, petroleum., Pollution: The contamination of air, water, soil with harmful substances is called pollution., Ganga Action Plan (GAP): The clearing of river Ganga is taken up by Govt. of India, it is called Ganga, Action Plan., Coliform: It is a bacteria which is found in the intestine of human beings. Their presence in water causes, many diseases. It is due to the contamination of water with waste products (faeces) and remains of dead bodies., Carbon prints: The international norms to regulate the emission of carbon dioxide., Pollutant: The substances which pollute environment are called pollutants. Some of them like Arsenic,, coliform in water even present in small amounts can be extremely harmful., pH: It helps to determine whether water is acidic, basic or neutral. pH of water can be tested with the help of, universal indicator., Reduce: We must reduce the use of non-renewable resources of energy like coal, petroleum, natural gas which, are limited., Recycle: Plastic, paper, glass, metals must be recycled so as to protect natural resources., Reuse: It is better than recycling because it saves energy. Use things again and again, e.g. jam or pickle, bottles can be reused., Sustainable development: It is the development which can be maintained over long period of time without, causing damage to the natural environment., Management of Natural resources: It is essential because food, clothes, books, toys, furniture, tools and, vehicles are obtained from natural resources. These resources are limited., , 178, , Science-10

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Exercise 8.1, I. Objective Type Questions (MCQs) , (1 Mark), 1. Which of the following community in Rajasthan has a religious tenet of conservation of forest and, wildlife?, (a) Agarwal, (b) Jaishwal, (c) Bishnoi, (d) Gujjar, 2. Which of the following is not an use of forest?, (a) Controls floods. , , (b) Used to make paper., , (c) Causes soil erosion. , , (d) Resin, gum and drugs are obtained., , 3. The pH range most conducive for life of fresh water plants and animals is, (a) 6.5 – 7.5, , (b) 2.0 – 3.5, , (c) 3.5 – 7.0, , (d) 9.0 – 10.5, , 4. Which environmental problem is associated with the construction of high rise dams?, (a) A large number of human settlements are submerged in the water., (b) It contributes to deforestation and loss of biodiversity., (c) It involves the spending of huge amounts of money., (d) All the above., 5. What are the three R’s to save the environment?, (a) Reduce, Recycle, Reuse , , (b) Replenish, Reduce, Reuse, , (c) Reconstruct, Recycle, Reduce, , (d) Reduce, Recycle, Remove, , II. Very Short Answer Type Questions , 1., 2., 3., 4., 5., 6., 7., 8., 9., 10., 11., 12., 13., , (1 Mark), , Name any two items which can be easily recycled but thrown in dustbins., List two causes of pollution of river Ganga., Name the bacteria whose presence in water indicate contamination of water, Name any two inexaustible resources., Define the term ‘Conservation of environment?, Name two resources which cannot be recycled., How can level of water pollution be measured? List any two ways., What are coliform bacteria?, How does inequitable distribution of water affect life of people?, Where are colliform bacteria found in human beings?, Write two methods of waste disposal. , Name any two wastes which can be recycled and reused., Mention the action taken by govt. to same river Ganga., , [Delhi 2014], [DOE], , [CBSE 2016], [CBSE 2015], [CBSE 2015], [CBSE 2014], , III. Short Answer Type Questions-I , (2 Marks), 1. What would be the advantages of exploiting resources with short term aims?, [NCERT], 2. Why is reuse better than recycle?, OR, “Reuse is better than recycling of materials”. Give reason to justify this statement., 3. Name two categories of natural resources., [Delhi 2016] [DOE], 4. Why do you think there should be equitable distribution of resources? What forces would be working, against an equitable distribution of our resources?, 5. What is sustainable development? How can it be achieved?, 6. List two main causes of pollution of water of the river Ganga. State how pollution and contamination of, river water prove harmful to the health of people of neighbouring areas., 7. Identify two local industries which pollute the local water bodies by throwing untreated sewage., 8. What do the three R’s refer to save environment? Which one of these would be the best for environment?, 9. Write the harmful effects of polythene bags on the environment. Suggest alternating to plastic bags., , [CBSE 2013], , Management of Natural Resources 179

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10. Name two fossil fuels. List one product of each forward when these are burnt in (a) sufficient oxygen, (b) Insufficient oxygen., 11. How do advantages of exploiting natural resources with short term gains in mind differ from the, advantages of managing our resources with a long-term perspective?, [Delhi 2013], IV. Short Answer Type Questions-II , , (3 Marks), , 1. Explain the interrelationship of population, environment and development., 2. How 3 R’s policy help in conservation of natural resources?, V. Long Answer Type Questions , (5 Marks), 1. What is Ganga Action Plan? What was the need for it? Give two reason of pollution in Ganga? What are, the two ways to check its level?, 2. Keeping in mind any five natural resources, discuss the 3 R’s ways of conserving them., , Answers 8.1, I. 1. (c) 2. (c) 3. (a) 4. (d) 5. (a), II. 1. (i) Bits of paper, (ii) Plastic water bottle, 2. (i) Human remains after death (ii) Industrial waste (iii) Religious festivals (Any two), 3. E. Coli bacteria, 4. Solar energy and bio-mass are inexaustible resources., 5. Conservation of environment refers to activities which can provide individual or commercial benefits,, but at the same time, prevent excessive use which are leading to environmental damage., 6. Two resources which cannot be recycled are metals and fossil fuels., 7. Two ways to check levels of water pollution is Coliform bacteria and pH, 8. Coliform bacteria are E.coli bacteria which live on organic matter and also found in human intestine., Presence of these bacteria indicates contamination of water by disease causing bacteria., 9. Only rich and powerful will become more and more powerful while others will suffer., 10. Intestine., 11. (i) Recycling of waste (ii) Reuse of waste., 12. Old newspapers, waste paper, plastic, metal, glass can be recycled and reused., 13. Ganga Action Plan (Namami Ganga Project), III. 1. Short term aim means use it today and don’t bother about future., , Advantages:, (i) It fulfills the immediate requirement of people., (ii) It provides industrial growth., (iii) It is needed for economic development., (iv) It leads to comforts in life., 2. Reuse saves energy needed for recycling, therefore it is better than recycling., 3. Two categories of natural resources are renewable and nonrenewable., (i) Renewable resources can be regenerated. For example, products from forests, grasslands, soil,, groundwater, biological species., (ii) Non-renewable sources cannot be regained or reconstructed once they are used up. For example,, fossil fuels, metals, minerals, etc., 4. I think there should be equitable distribution of resources as resources are limited and demand is more., It will ensure distribution to all and not to only rich and powerful., Forces would be working against an equitable distribution of our resources may be political and social, forces., 5. Sustainable development is the form of growth that meets current basic human needs while preserving, the resources for needs of the future generations., To maintain balance between environment and human development, it is necessary to strive for, sustainable development to meet the needs of present generation and conserving it for the future, , 180, , Science-10

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generation. To achieve this we have to consider the different aspects of development. Conservation,, sustainability and biological diversity are interrelated. In order to survive man has to live in harmony, with nature., 6. Causes of water pollution are:, (i) Disposal of industrial wastes, (ii) Dispersion of untreated sewage, (iii) Bathing, washing, (iv) Immersion of ashes., (Any two), Harmful effects are:, , (i) Water born disease, (ii) Consumption of contaminated fishes., (i) R, 7. (i) Paper, , (ii) Sugar, (iii) Paint , (iv) Chemical and fertilizer., 8. Reuse, recycle, and reduce. Reducing wastage is the best out of these., 9. (i) Plastics are non-biodegradable, therefore, disposal becomes difficult, however can be recycled., Burning of polythene creates lot of pollution., (ii) Plastic bags when mixed with soil reduce its fertility and animals eating polythene will die because, these are poisonous., 10. Coal and Petroleum., (i) Carbon dioxide, water, sulphur dioxide, nitrogen dioxide, (ii) Carbon monoxide, nitrogen monoxide., 11. Exploiting natural resources with short term gains in mind will lead to unwanted and excessive use of, resources, that will lead to the depletion of these resources., On the other hand managing our resources with a long term perspective involves judicious use of the, resources that can conserve resources for the future., IV. 1. Population explosion is one of the main causes of environmental imbalance. India’s population has, crossed one billion. In order to meet the basic demands the human beings are forced to encroach upon, forests, mountains, seas, rivers for space and food. They need more cultivable and habitable land. They, kill more animals for food, money and pleasure, cut trees for fuel, timber and paper industry. They use, more fertilizers and pesticides to increase crop production. All these activities of man cause ecological, imbalance and pollution. Population explosion causes physical discomfort which in turn causes mental, tension hence health and social disorders., 2. Advantage of 3R’s policy are:, ,  Reducing pollution of environment by reducing garbage., ,  Reduces stress on industries as they have less demand on them, ,  Save sources for fresh raw materials, ,  Helps save energy demand by industries, ,  Less litter and garbage is generated., V. 1. Exploitation of resources have led to their depletion and pollution. Once people are made aware some, action follow. One such example is Ganga action Plan - A multicore project taken up in 1965 to improve, the quality of Ganga water., Department of environment in December 1984, prepared an action plan for immediate reduction of, pollution load on the river Ganga.There was a need of Ganga action plan as quality of Ganga water, reduced a lot. Ganga water had shown presence of coliform bacteria which are found in human intestine., Presence of these bacteria indicated contamination of water by disease causing bacteria. Pollution of, Ganga water was caused by human activities like releasing domestic and industrial effluents, bathing,, defecating, washing, emerging dead bodies or ashes etc., 2. The 3 R’s are Reduce’ recycle and reuse, , Reduce means using less, (i) Electricity by switching lights and fans not in use., (ii) Water by repairing leakage in taps, using mugs in place of shower or pipes, using water after, bathing or washing utensils to water the plants., (iii) Paper by using its both sides, buying things with less packing material., , Management of Natural Resources 181

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(iv) Food by taking small serving at a time, buying only as much as is needed, not buying too many, luxury items., (v) Carrying shopping bags instead of accepting polythene or paper bags while shopping, (vi) Managing carpools, using bicycle or even walking small distances instead of using individual, vehicles. Nowadays metro service in big cities is helping in this regard a great deal., (vii) Buy appliances which economize energy and fuel consumption, (viii) Buy quality products, which last longer, hence do not get discarded easily., (ix) Make less use of disposal items., , Recycle means converting waste to something useful. It means avoiding wastage of raw material and, energy to produce fresh things. We can recycle, (i) Domestic and farm wastes to produce compost, farmyard manure and biogas., (ii) Metal, plastic, glass and paper can be segregated to be converted to recycled items,, (iii) Leftover food can be converted to tasty snacks., (iv) Card, gift-wraps and other waste can be made into useful and beautiful household items, , Reuse means making something useful even after it has served its actual purpose. Since it means not, wasting least of energy it is better than recycling. Some examples are, (i) Using envelopes, bags, cans, bottles etc. once the product packed in them has been used up., (ii) As far as possible, repair rubber tyres, bicycle and household appliances and use them for longer, instead of buying new ones., (iii) Use the clothes till they can be used in household even they are not being worn. They can be made, into bags, napkins etc., , Topic 2., , Forests and wildlife, Water for all, coal and petroleum, , Biodiversity: It refers to the variety within and between all species of plants, animals microorganisms and, ecosystem within which they live and interact., Hotspots: Those areas which have large number of species of plants, animals are called hotspots, e.g. forests, are hotspots of biodiversity., Stake Holders: Those people having interest or concern for something are called stake holders., Wildlife: It means all naturally occurring animals, plants and their species which are in their natural, environment., Conservation: The protection of natural resources to avoid excessive use and wastage is called conservation., Afforestation: Planting more trees at home, on roads, schools and office building is afforestation, which helps, in cleaning environment., Amrita Devi Bishnoi National Award: It is a national award given to the people who helps in wildlife, conservation., Chipko Movement (Andolan): Women of Garhwal protested against destruction of forests by hugging the, trees, when they were about to cut., Water: Water is necessary for all forms of life., • Rain, river, oceans, lakes, ponds are natural sources of water., • Dams, canals, water pumps are used to get water for irrigation., • River water is purified and supplied to home in urban areas., • People use well water and hand pump, i.e. underground water in rural areas., • In Gulf countries, sea water is made fit for drinking by distillation or reverse osmosis (R.O. purifier), Dams: These are large barriers built across river and stream to confine and utilise the flow of water for, irrigation, domestic purposes and electricity., • They are used to save people from floods., • Tehri Dam is the highest dam in Asia, 260 m high on river Ganga., • Hirakud Dam build across Mahanadi river is the longest manmade dam (about 15 km), in the world., • Sardar Sarovar dam is built on Narmada river., , 182, , Science-10

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• Bhakhra Nangal Dam is Asia’s second highest dam, 225.5 m is built on Sutlej river in Punjab., • Construction of dams may cause some problems too., Rainwater Harvesting: It is the process in which rain water percolate (seeps) under the ground so as to, recharge the underground water., • Rainwater harvesting is being done in urban areas in these days., • Tanks, Tals, Bundhis, Ponds, Bawlis are some ancient methods for conservation of rain water., • It is done traditionally in rural areas all over the country., • There are many advantages of storing the ground water, e.g., (i) It does not evaporate, (ii) It does not get contaminated by human and animal waste, (iii) It provides moisture for vegetation and rain., (iv) It spreads out to recharge wells and underground water, Coal and Petroleum:, • These are non-renewable sources of energy., • Excessive use of these fossil fuels will lead to energy crisis as they are exaustible., • Cost of coal and petroleum is increasing due to more demand., • Coal and petroleum are formed by decomposition of remains of plants and animals under high pressure, and temperature., • It take millions of years in their formation., Harmful effects of Fossil fuels:, • Air pollution: Combustion of coal and petroleum generates CO2, NO2, SO2 which causes air pollution and, acid rain., • Diseases: Air pollution is the cause of respiratory, heart problems, irritation in eyes, headache and, depression., • Global warming: Carbon dioxide, methane, water vapour, nitrous oxide can trap infrared radiations of, sun and causes greenhouse effect which leads to global warming and climate change., Steps to conserve fossil fuels:, • Electric vehicles are better than vehicles run by fossil fuels., • Switch off electric appliances when not in use., • Switch off the engine at red lights while driving., • Proper air pressure in tyres, turning off engines are helpful in saving fuel., • Use LED’s, CFL’s instead of normal bulbs and tube lights., • Use public transport like metro, buses instead of personal vehicles., • Walk or use bicycle for short distances., • Use stairs instead of lift or escalators., • Use solar cooler, solar water heater and solar cells to produce electricity instead of inverter., , Exercise 8.2,  , , I. Objective Type Questions , , (1 Mark), , I. Fill in the Blanks, 1. The bacteria present in contaminated water is _____________., 2. Sanctuaries are established to _____________ ., 3. Red Data book provides a list of _____________ ., 4. Tehri Dam is being constructed on _____________ ., 5. Kulhs system of irrigation is common in _____________ ., II. True or False, 1. Soil and water are non-renewable natural resources. [True/False], 2. Revival of ancient systems of water harvesting is better than big dams. [True/False], , Management of Natural Resources 183

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3. Monoculture forestry is more suitable for industries but it is not good for the environment. [True/False], 4. Control of local people over their own water resources may cause mismanagement and over-exploitation, of these resources. [True/False], 5. The river water is said to be polluted with acidic wastes when the pH of river water above 7. [True/, False], III. Match the following:,    Direction (Q1 and Q2): Match Column I with Column II., 1. Column I Column II, (i) Reduce, (a) Reprocess to make desired things, (ii) Recycle, (b) Use again and again., (iii) Reuse, (c) Sustainable development., (iv) Safe disposal of waste (d) Less use of things., 2. Column I Column II, (i) Himachal Pradesh, (a) Surangams, (ii) Rajasthan, (b) Bandharas, (iii) Bihar, (c) Kulhs, (iv) Karnataka, (d) Khadins, , (e) Kattas, , (f) Ahars, II. Very Short Answer Type Questions , (1 Mark), 1. What is biodiversity?, [DOE], 2. Write the full form of GAP?, 3. Name the person who is remembered for the protection of Khejri trees in Rajasthan., [DOE], 4. Who are called stake holders?, [DOE], 5. Name two exhaustible natural resources., 6. List two measures that you would suggest for the better management of water resources. [Delhi 2014], 7. Give one example each from your daily life where the domestic waste can be effectively reused and, recycled., 8. Write one negative effect of affluent lifestyle of few persons on the environment., , [Delhi 2014], 9. A person lives near a forest. Make a list of four items which he can get from forest to meet his daily, needs., [Delhi 2010], 10. Name the state in which Indira Gandhi Canal has brought greenery?, [Delhi 2015], 11. Mention two renewable sources of energy., 12. Mention the action taken by Government to save river Ganga?, [Delhi 2014], 13. Write the context in which Amrita Devi Bishnoi National award is given?, [Delhi 2014], 14. What are ways to conserve natural resources?, [Delhi 2015], 15. List two advantages of building dams?, [Delhi 2013], 16. List any two industries based on forest produce., [Delhi 2010] [NCERT], 17. Name a programme which was started to avoid alienation of common man from trees. Who started it?, 18. Name the ancient water harvesting structures in Maharashtra., [CBSE 2016], 19. Give one protective function of forest. , [CBSE 2015], 20. Mention any two reasons for failure to sustain underground water., 21. Why do we need alternate sources of energy?, 22. What is meant by bio diversity hot spots’? , [CBSE 2015], 23. State one reason for conservation of forest and wild life., [CBSE 2011, 13], III. Short Answer Type Questions-I , , , (2 Marks), , 1. Write any two ways that you can suggest at home to save water which is a valuable resource?, [Delhi 2013, 2014], , 184, , Science-10

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2. Give two uses of coal., 3. “We need to manage our resources”. List two reasons to justify this statement., [Delhi 2014], 4. What will happen if biodiversity of an area is not preserved? Mention one effect of it., , [Delhi 2015] [HOTS], 5. In what ways poor tribals are affected by dam development projects?, [Delhi, 2016] [HOTS], 6. What changes can you make in your habits to become more environment-friendly?, [Delhi, 2016] [HOTS], 7. What is sustainable developmental? State its two main objectives., [Delhi, 2016] [HOTS], 8. What is water harvesting? What is its importance?, [NCERT], 9. Why do we need to resort to water harvesting when we can just collect rain water and use it?, 10. What are the advantages of groundwater over surface water?, 11. List some traditional ways used by local organizations for water harvesting., 12. Can you suggest some changes in your school which would make it environment friendly?, 13. List any two advantages associated with water stored in the ground., 14. We often observe domestic waste decomposing in the by lanes of our homes. List two ways to make the, residents aware that the improper disposal of wastes is harmful to the environment and also for their, own health., 15. State the main purpose of water harvesting management and mention the source which fills the ponds, besides harvesting structures., 16. Though the Kulhads are made up of clay which is an ecofriendly substances but their use has been, continued in the trains these days. Explain two reasons which lead to discontinuance of this practice., , [CBSE 2015], 17. Industrialisation are one of the major causes of deforestation. State two reasons., [CBSE 2015], 18. Mention the steps taken by west Bengal Govt. to protect badly degraded sal forests., [CBSE 2013], 19. , List two measures to conserve the natural resources of the environment., 20. What is sustainable management? Why is reuse considered better in comparison to recycle?, , [Delhi 2017], 21. Why is sustainable management of natural resources necessary? Why is reuse better as compared to, recycle?, [Delhi 2017], 22. Explain how would the involvement of local people be useful for successful management of forests., , [Delhi 2017], 23. State two advantages of conserving ( ) forests, (ii) wild life., [CBSE 2017], 24. What is meant by wildlife? How is it important for us?, [Delhi 2017], 25. Management of forest and wild life resources is a very challenging task. Why? Give any two reasons., , [Delhi 2017], 26. Explain two main advantages associated with water harvesting at the community level. [CBSE 2017], IV. Short Answer Type Questions-II , , (3 Marks), , 1. After the examination Rakesh with his friends went on a picnic to a nearby park. All friends carried, cooked food packed in plastic bags or plastic cans. After eating the food some friends collected the, leftover food and plastic bags etc and planned to dispose them off by burning. Rakesh immediately, checked them and suggested to segregate the leftover food and peels of fruits from the plastic materials, and respectively dispose them off separately in the green and blue dustbins placed in the corner of the, park., (i) In your opinion, is burning plastic an eco-friendly method of waste disposal? Why? State the, advantage of method suggested by Rakesh., (ii) How can we contribute in maintaining the parks and roads neat and clean?, [Delhi 2015] [HOTS], 2. What are ’biodiversity hot spots’? What is the measure of biodiversity in an area? How is it being, affected?, , Management of Natural Resources 185

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3. What are the reasons of destruction of forests?, 4. Why should we conserve forests and wild life?, 5. Suggest some approaches towards the conservation of forests , [NCERT], 6. Describe the structure of a traditional water harvesting system with the help of a diagram., 7. Name the terms used in different states and languages that is used for water harvesting structures., 8. What changes would you suggest in your home in order to be environment friendly?, 9. Dams are bane or boon? Justify your answer., OR, Give three points to justify that dams can have advantages or disadvantages., 10. What were main reasons behind ‘Ganga Action Plan’ which was initiated in 1985? What values can be, learnt from such plans? , [CBSE 2016], V. Long Answer Type Questions , (5 Marks), 1. How degraded Sal forests of Arabari forest range in Midnapore district were protected? What ways were, followed to save them? Who was the person behind it? What conclusion do you derive from it?, 2. What is the meaning of Chipko Movement? Who started it? State any three objectives of starting it?, 3. We saw in this chapter that there are four main stake holders when it comes to forests and wildlife. Which, among these should get the maximum benefit of forest produce? Why do you think so? , [NCERT], , Answers, I. 1. Coliform 2. Protect 3. Rare, endangered or endemic species 4. Ganga 5. Himachal Pradesh, II. 1. False 2. True 3. True 4. False 5. False, III. 1. (i) (d) (ii) (a) (iii) (b) (iv) (c), , 2. (i) (c) (ii) (d) (iii) (f) (iv) (e), II. 1. The existence of variety of life in a natural ecosystem is called biodiversity., 2. GAP stands for Ganga Action Plan. Nowadays it is named as ‘Namami Ganga Project.’, 3. Amrita Devi Bishnoi, 4. Those people who are affected by a project are called stake holders., 5. Coal and petroleum, 6. (i) Wastewater treatment (ii) Drip irrigation (iii) Avoid leakage, (Any two), 7. Domestic waste should be converted into compost and used in the kitchen garden., 8. Air pollution and acid rain are negative effects on environment by the excessive use of vehicles and, generators., 9. (i) Food, (ii) Fuel (iii) fodder for animals (iv) cotton for making clothes., 10. Rajasthan, 11. (i) Solar Energy, (ii) Wind Energy., 12. Ganga Action Plan to prevent pollution of Ganga., 13. Amrita Devi Bishnoi National award is given for wild life conservation in honour of Amrita Devi Bishnoi, who scarified her life along with 363 others for the protection of Khejri trees in a village of Rajasthan in, 1731., 14. (i) Reduce, (ii) Reuse, (iii) Recycling of non-biodegradable wastes., 15. (i) Dams control floods (ii) They help to produce electricity., 16. (i) Timber (Furniture) industry (ii)Sports good (iii) Paper, (Any two), 17. Chipko movement started by Sunder Lal Bahuguna to avoid alienation of common man from trees., 18. Bandharas and Tals., 19. Forest is habitat of large number of animal and plants which are not found anywhere else. It provides, bio-diversity to our environment., 20., (i) Loss of vegetation cover, (ii) Water demanding crops, (iii) Wastage of water, (iv) Leakage, 21. (i) Increase in demand, (ii) Non-renewable source of energy are limited., I., , 186, , Science-10

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22., 23., III. 1., , , 2., , 3., , 4., 5., , 6., , , , , 7., , , , 8., 9., , 10., , , , , 11., , , , 12., , , , , 13., , 14., , 15., , It is region where there is significant reservoir of biodiversity., Restoring of ecological balance., (i) Use bucket instead of shower., (ii) Use mug for shaving or washing hands instead of running water., (iii) Get repaired all type of leakage in water pipes., (Any two), (i) Coal is used as a fuel., (ii) It is used to make coke which acts as reducing agents., (i) Fossil fuels are limited. Their use must be reduced to meet future needs., (ii) Plant more trees to prevent air pollution and soil erosion. Trees absorb noise and keep the area, cool., Loss of biodiversity will lead to ecological imbalance, e.g. on cutting trees in forest, lions, tigers will not, get food and enter human population and will harm them., (i) Poor tribals lose their fertile land which they use for their livelihood., (ii) They lose their residences and are alloted new places where they start their life all over again., (i) Walk or go to school on bicycle if it is not far way. If it is far away use Metro or school bus instead, of personal car., (ii) Switch off car engine at red light., (iii) Recycle all items which can be recycled., (iv) Reuse the discarded items if possible., (v) Reduce the use of non-renewable sources of energy, e.g. solar energy can be used for heating water., The development which can be maintained for a long time without causing any damage to the, environment is called sustainable development., Two objectives are:, (i) The purpose is to provide comfortable life to people and future generation., (ii) It helps to meet present needs and also saves resources for future needs e.g. metro trains are, making sustainable development for people in Delhi and other states., Water harvesting is a technique to catch every drop that falls on land as rain or snow to recharge, ground water. It helps in conservation of soil and water in order to increase biomass production., Collecting rain water in water bodies is possible only in rainy season but retaining it throughout the, year may not be possible as it will evaporate. It may also get contaminated and mosquitoes may also, breed in it. Groundwater recharged due to water harvesting will be cleaner and available throughout, the year., The advantages of groundwater over surface water are:, (i) Ground water does not evaporate., (ii) Spreads out to recharge wells, provides moisture to vegetation over a wide area., (iii) It does not provide breeding ground for mosquitoes like stagnant water., (iv) It is protected from contamination and pollution by human and animal waste., Some traditional ways used by local organizations for water harvesting are, (i) Digging small pits and lakes, (ii) Simple watershed systems, (iii) Building small earthen dams, (iv) Constructing dykes, sand and limestone reservoirs, (v) Set up rooftop water collecting units., (i) Making a compost pit at the backyard of garden, (ii) Switching on fans and light in the rooms which are not being used, (iii) Throwing organic and recyclable waste in separate bins, (iv) Growing more plants, (v) Using paper on both side., Two advantages of water stored in the ground are:, (i) Recharges the ground water., (ii) Prevents evaporation of water., (i) Distributing leaflets to residents, (ii) Calling meeting and organising waste disposal system., Water harvesting management will recharge ground water and raise underground water level. Monsoon, rain also fills the ponds beside harvesting structures., , Management of Natural Resources 187

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16. (i) Use of clay for making Kulhards removes top fertile soil., (ii) Reuse of Kulhard is unhygnic., 17. (i) Industries consider forest produce as a raw material., (ii) They are not keen for sustainability of forest which is essential for getting raw materials for long, time., 18. (i) Involvement of local people by giving employment in silviculture and harvesting operation., (ii) Collection of fuel, wood and fodder by paying nominal fees., 19. (i) Maintain green grassy patches between concrete building, (ii) Use more of environment friendly (biodegradable) materials., 20. Sustainable management is a resource management technique which aims to conserve the resources, and use them efficiently to avoid their misuse for individual purposes such that they are conserved for, the future., Reuse is better than recycle because of the following reasons:, (i) Recycling needs some processes to use the same material again., (ii) Reuse saves energy by using material again without any changes., (iii) Reuse prevents environmental pollution by not creating any waste., (iv) Reuse saves cost as same material is used again without any process., 21. Natural resources are an integral part of our life. As some resources are exhaustible, non-judicious, use of such resources will lead to their depletion and ultimate banishment, which will affect the life on, Earth. By sustainable use of these natural resources, we are able to conserve our environment. Hence,, sustainable management of resources is very necessary., Reuse is better than recycle because, (i) Recycling needs some energy consuming processes to use the same material again., (ii) Reuse saves energy by using material again without any change., (iii) Reuse prevents environmental pollution by not creating any waste., (iv) It also saves cost as same material is used again without any processing., 22. The involvement of local people will be useful for the successful management of forests in the following, ways:, (i) They should be aware of the fact that diminishing forest cover would disturb the ecological balance., If they show their objection against any such illegal activity that would destroy the forests, it can, lead to a massive effect that will help in management of forests more effectively as it happened, during Chipko Andolan., (ii) Phenomenon forest fires must be reported immediately to the forest officers. The sooner the action, is taken, more the area will be protected. Forest fires purposely caused by local people must not be, practiced., 23. There are innumerable advantages of conserving forests, such as:, (i) It supports life, helps in maintaining the quality of air, water and basic essentials of existence of, life., (ii) Stability in soil is possible by trees. It enables the land based plants and animals to live., (iii) Forests also supply raw materials to many industries, such as wood, spices, medicinal herbs, etc., , (Any two), Advantages of conserving wildlife:, (i) It helps in maintaining ecological balance and biodiversity., (ii) We depend upon wildlife for food, clothing, medicines and many other products., 24. All the living forms, including both plants and animals that live in their natural environment, i.e., forests is wildlife., Wildlife is of great importance for us:, (i) It maintains the ecological balance of the nature., (ii) It provides us with many useful resources., 25. Management of forest and wildlife resources is considered as a challenging task because:, (i) There are many stakeholders of forest. They are those people who are directly or indirectly involved, in forest. Management of forest and wildlife has to take into account the interests of all these, stakeholders which become a challenging task., , 188, , Science-10

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(ii) Industries would consider the forest as merely a source of raw material for its factories and huge, interest-groups lobby the government for access to these raw materials at artificially low rates, which further poses a challenge to manage the forest and wildlife resources., 26. Two advantages associated with water harvesting at community level are:, (i) Water harvesting is an ideal solution to water problems in areas having inadequate water, resources. It mitigates the effect of drought., (ii) It improves the quality of water and helps in raising groundwater level., IV. 1. (i) No, burning plastic creates lot of pollution and has health hazards., Rakesh separated biodegradable and non-biodegradable wastes which saves time and energy for, separation in green and blue dustbins respectively. Green dustbin waste is sent to compost forming, unit or waste to energy conversion plant whereas wastes from blue dust bin is sent for recycling., (iii) We should not throw anything in the park. We should not use polythene., 2. Forests are a store house of biodiversity (hotspots of biodiversity). One measure of biodiversity of, an area is the types and number of species found there. Biodiversity of an area is being affected by, destruction of forests., 3. Forests are destroyed:, (i) For Cultivation of crops (Deforestation.), (ii) For firewood, charcoal, mineral ores, timber, bamboo, fodder and raw materials for paper, rubber, and other forest products like gum, resin, medicinal plants, spices, oils, ‘etc. Due to extensive, deforestation animals and birds migrate to other places or die of hunger and their number, decreases., (iii) Because of water, land and air pollution caused by industries resulting in the death of wild animals, and plants., (iv) Because of urbanization (building cities and establishment of estates) leads to the death of wildlife., (v) Because of forest fires, heavy floods, etc. kill the wildlife, extensive hunting of animals for food,, money and luxury items decreases the number of wildlife., 4. (i) Forests purify the air and also prevent pollution of air., (ii) Forests regulate the climate by maintaining the level of rainfall necessary for their own existence., (iii) Forests also provide rubber, wood, timber, fuel, wood, paper, fodder, gum, resin, kattha, edible, fruits and medicinal plants for industries as well as local people., (iv) Forests serve as a source of income to tribal societies even today, 5. Following steps should be taken to conserve forests:, (i) Silviculture is one of the major programme started to replenish forests. Some of the benefits, achieved through this programme are, • It has helped in preserving the environment by bringing more and more area under forests, • It produces large quantities of raw materials for various industries, (ii) Afforestation should be there in the areas which are unfit for agriculture, along the highways and, rivers, (iii) Awareness programme should be there. A special programme of tree plantation called Van, Mahotsava is held every year in our country. It should be made more popular., 6., , Traditional water harvesting system – an ideal setting of the khadin system, , Management of Natural Resources 189

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In largely level terrain, water harvesting system are generally crescent shaped, earthen embankments, or low, straight, concrete- and rubble check dams built across a seasonally flooded gullies. Monsoon, rains fill the ponds behind structures. Only the largest structure hold the water year round. Most of, them dry up six months or less after the monsoon., 7. The terms used in different states and languages that is used for water harvesting structures, (i) Khadins, tanks and nadis, –, Rajasthan., (ii) Bandharas and tals, –, Maharashtara, (iii) Bundhis , –, MP and UP, (iv) Ahars and pynes, –, Bihar, (v) Kulhs , –, HP, (vi) Ponds , –, kandli belt of Jammu, (vii) Eris , –, Tamilnadu, (viii) Surangams , –, Kerala, (ix) Kattas , –, Karnatatka., 8. Changes that I would suggest at my home in order to be environment friendly are, (i) Using a jute bag instead of plastic or polythene bag., (ii) Switching off fans and light in the rooms which are not being used, (iii) Avoiding AC as far as possible and using fans or coolers., (iv) Using water again and again like water after washing vegetable can be used to water the plants., (v) Recycling clothes till they can be used for different purposes, (vi) Throwing organic and recyclable waste in separate bins, 9. Dams are useful in producing hydroelectricity, fishing, irrigation and tourism , If their construction is not planned properly it may lead to, (i) Economic problems (ii)Ecological problems, (iii) Social problems, Example: Tehri Dam, Tawa Dam., 10. Main aims of Ganga Action Plan were:, (i) To improve quality of river water, (ii) To check growth of E.coli bacteria and other micro-organism., (iii) To prevent disposal of industrial, domestic, sewage waste., (iv) To prevent immersion dead remains of humanbeings., Values:, (i) Conservation of most important natural resource i.e. water., (ii) Preservation of cultural values, (iii) Cleanliness, V. 1. In 1972, West Bengal forest department recognized its failures in the revival of the degraded sal forest, in southwestern districts of the state. This had led to alienation of people by the administration. Result, was clash between forest officials and villagers. These conflicts were major factor in fueling the militant, peasant movements led by the nexalities. Later the department changed its strategy. In the Arbari, forest range of Midnapore district, far seeing forest officer A.K. Banerjee and villager got involved in the, protection of 1,272 hectares of badly degraded Sal forest., (i) Villager were given employment in the programme of replenishment of forests i.e., silviculture, and harvesting operations, (ii) 25 percent of the final harvest., (iii) Allowed fuel, wood and fodder collection on payment of nominal fee., As a result of active participation of people mainly the local community, the Sal forests of Arbari, underwent recovery by the year 1983., From above example we can reach to the conclusion that by keeping local people out and using forests, cannot prove to be successful in the long run. Forest has to be used sensibly keeping both environment, and development sound., 2. Chipko movement i.e. “hug the trees movement” is one of the movements in India to conserve biodiversity, and to end the alienation of people from their forests which started in March 1973. Sunder lal Bahuguna, of Tehri and Chandi Prasad Bhatt of Gopeshwar are prominent leaders of this movement. It was, Sunderlal Bahugana who was able to transfer ecological perspective to Chipko Movement are:, (i) To protect existing forest cover., , 190, , Science-10

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3., , , , (ii) Afforestation, (iii) To utilize forest wealth keeping in mind its conservation., (iv) Leaders of Chipko movement believes in food, fodder, fuel, fertilizers and fibers, Stakeholders are:, (i) People living in or around forests who are fully dependent on forests for their life, (ii) The forests Department of Government, owners of the land are working to control the resources, from forests, (iii) The industrialists using forest produce but not dependent on the forests in any one area., (iv) People involved in wild life and nature conservation., Each of the above groups depends on forests in a different way, I. Local people Around Forests Used, (i) Use of bamboo to make huts, (ii) Use of baskets for collecting and storing food materials, (iii) Use of wood to make implements for agriculture, fishing and hunting, (iv) Do fishing and hunting for forest, (v) Gather fruits, nuts and medicines from forests, (vi) Graze cattle in forests, These people lived in forests for centuries and ensured sustainable use of resources, II. The forest department of government, (i) Later British took over most of the forest areas and exploited forests ruthlessly for their needs, (ii) Local people were forced to depend on smaller areas, (iii) Forests started becoming over exploited due to monoculture (growing same crop again and again, on a piece of land)., (iv) After India became independent, forest department took over, (v) Management practices ignored local needs and knowledge, (vi) Large areas were cleared and were converted to monoculture of pine, teak or eucalyptus., (vii) This lead to destruction of biodiversity in the area, (viii) Needs of local people could no longer be met from such forests, (ix) But these plantations worked as an important source of revenue for the forest of department, (x) These plantations are being used by industrialists to reveal timber, paper, lac and sports equipment., III. The industrialists, (i) Forests provide raw material for various industries, (ii) Industrialists have access to these raw materials at artificially low rates, (iii) Industries have greater reach than local people, (iv) Industrialists are not interested in sustainability of forests, (v) After cutting teak trees in one area, they shift to another., They do not ensure that one particular area should yield optimal amount of some produce for all coming, up generations., IV. Nature and wildlife enthusiastic, (i) They are not dependent on the forests, (ii) They have realized the need to preserve bio-diversity, (iii) For example, Bishnoi community in Rajasthan take forests and wildlife conservation as a religious, tenet, Out of all stakeholders, local people should be involved in management of forests and get maximum, benefit from them as they look after them as their own sustenance is dependent on them., , Management of Natural Resources 191

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Common Errors, Errors, , Corrections, , • Students are not able to differentiate between ☞ Renewable can be used again and again. Nonrenewable and non-renewable., renewable will get exhausted if their demand keep, on increasing., • Students do not know how to save water., , ☞ Saving water is essential. Leakage must be stopped., Vehicles should be washed with used water. Use, bucket instead of shower., , • Students feel there are no disadvantages of ☞ There are disadvantages of dams children should, dams., read and learn about it., • Students do not understand the importance of ☞ It is the best way to restore underground water, Rain water harvesting., level., • Students do not know how to dispose off waste ☞ Children should separate biodegradable and nonmaterials properly., biodegradable wastes and collect them in separate, bins. Biodegradable waste is used to make compost, and non-biodegradable waste is reused and recycled., , Assignment, I. Very Short Answer Type Questions , 1., 2., 3., 4., 5., , (1 Mark), , Mention the two areas emphasized by watershed management., Why are diesel vehicles 15 years old or more are banned in Delhi?, Why is biodiversity. Essential?, List any two traditional systems of water harvesting., Name two industries which are affected due to fast depletion of forest resources., , II. Short Answer Type Questions-I , , (2 Marks), , 6. Coal produces energy on burning, but we do not get energy by eating it while eating an apple gives us, energy. Explain why is it so., [HOTS], 7. You being an environmentalist is interested in contributing towards the conservation of natural, resources. List four activities that you can do on your own., [Delhi 2017], 8. List any four suggestions you would recommend to your friends to make them more environment, friendly., III. Short Answer Type Questions-II , , (3 Marks), , 9. What are dams? Give two advantages and two disadvantages of dams., 10. Discuss three ways for safe disposal of waste materials., 11. (a) Water is an elixir of life, a very important natural resource. Your science teacher wants you to, prepare a plan, “How to save water, a vital resource”. Write any two ways that you will suggest to, bring awareness in your neighborhood on how to save water., (b) Name and explain any one way by which underground water table does not go down further., (c) State one advantage of disposable paper cups over disposable plastic cups., [Delhi 2017], 12. Explain why does need to manage our natural resources?, [Delhi 2017], 13. Fresh water, forest products and clean air are for everyone. We must have equal right over them. But, everyone is not getting their share. If no then what are the forces working against it., IV. Long Answer Type Questions , , (5 Marks), , 14. In Rajasthan, unlike earlier people do not face so much shortage of ground water. How has it been made, possible. Discuss the role of gram panchyats and villagers in bringing about this change., 15. How does people’s participation may save a precious natural resources. Elaborate on it by taking a, suitable example., , 192, , Science-10

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Sample Paper–1, Time: 2 Hours, , Maximum Marks: 40, , General Instructions:, There are total 15 questions and four sections in the question paper. All questions are compulsory., , Section-A, I. Case Study Question (3 Marks), 1. Modern periodic table has 18 vertical columns known as groups and 7 horizontal rows known as periods. First period contains 2 elements second and third period contain 8 elements. 4th and 5th period, contains 18 elements and 6th and 7th period contains 32 elements. The graph is plotted between atomic, number and atomic radius of group 17 and group 1 elements., , (i) Which group elements will have largest atomic size?, (ii) Which group elements will gain electrons to form negative ions?, (iii) Which element in group 17 has smallest size?, , 1, 1, 1, , Ans. (i) Group 18   (ii) Group 17   (iii) Fluorine, , Section-B, II. Very Short Answer Type Questions (1 Mark), 2. Name two infectious diseases which can be sexually transmitted in human being., Ans. (i) AIDS  (ii) Gonorrhea, 3. What is unit of electric current?, Ans. Ampere., 4. What is principle on which electric motor works?, Ans. When rectangular coil is placed in magnetic field and current is passed through it, coil experiences, torque which rotates it continuously., , 1, 1, 1, a, , Section-C, III. Short Answer Type Questions (2 Marks), 5. How does electronegativity varies along a period and why?, 2, Ans. Electronegativity increases along a period from left to right. It is because atomic size decreases, tendency, to gain electron increases., 6. What is heredity? Name the plant on which Mendel performed his experiments., 2, Ans. The continuity of characteristics (traits) from one generation to another is called heredity. Mendel, performed his experiments on the plant, Pisum Sativum, the garden pea plant., , 193

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7. Mention the mode of reproduction used by, 2, (i) Amoeba, (ii) Planaria, Ans. (i) Amoeba reproduce by binary fission., (ii) Planaria reproduces by regeneration., 8. If you connect three resistors having values 2 W, 3 W and 5 W in parallel, calculate the equivalent, resistance., 2, Ans., , 1, 1, 1, 1, 1 1 1, +, +, = + + = 15 + 10 + 6 = 31, =, R, R1 R 2 R 3 2 3 5, 30, 30, , 30, = 0.967 Ω, 31, 9 Give an example of natural and an artificial ecosystem., , R =, , 2, , Ans. Natural ecosystem: Forest or pond, , Artificial ecosystem: Aquarium, , Section-d, IV. Short Answer Type Questions (3 Marks), 10. (i) Why is ozone layer getting depleted in stratosphere?, (ii) Name any two abiotic components of environment., 3, , (iii) Why are green plants called producers?, , Ans. (i) Chlorofluorocarbons (CFCs) from fire extinguishers and refrigants, nitrogen monoxide released by, jets and aeroplanes cause depletion of ozone layer., (ii) (a) Climatic factor (light, temperature, rain fall)., (b) Soil and its condition, (iii) It is because they can synthesise organic food from CO2 and H2O in presence of sun light (photosynthesis). This food is used by green plants and also other organisms called consumers., 11. (i) Draw a closed circuit diagram consists of 1 m long nichrome wire XY, an ammeter, a voltmeter, four, cells of 1.5 V each and a plug key., (ii) The values of current I flowing in a given resistor for the corresponding values of potential difference, V across the resistor are given below :, I (amperes), , 0.5, , 1.0, , 2.0, , 3.0, , 4.0, , V (volts), , 1.6, , 3.4, , 6.7, , 10.2, , 13.2, , Plot a graph between V and I and calculate the resistance of that resistor., Ans. (i), , 194, , Science-10, , 3

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(ii) The slope of the graph is equal to the resistance.,               R = Change in V = ∆V = 13.2 − 1.6, Change in I, ∆I, 4 .0 − 0 .5,              R = 11.6 = 3.314 Ω, 3 .5, , 12. (i) What is fertilisation? Distinguish between external and internal fertilisation., (ii) What is the site of fertilisation in human beings?, 3, Ans. (i) Fertilisation is a process in which fusion of male gamete (sperm) with a female gamete (an ovum), takes place to form a zygote during sexual reproduction., , External fertilisation, (i), , Internal fertilisation, , The formation of zygote takes, place outside the body., , (i), , (ii) Development occurs outside the, body where individual discharge, gametes. e.g. Frog., , The formation of zygote takes place, inside the body, , (ii) Development occurs inside the, body after male discharges sperms, in female genital tract. e.g. Human, being., , (ii) The site of fertilisation is fallopian tube of female in human being., , Section-E, V. Long Answer Type Questions (5 Marks), 13. (i) Write electronic configuration of carbon. How does carbon becomes stable in compounds?, (ii) What is meant by homologous series?, (iii) What is difference between successive members of homologous series in terms of mass and number, of atoms?, (iv) Draw electron dot structures of: (a) C2H4 (b) NH3, 5, Ans. (i) Carbon has electronic configuration 2,4 ., It can share 4 electrons to become stable and forms covalent bonds., (ii) Homologous series is series of organic compounds having same general formula and functional group., They have similar chemical properties but gradation is in physical properties., (iii) Each successive members differ by —CH2 in terms of atoms and 14u in terms of mass., (iv) (a) C2H4, , (b) NH3, , OR, , Sample Paper-1 195

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(i) Why does carbon not form C4+ and C4– ion?, (ii) Write first 2 members of alkyne homologous series., (iii) The molecular formula of ‘A’ C10H18 and ‘B’ is C18H36. Name the homologous series to which they, belong., (iv) Which part of organic compound determines its chemical properties?, (v) Which part of organic compound determines its physical properties?, Ans. (i) Carbon cannot lose 4 electrons because very high energy is needed. Carbon cannot gain 4 electrons, because 6 protons cannot hold 10 electrons., (ii) HC≡CH, Ethyne, HC≡C—CH3 Propyne, (iii) ‘A’ belongs to alkynes,‘B’ belongs to alkenes., (iv) Functional group determines chemical properties., (v) Alkyl group determines physical properties., 14. What do you understand by the following terms:, (i) Phenotype, (iii) Dominant trait, , (ii) Genotype, (iv) Recessive trait, , (v) Factors or Genes , , 5, , OR, (i) If we cross pure-bred tall (dominant) pea plant with pure bred dwarf (recessive) pea plant, we will, get pea plants of F1 generation. If we now self cross the pea plant of F1 generation, then we obtain, pea plants of F2 generation., (a) What do the plants F1 generation look like?, (b) State the ratio of tall plants to dwarf plants in F2 generation., (c) State the type of plants not found in F1 generation but appeared in F2 generation giving reason., (ii) A study found that children with light-coloured eyes are likely to have parents with light-coloured, eyes. On this basis, can we say anything whether the light eye colour trait is dominant or recessive?, Why or why not?, Ans. (i) P,  henotype: The set of characteristics observed in an individual as a result of interaction of its, genotype with the environment., (ii) Genotype: The genetic make up of the cell which determines the characteristics (phenotype) of an, organism., (iii) Dominant trait: The trait of the parent that expresses itself in the offspring., (iv) Recessive trait: The trait of the parent appearing in the offspring which cannot express itself in, the presence of dominant trait., (v) Factors or Genes: The units of inheritance responsible for a trait in an individual., OR, (i), , (a) All plants of F1 generation will be tall plants., , (b) 3 : 1, (c) Dwarf trait is recessive trait which was not expressed in F1 generation but it gets reflected in, F2 generation after self pollination., (ii) We cannot predict because information is not sufficient. We can decide dominant or recessive trait, if we have the data for at least three generations. More information is required., 15. (i) What are magnetic field lines? Justify the following statements:, (a) Two magnetic field lines never intersect each other., (b) Magnetic field lines are closed curves., , 196, , Science-10

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(ii) Why and when does a current carrying conductor kept in a magnetic field experience force? Give, factors on which direction of force depends., 5, OR, (i) How is strength of magnetic field near current carrying conductor:, (a) related to strength of current in the conductor?, (b) is affected by changing the direction of flow of current in conductor?, (ii) Identify the poles of the magnet as shown in the given figure:, , (iii) Draw a diagram to represent the uniform magnetic field in the region around the magnet., Ans. (i) The closed path traced by the unit North pole (imaginary) in a magnetic field are called magnetic, field lines., (a) If magnetic field lines intersect, there will be two different direction of same magnetic field,, which is not possible., (b) They diverge from north pole of magnet and converge at the south pole, therefore form closed, curves., (ii) The drifting of free electrons of a conductor in a definite direction causes current to flow through it, when it is placed in uniform magnetic field, each drifted electron experiences a magnetic force., The direction of magnetic force depends upon:, (a) direction of current through the conductor., (b) direction of magnetic field., OR, (i), , (a) The strength of magnetic field increases with increase in strength of current., , (b) The direction of magnetic field is reversed if direction of current is reversed., (ii) A1 represents North pole and B1 represents South pole., (iii), , qqq, , Sample Paper-1 197

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Sample Paper–2, Time: 2 Hours, , Maximum Marks: 40, , General Instructions:, There are total 15 questions and four sections in the question paper. All questions are compulsory., , Section-A, I. Case Study Question (3 Marks), 1. Study the table related to sex ratio at birth of females/1000 males in different states UTs based, on sample registration system and answer the questions that follow:, State/UT, , 2012-14, , 2013-15, , Andhra Pradesh, , 919, , 918, , Assam, , 918, , 900, , Bihar, , 907, , 916, , Chhattisgarh, , 973, , 961, , Delhi, , 876, , 869, , Gujarat, , 907, , 854, , Haryana, , 866, , 831, , Himachal Pradesh, , 938, , 924, , Jammu & Kashmir, , 899, , 899, , Jharkhand, , 910, , 902, , Karnataka, , 950, , 939, , Kerala, , 974, , 967, , Madhya Pradesh, , 927, , 919, , Maharashtra, , 896, , 878, , Odisha, , 953, , 950, , Punjab, , 870, , 889, , Rajasthan, , 893, , 861, , Tamil Nadu, , 921, , 911, , Uttar Pradesh, , 869, , 879, , Uttrakhand, , 871, , 844, , West Bengal, , 952, , 951, , India, , 906, , 900, , , (i) Name the state which has males to female ratio to maximum extent in 2012-14., (ii) What is major cause of less females than males in India?, , (iv) Which state of India has lowest sex ratio in 2013-15?, Ans. (i) Kerala   , (ii) Female Foeticide  (iii) Haryana, , 198, , 1, 1, 1

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Section-B, II. Very Short Answer Type Questions (1 Mark), 2. Why are seeds called products of sexual reproduction?, 1, Ans. Seeds are formed by fusion of gamete that is why called products of sexual reproduction., 3. Mention two reasons why tungsten is used for making filaments of electric lamps., 1, Ans. (a) High resistivity, (b) High melting point, 4. Fan works on electric motor. What is principle of electric motor?, 1, Ans. It is used on magnetic effect of current. A current carrying conductor produces a magnetic field around, it., , Section-C, III. Short Answer Type Questions (2 Marks), 5. (i) Write the molecular formula of an alkyne containing 10 atoms of hydrogen., (ii) Why CH3OH, C2H5–OH, C3H7OH belong to homologous series?, 2, Ans. (i) C6H10, (ii) It is because they have same functional group., 6. Distinguish between biodegradable and non-biodegradable pollutants. Give one example of each., 2, Ans. Biodegradable pollutant can be broken down into non-poisonous substance by action of micro-organisms, Whereas those pollutants which cannot be degrades to harmless substances by nature (micro-organisms), are non-biodegradable., Sewage and agricultural waste are biodegradable., DDT, radioactive waste are non-biodegradable., 7. How does fuse wire protects electrical appliances?, 2, Ans. When large amount of current flows through the circuit, temperates of the wire increases and fuse wire, gets melted. It prevents the flow current in other circuits of the house by breaking the circuit and saves, electrical appliances., 8. What are acquired traits? Why acquired traits are not inherited?, 2, Ans. Acquired traits are those which are developed in the organisms during their life time. These traits are not, inherited because these do not involve reproductive tissues or gene which transfers genetic characteristics., 9. Name the various types of asexual reproduction. What is meant by vegetative propagation?, 2, Ans. (i) Fission (ii) Budding (iii) Spore formation (iv) Regeneration, Vegetative propagation is a process in which vegetative parts like roots, stem and leaves develops into, new plants under appropriate conditions. It can occur naturally or be involved by horticulturists., , Section-d, IV. Short Answer Type Questions (3 Marks), 10. (i) Why are covalent compounds generally poor conductor of electricity?, (ii) Why does carbon forms large number of compounds?, (iii) Which of the following organic compounds belong to same homologous series?, 3, CH4, C2H6, C2H4, C2H6O2, CH4O, Ans. (i) It is because these are non-polar and do not form ions., (ii) It is due to tetravelency and catenation property., (iii) CH4 and C2H6 belong to alkanes., C2H6O2 and CH4O belong to alcohols., 11. Explain why is a food chain consists of few steps only. Write a food chain having five steps. Mention, producer, secondary and tertiary consumer., 3, Ans. Food chain has only few steps because energy decreases at each successive trophic level due to which, less energy in available for further level. If food chain has 6 steps, energy available at 6th step will not, be sufficient for survival of organisms of 6th trophic level., , Sample Paper-2 199

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Vulture (Tertiary consumer), ↑, Snake (Secondary consumer), ↑, Frog (Secondary consumer), ↑, Grasshopper (Primary consumer), ↑, Plants (Producer), 12. Find the current drawn from the battery by the network of four resistors as shown in the figure., , 3, , Ans. R1, R2, R3 are in series combination and R4 is in parallel combination to these combination of resistors., Equivalent resistance of the given network is given as:, 1, 1, 1, +, , =, R, R 4 R1 + R 2 + R 3, , , =, , 1, 1, 1, 1, 3+1, 4, +, =, +, =, =, 10 10 + 10 + 10 10 30, 30, 30, , 30, = 7 .5 Ω, 4, Current drawn from the battery, \, , R=, , , , I=, , V, 30 2, 3, =, =, =, R 7.5 75 5, , ⇒ I = 0.4 A, , Section–E, V. Long Answer Type Questions (5 Marks), 13. (i) Why should we classify elements?, (ii) How many groups and periods are there in periodic table?, (iii) Why is position of isotope not disputed in modern periodic table?, (iv) What is the cause of periodicity of properties in periodic table?, 5, , (v) Name the type of elements present on zig-zag line between metals and non-metals., OR, The position of certain elements in the Modern Periodic Table are shown below:, Group, →, , 1, , 2, , 3 to 12, , 13, , 14, , 15, , 16, , 17, , 18, , ↓Period, 1, , G, , 2, , A, , 3, , 200, , H, I, D, , Science-10, , B, E, , C, F

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Using the above table answer the following questions giving reasons in each case:, , (i) Which element will form only covalent compounds?, (ii) Which element is a non-metal with valency 2?, (iii) Which element is a metal with valency 2?, (iv) Out of H, C and F which has largest atomic size?, (v) To which family does H, C and F belong?, Ans. (i) It helps in studying 118 element by studying properties of few groups and few periods., (ii) There are 18 groups and 7 periods., (iii) Isotopes differ in atomic mass but not in atomic number thus their position is not disputed., (iv) It is due to recurrent similar electronic configuration., (v) Metalloids (Semi metals), OR, (i) E will form only covalent compounds., (ii) B is non-metal with valency 2., (iii) D is metal with valency 2., (iv) ‘F’ has largest atomic radius., (v) It belongs to noble gases., 14. (i) Who provided exchanges of DNA as genetic material?, (ii) Explain the Mendel’s concept of heredity, by giving three points., (iii) A man with blood group ‘A’ marries a woman with blood group ‘O’ and their daughter has blood group, O. Is this information enough to tell you which of the traits-blood group A or O is dominant? Why, or why not? , 5, OR, (i) Where are genes located? What is the chemical nature of genes?, (ii) ‘DNA is the carrier of the genetic information’. Justify., Ans. (i) Mendel, (ii) (a) Mendel worked on pea plant., (b) He found that traits are controlled by genes which come in pairs., (c)  Genes are inherited as separate units, one from each parent., (iii) The information is not sufficient because information is confined upto two generation. We need, information about third generations to predict the dominant trait., OR, (i) Genes are located on chromosomes at fixed positions. They are made of nucleic acid (DNA) therefore, acidic in nature., (ii) Most of the characters or traits of an organism are controlled by the genes. Genes are actually, segments of DNA guiding the formation of proteins by the cellular organelles. These proteins may, be enzymes, hormones, antibodies, and structural components of different types of tissues. In other, words, DNA (genes) is responsible for structure and functioning of a living body. Genotype of an, individual controls its phenotype., In human beings there are 23 pairs of chromosome. We inherit half of our chromosomes (genes) from, our two parents. This means half of DNA in each cell has been inherited from each parent, hence we, resemble both of them or their side of family members., 15. (i), (ii), (iii), (iv), , How do magnetic field lines move inside the magnet?, How is relative strength of magnetic field lines can be determined?, By which instrument presence of magnetic field determines?, Which rule help in defining the direction of current in a straight current carrying conductor?, , (v) How is direction of electron movement is determined in solenoid?, , 5, , Sample Paper-2 201

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OR, Describe an activity to show that the magnetic field lines produced when current is passed through the, circular coil. Explain with the help of diagram., Ans. (i) Magnetic field line will move from south pole to north pole inside the magnet., (ii) The strength of magnetic field is determined by closeness of magnetic field lines., (iii) Magnetic needle (compass), (iv) We can use the right hand thumb rule for polarity i.e direction of current., (v) The direction of movement of electron is opposite to current, determined by left hand thumb rule., OR, (i) T,  ake a rectangular cardboard having two holes., (ii) Insert a circular coil through these holes, normal to the plane of, paper., (iii) Connect the ends of coil in series with a battery, and key., (iv) Sprinkle iron filings uniformly on the cardboard., (v) Plug the key., (vi) Tap the cardboard gently a few times. Note the pattern of the, iron filings., (vii) The pattern of magnetic field lines will be same as the pattern, of iron filings., Observations, • Iron fillings are arranged in form of concentric circles., • The circles become larger as we move away from wire., • At center of loop, lines are perpendicular to the plane of loop., Conclusion, • The concentric circle at every point represent magnetic field around it., • Magnetic field lines close to the axis of loop is perpendicular to the coil and loop and converging on, the center of loop., • Magnetic field lines keep on diverging as we move away from the center of the loop., , qqq, , 202, , Science-10

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Sample Paper–3, Time: 2 Hours, , Maximum Marks: 40, , General Instructions:, There are total 15 questions and four sections in the question paper. All questions are compulsory., , Section-A, I. Case Study Questions., 1. Ohm’s law gives the relationship between current flowing through a conductor with potential difference, across it provided the physical conditions and temperature remains constant. The electric current flowing in a circuit can be measured by an ammeter., , Potential difference is measured by voltmeter connected in parallel to the battery or cell. Resistances can, reduce current in the circuit. A variable resistor or rheostat is used to vary the current in the circuit., , , (i) What type of conductor is represented by the following graph? , , 1, , Current, , I, , V, Voltage, , , (ii) What type of conductors are represented by the following graph? , , 1, , Current, , I, , V, Voltage, , (iii) What is the slope of graph in (i) equal to? , , 203, , 1

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Ans. (i) Ohmic conductor like copper, , (ii) Non-ohmic conductor like metal filament,    , (iii) Resistance, , Section-B, II. Very Short Answer Type Questions (1 Mark), 2. Name the part of stamen where pollen is produced., , 1, , Ans. Anther., 3. What will happen when magnet is freely suspended?, , 1, , Ans. It will always align towards north south-direction., 4. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?, , 1, , Ans. Energy consumed by 250 W TV in 1 h = 250 × 1 = 250 W h, Energy consumed by 1200 W toaster in 10 minutes = 1200 × 10 = 200 W h, 60, Here total energy consumed by the TV is more than toaster., , Section-C, III. Short Answer Type Questions (2 Marks), 5. (i) How many covalent bonds are present in ethane?, (ii) Write structural formula of cyclic hydrocarbon (saturated) contain six carbon atoms., , 2, , H H, | |, Ans. (i) There are 7 covalent bonds in ethane, H— C — C —H, | |, H H, HH HH, , C C, H, H, C, C, (ii), H, H, C C, HHHH, 6. (i) Name the part of Bryophyllum where buds are produced for vegetative propagation., (ii) Name the method by which hydra reproduces. Is this method sexual or asexual?, , 2, , Ans. (i) Leaf notches of Bryophylum are involved in vegetative propagation., (ii) Hydra reproduce by Budding. It is an asexual reproduction., 7. Sex determination in man depends upon 23rd pair of chromosomes, called the sex chromosomes. If it, were a homologous pair-XX, it would be a female. If it were a heterologous pair – XY, it would be a male., Based on this statement, answer these questions:, , (i) How many types of eggs/ova and how many type of sperms female and male human being will, produce respectively ?, (ii) Which parent’s contribution of sex chromosomes determines sex of the child?, , 2, , Ans. (i) Male produces two genetic types of sperms, half with X and other half with Y chromosome. The, female produces only one genetic type of ova, all carrying X chromosome., (ii) Sex of children will be determined by what they inherit from their father, and not from their mother., , 204, , Science-10

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8. State the rule which determines the direction of force experienced by a current carrying straight conductor, placed in perpendicular magnetic field., 2, Ans. Fleming’s Left hand Rule., It states that ‘if we stretch the left hand such that all the three are at 90° (perpendicular) to each other), then the thumb represents the direction of force, middle finger represents magnetic field and index finger, gives direction of current., 9 In the given food chain if the amount of energy at fourth trophic level is 4 kJ, what will be the energy, available to that of first second and third trophic level?, 2, Ans. First trophic level will have 4000 kJ., 10, = 400 kJ, 100, 10, = 40 kJ, Third trophic level will have 400 ×, 100, 10, = 4 kJ, Fourth trophic level will have 40 ×, 100, Second trophic level will have 4000 ×, , Section-d, IV. Short Answer Type Questions (3 Marks), 10. (i) Write general formula of alkyne homologous series., (ii) Draw electron dot diagram of N2., 3, , (iii) Why diamond is a poor conductor of electricity?, Ans. (i) CnH2n–2 is general formula of alkynes., (ii), , It has triple bond, (iii) Diamond does not have free electrons because each carbon atom forms covalent bonds with other, four carbon atoms., 11. (i) What is food web?, , (ii) Why is it necessary to manage our garbage?, , (iii) How is ozone formed in stratosphere?, 3, Ans. (a) The interconnection of food chains form a food web., (ii) Healthy living needs clean surroundings. Hence, it is essential to manage our garbage properly so, as to avoid communicable disease., UV, , , (iii) Ozone is formed from oxygen in stratosphere with the help of U.V. light 3 O2 ( g) , ,  2 O3 ( g), , 12. (i) Give four differences between self pollination and cross pollination., (ii) Why is temperature of scrotal sac 2°C less than the body temperature?, Ans. (i), , Self pollination, , 3, , Cross pollination, , (i), , It occurs within flowers of same plant, , (i), , It occurs between two flowers of different, plants of same species., , (ii), , External agency is not involved., , (ii), , Insects, water, wind is involved in pollination., , (iii), , Pollen grains occur in small numbers., , (iii) Pollen grains are produced in large numbers., , (iv), , Flowers do not produce sector so do not, attract insects., , (iv) Flowers produce sector and attract insects., , Sample Paper-3 205

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(ii) Scrotal sac temperature is less by 2° because sperms are safe at a little lower temperature than body, temperature. It is outside the body that is why it has lower temperature than body., , Section-E, V. Long Answer Type Questions (5 Marks), 13. (i) How does metallic character vary down the group?, (ii) Name two elements which belong to first period of periodic table., (iii) How many elements are present in 4th period of periodic table., (iv) How does reactivity vary down the group 17?, (v) Out of Li, K, Na which one is most reactive and why?, , 5, , OR, An element ‘X’ has atomic number 12 and ‘Y’ has atomic number 17., (i) Write the electronic configuration of X and Y., (i) To which groups ‘X’ and ’Y’ belong?, (ii) What is the valency of ‘X’ and ‘Y’?, (iv) Out of ‘X’ and ‘Y’ which one is metal and when one is non-metal?, (v) Which is larger in size among ‘X’ and ‘Y’?, Ans. (i) Metallic character increases down the group., (ii) Hydrogen, Helium., (iii) 18 elements are present in 4th period., (iv) Reactivity goes on decreasing down the group 17., (v) K is most reactive due to larger atomic size, least effective nuclear charge, it can lose electron easily., OR, (i) ‘X’ 2, 8, 2, , ‘Y’ 2, 8, 7, , (ii) ‘X’ belongs to group 2,, , ‘Y’ belongs to group 17, , (iii) ‘X’ has valency equal to 2, , ‘Y’ has valency equal to 1, , (iv) ‘X’ is metal, , ‘Y’ is non-metal, , (v) ‘X’ is larger in size., 14. (i) What is meant by solenoid? How does a current carrying solenoid behave? Give its main use., (ii) For the circular coil carrying current shown below draw magnetic field lines. Decide which of its face, behaves as north pole and which face behaves as south pole. Give reason to justify your answer., , 5, , , Ans. (i) Solenoid is a long coil of many circular turns of insulated copper wire wound on cylindrical soft iron, or steel core., When current is flowing through a solenoid, the magnetic field lines resemble exactly with a bar, magnet with fixed polarity. It behaves as a bar magnet., , 206, , Science-10

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(ii) Front face behaves like a north pole as field emerges out of it. Rear face behaves as south pole as, field enters into this face., , 15. (i) Draw a neat and labelled diagram of female reproductive systems and describe its parts., (ii) Differentiate between asexual and sexual reproduction giving four differences., 5, OR, (i) Draw well labelled diagram of male reproductive system and describe its parts., (ii) What is need of population control? Give four reasons., Ans. (i) (a) A pair of ovaries: Ovaries produces ova and female sex hormones. One egg is produced every, month by one of the ovaries. Ova are picked up by the funnel shaped fallopian tubes., (b) Fallopian tube: There are two fallopian tube, which carry ova from ovary to the uterus., Fertilisation occurs in fallopian tube., (c) Uterus: Pear shaped hollow muscular organ. Fertilized ovum remains attached to the uterus, wall., (d) Vagina: It is a narrow muscular tube. Its upper end is connected to cervix of the uterus and, lower end opens outside through an opening. It is the place for copulation., , Female Reproductive System, , (ii), , Asexual reproduction, , Sexual reproduction, , (a) Only one percent is involved., , (a) Both the parents are involved., , (b) Offspring resemble, exactly with, parent., , (b) Organism may resemble is certain, features of both the parents., , (c) Cell divides by mitosis., , (c) Cell divides by both mitosis and, meosis., , (d) Gametes are not produced., , (d) Gametes are produced., Sample Paper-3 207

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OR, (a) A pair of testis: Each testis produces sperms and male sex hormone,called testosterone. Testis, are present in small pouch called scrotum., (b) Epididymis: It is long coiled tube whose head is connected with testis and tail with Vas deferens., (c) Vas deferens: It is long tube carrying sperms from testis to the urethra., (d) Urethra: It receive the Vas deferens from both the testis. It opens outside the penis. It carries, both sperms and urine., (i), , (ii) Over population leads to large number of problems given below:, (a) Unemployment: India has large population, therefore, unemployment is increasing every year., (b) Poverty: Large population lead to poverty due to low income., (c) Food supply: Food production may not increase at the same rate as population., (d) Hygienic condition: More people live in small area generally, leads to unhygienic condition, which leads to diseases and health issues., , qqq, , 208, , Science-10