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CHAPTER, 2, Electricity, Magnetism, and Semiconductors, Unit II, MSBTE Prescribed Syllabue, 2.1 Concept of charge, Coulomb's inverse square law, Electric field, Electric field intensity, potential and, potential difference, 2(a) Calculate electric field, potential and potential difference of the given static charge., 2.2 Magnetic field and magnetic field intensity and its units, magnetic lines of force, magnetic flux., 2(b) Describe the concept of given magnetic intensity and flux with relevant units., 2.3 Electric current, Ohm's law, specific resistance, laws of series and parallel combination of resistance,, heating effecting of electric current., 2(c) Explain the heating effect of the given electric current., 2(d) Apply laws of series and parallel combination in the given electric circuits., 2.4 Conductors, Insulators and Semiconductors, Energy bands, intrinsic and extrinsic semiconductors, 2(0) Distinguish the given conductors, semiconductors and insulators on the basis of energy bands., 2.5 P-N junction diode, I-V characteristics of p-n junction, applications of p-n junction diode., 2(0 Explain the I-V characteristics and applications of the given p-n junction diodes., Objectives, After studying this unit, students should be able to,, State Coulomb's law and explain the concept of electric field., Define and calculate electric field, potential and potential difference of glven static charges., Explain the concept of magnetic field, magnetic field intensity and magnetic flux with relevant units., State Ohm's law., Apply laws of series and parallel combination in given electric circuit., Explain heating effect of electric current., Distinguish between conductors, semiconductors and insulators on the basis of energy bands., Formation of P-N junction diode, its characteristics and applications., Introduction, In subunit 2.1, you will learn concept of charge, laws, governing the behaviour of electric charge and concept, of electric field, electric potential and potential, Electricity plays an important role in everyday life., difference., Electricity is used in all kind of gadgets such as electric, iron, electric bulbs and tubes, electric fans, in, In subunit 2.2, you will learn concept of magnetic field, and various terms such as magnetic lines of force and, transportation systems, in communication systems etc., Electricity and its various applications became possible, after the discovery of electric charge. Like mass,, magnetic flux., It is to be noted that numerous applications d, electricity have become possible because of the fac, electric charge is an intrinsic property of matter.

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Basic Science (Physics) (MSBTE-I Scheme), 2-2, Electricity, Magnetism and Semiconductors, that electric current produces magnetic effects., Magnetism or magnetic properties of material are, known since olden days., We know atom consists of three types of particles, namely electron, proton and neutron. These particles, are distinguished from each other on the basis of, nature of electric charges., Discovery says that some oxide of iron called mineral, magnetite attracted small pleces of iron, magnetic, compass has been used for navigation purpose for a, Electron is negatively charged, proton is posítively, charged and neutron is electrically neutral particle., very long time., In a neutral atom, amount of charge possessed, electron and proton is equal. Hence neutron atom, contains equal number of electrons and protons., In subunit 2.3, you will learn concept of electric current, and behaviour of resistance using certain laws. You will, also learn large number of applications of electricity, due to flow of current through the conducting material, produces heat and induces chemical changes. So, heating effect of electric current will be studied., Behaviour of electric charge can be broadly studied in, two categories, electrostatics and electromagnetics., When we study the behaviour of charges at rest, it is, called electrostatics. However, when charges are in, In subunit 2.4 and 2.5, you will learn the types of, material and its behaviour as conductor, insulator and, semiconductor on the basis of energy band diagram., motion, they give rise to magnetic effects as well and, this behaviour of charge is studied as electromagnetic., All the three types are useful for us in everyday life. But, to semiconductors will be focused in this unit. You will, study types of semiconductors and its need., As mentioned earlier, like charges repel each other and, unlike charges attract each other, you may be curious, to know factors that govern the strength of attraction, or repulsion between the charges. To understand this, one should know Coulomb's inverse square law., In section 2.6, you will learn the concept of formation, of P-N junction diode, its -V characteristics and, applications in electronic circuits., 2.1.2, Coulomb's Inverse Square Law, 21 Concept of Charge, - From your school, you know that electric charge is, nothing but an intrinsic property of matter. We know, that there are basically two types of electric charge,, Experimentally it is observed that when two charged, bodies are brought near each other, they either attract, or repei. This shows that electric charges exert force on, each other. This force is called electric force and is, fundamental force of nature., positive charge and negative charge. Further these, charges are characterised as,, To determine the strength of this force, its dependency, on the amount of charge and separation between the, charges, one should understand Coulomb's inverse, i., The like charges repel each other., ii., The unlike charges attract each other., square law., The material body contains an equal amount of, positive and negative charges. It is possible to transfer, charge from one body to another., Statement : The force of attraction or the force of, repulsion between two charges is directly proportionol to, the product of magnitudes of the charges and is inversely, proportional to the square of the distance between them,, olso the force between the two charges acts along the, For example, when we rub a glass rod with a piece of, silk cloth, the rod becomes positively charged, that, means it has excess of positive charge and silk cloth, becomes negatively charged, that means it has excess, negative charge., line joining them., Derivation, 2.1.1, Conservation of Electric Charge, Consider two charges q, and q separated by a, distance 'r (Fig. 2.1.1). According to Coulomb's inverse, Electric charge can neither be created nor destroyed, it, can only be transferred from one body to another., square law the electric force 'F' between the charges is,, F« 9, 92, ..(2.1.1), Electric charge plays very important role in atomic, F -, structure of matter., ..(2.1.2), Techkauled, Scanned by CamScanner

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Basic Science (Physics) (MSBTE-I Scheme), Electricity, Magnetism and Semiconducton, 2-3, The constant of proportionality 'K' includes the, that the magnitude of electric force depends on, medium in whlch the charges are located., 9,, (Two chargee q, and q, separated by dietance 'r'), Fig. 2.1.1, When the same charges q, and 4; are kept at same, distance 'r in a medium whose permittivity is E then, Equation (2.1.3) becomes,, Combining Equations (2.1.1) and (2.1.2), we get,, tb. 'b, Fred, ..(2.1.4), %3D, 4 REm, Divide Equation (2.1.3) by (2.1.4),, tb. 'b, ...(2.1.3), Fre sss, 4TE, ..(2.1.5), Fmed, Kis called electrostatic force constant., tb. 'b, 4TE, m, Equation (2.1.3) takes into account that two like, charges repel each other and vice versa., This ratio, is called relative permittivity or the, dielectric constant of the medium denoted by e,., 2.1.2.1 Unit Charge or 1 Coulomb Charge, (a) Force of repulsion between charges, 9,, 92, When two charges having equal strengths are placed, in air 1 m apart and they exert a force of 9 x 10 N. Then, each charge is said to be unit charge or 1 coulomb charge., (b) Force of attraction between charges, 2.1.2.2 Relative Permittivity (Dielectric, Constant), Flg. 2.1.2, SI, Case 1: When q, and q, have same sign, the product, 9, 9; is positive and force 'F' indicates repulsive, force (Fig. 2.1.2(a)), It is defined as the ratio of the magnitude of force, between the two charges placed some distance apart, in vacuum to the force between the same charges, placed same distance apart in the medium., Case 2: When q, and q, have opposite signs, the product, 9, 4, is negative and force 'F' indicates, attractive force. (Fig. 2.1.2(b)), 1., Since the relative permittivity (e,) is a ratio of two, similar quantities, it is a dimensionless quantity., In Sl units, electrostatic force constant 'K' is given as:, 2.1.3, Electric Field, Consider a positive charge 'q' placed at a point 'O'. The, electric field due to this charge at some point say 'P is, defined as the electric force experienced by a positive, test charge q, placed at point 'P'., K =, 4REO, where E, is called absolute permittivity of free space., 12, The value of e is 8.854 x 10 " c'/Nm., y, 2., Permittivity is the characteristics of medium., The SI unit of, electric charge is Coulomb (C) and, Electric force is Newton (N)., e and, The charge on electron is denoted by, proton is denoted by, charge, е., the charge on, The, magnitude, of, fundamental, is, 1.602 x 10"C., Fig. 2.1.3: Electric field at polnt 'P' due to charge 'q', Tekautol, Scanned by CamScanner

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Basic Science (Physica) (MSBTE - I Scheme), 2-4, Electricity, Magnetiam and Semiconductors, Mathematically electric field 'E' can be written as,, 2.1.3.3 Electric Lines of Force, E =, ...(2.1.6), When we talk about attractive and repulsive forces, we, It is very important to note that the amount of charge, on the test charge should be small so that its effect of, can visualise the force between the charges., But to visualise the abstract concept of electric field,, force on charge 'a' is negligible. This is the necessary, condition to ensure that the electric field is, we need to use graphical method called electric lines of, forces., independent of magnitude of test charge., The Si unit of electric field is N/C. It is a vector quantity., The directions of electric field is same as direction of, electric force., Using Equations (2.1.3) and (2.1.6) we have,, É =, 4RE, r, ..(2.1.7), Where 'r is the distance between charge 'q' and point, "P' where field is measured. Equation (2.1.7) shows, that the magnitude of field decreases as the distance, (a) Vectors representing, electric fleld In the space, due to +q charge, (b) Electric lines of force, due to +q charge, increases., Fig. 2.1.4, 2.1.3.1 Definition of Electric Fleld, It is space surrounding a point charge where its effects, such as force of attraction or repulsion can be experienced., 2.1.3.2 Advantages of using Electric Field, over Coulomb's Law to determine, Electric Force between Charges, 1 Electric field is associated with the position. Hence the, value of electric field at a given point in space due to, Fig. 2.1.4(c): Electric line of force due to - q charge, some given charge or group of charges is fixed. Electric, Vector quantity can be characterized in magnitude and, direction. Therefore, the electric field at point A due to, positive charge q can be represented by vector AB as, shown in Fig. 2.1.4(a), field depends only on charges producing it and the, distance of point where it is measured. It is easy to, determine electric force experienced by given charges, Length AB denotes magnitude of electric field at point, A and arrow indicates direction of electric field., in that region as electric field of given region in space, is known., When charges are moving, the electric field and, Coulomb's law do not describe electric forces in similar, As we go away from the charge 'q', say point 'c',, magnitude of field decreases. This is indicated by, length CD. However, direction of point at C is same as, 2., manner. The Coulomb's law tells that effect of motion, A., of a charge is felt immediately by other charges. But, this is not supported by experimental observations., The effect is actually felt after some time. This, If we join all such vectors on the same line, we obtain, electric lines of force, as shown in Fig. 2.1.4(b)., Similarly, the electric field lines can be drawn for - q, charge., limitation of Coulomb's law is taken into account by an, electric field., Teh Kaouledgi, DItati, Scanned py CamScanner

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Basic Science (Physics) (MSBTE -I Scheme), Electricity, Magnetism and Semiconductors, 2-5, 아, Note that the electric lines of force for + q charge are, . E =, 4 TEO., directed away from the charge and for- q charge; they, are directed towards the charge., b., ..E = 9x 10'x, Characteristics of electric llnes of force, 1., = 9x 10°, The direction of field lines at any point in space, indicates the direction of electric field at that point., 4 TE,, Unlts of electric fleld intensity,, Electric lines of force start at positive charge and ends, at negative charge., 2., Sl unlt, 3., Electric lines of force never intersect each other., Newton per Coulomb N/C, The number of electric lines of force per unit cross-, sectional area at a point is directly proportional to the, magnitude of electric field at that point., 4., Alternative unit, Volt per meter V/m, Bigger the field more rapidly does the potential change, with distance., While representing electric field by field lines, the, number of field lines are drawn in proportion to, magnitude of charge so that density of lines truly, represents magnitude of field at given point., 5., e.g. Van de Graff generator., If you stand near Van de Graff generator your hair, 6., There are no lines of force inside the conductor., stands at one end., Electric field lines due to system of two charges of equal 2.1.4.1 Factors affecting Electric Field, magnitude, Intensity at a Point, 1., Distance from the charge., 2. Strength of the charge., 3., Medium in which charge is placed., 4., Position inside the electric field., Fig. 2.1.5, 2.1.5, Electric Potential, 2.1.4, Electric Field Intensity, Description of electric lines of forces in terms of, vectors is a tedious task., The strength of electric field is measured using quantity, called electric field intensity., The task becomes much easier if we define a scalar, quantity which is equally effective in describing electric, forces due to charge. This can be achieved with a, quantity called electric potential., The greater the electric field intensity, the stronger is, the electric field., Definition of electric field intensity, It is defined as the electric force on a unit positive, charge placed at that point in the electric field., Suppose charge Q is placed at some point in the space., Let us bring another charge say 'q' near charge 'Q', from a far off distance say infinity (o0). For this we need, In uniform electric field intensity is constant given by,, to do the work., V, E =, Definition of electric potentlal, It is defined as the work done in bringing a unit positive, In a radial electrical field intensity decreases as the, distance from central charge increases. It is given by,, charge from infinity to that point., The electric potential due to a charge Q at a point, located at a distance r from charge is given by,, E =, 4 TTE E,, It e, = 1, %3D, Tech Kaeuledgi, Scanned poy Camscanner