Page 1 : Chapter 15 — Some Natural Phenomena, , 1. Which of the following cannot be charged easily by friction?, {a) A plastic scale, , ({b)A copper rod, , {c) An inflated balloon, , (4) A woollen cloth, , Ans: (b) A copper rod, , When insulating materials such as plastic scales, balloons, and woollen clothes rub, , against each other, they may become electrically charged, Charging by friction is, used to charge only non-conducting materials (poor conductors of electricity), As, copper is a highly conducting material, it cannot be charged easily by friction,, , 2. When a glass rod is rubbed with a piece of silk cloth the rod, , (a) and the cloth both acquire positive charge., , {b) becomes positively charged while the cloth has a negative charge., {c) and the cloth both acquire negative charge,, , (d) becomes negatively charged while the cloth has a positive charge,, Ans: (b) becomes positively charged while the cloth has a negative charge.

Page 2 : When an object is charged by rubbing it against another object, the two objects, acquire opposite charges. By convention, it is considered that the charge acquired, , by the silk cloth is negative and the charge acquired by the glass rod is positive., Therefore, the glass rod becomes positively charged, whereas the silk cloth becomes, , negatively charged., , 3. Write T against true and F against false in the following statements., , (a) Like charges attract each other. (T/F), Ans: F, , Like charges (positive-positive or negative-negative) repel each other, whereas, unlike charges (positive-negative) attract each other., , (b) A charged glass rod attracts a charged plastic straw. (TIF), Ans: T, , Both objects have opposite charges on them. A charged glass rod (positively, charged) attracts a charged plastic straw (negatively charged) because opposite, charges attract each other., , {(c) Lightning conductors cannot protect a building from lightning. (TIF), Ans: F, , When lightning strikes, the lightning conductor conducts all of the atmospheric, charges directly to the Earth, keeping the building safe. As a result, a lightning, conductor protects a building against lightning strikes., , (d) Earthquakes can be predicted in advance. (TIF), Ans: F, , Despite the fact that the causes of earthquakes are known, no instruments have been, , developed to detect them in advance. As a result, earthquakes cannot be predicted in, advance.

Page 3 : 4. Sometimes, a crackling sound is heard while taking off a sweater during, winters. Explain., , Ans: When we take off a sweater during winter, the woollen sweater gets charged, due to friction between the body and the sweater. The discharge of these electric, charges produces tiny sparks of light and a crackling sound., , 5. Explain why a charged body loses its charge if we touch it with our hand., , Ans: Electricity can flow through the human body because the human body is a, conductor of electricity. When we come into contact with a charged object, our body, conducts its charges to the Earth. That is why if we touch a charged body with our, hand, it loses its charge. This is referred to as an electric discharge., , 6. Name the scale on which the destructive energy of an earthquake is, measured. An earthquake measures 3 on this scale. Would it be recorded by a, , seismograph? Is it likely to cause much damage?, , Ans: The Richter scale is used to determine how destructive an earthquake is. The, scale ranges from one to ten. A seismograph would record a reading of magnitude 3, on the Richter scale., , If the earthquake has 2 magnitude of 3 on the Richter scale, it is unlikely to cause, , significant damage. Earthquakes of a magnitude greater than 5 are generally, considered destructive in nature., , 7. Suggest three measures to protect ourselves from lightning., Ans: Three protective measures against lightning are, (i) Always remain in a covered area or stay indoors. If you are moving in a car, stay, there until the lightning is over and keep the windows shut.

Page 4 : (ii) Do not bathe in running water during lightning., , (iii) Do not touch any electrical appliances, wires, telephone cables, metal pipes ete,, during lightning., , 8. Explain why a charged balloon is repelled by another charged balloon, whereas an uncharged balloon is attracted by another charged balloon?, , Ans: A charged balloon repels another charged balloon because both carry the same, type of charges and the same charges repel each other,, , When an uncharged balloon is brought near to a charged balloon, the uncharged, balloon acquires the opposite charge on its surface by the process of induction. Thus,, an uncharged balloon is attracted by another charged balloon because opposite, charges attract each other., , 9. Describe with the help of a diagram an instrument which can be used to, detect a charged body., , Ans; An electroscope is a device which is used to detect the charge on a body, It, works on the principle that charges (positive-positive or negative-negative) repel, each other while unlike charges (positive-negative) attract each other,, , Moral Disc, , [Cork, jetal Ros, , ———— Aluminie Foil, , Electroscope

Page 5 : This device has a metal rod. At one end of the metal rod, two strips of aluminium, foil are fixed and at the other end, there is a metal disc. The bottom of the rod and, Strips of aluminium foil are placed inside a conical flask for protection. When the, metal disc of the electroscope is touched with a charged body (ebonite or glass rod),, the aluminium strips diverge or move away from each other. This happens because, some of the charges of the charged body are transferred to the aluminium strips, through the metal rod. The nature of charges on both the aluminium strips is similar., Hence, both the strips of the aluminium foil move away from each other. If the body, is not charged, then the two strips of aluminium remain as they are. They do not, repel each other., , The extent of divergence depends upon the amount of charge on the electroscope., ‘When the aluminium strips repel each other proves that the body is charged because, repulsion is the sure test to detect if the body is charged or not through an, electroscope., , 10. List three states in India where earthquakes are more likely to strike., , Ans: The following are the three Indian states where earthquakes are more likely to, occur:, , (i) Jammu and Kashmir, (i) Assam, (iii) Gujarat, , 11. Suppose you are outside your home and an earthquake strikes. What, Precaution would you take to protect yourself?, , Ans: If we are outside our home and an earthquake strikes, then the following, precautions must be followed: