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Chapter 15: Some Natural Phenomena, A. Tick (7) the correct options., , 1. (d) 2. (b) 3. (b) 4. (c) 5. (b) 6. (a), B. Fill in the blanks., , 1. electric current 2. thunder 3. faults, 4. Seismic waves 5. repel, attract 6. Repulsion, 7. induction 8. lightning strike, , C. Very Short Answer Questions., , 1. Abody is said to be charged when it acquires electric charges by rubbing, or by other method from another body., , 2. Seismograph, , 3. large amount of heat produced during lightning causes air to expand, suddenly. This rapid expansion of air sends a disturbance in the form, of vibrations through the air producing a loud sound. This loud sound, produced during lightning is called thunder., , 4. Acomb rubbed on hair attract pieces of paper because a kind of force is, produced between them called electrostatic force., , 5. Epicentre 6. Seismic waves 7. Charged, , D. Short Answer Type-! Questions., , 1. Charging an object by rubbing it with another object is called charging, by friction., , 2. An earthquake is a sudden shaking of the Earth’s crust which lasts for a, very short time., , 3. The force exerted by a charged body on another charged or uncharged, body is known as electrostatic force., , 4, We say that repulsion is a sure test of charge on a body because when, the body being tested is repelled by a charged body, we sure that, body under examination is charged and has the same charge as on the, charged body., , 5. Storms, Cyclones, lightning and earthquake, , 6. When an ebonite rod is rubbed with wool, it gets negatively charged., , 7. The point on the surface of the earth, directly above the focus of an, earthquake is called an epicentre., , 8. Richter scale is a scale used for measuring the magnitude of earthquake., , —. Short Answer Type-!I Questions., , 1. The three causes of earthquake are ~, , (i) Movement of the tectonic piates, Volcanic eruptions, (iii) Dislocation (or faults) of the crust, , The three effects of earthquake are ~, , (i) Human-made structure like buildings, railway tracks, roads, bridges,, dams, etc., get severly damaged in earthquake. People can get, trapped inside the collapsed structures and many may die., , (ii) Fire often breaks out following earthquakes which can be caused by, sparking from electrical short circuits., , (iii) Groundwater pipes usually rupture, totally disrupting municipal, water supply systems., , 2. The harmful effects of lightning are , (i) It can cause fire and shatter buildings resulting in lot of destruction, and damage to the property., , (ii) It can burn trees and also cause forest fires., , (iii) It injures or sometimes even kills animals and people instantly., , 3. (a) Sameer and Sachin not take shelter under the tree because trees, provide a good conducting path for lightning., , (b) Yes, he did the right thing to save him and his brother's life., , 4. Precautions to be taken during an earthquake:, , (i) Move to an open area immediately.

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(ii), , Move away from buildings, trees, bridges, flyovers or overhead, electric cable lines or any other structures that can collapse., , F. Long Answer Questions., , 1., , (a), , (b), (c), , (a), , (b), , (c), , (d), , An electroscope is an instrument pee — brass disc, used for detecting electrical, charge and its nature on a body., , See fig. (a), Uses of a gold leaf electroscope, are:, , (i) Detection of charge, (ii) To identify the nature of, charge, , A cloud has the negative charges, concentrated at the base and, positive charges concentrated at, its upper region. When a charged cloud passes over a tall building, or a tall tree, it induces an opposite charge on them. The negative, charges at the base of the clouds pull the positive charges induced, on the tall buildings upwards at a tremendous speed. As soon as, the negative and positive charges connect, a continuous path is, formed from the cloud to the tall building or a tree on the ground., The large amount of negative charges accumulated in the clouds, rushes down this path, giving rise to an electric discharge in the, form of lightning strike., , A lightning conductor is a device which is fixed on the top of tall, buildings to protect them from damage due to lightning., , When the lightning strikes, the lightning conductor provides an, , easy path for the charge to pass through to the earth and thus,, protects the building., , Safety measures to be taken during thunderstorm are:, , (i) Do not take shelter under a tree because trees provide a good, conducting path for lightning., , (ii) Do not take baths or showers during storms, as water is an, excellent conductor of electricity., , , , Gold-leaf electroscope