Some Natural Phenomena Class 8 Worksheet Science Chapter 12

Q.1. What type of electric charge is acquired by a rubber balloon when rubbed with a woolen cloth?

When balloon is rubbed with a woolen cloth, it acquires negative electric charge.

Q.2. Sometime, a crackling sound is heard while taking off sweater during winters. Explain.

When we take off a woolen (or synthetic) sweater, it rubs against our shirt. Due to rubbing, opposite electric charges develop on them, which attract each other. The discharge of these electric charges produces tiny sparks of light as well as crackling sound.

Q.3. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

A charged balloon is repelled by another charged balloon because both the balloons have same type of charges and like charges repel each other. Whereas an uncharged balloon is attracted by another charged balloon because charged balloon induces opposite charges in the nearer end of the uncharged balloon by electric induction and unlike charges attract each other.

Q.4. What causes lightning in the sky?

During the development of a thunderstorm, the air currents move upward while the water droplets move downward. These vigorous movements cause separation of charges. The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is accumulation of positive charges near the ground also. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. We see streaks as lightning. The process is called an electric discharge.

Q.5. List three states in India where earthquakes are more likely to strike.

Gujarat, Kashmir, Rajasthan

Q.6. The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.

Carrying umbrella is not a good idea at all during thunderstorms because lightning may strike the top end of the metal rod of umbrella and harm us.

Q.7. What will you do to protect yourself from lightning if you are in an open field?

If no shelter is available and we are in an open field, we should stay far away from all trees. We should stay away from poles or other metal objects. We should not lie on the ground instead we should squat low on the ground. We should place our hands on our knees with our head between the hands. This position will make us the smallest target to be struck.

Q.8. What precautions would you take to protect yourself during an earthquake if you are at home?

In order to protect ourselves during an earthquake we must take following precautions:
(i) We should take shelter under a table and stay there till shaking stops.
(ii) We should stay away from tall and heavy objects that may fall on us.
(iii) If we are in bed then we should not get up and should protect our head with a pillow.

Q.9. What are the two kinds of electric charges?

There are two kinds of charges — positive charge and negative charge.

Q.10. What happens when plates brush past one another, or a plate goes under another due to collision?

When plates brush past one another, or a plate goes under another due to collision, they cause disturbance in the earth’s crust. It is this disturbance that shows up as an earthquake on the surface of the earth.

Q.11. When a charged refill is touched with the metal top of an electroscope, its aluminium leaves diverge. Give reason.

The aluminium foil strips receive the same charge from the charged refill through the paper clip. The strips carrying similar charges repel each other and they become wide open.

Q.12. What is lightning conductor? How does it work?

Lightning Conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground. The rod provides easy route for the transfer of electric charge to the ground.

Q.13. 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?

The destructive energy of an earthquake is measured by Richter scale. An earthquake of 3 Richter can be recorded by a seismograph. An earthquake of magnitude 3 on Richter scale is often felt but not likely to cause much damage. Really destructive earthquakes have magnitudes higher than 7 on the Richter scale.

Q.14. How will you charge a glass rod by the method of friction?

A glass rod can be charged by rubbing it with silk cloth.

Q.15. Why is it not safe to stay under a tree during a thunderstorm?

During a thunderstorm, there is danger of lightning striking the tree and burning it up. This lightning can also pass through the body of the person standing under the tree and may kill him. Therefore, it is not wise to stand under a tree during a thunderstorm.