Some Natural Phenomena

Q18. What are seismic waves?

Ans. The tremors produce waves on the surface of the earth. These are called seismic waves.

Q19. Which device is used to protect buildings from the effect of lightning?

Ans. Lightning Conductor is a device used to protect buildings from the effect of lightning.

Q20. What is an earthquake? What causes them to happen?

Ans. An earthquake is a sudden shaking or trembling of the earth lasting for a very short time. It is caused by a disturbance deep inside the earth’s crust.

Q21. If scientists know so much about earthquakes, can they also predict when and where the next one will strike?

Ans. Although, we know for sure what causes an earthquake, it is not yet possible to predict when and where the next earthquake might occur.

Q22. Other than earthquakes what causes tremors on the earth?

Ans. Tremors on the earth can also be caused when a volcano erupts, or a meteor hits the earth, or an underground nuclear explosion is carried out.

Q23. A positively charged object attracts another charged object placed near it. What is the nature of charge on the other object?

Ans. The nature of charge on the other object will be negative. This is because like charges repel each other and unlike charges attract each other.

Q24. Explain why a charged body loses its charge if we touch it with our hand.

Ans. When we touch a charged body with our hand, then the electric charge present on it flows to the earth through our hand and body. That is why a charged body loses its charge if we touch it with our hand.

Q25. What was the magnitude of Bhuj and Kashmir earthquakes on the Richter scale?

Ans. Really destructive earthquakes have magnitudes higher than 7 on the Richter scale. Both Bhuj and Kashmir earthquakes had magnitudes greater than 7.5.

Q26. Why does a plastic comb rubbed with dry hair attract tiny pieces of paper?

Ans. When a plastic comb is rubbed with dry hair, it acquires a small charge due to friction. The electrically charged comb then exerts an electric force on the tiny pieces of paper and attracts them.

Q27. Name the scientist who showed that lightning and the spark from your clothes are essentially the same phenomena.

Ans. In 1752 Benjamin Franklin, an American scientist, showed that lightning and the spark from your clothes are essentially the same phenomena.

Q28. Why is it not safe to stay under a tree during a thunderstorm?

Ans. 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.

Q29. When a charged refill is touched with the metal top of an electroscope, its aluminium leaves diverge. Give reason.

Ans. 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.

Q30. What happens when plates brush past one another, or a plate goes under another due to collision?

Ans. 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.

Q31. 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.

Ans. 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.

Q32. Sometime, a crackling sound is heard while taking off sweater during winters. Explain.

Ans. 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.