NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena

Exercises

Select the correct option in Questions 1 and 2.

Question:- 1. Which of the following cannot be charged easily by friction?

(a) A plastic scale

(b) A copper rod

(c) An inflated balloon

(d) A woollen cloth.

Answer:- (b) A copper rod

Question:- 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.

Answer:- (b) becomes positively charged while the cloth has a negative charge.

Question:- 3. Write T against true and F against false in the following statements.

(a) Like charges attract each other (T/F)

(b) A charged glass rod attract a charged plastic straw (T/F)

(c) Lightning conductor cannot protect a building from lightning (T/F)

(d) Earthquakes can be predicted in advance (T/F)

Answer:- (a) False

(b) True

(d) False

Question:- 4. Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

Answer:- Due to friction, an electric discharge occurs between the body and the sweater. Some energy is released during an electric discharge. The energy discharged here as a crackling sound.

Question:- 5. Explain why a charged body loses its charge if we touch it with our hand.

Answer:- The human body is an electrical conductor. When we touched a charged body, the charges get transferred to the earth. As a result, the charged body loses its charge.

Question:- 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?

Answer:- An earthquake’s destructive energy is measured on a scale known as the Richter Scale.

Yes, an earthquake measuring 3 would be recorded by a seismograph because this scale provides readings from 1 to 10.

No, the magnitude of scale 3 would not cause much damage as an Earthquake of magnitude more than 5 is considered destructive in nature.

Question:- 7. Suggest three measures to protect ourselves from lightning.

Answer:- Three measures to protect ourselves from lightning are following:-

(i) Don’t watch TV or talk on the phone during a storm.
(ii) Remain indoors.
(iii) Avoid bathing during a thunderstorm.

Question:- 8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Answer:– As we already know that same charges repel and opposite charges attract each other. Thus a charged balloon is repelled by another charged balloon as they both contain same type of charges. On the other hand, an uncharged balloon is attracted by another charged balloon as they contain opposite charges.

Question:- 9. Describe with the help of a diagram an instrument which can be used to detect a charged body.

Answer:-

An electroscope is a device that detects the charge on a body. It works on the concept that opposite charges attract one other while similar charges repel each other. It is made up of a metal rod with a thin metal strip or leaf connected to the bottom of it.
The metal rod is inserted into a metallic cup or disc at the top. For safety, the bottom of the rod and the metal leaf are encased in a glass box. When a charged ebonite or glass rod is placed on the electroscope’s disc, the metal leaves open out or diverge.
The quantity of charge on the electroscope determines the extent of divergence. When the metal strips reject each other, this indicates that the body is charged, as repulsion is a sure way to determine whether or not a body is charged using an electroscope.

Question:- 10. List three states in India where earthquakes are more likely to strike.

Answer:- Kashmir, Rajasthan and Gujarat.

Question:- 11. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Answer:-I will take the following precautions to protect myself :-

(i) I will run towards a wide open space.
(ii) I will stand far away from buildings, electric polls and tress etc.
(iii) If I would be in a car or bus, I would ask the driver to slow down the speed and will never move out from it until earthquake stops.

Question:- 12. 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.

Answer:- No, it is not a good idea to carry an umbrella during thunderstorm. As its metallic objects are more likely to get stroke of lightning. So an umbrella increases the risk.