NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena

Select the correct option in Questions 1 and 2.

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: Friction can charge non conducting material. In given, options copper rod is conducting material, therefore, copper rod cannot be charged easily.

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) rod becomes positively charged while the cloth has a negative charge.

When two objects are rubbed on each other both acquire opposite charges. Therefore by conventions, it is considered that glass acquire a positive charge and cloth acquire negative charge. Thus, option b is correct for given statement.

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

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

Answer: False (F). [ Unlike charges attract each other. ]

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

Answer: True (T).

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

Answer: False (F). [ Lightning conductor protects building from lightning. It conducts atmospheric charges directly to the earth. ]

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

Answer: False (F). [ Earthquakes cannot be predicted in advance. ]

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

Answer: Woollen sweater gets charged due to friction between body and sweater. Due to this crackling sound can be heard while taking off sweater during winters.

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

Answer: This is due to phenomena of electric discharge. When we touch charged body with our hands, our body transfers the charge directly to the earth. This causes loss of charge in charged body.

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: Destructive energy of an earthquake is measured using Richter Scale. Seismograph will record earthquake of magnitude 3. Earthquake having magnitude higher than 5, causes damage. Therefore, earthquake of magnitude 3 will not cause much damage.

7. Suggest three measures to protect ourselves from lightning.

Answer: Following are some measures to protect ourselves from lightning-

1. Stay in closed room.
2. While travelling stay inside the bus or car and keep windows and door shut.
3. Do not touch metal pipes, electrical wires,etc.
4. Do not bath in running water, as it can cause electric shock to you.

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

Answer: Charged balloon have same charge on them. As like charges repel each other, therefore, one charged balloon is repelled by another charged balloon. When charged balloon is brought near uncharged balloon, charges on balloon are opposite. As unlike charges attract each other, therefore, uncharged balloon is attracted towards charged balloon.

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

Answer: Instrument used to measure charged body is called electroscope.

It is made up of metal rod, metal disc and leaves of aluminium foil. Leave of the aluminium foil are attached to one end of the rod. Other end of the rod is fixed with the metal disc. Leaves of aluminium foil is placed in the conical flask. Conical flask is covered with cork. By doing this leaves get isolated from air. A charged body is touch to metal disc, aluminium leaves move away from each other. This is observed because charges from charged body is transferred to aluminium leaves. If body is not charged, then aluminium leaves will remain like their initial position.

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

Answer: Jammu and Kashmir, Gujarat and Assam are the earthquake prone area in India.

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

Answer: In this situation, one must find open area, that is away from tall buildings, electric wires, bridges, etc. While travelling drive towards the open area and do not come out of the car bus or other vehicle.

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: During thunderstorms lightning also occurs. Electric discharge from the sky can travel through metal rod of umbrella, which can give shock to person carrying the umbrella. Thus, it is not safe to carry umbrella in thunderstorms.

Check other lessons NCERT Solutions for Class 8

Download free NCERT textbook class 8 Science – Chapter 15 Some Natural Phenomena