Science Class 8 – Chapter 15- Some natural phenomena- NCERT exercise solution (Question-Answer)

Select the correct option in Questions 1 and 2.

Q1.  Which of the following cannot be changed easily by friction?

(a) A plastic scale

(b) A copper rod

(c) An inflated balloon

(d) A woolen cloth

Answer – (b) A copper rod

Q2. When a glass rod is rubbed with a piece of silk cloth the rod

(a) and the cloth both acquire a positive charge.

(b) becomes positively charged while the cloth has a negative charge

(c) and the cloth both acquire a 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

Q3. 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 attracts a charged plastic straw (T/F)

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

(d) The earthquake can be predicted in advance (T/F)

Answer-

(a) Like charges attract each other.  (F)

(b) A charged glass rod attracts a charged plastic straw. (T)

(c) A lightning conductor cannot protect a building from lightning. (F)

(d) The earthquake can be predicted in advance. (F)

Q4. Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

Answer- A crackling sound is heard while taking off a sweater during winter because due to friction electric charge takes place between the sweater and body. At the time of electric discharge, some energy released and that released energy is the form of crackling sound.

Q5. Explain why a charged body loses its charge if we touch it with our hand.

Answer- A charged body loses its charge if we touch it with our hand because human body is a good conductor of the electricity. Our body conducts charge of charge body to the earth when we touch it.

Q6. 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- Richter scale measures the destructive energy of the earthquake.

Yes, if the earthquake measures 3 on the Richter scale it would be recorded by seismograph because this scale (seismograph) has the reading from 1 to 10.

No, it is not likely to cause much damage. If the earthquake of the magnitude of higher than 5 then it causes much more damage and destructive in nature which is measured by the Richter scale.

Q7. Suggest three measures to protect ourselves from lightning.

Answer- Following are the three measures to protect ourselves from lightning.

• Don’t touch any electric wire, telephone, etc.
• Don’t take bath in running water.
• Stay indoors or under the covered area.

Q8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Answer – A charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon because like charges repel each other and unlike charge attract each other.

Q9. Describe with the help of a diagram an instrument which can be used to detect a charged body.

Answer – An electroscope is a device which is used to detect whether a body is charged or not.

It consists of a metal rod on which two leaves of aluminium foil are put the one end of this rod and there is metal disc at the other end. When leaves of aluminium foil are placed inside the conical flask, the conical flask is corked to isolate the leaves from the air.

When metal disc touched with a charged body, the leaves of aluminium are moved away from each other because the nature of charges on both leaves are same and like charge repel other.

If the body is not charged then leaves remain as they are, they don’t repel.

Q10. List three states in India where earthquakes are more likely to strike.

Answer- Kashmir, Rajasthan and Gujrat.

Q11. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Answer- We take some precaution to protect ourselves-

• Go to open place or field which is away from buildings, trees, overhead powerlines.
• If we are travelling by bus or car, then we should not come out, we should drive slowly to a clear spot away from buildings, trees, etc.

Q12. 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, we should not carry an umbrella because the metallic rod of umbrella allows the electric discharge from the cloud can travel. It may give an electric shock. Hence, the umbrella increases the risk of getting shocked.

Therefore, it is not safe.