NCERT solutions for class 8 Science Chapter 15 Some Natural Phenomena

Solution for Exercise

Select the correct option in Questions 1 and 2.

Q.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.


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Answer :

(b) A copper rod

Q.2 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


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Answer :

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

Q.3 Write T against true and F against false in the following statements.
(a) Like charges attract each other.
(b) A charged glass rod attracts a charged plastic straw.
(c) Lightning conductor cannot protect a building from lightning.
(d) Earthquakes can be predicted in advance.


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Answer :

(a) False
(b) True
(c) False
(d) False

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


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Answer :

Whena sweater is taken off, the woollen sweater gets charged because of the friction between the sweater and the body. Hence,one can hear a crackling sound during the given process.

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


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Answer :

When we touch a charged object, our body conducts its charges to the earth. That is why a charged body loses its charge, if we touch it with our hand. This phenomenon is known as electric discharge.

Q.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?


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Answer :

The destructive energy of an earthquake is measured by the Richter scale. This scale has the readings from 1 to 10. The reading of magnitude 3 on the Richter scale would be recorded by a seismograph. If the Richter scale gives a reading of magnitude 3, then the earthquake is not likely to cause much damage. Generally, earthquake of magnitudes higher than 5 is considered destructive in nature.

Q.7 Suggest three measures to protect ourselves from lightning.


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Answer :

(i) Never touch any electrical wires, telephone cables, metal pipes.
(ii) Stay indoor or under covered area.
(iii) Don’t take bath during lightning.

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


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Answer :

A charged balloon is repelled by another charged balloon because both carry same type of charges. Because We know that same charges repel.On the other hand, an uncharged balloon is attracted by another charged balloon as they have opposite charges. Because opposite charges attract each other.

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


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Answer :

It consists of a metal rod on which two leaves of aluminium foil are fixed to one end and a metal disc at the other end. The leaves are kept inside a conical flask and it is corked to isolate it from the atmospheric air. When a charged body comes in contact with the metal disc, the aluminium leaves move away from each other because some charges get transferred to aluminium leaves through the metal rod. This process is called charging by conduction. The charges on the leaves and the charged body are of same in nature and thus the leaves of aluminium repel each other. If the body is not charged then they would attract each other.

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


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Answer :

Gujrat, assam and jammu Kashmir

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


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Answer :

We will take the following precautions to protect ourselves:
(i) Try to find an open field away from tall buildings, installations, tall trees, and electric wires and poles.
(ii) If travelling in a bus or a car, then do not come out when an earthquake strikes. Ask the driver to drive in an open field.

Q.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.


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Answer :

No, it is not advisable to carry an umbrella at all. Its metallic objects are more prone to lightning stroke. So an umbrella increases the risk.



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