Chapter 15 Some Natural Phenomena

By | June 7, 2018

Class 8 | Science | Ch 15 |Some Natural Phenomena| NCERT Solutions

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: (b) A copper rod

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.

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) Like charges attract each other (F)

(b) A charged glass rod attract a charged plastic straw (T)
(c) Lightning conductor cannot protect a building from lightning (F)
(d) Earthquakes can be predicted in advance (F)

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

Answer:
Due to friction between sweater and body or inner clothes( made of cotton or synthetic fibres) , the sweater gets static charge.As a result of which a crackling sound is heard while taking off a sweater during winter season.

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

Answer:
A charged body loses its charge when we touch it with hand because the charges get transferred through our body to earth.

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:
Richter Scale measures the destructive energy of an earthquake.The scale has a reading from 1 to 10.If the richter scale gives a reading of magnitude 3, then the earthquake is not likely to cause much damage.An Earthquake of magnitude 5 is considered destructive in nature.

7. Suggest three measures to protect ourselves from lightning.

Answer:
Three measures to protect ourselves from lightning are:

1) Stay in completely closed space.

2) Never touch any electrical wires, telephone cables, metal pipes.

3) Never bath in running water, this may cause electric shock.

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

Answer:
We know that like charges repel each other whereas unlike charges attract each other.The nature of charges present on the surface of charged balloon is similar therefore they repel each other.When an uncharged balloon is brought near to a charged balloon ,the uncharged balloon acquires charge on its surface.Since the charges are of opposite nature therefore they attract each other.

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

Answer:
An electroscope is used to detect whether a body is charged or not.

Electroscope

Electroscope consist of copper wire.At one end of the rod, two leaves of aluminium foil are fixed at one end and at the other end, there is a metal disc.The leaves of aluminium foil are placed inside a flask and the flask is corked to isolate the leaves from air.When the metal disc is touched with a charged body , the aluminium strips move away from each other because some of the charges of the body are transferred to the strips through the copper wire.The nature of charges are same on both i.e. aluminium foil and charged body.Hence both the leaves of aluminium foil will move away from each other.If the body is not charged then leaves of aluminium foil will not move away from each other.

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

Answer:
Gujarat, Himachal Pradesh and Jammu & Kashmir are the three states where earthquake are more likely to strike.

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

Answer:
Precautions to be taken when earthquake strikes are:

1) Stay away from bookcases or furniture that can fall on you.

2) If you are outdoors, find a clear spot away from buildings, trees, and power lines. Drop to the ground.

3)  If you are in a car, slow down and drive to a clear place. Stay in the car until the shaking stops

4) Cover the back of your head and your eyes to minimise injury from flying debris.5) Do not take elevators during an earthquake.

5) Cover the back of your head and your eyes to minimise injury from flying debris.

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:
It is not safe to carry umbrella during thunderstorm because thunderstorm are accompanied with lightning and electric discharge which can travel through the metallic rod of umbrella.This may give electric s
hock to person who is carrying it.

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