NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena

Select the correct option in Questions 1.
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 cannot be charged easily by friction.

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, some electrons from the rod gets transferred to the cloth.

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 , like charges, repel each other and unlike charges attract each other.

(b) True , a charged glass rod is positively charged while a charged plastic straw is negatively charged.

(c) False, lightning conductor rod provides an easy route for the transfer of electric charge to the ground hence is used to protect buildings from the effect of lightning.

(d) False , prediction of the earthquake in advance has not been yet invented but we can determine the magnitude of the earthquake.

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

Answer:

A cracking sound is heard while taking off a sweater during winters because of electric discharge where positive and negative charges meet, releases some energy in the form of streaks of bright light and sound.

5 . 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 of earthing. Our body is a good conductor of electricity so, there is charge transfer from the charged body to the 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:

The destructive energy of an earthquake is measured on the Richter scale. If an earthquake measures 3 on this scale then it would be recorded by a seismograph and it is not more likely to cause much damage.

7 . Suggest three measures to protect ourselves from lightning.

Answer:

Three measures to protect ourselves from lightning are:

(i) We should not use telephone cords, electrical wires and metal pipes instead use mobile phones and cordless phones.

(ii) Bathing should be avoided during thunderstorms to avoid contact with running water.

(iii) If you are outside, then stay far away from tall trees, poles or other metal objects.

8 . 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 as they both have same charges and as we know like charges repel each other, while an uncharged balloon has no charge and is different from the charged balloon hence 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 device is used to determine whether an object is carrying charge.

When the metal strips repel each other proves that the body is charged because repulsion is the sure test to detect that a body is charged or not.

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

Answer:

Three states in India where earthquakes are more likely to strike are:

(i) Kashmir

(ii) Gujarat

(iii) Assam.

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

Answer:

The precaution that we would take to protect ourselves from the earthquake are:

(i) Take shelter under a table and stay there till the shaking stops.

(ii) Find a clear spot, away from buildings, trees, and overhead power lines. Drop to the ground.

(iii) If you are in a car or a bus, do not come out.  Ask the driver to drive slowly to a clear spot.  Do not come out until the tremors stop.

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, carrying an umbrella is not at all a good idea during thunderstorms. Wide objects like umbrella are more prone to get stuck by lightning.