Class 8 - Physics - Some Natural Phenomena

Question1.

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.

Correct option is (b) copper rod. Plastic scale, an inflated balloon and a woollen cloth are poor conductors of

electricity so they can be charged easily by friction.

Question2.

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.

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

When a glass rod is rubbed with a piece of silk cloth, transfer of charge takes place as a result of this glass

the rod acquires positive charge while the piece of silk cloth acquires negative charge.

Electrons from glass rod tend to flow from glass rod to the silk cloth.

Question 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)

(a) Like charges attract each other (False)

(b) A charged glass rod attract a charged plastic straw (True)

(c) Lightning conductor cannot protect a building from lightning (False)

(d) Earthquakes can be predicted in advance (False).

Question 4.

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

Sweaters are made up of wool and wool is poor conductor of electricity. During winters our body is very dry.

So when we are wearing the sweater the wool is in contact with our body, there is friction as there is rubbing between the body and the wool.

Due to this rubbing wool gets charged so there is some kind of force which is experienced between the wool and our body

due to this we hear the crackling sound while taking off the sweater during winters.

Question 5.

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

Human body is a good conductor which provides the path to the charge to ground.

Charge will flow through our body and will go to the ground. All the excess is flowing through the body and going to the ground,

therefore the charge body is losing its extra charge this is known as discharge of the body. This concept is known as earthing.

Question 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?

Richter scale measures the energy of an earthquake. X-axis represents the magnitude of the earthquake and

y-axis represents the amplitude of the seismic waves which are caused by the earthquake.

Yes, seismograph can measure an earthquake of magnitude 3 on Richter scale.

Any earthquake of magnitude 3 won’t cause any damage; sometimes it won’t be even felt.

Question 7.

Suggest three measures to protect ourselves from lightning.

The three measures should be taken to protect ourselves from lightening are as flows:-

1. Avoid open spaces.
2. Stay inside a building or a vehicle with closed windows.
3. Avoid shelter under tall trees.
4. Avoid contact with water.

Question 8.

Explain why a charged balloon is repelled by another charged balloon

whereas an uncharged balloon is attracted by another charged balloon?

Like charges repel each other and unlike charges attract each other. When we charge a balloon by

rubbing on our hair and take it near another balloon which is also been charged in the similar way,

both balloons being negatively charged repel each other.

Question 9.

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

Electroscope is a device which is used to test if an object is carrying charge or not.

It consists of 2 metal leaves which are connected to a metal rod which in turn is connected to a disc.

Whenever an object strikes the electroscope which has a positive charge, the same positive charge will be conducted to the leaves.

These leaves are metallic and as they carry same charge so they repel each other.

When the leaves move away from each other this means the object is a charged body and

if they come close to each other this implies object is uncharged.

Question 10.

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

Plate boundaries are more prone to earthquakes. Weak zones are termed as Fault/Seismic zones.

• Jammu & Kashmir
• North-east
• Uttarkhand

Question 11.

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

The precautions which we should try to take if an earthquake strikes are as follows:-

1. Find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground.
2. 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 till the tremors stop.

Question 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.

Carrying an umbrella on a thunderstorm day is not advisable because thunderstorms are accompanied with lightning,

electric charges from clouds travel to the metallic rod of the umbrella.

The metallic rod of the umbrella is good conductor of electricity so we may get an electric shock if carrying an umbrella.