Some Natural Phenomena

Exercises

Question 1

Which of the following cannot be charged easily by friction?

1. A plastic scale
2. A copper rod
3. An inflated balloon
4. A woollen cloth.

Answer

A copper rod.

Reason — When an object is charged by friction, charges develop on the two materials involved in friction. Copper being a good conductor, allows the charges to move easily and redistributes the excess charges quickly and doesn't retain a significant charge through friction. Therefore, it's difficult to charge a copper rod through friction.

Question 2

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

1. and the cloth both acquire a positive charge.
2. becomes positively charged while the cloth has a negative charge.
3. and the cloth both acquire a negative charge.
4. becomes negatively charged while the cloth has a positive charge.

Answer

becomes positively charged while the cloth has a negative charge.

Reason — When two objects are rubbed against each other, electrons transfer from one material to the other. This transfer of electrons leads to one material becoming positively charged (losing electrons) and the other becoming negatively charged (gaining electrons). It is a convention to call the charge acquired by a glass rod when it is rubbed with silk as positive. The other kind of charge is said to be negative.

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 attracts a charged plastic straw. (T/F)

(c) Lightning conductors cannot protect a building from lightning. (T/F)

(d) Earthquakes can be predicted in advance. (T/F)

Answer

(a) Like charges attract each other. — False
Reason — Like charges repel each other.

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

(c) Lightning conductors cannot protect a building from lightning. — False
Reason — Lightning conductors protect a building from lightning.

(d) Earthquakes can be predicted in advance. — False
Reason — Earthquakes cannot be predicted in advance.

Question 4

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

Answer

The crackling sound heard when removing a sweater in winter is a result of the friction between the woollen fabric and the body or the shirt worn underneath. This friction generates opposite electric charges, and the discharge of these charges produces the audible crackling sound.

Question 5

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

Answer

When we touch a charged body, the charges get conducted to the earth through our body and the conductor loses its charge. This process of transferring of charge from a charged object to the earth is called 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?

Answer

The destructive energy of an earthquake is measured on Richter scale. This scale has the readings from 1 to 10. An earthquake measuring 3 on Richter scale would be recorded by a seismograph. However, earthquakes of this magnitude are not likely to cause significant damage.

Question 7

Suggest three measures to protect ourselves from lightning.

Answer

Three measures to protect ourselves from lightning are:

1. During lightning, no open place is safe. We should be inside a house or a building. If travelling by car or bus, we should shut the doors and windows of the vehicle.
2. Electric wire, telephone lines, and metal surfaces should never be touched during lightning.
3. Incase no shelter is available, we should not lie on the ground. Instead, we should squat low on the ground with hands on the knees and head between the hands. This position makes us the smallest target to be struck.

Question 8

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

Answer

The repulsion between two charged balloons occurs because both balloons carry the same type of charge, resulting in like charges repelling each other. On the other hand, when a charged balloon is brought close to an uncharged balloon, due to induction, the uncharged balloon acquires opposite charge. Due to this they are attracted to each other.

Question 9

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

Answer

The instrument used to detect a charged body is known as electroscope.

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 them 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 the same nature, and thus, the leaves of aluminium repel each other. If the body is not charged then they would attract each other.

Question 10

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

Answer

Three earthquake prone states in India are:

1. Kashmir
2. Gujarat
3. Assam

Question 11

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

Answer

Precautions that I will take to protect myself in case of an earthquake while I am outside are:

1. I will find a clear spot, away from buildings, trees and overhead power lines and then I will drop to the ground.
2. If I am in a car or a bus, I will not come out. I will ssk the driver to drive slowly to a clear spot. I will stay inside the vehicle 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.

Answer

I will not carry an umbrella during a predicted thunderstorm. A thunderstorm is accompanied by lightning. The lightning might travel along the metallic rod of the umbrella and cause an electric shock to the person holding it, making it an unsafe choice in such weather conditions.