In this blog, we are going to learn about electric charge. You must have rubbed comb on your dry hair and brought it near to the small pieces of paper, what happens? The comb attracts pieces of paper. Why? When a plastic comb or a plastic scale is rubbed with dry hair, it acquires a small charge and the object is called a charged object.

 

When a charged object is brought near the pieces of paper it induces an opposite charge in the pieces of paper and the pieces of paper get attracted to the comb or plastic scale. So, we see that a body gets charged by rubbing. It is a convention to call the charge acquired by a glass rod when it is rubbed with silk as positive. When a charged glass rod is brought near to a charged plastic straw or refill which is rubbed with polythene there is an attraction between the two.

 

What do you think about the kind of charge on the plastic straw? Yes, plastic straw carries a negative charge that is why it is being attracted to the glass rod with a positive charge. So, we can conclude that when we rub objects, electrical charges are generated.

 

Let us do an activity to understand the concept of transfer of electric charge.

 

Take an empty jam bottle. Take a piece of cardboard slightly bigger in size than the mouth of the bottle. Pierce a hole in it so that a metal paper clip could be inserted. Open out the paper clip as shown.

 

Cut two strips of aluminum foil about 4 cm � 1 cm each. Hang them on the paper clip as shown. Insert the paper clip in the cardboard lid so that it is perpendicular to it.

 

Charge a refill and touch it with the end of the paper clip. Observe what happens. Is there any effect on the foil strips? Do they repel each other or attract each other? Touch now, other charged bodies with the end of the paper clip.

 

Do foil strips behave in the same way in all cases? Can this apparatus be used to detect whether a body is charged or not? Can you explain why the foil strips repel each other?

 

The aluminum foil strips receive the same charge from the charged refill through the paper clip (remember that metals are good conductors of electricity). The strips carrying similar charges repel each other and they become wide open. Such a device can be used to test whether an object is carrying charge or not. This device is known as an electroscope.

 

Thus, we find that electric charge can be transferred from a charged object to another through a metal conductor. Touch the end of the paper clip gently with hand and you will find a change in the foil strips. They come back to their original state. Repeat charging of foil strips and touching the paper clip.

 

Every time you will find that the foil strips collapse as soon as you touch the paperclip with your hand. Why does it happen? The reason is that the foil strips lose electric charge to the earth through your body. We say that the foil strips are discharged.

 

Earthing

 

The process of transferring electric charge from a charged object to the earth is called earthing. Earthing is provided in buildings to protect us from electrical shocks due to any leakage of electrical current.

 

Types of Electric Charges

 

There are two types of charges:-
� Positive charge
� Negative charge

 

Interaction between the charged bodies

 

We know that charged bodies attract or repel each other. Why does this happen? Let's study the interaction between the charged bodies.

 

Let us do an activity-
� Take two inflated balloons.
� Hang them in such a way that they do not touch each other.
� Rub both the balloons with a woolen cloth and release them.
� What do you observe?
� The balloons repel each other.
� Now take a refill and hang it.
� Rub that refills with polythene.
� Take one more refill; rub this also with polythene.
� Bring it close to the already charged refill.

 

Be careful not to touch the charged end with your hand. Now, what do you observe? You will observe that the refills repel each other.

 

So we see that-
� A charged balloon repels a charged balloon
� A charged refill repels a charged refill.

 

This means that both the charged balloons have the same charge and so repel each other.
Similarly, both charged refills have the same charge so they repel each other. Now once again charge the balloon by rubbing it with a woolen cloth and bring a refill charged by rubbing with polythene, close to it. What do you observe? They attract each other.

 

Why a charged balloon attracts a charged refill?

 

This is because the charge on the balloon is of a different kind from the charge on the refill and so the opposite charges attract each other.

 

So, we can conclude that similar charges repel each other and opposite charges attract each other