(a) Inflate two balloons. Hang them in such a way that they do not touch each other (Fig.). Rub both the balloons with a woollen cloth and release them. What do you observe?
Now let us repeat this activity with the used pen refills. Rub one refill with polythene. Place it carefully in a glass tumbler using the tumbler as a stand (Fig.).
Rub the other refill also with polythene. Bring it close to the charged refill. Be careful not to touch the charged end with your hand. Is there any effect on the refill in the tumbler? Do the two attract each other, or repel each other?
In this activity we have brought close together the charged objects that were made of the same material. What happens if two charged objects made of different materials are brought close to each other? Let’s find out.
(b) Rub a refill and place it gently in a glass tumbler as before (Fig.). Bring an inflated charged balloon near the refill and observe.
(a) (i) We observed that balloons repelled each other in the first case. Thus, like charges repel each other.
(ii) In second case, a charged refill repelled another charged refill due to presence of like charges on them.
(b) A charged balloon attracted a charged refill because balloon had charges opposite to that on a refill. Thus, opposite charges attract each other.