Question

When a comb is rubbed with hair, it attracts paper bits. Choose the right explanation:
(A) Bits of paper gets attracted due to gravitational force.
(B) Due to the electromagnetic effect, bits of paper are attracted.
(C) Comb gets charged by friction and attracts bits of paper.
(D) None of these.

Answer 1

Hint: When a comb is rubbed with hair, some electrons are brushed off from the hair and stick on the surface of the comb. The surface of the comb, being made of plastic (which is a poor conductor of electricity), does not allow these electrons to move within the surface easily. This creates an imbalance in the charge distribution and causes the comb to attract bits of paper.

Complete Answer:
When dry hair is rubbed with a comb, the type of motion taking place is not smooth. Some friction force is generated due to the process of brushing. When it is repeated, rubbing the hair with a comb easily gives off the loosely bound electrons on the surface of the hair. These electrons are acquired by the comb as it brushes the hair. Since a comb is generally made of plastic or wood, both of which are poor conductors of electricity, the electrons acquired by the comb are unable to leave the surface or travel along the surface. This causes the comb to get charged.
When the charged comb is brought near bits of paper, the electrostatic force of attraction between the atoms of the paper and the comb caused by the electrons on the surface of the comb polarizes them which attracts the pieces of paper towards the comb. The paper bits, being small in weight defy gravity and stick to the comb.
Thus the reason why a charged comb attracts bits of paper is that it gets charged by friction. Therefore, option (C) is the correct answer.

Note:
Objects like wool, hair or glass rod tend to give off electrons, and get positively charged. While objects like silk or plastic comb acquire electrons and get negatively charged. It is to be noted that all of these materials are insulators. Conductors are hard to get charged with electrons because they allow electrons to flow through their body and lose them immediately.