Assertion Explained: Attraction of Paper by Comb

When a comb is rubbed vigorously with dry hair, it picks up an electric charge. This phenomenon is a classic demonstration of static electricity. The charged comb can then attract small, lightweight, uncharged objects like tiny pieces of paper. This attraction occurs because the charged comb influences the distribution of charges in the nearby paper bits (polarization), leading to an attractive electrostatic force between the comb and the paper. Thus, the statement that a comb rubbed with dry hair attracts small bits of paper is correct.

Reason Explained: Charging Mechanism and Electron Transfer

The process of rubbing two different materials together, like a comb and hair, can cause a transfer of electrons between them. This is known as charging by friction or the triboelectric effect. Depending on the materials involved, one object tends to lose electrons and become positively charged, while the other gains electrons and becomes negatively charged. The reason states that the comb gains electrons from the hair, acquiring a negative charge. This is a common outcome when certain types of combs (like plastic) are rubbed with hair. The gained electrons make the comb negatively charged.

Linking Assertion and Reason

The phenomenon described in the Assertion (attraction of paper bits) is directly caused by the charging process described in the Reason. When the comb acquires a negative charge by gaining electrons from the hair, this charge enables it to exert electrostatic forces on nearby objects, such as the small bits of paper. The negatively charged comb attracts the positive ends of the induced dipoles in the paper bits, resulting in the observed attraction. Therefore, both the Assertion and the Reason are true, and the Reason correctly explains the Assertion.