When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

Explanation

When two electrically neutral bodies (with net charge zero) are rubbed with each other part of energy spent for rubbing is given to some electrons which get transferred from one body to another body. If first body loses N no. of electrons then second body gains equal no. of electrons. Thus, in this process of "charging by friction" final charge on first body becomes + Ne and final charge on second body becomes - Ne. Hence, total final charge in the final condition would be Ne + (- Ne) = 0, same as total initial charge which was 0 + 0 = 0. Thus, total charge gets conserved. (It should be noted that here, total mass is also conserved).