Question

What will happen when we rub a glass rod with silk cloth?
A. Some electrons from the glass rod are transferred to the silk cloth.
B. The glass rod gets positive charge and silk cloth gets negative charge.
C. New charge is created in the process of rubbing.
D. Both (A) and (B) are correct.

Answer 1

When a glass rod is rubbed over some surface, it gains energy due to friction. Friction between the surface and glass rod does some work, which goes in the energy of the electrons of the material of the rod. These electrons after getting a particular amount of energy, called the ionization energy of the material of rod gets transferred to the cloth and hence cloth becomes rich in electrons (charged).

Complete answer:
As charge can neither be created nor be destroyed, hence no new charge is created during the process of rubbing. The rod after achieving its ionization energy loses some electrons which gets transferred to the cloth. Now it means that cloth is electron rich or excess in electrons. As electrons carry negative charge, hence on cloth, negative charge gets in excess.
Now, positive charge means deficiency of electrons. As some electrons get transferred from glass rod to the silk cloth, hence glass rod becomes electron deficient and hence it achieves positive charge.
Hence both options (A) and (B) are correct, option D. is correct.

Note:
There is a misconception in the mind of students that positive charge means that there is an excess of protons. But one must understand that protons are bound in a dense nucleus and hence can be separated. Hence proton transfer is not possible in ordinary conditions. Positive charge means that there is electron deficiency in the region.