Question

When ebonite rod is rubbed with cat’s skin, charge developed on ebonite rod is
A) Positive
B) Negative
C) Cannot be said
D) None of the above

Answer 1

Hint: The electrons of the rod are more tightly bound than the electrons in cat’s fur. Due to this when ebonite rod is rubbed with cat’s fur, the fur loses electrons and the rod gains them. This increases negative charge in the rod. While the rod does not lose any electrons. The exchange of electrons takes place due to the chemical bond of rod and fur while rubbing.

Complete answer:
Whenever an ebonite rod is rubbed with cat’s fur, the rod develops negative charge. Ebonite rod is special vulcanized rubber used in many ways like electrical insulation materials, instruments, fountain pens etc. this ebonite rod has tightly bound particles which do not easily lose electrons from it. So when it is rubbed with cat’s fur, the fur easily loses electrons from it but the rod does not. So the rod gains negative charge and fur gains positive charge.

The same process happens when a glass rod is rubbed with silk cloth. In both phenomena all materials gain some charge. This is due to the chemical bonding between the surfaces. They transfer their charges to get neutralized. According to the law of conservation of charges, charges can neither be created nor be destroyed, they can only be transferred from one form to another. This law is applicable in all conditions. So in these phenomena charges are not created they just get transferred from one body to another because of charge density. Therefore ebonite rod gets negative charge and fur acquires positive charge.

Therefore, option (B) is the correct answer.

Note: Here, no charge is being created or destroyed. The electrons from the cat's fur are transferred to the rod. Therefore the rod acquires negative charge and fur acquires positive charge. And this is because of the frictions produced by rod and fur. Friction causes difference in charges. When the density of charges changes in both the bodies, transfer of electrons takes place.