Electric Charge

When we rub our shoes across a carpet and reach for a metal doorknob, we can be zapped by a spark of electricity. The answers to this lies in the branch of Physics called Electrostatics. The word electricity comes from the Greek word electron, which means "amber." Amber is petrified tree resin, and it was well known to the ancients that if we rub an amber rod with a piece of cloth, the amber attracts small pieces of dry leaves or paper. A piece of hard rubber, a glass rod or a plastic comb rubbed with cloth also display this "amber effect" or static electricity or frictional electricity as we call it today.

Experiments show that there are exactly two kinds of electric charges :

(i) Negative charge

(ii) Positive charge

These also show that unlike charges attract each other while like charges repel each other. The S.I. unit of electric charge is coulomb. It is denoted by symbol C.