Electric Current

When a potential difference is applied across a conductor, an electric field is set up within it. The free electrons move in a direction opposite to the field through the conductor. This constitutes an electric current. Conventionally, the direction of current is taken as the direction in which a positive charge moves. The electrons move in the opposite direction.

The electric current through a conductor is the rate of transfer of charge across a surface placed normal to the direction of flow. The SI unit of current is ampere. Its symbol is A.

I = dq/dt

The current can arise due to flow of negative charges (electrons), as in metals. In a semiconductor, flow of electrons (negative charge) and holes constitutes current. Holes are vacancies in a crystal. These are taken as positively charged particles having the same amount of charge as that on an electron.