Energy per unit electric charge that is imparted by an energy source, such as an electric generator or a battery .
As the device does work on the electric charge being transferred within itself, energy is converted from one form to another. The work done on a unit of electric charge or the energy gained by the unit charge is the electromotive force emf (or E) and is characteristic of any energy source capable of driving electric charge around a circuit. A common unit of electromotive force is the volt V , a unit equal to the difference in electric potential between two points in a conductor carrying a current of one ampere and dissipating one watt of power between the two points.