In a circuit, the electromotive force is the energy per unit charge converted from the other forms of energy into electrical energy to move the charge across the whole circuit. In equation, where E = e.m.f., W = energy converted from non-electrical forms to electrical form Q = positive charge.
The unit of e.m.f. is JC-1 or V (Volt)
The electromotive force of 1 Volt means that 1 Joule of electrical energy is supplied to the circuit to move 1 Coulomb of charge across the whole circuit.