Ans. The electromotive force (emf) of a battery or a cell is the total energy supplied in driving one coulomb of charge round a complete circuit in which the cell is connected. The complete circuit includes the cell itself and an external circuit connected to the terminals. Whereas the potential difference determines the energy required between any two points of the circuit, in moving a charge from one point to another.
Unit: The e.m.f. and potential difference both are measured in volts.