Electromotive Force (e.m.f.)

The e.m.f. of a source is the total energy it provides per coulomb of charge:

$\varepsilon = \frac{W}{Q}$

Despite its name, e.m.f. is not a force. It is measured in volts (joules per coulomb).

In a circuit, the e.m.f. of the source equals the sum of the potential differences across all components (including any internal resistance of the source).