An electromotive force (e.m.f.) is induced in a circuit if the flux linkage through the circuit changes.

Faraday’s Law states that the induced e.m.f. $\epsilon$ is directly proportional to the rate of change of magnetic flux linkage $\Phi$ or rate of cutting of magnetic flux linkage $\Phi$.

$\epsilon = \: – \frac{d \Phi}{dt}$

An e.m.f. can be induced by:

- Change in magnitude of B
- Change in the area A enclosed by the coil
- Change in the angle $\theta$
- Any combination of the above