What is electromotive force?

Electromotive force

An external energy source is required by most electrical circuits to move charge through the circuit. The circuit therefore must include a device that maintains a potential difference between two points in the circuit, just as a circulating fluid requires an analogous device that maintains a pressure difference between two points.

Any device that performs this task in an electrical circuit is called a source of electromotive force. It is sometimes useful to consider a source of emf as a mechanism that creates a “hill” of potential and moves charge “uphill” from which the charge flows “downhill” through the rest of the circuit. A common source of emf is the ordinary battery; another is the electric generator found in power plants. Solar cells are sources of emf used both in found sources of emf are fuel cells and thermopiles.