Question

Electromotive force of a cell

Answer 1

By definition, the electromotive force (emf) of a cell is the sum of the electric potential differences produced by a separation of charges that can occur at each phase boundary in the cell.

Devices (known as transducers) provide an emf by converting other forms of energy into electrical energy, such as batteries (which convert chemical energy) or generators (which convert mechanical energy).

See https://en.wikipedia.org/wiki/Electromotive_force.