Electro-motive Force

Electromotive force (emf) is the source of electrical energy for a whole circuit. It is measured in volts (V).

Emf (in volts) is the amount of energy (in joules) given to each coulomb of charge as it passes round the circuit.

The battery in an electrical circuit can be thought of as pushing electrical charge round the circuit to make a current. It also transfers energy to the electrical charge. The electro-motive force (e.m.f.) of the battery, measured in volts, measures how much ‘push’ it can provide and how much energy it can transfer to the charge.emf

Scientists now know that electric current is really a flow of electrons around the circuit from negative to positive. Unfortunately, early scientists guessed the direction of flow incorrectly. Consequently all diagrams were drawn showing the current flowing from positive to negative. This way of showing the current has not been changed and so the conventional current that everyone uses gives the direction that positive charges would flow.

Current Convention