The Emf of a Source

The emf (electromotive force) ε of a source is the energy transferred into electrical energy per unit charge passing through the source, ε = W/Q. It is measured in volts, where 1 V = 1 J C^-1.A source such as a cell, battery or generator does work on the charge carriers, giving them electrical energy. A cell converts chemical energy, a solar cell converts light energy, and a generator converts kinetic energy.Despite its name, emf is not a force. It describes the energy supplied per coulomb by the source, while potential difference describes the energy transferred per coulomb by the charge to the components in the circuit.For example, a 1.5 V cell gives each coulomb of charge 1.5 J of electrical energy. In one minute with a current of 2 A, 120 C of charge passes through it and it transfers 1.5 × 120 = 180 J.In a complete circuit, the emf equals the sum of the potential differences around the circuit. Real sources also have internal resistance, so some of this energy is wasted inside the source itself.