Electromotive force - the charge


Electromotive force, abbreviated emf (denoted ℰ and measured in volts) is the electrical intensity or “pressure” developed by a source of electrical energy such as a battery or generator. A device that converts other forms of energy into electrical energy (a “transducer”) provides an emf as its output. (The word “force” in this case is not used to mean mechanical force, as may be measured in pounds or newtons.)

Inside a source of emf that is open-circuited, the conservative electrostatic field created by separation of charge exactly cancels the forces producing the emf. Thus, the emf has the same value but opposite sign as the integral of the electric field aligned with an internal path between two terminals A and B of a source of emf in open-circuit condition (the path is taken from the negative terminal to the positive terminal to yield a positive emf, indicating work done on the electrons moving in the circuit).

If a mole of ions goes into solution (for example, in a Daniell cell, as discussed below) the charge through the external circuit is calculated by the shown formula

Related formulas


ΔQcharge through the external circuit (C)
n0number of electrons/ion (mol)
F0Faraday constant