Practical Physics is a free textbook on basic laboratory physics. See the editorial for more information....

# Electromotive Force

The work done in moving a unit quantity of positive electricity from one point to another is called the electromotive force between those points.

Hence, if the electromotive force (denoted by the symbols E.M.F.), between two points be E, the work done in moving a quantity e of positive electricity from the one point to the other is Ee. Electromotive force is sometimes defined as the force which tends to move electricity; the definition is misleading. The name itself is perhaps ambiguous, for the electromotive force between two points is not force, but work done in moving a unit of positive electricity; it, therefore, has the dimensions of work divided by electrical quantity (see p. 20). The term electromotive force at a point, however, is sometimes used as equivalent to the resultant electrical force. We shall avoid the term.

Suppose that a single body charged with positive electricity is being considered, then it is found that the force which this body exerts on any electrified body decreases very rapidly as the distance between the two bodies is increased, becoming practically insensible when the distance is considerable. We may define as the field of action of an electrified system of bodies that portion of space throughout which the electrical force which arises from the action of those bodies has a sensible value. If a quantity of positive electricity be moved from any point of the field to its boundary by the action of the electrical forces, work is done.

Last Update: 2011-03-19