The strength of an electric current in any circuit is directly proportional to the electromotive force developed in that circuit and inversely proportional to the resistance of the circuit; i. e., is equal to the quotient obtained by dividing the electromotive force by the resistance.

Ohm's law may be expressed thus:

Strength of current = electromotive force.

resistance (1.)

6. The three principal units used in practical measurements of a current of electricity are:

(a) The ampere, or the practical unit denoting the rate of flow of an electric current, or the strength of an electric current.

(b) The ohm, or the practical unit of resistance.

(c) The volt, or the practical unit of electrical potential or pressure.

The usual form in which Ohm's law is given is

C= E/R.


The electromotive force, or pressure, (E) is here expressed in volts, the resistance (R) in ohms, and the current (C) in amperes.