# Ohm's law

## Ohm's law

Relationship between the potential difference (voltage), electric current, and resistance in an electric circuit. In 1827 Georg Simon Ohm discovered that at constant temperature, the current I in a circuit is directly proportional to the potential difference V, and inversely proportional to the resistance R, or I = V/R. Resistance is generally measured in ohms (). Ohm's law may also be expressed in terms of the electromotive force E of an electric energy source, such as a battery, or E = IR. In an alternating-current circuit, when the combination of resistance and reactance, called impedance Z, is constant, Ohm's law is applicable and V/I = Z.

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