A rule devised by Georg Simon Ohm, a 19th-century German physicist, to formulate the relationship between the electric current passing through the material of an electrical circuit and the resistance of the material in the electrical circuit.

The basic statement made by Ohm's law is that the current in any circuit is proportional to the voltage that is applied to the circuit.

The value of the resistance depends on the material of which the circuit is made and varies with the temperature of the material. A pure metal whose temperature is drastically reduced usually has its resistivity lowered by many orders of magnitude.

Ohm's law is extremely useful in the design and analysis of electric circuits made of many different kinds of material.