The volt is the SI derived unit for electric potential and voltage (derived from the ampere and watt). It is named in honor of Alessandro Volta, who, in 1800, invented the voltaic pile, the first chemical battery.

The volt is defined as the potential difference across a conductor when a current of one ampere dissipates one watt of power. Hence, it is has the base SI representation m² · kg · s^-3 · A^-1, which can be equally represented as one joule of energy per coulomb of charge, J/C.

Since 1990 the volt is maintained internationally using the Josephson effect, where a conventional value is used for the Josephson constant, fixed by the 18th CGPM as

K_{J-90} = 0.4835979 GHz/µV.

SI electricity units

See also

• SI
• Ohm's Law
• Alternating current
• VAC