The volt (symbol: V) is the SI derived unit of electric potential difference or electromotive force . It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first modern chemical battery.

## Definition

One volt is the potential difference between two points measured in joules per coulomb (1 volt is one joule per coulomb). Hence, it is 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. #### Josephson junction definition

Since 1990 the volt is maintained internationally for practical measurement using the Josephson effect, where a conventional value is used for the Josephson constant, fixed by the 18th General Conference on Weights and Measures as

K{J-90} = 0.4835979 GHz/µV.

## Hydraulic analogy

In the hydraulic analogy sometimes used to explain electric circuits by comparing them to water-filled pipes, voltage is likened to water pressure - it determines how fast the electrons will travel through the circuit. Current (in amperes), in the same analogy, is a measure of the volume of water that flows past a given point, the rate of which is determined by the voltage, and the total output measured in watts. The equation that brings all three components together is: volts × amperes = watts