unit of electrical potential, potential difference and electromotive force in the metre–kilogram–second system (SI); it is equal to the difference in potential between two points in a conductor carrying one ampere current when the power dissipated between the points is one watt. An equivalent is the potential difference across a resistance of one ohm when one ampere is flowing through it. The volt is named in honour of the 18th–19th-century Italian physicist Alessandro Volta. These units are defined in accordance with Ohm's law, that resistance equals the ratio of potential to current, and the respective units of ohm, volt, and ampere are used universally for expressing electrical quantities. See also electric potential; electromotive force.