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The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second,[1] and is used to quantify the rate of energy transfer. In SI base units, the watt is described as kg⋅m2⋅s−3.[2] The watt is named after James Watt, an 18th-century Scottish inventor.

Examples

When an object's velocity is held constant at one meter per second against a constant opposing force of one newton, the rate at which work is done is one watt.

${\displaystyle \mathrm {1~W=1~{\frac {J}{s}}=1~{\frac {N{\cdot }m}{s}}=1~{\frac {kg{\cdot }m^{2}}{s^{3}}}} }$

In terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V), meaning the watt is equivalent to the volt-ampere (the latter unit, however, is used for a different quantity from the real power of an electrical circuit).