watt [for James Watt], abbr. W, unit of power, or work done per unit time, equal to 1 joule per second. It is used as a measure of electrical and mechanical power. One watt is the amount of power that is delivered to a component of an electric circuit when a current of 1 ampere flows through the component and a voltage of 1 volt exists across it. The derivative units are kilowatt (1,000 W; kW) and megawatt (1,000,000 W; MW), used in electric power systems, and milliwatt (0.001 W; mW) and microwatt (0.000001 W; μW), used in electronics.

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