ampere ămˈpēr [key], abbr. amp or A, basic unit of electric current. It is the fundamental electrical unit used with the mks system of units of the metric system. The ampere is officially defined as the current in a pair of equally long, parallel, straight wires 1 meter apart that produces a force of 0.0000002 newton (2 × 10−7 N) between the wires for each meter of their length. Current meters such as ammeters and galvanometers are calibrated in reference to a current balance that actually measures the force between two wires.

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