ampere ăm´pēr [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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