Ampere

Ampere, pronounced AM pihr, is the unit used to measure the rate of flow of an electric current. It is one of seven base units in the metric system. There is an electric current of 1 ampere when 1 unit of electric charge flows past a cross section of an electric circuit in 1 second. The unit of electric charge is called a coulomb (see Coulomb). Thus, 1 ampere equals 1 coulomb per second. Physicists also define amperes in terms of the magnetic force produced by electric currents in parallel wires.

A 100-watt light bulb requires about 1 ampere of current at 100 volts. Calculators and computers use currents so tiny they are measured in microamperes (millionths of amperes). Large industrial equipment uses currents measured in kiloamperes (thousands of amperes). The ampere was named for the French physicist Andre Marie Ampere. He was the first person to show that currents flowing through parallel wires cause magnetic forces between the wires (see Ampere, Andre Marie).

Contributor: Raymond D. Findlay, Ph.D., Director, Engineering and Management, McMaster Univ.

Ampere

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