Induction of an electromotive force in a circuit by varying the magnetic flux linked with the circuit. The phenomenon was first investigated in 1830–31 by Joseph Henry and Michael Faraday, who discovered that when the magnetic field around an electromagnet was increased or decreased, an electric current could be detected in a separate nearby conductor. A current can also be induced by constantly moving a permanent magnet in and out of a coil of wire, or by constantly moving a conductor near a stationary permanent magnet. The induced electromotive force is proportional to the rate of change of the magnetic flux cutting across the circuit.
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