Induction of an electromotive force in a circuit by varying the magnetic flux linked with the circuit.
The phenomenon was first investigated in 183031 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.