Induction of an electromotive force (EMF) in a circuit by varying the magnetic flux linked with the circuit is called Electromagnetic Induction. The phenomenon was first investigated in 1830-31 by Henry and 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 and is in such a direction as to oppose any further change in the magnetic flux.