eddy current

Eddy currents

Eddy currents (I, red) induced in a conductive metal plate (C) as it moves to the right under a magnet (N). The magnetic field (B, green) is directed down through the plate. The Lorentz force of the magnetic field on the electrons in the metal induces a sideways current under the magnet. The magnetic field, acting on the sideways moving electrons, creates a Lorentz force opposite to the velocity of the sheet, which acts as a drag force on the sheet. The blue arrows are counter magnetic fields generated by the circular motion of the charges.

An eddy current is a circulatory current induced (see induction) in a conductor when subjected to a varying magnetic field. Eddy currents cause a loss of energy in AC generators and motors: the reaction between the eddy currents in a moving conductor and the field in which it moves retards the motion of the conductor.