File:Eddy current brake diagram.svg

English: A diagram showing how a disk-type eddy current brake works. Eddy current brakes are used in power tools like circular saws to stop the blade quickly, and in electric meters. The brake consists of a spinning conductive metal disk (D) spinning counterclockwise in this example, whose surface is positioned between the poles of a magnet (N and S). The magnetic field (B, green) passing downward through the disk, induces circular electric currents (I, red), called eddy currents in the metal of the disk. At the leading edge of the magnet (left) the magnetic flux is increasing, so the eddy current is counterclockwise. At the trailing edge of the magnet (right) the magnetic flux is decreasing, so the eddy current is clockwise. Due to Lenz's law, the eddy currents create counter magnetic fields (blue) which oppose the magnetic field which created them. At the leading edge of the magnet (left), the counterfield is directed up, creating an opposing force between the advancing surface of the disk and the magnet. At the trailing edge (right) the counterfield is directed down, creating an attractive force between the departing surface of the disk and the magnet. Both these forces oppose the motion of the disk, acting as a drag force slowing it down. The kinetic energy of the disk's rotation is dissipated as heat by the eddy currents flowing through the resistance of the metal. In this drawing, in order to reveal the currents the North pole of the magnet is drawn some distance above the disk. In actual brakes the magnet's poles are located as close as possible to the disk.