Eddy current - Definition and Overview

An Eddy Current is a phenomenon caused by a moving magnetic field intersecting a conductor. The moving magnetic field causes a flow of electrons or current in the conductor that creates an opposing magnetic field, an electro-magnet(see Lenz's law.) The stronger the magnetic field and greater the conductivity of the conductor the greater the opposing force. This is used to great effect in movement to electricity converters such as electrical generators and dynamic microphones. Friction within the conductor, or resistance, cause a dragging effect that has been used for braking and damping. Superconductors which allow perfect, loss-less conduction create a perfect eddy current that entirely cancels the opposing magnetic force allowing magnetic levitation.

Eddy currents are used for braking at the end of some roller coasters; this mechanism has no mechanical wear, and produces a very precise braking force. Typically extensions on the car are moved between pairs of very strong permanent magnets.

An analogous eddy current is seen in water when dragging an oar, localised areas of turbulence give rise to vortices, which persist for a while then dissipate.