Eddy Currents

Foucault in the year 1895 observed that when a mass of metal moves in a magnetic field or when the magnetic field through a stationary mass of metal is altered, induced current is produced in the metal.

This induced current flows in the metal in the form of closed loops resembling ‘eddies’ or whirl pool. Hence this current is called eddy current. The direction of the eddy current is given by Lenz’s law.

When a conductor in the form of a disc or a metallic plate swings between the poles of a magnet, eddy currents are set up inside the plate.

This current acts in a direction so as to oppose the motion of the conductor with a strong retarding force, which the conductor almost comes to rest.

If the metallic plate with holes drilled in it is made to swing inside the magnetic field, the effect of eddy current is greatly reduced consequently the plate swings freely inside the field.

Eddy current can be minimised by using thin laminated sheets instead of solid metal.

Applications of eddy currents:

Ø Dead beat galvanometer

Ø Induction furnace

Ø Induction motors

Ø Electromagnetic brakes

Ø Speedometer

Disadvantages:

Ø Dissipate electrical energy in the form of heat.

Ø Overheating of metallic cores of transformers, electric motors and other such devices.