Eddy Currents

Discovered by Foucault, aka Foucault's Currents.

Eddy cause they look like eddies or whirl-pools in water

Eddy currents are the currents induced in solid metallic masses when the metallic flux threading through them changes.

it is found that the motion of a copper plate pendulum is damped and in a little while the plate comes to a halt in the magnetic field. Magnetic flux associated with the plate keeps on changing as the plate moves in and out of the region between magnetic poles. The flux change induces eddy currents in the plate. Directions of eddy currents are opposite when the plate swings into the region between the poles and when it swings out of the region

area available to the flow of eddy currents is less in the pendulum plate with holes or slots and thus reduces electromagnetic damping and the plate swings more freely

Eddy currents are undesirable since they heat up the core and dissipate electrical energy in the form of heat. They are produced inside the iron cores of rotating armatures and dynamos and cores of transformers. They might even damage the insulation of coils.

Eddy currents are minimised by using laminated cores which consist of thin sheets of metal insulated from each other by a thin layer of varnish like lacquer. The planes of these sheets are placed perpendicular to the direction of currents. This arrangement reduces the strength of the eddy currents.

Applications :

Magnetic brakes in trains : Strong electromagnets are situated above the rails in some electrically powered trains. When the electromagnets are activated, the eddy currents induced in the rails oppose the motion of the train. As there are no mechanical linkages, the braking effect is smooth.
Electromagnetic Damping: Certain galvanometers have a fixed core made of nonmagnetic metallic material. When the coil oscillates, the eddy currents generated in the core oppose the motion and bring the coil to rest quickly.
Induction furnace : Induction furnace can be used to produce high temperatures and can be utilised to prepare alloys, by melting the constituent metals. A high frequency alternating current is passed through a coil which surrounds the metals to be melted. The eddy currents generated in the metals produce high temperatures sufficient to melt it.
Electric power meters: The shiny metal disc in the electric power meter (analogue type) rotates due to the eddy currents. Electric currents are induced in the disc by magnetic fields produced by simultaneously varying currents in a coil.

	Created by Mahek Agarwal over 3 years ago

XI Physics Note on electromagnetic induction, created by Mahek Agarwal on 26/08/2021.