Eddy Currents - Practice Questions & MCQ

 Eddy currents:

An eddy current is a current set up in a conductor in response to a changing magnetic field. They flow in closed loops in a plane perpendicular to the magnetic field. By Lenz law, the current swirls in such a way as to create a magnetic field opposing the change. They are known as eddy currents as they are in the pattern of eddies in the water. Because of the tendency of eddy currents to oppose, eddy currents cause a loss of energy. Eddy currents are undesirable since they heat up the core and dissipate electrical energy in the form of heat.

 Direction of eddy current:

For the above figure, the 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 as shown in the above figure.

Eddy currents are used to advantage in certain applications like-

1. Magnetic braking in trains-Strong electromagnets is 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.
2. Induction furnace-Induction furnace can be used to produce high temperatures and can be utilized to prepare alloys, by melting the constituent metals. A high-frequency alternating current is passed through a coil that surrounds the metals to be melted. The eddy currents generated in the metals produce high temperatures sufficient to melt it.
3. Electromagnetic damping
4. Electric power meters

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