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What are eddy currents ? How the eddy currents are reduced in metallic cores ?
State two uses of eddy currents ?

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Hint: The term eddy current comes from analogous currents seen in water in fluid dynamics, causing localized areas of turbulence known as eddies giving rise to persistent vortices.
Somewhat analogously, eddy currents can take time to build up and can persist for very short times in conductors due to their inductance.

Complete step by step answer:
Eddy currents:- These are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday’s law of electromagnetic induction.
Eddy current flow in circular or closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet or the transformer.
The magnitude of the eddy current in a given loop is proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux, and inversely proportional to the resistivity of the material.
Methods to reduce eddy currents :-
The eddy’s current are a cause of energy loss in alternating current (AC) inductors, transformers, electric motors and generators and other AC appliances or machinery they are reduced by laminating the magnetic cores.
Eddy currents are reduced by using multiple plates instead of using a large plate.
Application of eddy currents:
- Electromagnetic braking
- Repulsive effects and levitation
- Identification of metals
- Vibration and position sensing
- Structural testing
- Induction heating
- Mechanical speedometer.

Note:
The first person to observe eddy currents was Francois Arago (1786-1853), the 25th prime minister of France, who was also a mathematician, physicist and astronomer.
In 1824 he observed what we called rotator magnetism, and that most conductive bodies could be magnetized; these discoveries were further completed and explained by Michael Faraday.