Q.Siddhi was a student of Class 12 Science. She went to visit a Science Centre with her friends. There she saw a magnet oscillating through a string. She observed that oscillation stops when a metal plate is kept under the oscillating magnet. She could not understand the reason. She discussed with her friends that oscillation will continue or stop when magnet is kept under the oscillating metal plate. Next day they went to their Science Teacher and became happy to know the reason of the phenomenon.

Eddy currents induced in the moving metal oppose the motion, so the oscillation is damped (electromagnetic damping).

When a metallic sphere oscillates in a magnetic field, the flux through the metal changes continuously. By Faraday's law this induces circulating eddy currents in the body of the metal. By Lenz's law these currents always flow in a direction that opposes the change producing them — i.e. they oppose the motion of the sphere.

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Eddy currents are induced circulating currents in any bulk conductor experiencing a changing flux, and they are deliberately exploited in all three listed devices.

Eddy currents arise whenever a conductor experiences a time-varying magnetic flux (Faraday's law), inducing loops of current within the body of the conductor itself (not confined to a wire), which by Lenz's law oppose the change and dissipate energy as heat ($I^2R$ loss) or produce a retarding force.

• Induction furnace: a high-frequency alternating magnetic field induces strong eddy currents in a metal sample placed inside a coil; the resistive ($I^2R$) heating from these currents melts the metal — used industrially to melt metals without any external heat source touching them. …

Eddy currents are induced circulating currents in a bulk conductor moving through (or exposed to a changing) magnetic field; their heating and opposing-force effects are put to practical use in several devices.

Eddy currents are induced whenever a conductor experiences a changing magnetic flux, and by Lenz's law they oppose the change that produces them. This gives useful applications:

• Magnetic braking in trains: electromagnets are switched on near the rails/wheels; the induced eddy currents oppose the motion, bringing the train to a smooth stop without mechanical contact wear. …

Currents induced in the bulk of a conductor by a changing magnetic flux, which dissipate energy as heat, are called eddy currents.

Whenever the magnetic flux linked with a piece of metal (not just a wire loop) changes with time, Faraday's law of electromagnetic induction still applies locally within the bulk of the conductor. This sets up circulating (swirling, or 'eddy'-like) induced currents inside the metal body itself. Because the metal has finite resistance, these currents dissipate electrical energy as heat (I²R loss) — this is used usefully in ind …

The core of a transformer is laminated with insulated iron sheets to reduce eddy currents, which otherwise cause wasteful heating and energy loss.