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A coil is suspended in a uniform magnetic field with the plane of the coil parallel to the field lines. When current is passed it begins to oscillate and is hard to stop. However, placing an aluminium plate nearby quickly damps the oscillations. The reason is:

1. Eddy currents (electromagnetic induction) in the aluminium plate cause electromagnetic damping
2. Air currents generated when the plate is placed
3. Electric charge induced on the plate
4. Aluminium shields the magnetic field lines because it is paramagnetic

Correct answer: Eddy currents (electromagnetic induction) in the aluminium plate cause electromagnetic damping

Solution

As the coil oscillates, the magnetic flux through the nearby aluminium plate changes, inducing eddy currents in it. By Lenz's law these currents oppose the change that produced them, exerting a retarding effect and dissipating energy as heat in the plate. This electromagnetic damping rapidly stops the oscillations.

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