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A coil is hung in a uniform magnetic field with its plane parallel to the field lines. When current flows through the coil, it begins to oscillate and is hard to bring to rest. However, if an aluminium sheet is brought close to the coil, the motion stops. This happens because:
- the sheet produces air currents when it is placed nearby
- electric charge is induced on the aluminium sheet
- the magnetic field lines are shielded since aluminium is a paramagnetic substance
- electromagnetic induction in the aluminium sheet produces damping
Correct answer: electromagnetic induction in the aluminium sheet produces damping
Solution
The moving/oscillating coil's changing flux induces eddy currents in the nearby aluminium sheet (electromagnetic induction). By Lenz's law these oppose the motion, dissipating energy and damping the oscillation to rest.
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