A coil is suspended in a uniform magnetic field, with the plane of the coil parallel to the magnetic lines…
A coil is suspended in a uniform magnetic field, with the plane of the coil parallel to the magnetic lines of force. When a current is passed through the coil it starts oscillating; it is very difficult to stop. But if an aluminium plate is placed near to the coil, it stops. This is due to :
development of air current when the plate is placed.
induction of electrical charge on the plate
shielding of magnetic lines of force as aluminium is a paramagnetic material.
electromagnetic induction in the aluminium plate giving rise to electromagnetic damping.
Solution
Oscillating coil produces time variable magnetic field. It cause eddy current in the aluminium plate which causes anti-torque on the coil, due to which is stops.