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 and it is very difficult to stop. But if an aluminium plate is placed near to the coil, it stops. This is due to :
1
development of air current when the plate is placed
2
induction of electrical charge on the plate
3
shielding of magnetic lines of force as aluminium is a paramagnetic material
4
electromagnetic induction in the aluminium plate giving rise to electromagnetic damping