Magnetised Aluminum You may already know that a magnet not attract an aluminum d

Question

Magnetised Aluminum You may already know that a magnet not attract an aluminum disk. But there is a case when it does and we would like you to argue a reason why. Suspend the magnet above the disk which is balanced and free to rotate over a support. If you set the magnet spinning then the disk will start spinning as well. Why does the aluminum disk spin in this case? and will it spin in the same direction as the magnet? Turning in the shade. Consider an alternating magnet (solenoid, with alternating current). Place a copper disk is free to one of the poles. The disc is repelled with no sign of rotation. Any idea it gets repelled? Next, insert a sheet of copper between magnet and disk, partially shading the magnetic field. The disk starts to rotate. Why?

Explanation / Answer

Aluminium is a paramagnetic material,

when an external magnetic field is applied the magnetic dipoles in the material are alligned to the applied field and the magentic field inside the material is more than the applied field, Under the influence of the applied field the alumnium disk is magnetised and it spins with the magnetic field , the spin is in the same direction.

c) copper is dia magnetic , the magnetic dipoles are aligned opposite to the direction of applied field. The magntic filed inside the disk is opposite to the applied field and hence the disk is repelled

when the field is partially shaded by the copper sheet, there is an imabalance of the mgnetic force on the two side of the disk resulting ina net torque on the disk and the disk rotates.

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