Answer to Question #45263 in Electricity and Magnetism for TAKUDZWA

Question

suggest three methods that can be used to demagnetise the bar.

Answer 1

The magnetized steel can be demagnetized by 1) hammering, by 2) heating or by 3) slowly pulling it out of a coil carrying an alternating current.

Hammering
When a magnet is hammered or dropped, the vibrations caused by the impact on the magnet randomize the magnetic molecules within the magnet, forcing them out of order and destroying the long-range order of the unit magnet.

Heating
Heating a piece of magnetized metal in a flame will cause demagnetization by destroying the long-range order of molecules within the magnet. By heating a magnet, each molecule is infused with energy. This forces it to move, pushing each molecule out of order within the magnet and leaving the piece of metal with very little or no magnetization.

Alternating Current (AC) Field
Using an AC current produces a magnetic field which can be moved and reduced to demagnetize materials. The field created by the AC current drags the magnetic molecules of the magnet in different directions. When the AC current is altered or reduced, the molecules within the magnet do not all return to previous positions, causing randomization of the molecules and reducing the force of the magnet.