Question

What are permanent magnets? What is an efficient way of preparing a
permanent magnet? Write two characteristic properties of materials which are required to select them for making permanent magnets.

Answer 1

Permanent Magnets: The magnets prepared from ferromagnetic materials that retain their magnetic properties for a long time are called permanent magnets.
An efficient way to make a permanent magnet is to place a ferromagnetic rod in a solenoid and pass current. The magnetic field of the solenoid magnetizes the rod.
The materials used for permanent magnet must have the following characteristic properties:

(i) High retentivity so that magnet may cause a strong magnetic field.

(ii) High coercivity so that the magnetization is not wiped out by strong external fields, mechanical ill-treatment, and temperature changes. The loss due to hysteresis is immaterial because the magnet in this case is never put to cyclic changes.