Question

Write two properties of a magnet suitable for making (a) a permanent magnet, and (b) an electromagnet.

Answer 1

Hint: Permanent magnets retain their magnetic properties even after the magnetizing factor (magnetizing current) is removed. On the other hand, electromagnets lose their magnetic properties as soon as the magnetizing factor (magnetizing current) is removed.

Complete step-by-step answer:
Permanent magnets are magnets that have magnetic properties even in the absence of any external magnetizing factors such as a magnetizing current. For making a permanent magnet, it is essential that the magnet does not get affected by the stray magnetic fields in its vicinity and hence, permanent magnets are made of materials that have high coercivity. Also, it is essential that permanent magnets retain their magnetic properties for a long time and hence, they are made of materials that have high retentivity.
Electromagnets are temporary magnets. They acquire magnetic properties only as long as they are subjected to a magnetizing current. They usually have an iron core would with a coil through which the current is passed.
For making electromagnets, it is essential that the core has high permeability, so that the magnet can be easily magnetized and the magnetic field produced is strong. Hence, electromagnets are made of materials with high permeability. Also, since electromagnets are magnetized and demagnetized repeatedly, they should be made of materials that have a small hysteresis loop to minimize hysteresis losses.

Note: The main difference in the properties of the materials of which permanent and electromagnets are made is that permanent magnets are made of materials having high retentivity (so that they retain their magnetic properties for a long time), whereas electromagnets are made of materials having low retentivity, since they are magnetized and demagnetized repeatedly, it is convenient if the magnetic properties of the magnet respond quickly to the switching on and off of the magnetizing currents.