Question

The materials suitable for making electromagnets should have:
(A) high retentivity and high coercivity
(B) low retentivity and low coercivity
(C) high retentivity and low coercivity
(D) low retentivity and high coercivity

Answer 1

Hint: The material used in an electromagnet should be such that on the removal of current it loses its magnetisation completely. And it should also have the ability to get demagnetised easily on passing an external electric field.

Complete step by step answer
The word retentivity of an electromagnet means the property of an electromagnet to retain the magnetism even in the absence of the magnetising field.
Now the electromagnet is a type of a magnet where the magnetic field is produced due to the electric current passing through it. It generally consists of a wire which is wound into a coil. While the electric current passes, it behaves similar to a magnet but as soon as the current is stopped then the substance becomes demagnetised.
So the property of the electromagnet should be such that it loses the magnetising property when the current is switched off. Hence a substance with low retentivity should be used in order to make an electromagnet.
The term coercivity means the ability of a material to withstand an external magnetic field without being demagnetised. So for an electromagnetic material, the magnetising field which is to be needed to demagnetise the material completely should be low. So the material with low coercivity should be used to make electromagnets.
Hence the correct answer will be option (B).

Note
A few very common uses of electromagnets in our daily life are as follows,
-Transformers
-Electric bells or buzzers
-Loud speakers and headphones, etc.