Question

Electromagnets are made of soft iron because soft iron has
A. high susceptibility and low retentivity
B. low susceptibility and high retentivity
C. low susceptibility and low retentivity
D. high susceptibility and high retentivity

Answer 1

Hint: Soft iron is a special kind of magnetic material which are generally used for making electromagnets because it gets easily magnetised and also loses its magnetism as soon as the inducing field is removed.

Complete step-by-step answer:
To find the answer to this question first of all we have to understand the meaning of terms of magnetic susceptibility and retentivity.
Magnetic susceptibility:- It is the magnetic response of a substance in the presence of an external magnetic field. Magnetic susceptibility is the ratio of the intensity of magnetisation to the magnetic intensity. It is denoted by \[\chi \] and it can be expressed as- \[\chi = \dfrac{I}{H}\], Where ‘I’ is the intensity of magnetisation and ‘H’ is the magnetic intensity.
Retentivity:- It is the ability of a substance to retain its magnetization even after removal of an induced magnetic field.

The soft iron gets easily magnetised due to its high susceptibility and also loses its magnetism as soon as the induced magnetic field is removed because of its low-retentivity.
The hysteresis loop of soft iron has a small area which suggests that there is a minimum loss of electromagnetic field energy in the form of thermal energy. This is also a great reason for choosing soft iron for the making of electromagnets.
Hence, Option (A) is the correct answer.

Note: For solving these kinds of theoretical questions one should have proper in-depth knowledge of the terms related to the magnetic properties of a substance. we also have to understand that magnetic susceptibility is the ratio of two vectors \[\vec I{\text{ and }}\vec H\] but we do not write them in vector form. we use the only ratio of their magnitudes.