Question

Susceptibility of a ferromagnetic substance is _______________ .
A) > 1
B) < 1
C) Zero
D) 1

Answer 1

Hint: Susceptibility of a material is defined as the ratio of the magnetization of the material to the field intensity. Ferromagnetic materials are substances that get strongly magnetized when placed in an external field. This suggests that they have large positive values for susceptibility.

Formula used:
Susceptibility of a material is given by, ${\chi _m} = \dfrac{M}{H}$ where $M$ is the magnetization of the material and $H$ is the magnetic intensity of the applied field.

Complete step by step answer:
Step 1: Mention the features of ferromagnetic substances which result in high positive values for susceptibility ${\chi _m}$ .
Ferromagnetic materials when placed in an external magnetic field get strongly attracted to the magnetic field. In the absence of the magnetic field, the dipole moments of the atoms interact with each other and spontaneously orient themselves along a common direction leading to the formation of domains. Each domain has a different direction. So when no external field is present, there is no bulk magnetization. But in the presence of a magnetic field, all these domains will align themselves in the direction of the applied field and thus give rise to strong magnetization. Now even if the field is removed, the magnetization persists in them and can be made to zero only on increasing the field in the reverse direction. So ferromagnetic materials are usually preferred to make permanent magnets.

Thus the susceptibility of a ferromagnetic material must be greater than 1. i.e., ${\chi _m} = \dfrac{M}{H} > 1$ where $M$ is the magnetization of the material and $H$ is the magnetic intensity of the applied field. So, the correct option is A.

Additional information:
The susceptibility of paramagnetic materials has small positive values whereas, diamagnetic materials have small negative values for susceptibility.
A graph depicting the difference in the susceptibility of the three different materials is given below.

Note:
Magnetic susceptibility is basically a measure of how well a given magnetic material gets magnetized. The susceptibility will be positive if the material gets attracted to the external field and it is negative if the material repels the external field. Ferromagnetic materials are strongly attracted to magnets.