Question

Identify the incorrect statement from the following.

• A. The susceptibility of a diamagnetic material is a positive quantity.
• B. Paramagnetic materials obey Curie's law.
• C. Ferromagnetic materials have permanent magnetic domains.
• D. In soft ferromagnetic material, the magnetisation disappear on removal of the external field.

Answer 1

Answer: (A)

Susceptibility of a diamagnetic material is a negative quantity, $(\chi <0)$ while paramagnetic; ferromagnetic and superparamagnetic material have positive susceptibility $(\chi >0)$, hence it is incorrect statement.
Paramagnetic materials obey Curie's law.
Ferromagnetic materials have permanent magnetic domains and each domain contains near about $10^{17}$ atoms.
Magnetisation of soft ferromagnetic substance disappear easily after removal of external magnetic field.
So, among the given statements statement $(a)$ is incorrect.