Question

The magnetic susceptibility is negative for
A. diamagnetic material only
B. paramagnetic material only
C. ferromagnetic material only
D. paramagnetic and ferromagnetic materials

Answer 1

Hint: Magnetic susceptibility is a proportionality constant that determines the degree of magnetization of a material with respect to the applied magnetic field. It is due to the interactions of electrons and nuclei with the applied magnetic field.

Complete step by step answer:
The expression for the magnetic susceptibility is given as the ratio of magnetization to the applied magnetizing field intensity. Magnetic susceptibility is a dimensionless quantity. The equation can be written as
$\chi =\dfrac{M}{H}$
Where, χ represents the magnetic susceptibility
     M is the magnetization and
     H is the field intensity
Based on the magnetic susceptibility, the magnetic materials can be classified into three types: paramagnetic, diamagnetic and ferromagnetic materials.
Paramagnetic material: These are the magnetic materials that align with the magnetic field. Their magnetic susceptibility is$\chi >0$. Which implies that a paramagnetic material always has a small positive value of magnetic susceptibility. These are temperature dependent and are attracted by magnets with 1.0001 to 1.003 permeability. Some examples are oxygen, metal and aluminum.
Diamagnetic material: These are the magnetic materials that align against the magnetic field. Their magnetic susceptibility is $\chi <0$. Which means that a diamagnetic material always has a negative value of magnetic susceptibility. They easily get repelled by magnets and move from a stronger to weaker field. These are temperature independent but do have a small amount of intensity. Some examples are gold, tin and water.
Ferromagnetic material: These are the highly magnetized materials. They are mostly attracted by magnets and move from weaker fields to stronger fields. These types of magnetic materials do not have constant permeability and they differ from 1000 to 100000. They have a very high and positive value of magnetic susceptibility. Some of the examples are cobalt, iron and nickel.
So, the correct answer for the given question is option (A).

Note: Magnetic susceptibility does not have a unit. It is a dimensionless number because it is the ratio of two magnetic fields i.e., the polarization is in the same direction as the applied field and magnetic lines are concentrated within the object which results in the formation of magnetic materials.