Question

Define magnetic susceptibility of a material. Name two elements, one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify?

Answer 1

Hint: Magnetic susceptibility of a material can be considered as a measure of the extent to which a material can get magnetized when placed in an external magnetic field. Some materials will attract the magnetic field while some may end up repelling the magnetic field in which it is placed.

Complete solution:
Try to explain magnetic susceptibility of a material and give the required examples.
Magnetic susceptibility is defined as the ratio of the magnetization $M$ to the magnetic field intensity $H$ . It is a dimensionless quantity and is represented by $\chi $ .
We have $\chi = \dfrac{M}{H}$ .
Now. the value of magnetic susceptibility can be positive or negative. Copper is an element that has a negative magnetic susceptibility. Iron is an element that has a large positive magnetic susceptibility.
From the above relation, we can obtain the magnetization of the material placed in the external magnetic field as $M = \chi H$ .
So a negative $\chi $ indicates that the magnetization $M$ is repelling in nature or in other words, the material having a negative magnetic susceptibility will oppose the magnetic field in which it is placed. These materials are referred to as diamagnetic materials.

Additional information: There are mainly three types of magnetic materials. Materials that get weakly attracted to the external magnetic field called paramagnetic materials, materials that get strongly attracted to the external field called ferromagnetic materials and materials that get repelled by the external field called diamagnetic materials.

Note: Diamagnetic materials tend to oppose the field because the dipole moments in the material in the presence of the external field will arrange themselves in such a way that the internal magnetic field is in the opposite direction to the external field. A large positive susceptibility implies that the material is ferromagnetic. So iron is a ferromagnetic material and copper is a diamagnetic material.