Question

Magnetic susceptibility of a diamagnetic substance
A) increases with an increase in temperature.
B) increases with a decrease in temperature.
C) remains constant with a change in temperature.
D) None of these.

Answer 1

Hint: A substance that aligns its magnetic dipoles in a direction opposite to the external magnetic field is termed as a diamagnetic substance. So in a diamagnetic substance, the electron spins are paired and will slightly repel the applied magnetic field. The pairing of spins in a magnetic substance is usually affected by a temperature change.

Complete answer:
Step 1: List the three main classifications of magnetic substances and try to explain the effect of temperature on the magnetic susceptibility of diamagnetic materials.

The three basic classifications of magnetic materials are – paramagnetic materials, diamagnetic materials and ferromagnetic materials. Out of these three, paramagnetic materials and ferromagnetic materials get attracted weakly and strongly to an applied magnetic field while diamagnetic materials get weakly repelled by the external field.

The weak repulsion of the applied field exhibited by diamagnetic materials is due to the pairing of spins of electrons in the material. Then the inner magnetic field will be opposite to the external field.

Magnetic susceptibility refers to the measure of magnetization of a material when it is placed in an external magnetic field. Since diamagnetic materials tend to repel the applied field, they will have negative susceptibility. When the temperature is increased, the interatomic vibrations in a diamagnetic material will increase but the energy will not be large enough to break apart the paired electrons in the ground state. So a change in the temperature does not cause any significant change in the magnetic susceptibility of the diamagnetic material.

So, the correct option is (C).

Note: Since Pauli’s exclusion principle states that no two electrons can occupy the same state, the electrons in a diamagnetic material in the ground energy state will pair up with electrons of opposite spins. The energy gap between the ground state and the excited state for the electrons in a diamagnetic material is very large and excitation of electrons cannot be obtained by a change in temperature.