Question

Assertion (A): When a ferromagnetic substance is heated to high temperature it becomes paramagnetic in nature.

Reason (R): The disappearance of magnetisation of a ferromagnet is abrupt and not gradual.

विकल्प

• Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

• Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

• Assertion (A) is true, but Reason (R) is false.

• Both Assertion (A) and Reason (R) are false.

Answer 1

Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

Explanation:

Domains in ferromagnetic materials are aligned. This arrangement is disrupted by heating because it causes thermal agitation.

The assertion (A) is true. The exchange coupling between atomic magnets is overcome by thermal energy at a particular temperature known as the Curie temperature (T_C). The material exhibits paramagnetic behavior over T_C.

Reason (R) is true. The spontaneous magnetization disappears at the Curie point, which marks the phase shift from ferromagnetism to paramagnetism. This shift at T_C is often regarded as “abrupt” since the long-range order disappears there.

Both are true; however, the abruptness of the switch to paramagnetism is not the only explanation; thermal agitation overriding exchange forces is the cause. The transition's “abruptness” characterizes its nature, but it doesn’t explain “why” it turns paramagnetic.