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.

पर्याय

• 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

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

Explanation:

The assertion (A) is true. Ferromagnetic materials have a domain structure in which magnetic moments are oriented in a certain direction. As the temperature rises, thermal agitation increases, disturbing this alignment. At a specific temperature known as the Curie temperature (T_C), the domain structure collapses, and the material begins to exhibit paramagnetic properties.

The reason (R) is false. The transition from a ferromagnetic state to a paramagnetic state occurs gradually with increasing temperature, rather than abruptly disappearing. The Curie temperature signifies the threshold at which long-range order is disrupted, whereas susceptibility varies continually according to the Curie-Weiss law:

χ = `C/(T - T_C)` for T > T_C​

Where C is the Curie constant. The magnetization decreases steadily as the temperature approaches T_C​ from below.