Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Consider a ferromagnetic material :
Assertion (A): The individual atoms in a ferromagnetic material possess a magnetic dipole moment and interact with one another in such a way that they spontaneously align themselves forming domains.
Reason (R): At high enough temperature, the domain structure of ferromagnetic material disintegrates. Thus, magnetization will disappear at high enough temperature known as Curie temperature.
In the light of the above statements, choose the correct answer from the options given below :

• A. (A) is false but (R) is true
• B. Both (A) and (R) are true but (R) is not the correct explanation of (A)
• C. Both (A) and (R) are true and (R) is the correct explanation of (A)
• D. (A) is true but (R) is false

Hint:

To check if R is the explanation of A, read A, then add "because" followed by R. If it sounds like a logical cause-effect relationship, it's the correct explanation.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Ferromagnetism is characterized by spontaneous magnetization and the formation of domains due to strong exchange interactions between atomic dipoles. The Curie temperature ($T_c$) marks the transition from ferromagnetic to paramagnetic behavior.
Step 3: Detailed Explanation:
Assertion (A) is true: Ferromagnetism is indeed explained by the domain theory where individual atomic dipoles align spontaneously in small regions called domains.
Reason (R) is true: Increasing temperature increases thermal agitation, which eventually overcomes the alignment forces, causing the material to become paramagnetic at the Curie temperature.
However, (R) describes the \textit{disappearance} of ferromagnetism with temperature, while (A) describes the \textit{cause} and structure of ferromagnetism. (R) does not explain \textit{why} the atoms align in the first place (which is due to exchange coupling). Therefore, (R) is not the correct explanation of (A).
Step 4: Final Answer:
Both (A) and (R) are true but (R) is not the correct explanation of (A).