Question

Which of the following figure best represents the variation of magnetic susceptibility (\(χ\)) with temperature for a diamagnetic substance?

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

Diamagnetic susceptibility is negative and almost independent of temperature, so look for a flat line below the axis.

Answer 1

The Correct Option is C

Step 1: Sign of the susceptibility
For diamagnets, the induced magnetisation opposes the applied field, so $\chi$ is negative. The line must be below the temperature axis.

Step 2: Temperature dependence
Thermal motion destroys the alignment of permanent dipoles in a paramagnet, giving $\chi=\frac{C}{T}$. A diamagnet has no permanent dipoles, so heating does not change $\chi$ much.

Step 3: Match the figure
Only the graph with a flat line under the axis fits both facts. That is the third picture, option (C). The curve of option (B) is the Curie law of a paramagnet, option (A) is a ferromagnet curve, and option (D) has the wrong sign.

Final Answer:
Option (C) is correct. \[ \boxed{\text{Option (C)}} \]