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: Recall the property
A diamagnetic material has a small negative susceptibility, \(\chi\approx -10^{-5}\). It does not depend on temperature, because diamagnetism comes from induced magnetic moments in every atom and not from the alignment of permanent dipoles.

Step 2: What the graph must look like
The graph of \(\chi\) against \(T\) must be a horizontal straight line, and it must lie below the \(T\)-axis because \(\chi\) is negative.

Step 3: Check each figure
Figure A is a curve that stays flat and then falls with temperature, like a Curie-Weiss law for a ferromagnet above its Curie point, so it is not diamagnetic. Figure B is a decreasing hyperbola \(\chi\propto 1/T\), the Curie law for a paramagnet. Figure C is a horizontal line below the T-axis, which is what we need. Figure D is a horizontal line above the T-axis, which would mean positive \(\chi\), so it is wrong.

Final Answer:
Figure C shows a constant negative susceptibility, so the answer is option (C). \[ \boxed{\text{Option (C)}} \]