A paramagnetic sample shows a net magnetisation of $6 \mathrm{~A} / \mathrm{m}$ when it is placed in an external magnetic field of $0.4 \mathrm{~T}$ at a temperature of $4 \mathrm{~K}$. When the sample is placed in an external magnetic field of $0.3 \mathrm{~T}$ at a temperature of $24 \mathrm{~K}$, then the magnetisation will be:
Correct Option: , 4
(4) For paramagnetic material. According to curies law
$\chi \propto \frac{1}{T}$
For two temperatures $T_{1}$ and $T_{2}$
$\chi_{1} T_{1}=\chi_{2} T_{2}$
But $\chi=\frac{I}{B}$
$\therefore \frac{I_{1}}{B_{1}} T_{1}=\frac{I_{2}}{B_{2}} T_{2}$
$\Rightarrow \frac{6}{0.4} \times 4=\frac{I_{2}}{0.3} \times 24 \Rightarrow I_{2}=\frac{0.3}{0.4}=0.75 \mathrm{~A} / \mathrm{m}$
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