Question

When temperature of a ferromagnetic material is decreased to $80\%$, what is the percentage change in its magnetic susceptibility?

• A. $40\%$
• B. $80\%$
• C. $25\%$
• D. $20\%$

Answer 1

The correct option is C $25\%$

According to the Curie's law,

$\chi \propto \frac{1}{T}$

$\Rightarrow \frac{{\chi }_2}{{\chi }_1}=\frac{T_1}{T_2}$

According to the problem,

$T_2=0.8T_1$

$\Rightarrow \frac{{\chi }_2}{{\chi }_1}=\frac{T_1}{0.8T_2}$

$\therefore {\chi }_2=1.25{\chi }_1$

Percentage change in susceptibility is,

$=\frac{{\chi }_2-{\chi }_1}{{\chi }_1}\times 100$

$=\frac{1.25{\chi }_1-{\chi }_1}{{\chi }_1}\times 100$

$=25\%$

Hence, option $\left(D\right)$ is correct.