Q 12-05-068JEE MainJEE Main 2020 (4 Sep, Shift 2)Medium
A paramagnetic sample shows a net magnetisation of $6\ \text{A/m}$ when it is placed in an external magnetic field of $0.4\ \text{T}$ at a temperature of $4\ \text{K}$. When the sample is placed in an external magnetic field of $0.3\ \text{T}$ at a temperature of $24\ \text{K}$, then the magnetisation will be:
Answer: (D) $0.75\ \text{A/m}$
Curie's law: $M \propto \dfrac BT$.
$$M_2 = 6\times\frac{0.3}{0.4}\times\frac{4}{24} = 0.75\ \text{A/m}$$
Solution by Sreeraj P, M.Sc Physics