JEE Main 2023 · 12 April · morning · Single correct · +4 / −1
Given below are two statements:
Statement I : The diamagnetic property depends on temperature.
Statement II : The induced magnetic dipole moment in a diamagnetic sample is always opposite to the magnetizing field.
In the light of given statements, choose the correct answer from the options given below.
- (a) Statement I is incorrect but Statement II is true.
- (b) Statement I is correct but Statement II is false.
- (c) Both Statement I and Statement II are False.
- (d) Both Statement I and Statement II are true.
Answer and solution
Answer (a) Statement I is incorrect but Statement II is true.
Solution
Physics sir · 4 steps
Diamagnetism comes from orbiting electrons resisting the field, and heat cannot disturb that.
- Where it comes from. In a diamagnetic atom the electron orbital moments cancel, so there is no permanent dipole. An applied field changes the orbital motion, and by Lenz's law the induced moment always opposes the field.
- Statement II. Because of Lenz's law, the induced dipole moment points opposite to the magnetizing field every time. That is why χ is small and negative. Statement II is true.
- Statement I. There are no permanent dipoles for thermal motion to scramble, and the induced moment comes from the electron orbits inside each atom. So diamagnetic susceptibility is practically independent of temperature. Statement I is incorrect.
- So. Statement I is incorrect and Statement II is true, which is option (a).
The idea to keep. Only permanent dipoles care about temperature: paramagnetic χ ∝ 1/T (Curie law). Diamagnetism is induced and opposes the field, so temperature does not affect it.
Answer from the NTA final answer key. Solution by PrepWiser.