The magnetic field lines are completely expelled from a material when (\( \chi \) is the susceptibility and \( \mu_{\mathrm{r}} \) is relative permeability)
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( \chi = -1 \) and \( \mu_{\mathrm{r}} = 0 \)
The relative permeability and the susceptibility are linked by \( \mu_{\mathrm{r}} = 1 + \chi \). If the field lines are completely expelled, the field inside the material is zero, so \( \mu_{\mathrm{r}} = 0 \) and therefore \( \chi = -1 \). This is perfect diamagnetism.
NCERT (2026-27):
Diamagnetism – “… The most exotic diamagnetic materials are superconductors. These are metals, cooled to very low temperatures which exhibits both perfect conductivity and perfect diamagnetism. Here the field lines are completely expelled! \( \chi = -1 \) and \( \mu_r = 0 \).”