When some diamagnetic materials are cooled to very low temperatures, they exhibit both perfect conductivity and perfect diamagnetism. In such a situation
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( \mu_{r} = 0,\ \chi = -1 \)
A material showing perfect conductivity and perfect diamagnetism at low temperature is a superconductor. It expels the magnetic field completely from its interior (the Meissner effect), so \( B = 0 \) inside.
\( B = \mu_{0}(1+\chi)H = 0 \Rightarrow \chi = -1 \)
\( \mu_{r} = 1+\chi = 0 \)
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 \( \mu_r = 0 \).”