Q 12-05-066JEE MainJEE Main 2020 (3 Sep, Shift 2)Easy
A perfectly diamagnetic sphere has a small spherical cavity at its centre, which is filled with a paramagnetic substance. The whole system is placed in a uniform magnetic field $\vec B$. Then the field inside the paramagnetic substance is:
Answer: (B) Zero
A perfect diamagnet ($\chi = -1$, like a superconductor) completely expels the magnetic field. No field lines enter the sphere, so none reach the cavity: the field inside the paramagnetic substance is zero.
Solution by Sreeraj P, M.Sc Physics