The susceptibility (chi_m) and permeability (μ) of a perfectly diamag…

The correct answer is Option (1) → \( \chi_m = -1 \) and \( \mu = 0 \)

A perfect diamagnet (a superconductor) expels the magnetic field from its interior completely, so \( B = 0 \) inside it (the Meissner effect). Its magnetisation cancels the applied field: \( M = -H \).

    \( \displaystyle \chi_m = \frac{M}{H} = -1 \)

The relative permeability follows from the susceptibility.

    \( \mu_r = 1 + \chi_m = 1 - 1 = 0 \)
    \( \mu = \mu_0\,\mu_r = 0 \)

So the susceptibility is \( -1 \) and the permeability is zero.

NCERT (2026-27):
Points to Ponder – “… There exists a perfect diamagnet, namely, a superconductor. This is a metal at very low temperatures. In this case χ = −1, μ_r = 0, μ = 0. The external magnetic field is totally expelled.”