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Asked in GUJCET 2026 · Dia, para and ferromagnetism
Idea: susceptibility is defined by ⃗M=χ⃗H, and inside a material ⃗B=μ₀(⃗H+⃗M)=μ₀(1+χ)⃗H.
A superconductor shows the Meissner effect: below its critical temperature the field is pushed entirely out of its interior, so ⃗B=0 inside.
Putting ⃗B=0 with ⃗H eq0 gives 1+χ=0, so χ=-1.
Equivalently ⃗M=-⃗H: the induced magnetisation cancels the applied field exactly.
So a superconductor is a perfect diamagnet, χ=-1, with relative permeability μᵣ=1+χ=0.
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