A weak linear isotropic magnetic material is placed in a uniform magnetic field along +x. Its magnetisation is found to be along -x. Which conclusion is correct?
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Question

A weak linear isotropic magnetic material is placed in a uniform magnetic field along +x. Its magnetisation is found to be along -x. Which conclusion is correct?

G1 Physics · Accepted Answer

For a linear material, I⃗ = χₘH⃗. Here I⃗ is opposite to H⃗, so χₘ must be negative: χₘ < 0. Also, μᵣ = 1+χₘ. For a weak diamagnetic substance, χₘ is small and negative, hence μᵣ < 1. Therefore the material is diamagnetic.