Practice portal › Magnetism and Matter › Magnetisation and Magnetic Materials
Asked in RS Academy GUJCET booklet · Dia, para and ferromagnetism
Idea: put the sample in the field and see which way it magnetises. In a diamagnetic material the response opposes the applied field, so the induced moment ⃗m points against ⃗B (its susceptibility is small and negative).
Poles: the face of the sample turned towards the magnet becomes the same kind of pole as the one facing it, so the sample is pushed away.
Energy: U=-⃗m·⃗B becomes +mB for an opposing moment, so the energy is lowest where the field is weakest, and the sample drifts there.
Both pictures agree, and both need the field to vary -- in a uniform field there would be no net force at all, only an alignment.
So the resultant force carries a diamagnetic substance from the region of strong field to the region of weak field.
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