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Asked in GUJCET 2025 · Dia, para and ferromagnetism
Idea: a paramagnetic substance magnetises along the applied field, so the induced moment ⃗m is parallel to ⃗B.
Its energy in the field is U=-⃗m·⃗B=-mB, which falls as B grows.
A body drifts towards lower energy, so the sample is pulled into the region where the field is stronger. The force comes from the gradient of B, which is why a uniform field would give no motion at all, only alignment.
The same behaviour shows up in the laboratory: a paramagnetic liquid rises in the limb of a U-tube that sits between the poles, where the field is strongest.
So the substance moves from a region of weak magnetic field to a region of strong magnetic field.
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