Practice portal › Magnetism and Matter › Bar Magnet and Dipole in a Field
Asked in RS Academy GUJCET booklet · Magnetic moment of magnets and loops
Idea: a small current loop of current I and area A has magnetic moment m=IA; a two-pole dipole of pole strength p and pole separation l has moment m=pl.
Two magnetic objects are equivalent when their moments are equal, so the replacement requires pl=IA.
That condition fixes the product and nothing else: strong poles close together and weak poles far apart represent the same loop.
The direction is fixed too - along ⃗m=I⃗A - but the question asks which quantity is fixed in size.
So the product pl is what is fixed.
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