Practice portal › Magnetism and Matter › Bar Magnet and Dipole in a Field
Asked in GSEB Board July 2017 · Field of a bar magnet and earth's field
Idea: magnetic field lines are always closed curves, because magnetic monopoles do not exist and so ∮⃗B· d⃗A=0 over any closed surface.
Outside a bar magnet the lines run from the N pole round to the S pole.
To close each loop they must run the opposite way inside the material: from the S pole to the N pole.
Inside the magnet, therefore, ⃗B points the same way as the magnetisation and the magnetic moment ⃗M, which is also S to N.
So the field lines inside a bar magnet are directed from the S pole to the N pole.
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