Depict the behaviour of magnetic field lines near (i) diamagnetic and (ii) paramagnetic substances. Justify, giving reasons.
Solution
Near a diamagnetic substance the field lines are pushed away and the field inside is reduced, because the induced magnetisation is opposite to the applied field (relative permeability <1). Near a paramagnetic substance the field lines are drawn in and the field inside is enhanced, because the atomic dipoles tend to align along the applied field (relative permeability >1). So the sign of the induced magnetisation (opposing for dia, aiding for para) explains why the lines are expelled in one case and concentrated in the other.
