A uniform magnetic field gets modified as shown below when two specimens X and Y are placed in it. (i) Identify the two specimens X and Y. (ii) State the reason for the behaviour of the field lines in X and Y.
Solution
(i) In specimen X the field lines are pushed out and the field inside is weakened - this is diamagnetic behaviour. In specimen Y the field lines crowd strongly into the specimen and the field inside is greatly enhanced - this is ferromagnetic behaviour. (ii) A diamagnetic (X) has relative permeability slightly less than 1, so it develops a magnetisation opposite to the applied field and expels the lines. A ferromagnetic (Y) has relative permeability very much greater than 1, so its domains align strongly with the applied field and pull the lines into the material.
