A uniform magnetic field gets modified as shown in Fig. 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.

Explanation

(i) Specimen X is diamagnetic but specimen Y is paramagnetic.
(ii) Individual atoms of a diamagnetic material (say X) do not possess a permanent dipole moment of their own. The application of an external magnetic field induces in each atom a small dipole moment in the opposite direction. As a result, magnetic field lines are repelled or expelled and the field inside the material is reduced.
Individual atoms of a paramagnetic material possess a permanent dipole moment of their own. On account of continuous random thermal motion of the atoms, the net magnetisation of the material is zero. In the presence of an external magnetic field, the individual atomic dipole moments tend to align in the same direction. As a result, field lines get concentrated inside the material and the field inside is enhanced.