Question

what are diamagnetic substances and there theory of magnetic moment.

Answer 1

Diamagnetic substance are those substance when they are placed in the external magnetic field becomes feebly magnetised in the direction opposite to the field.

In this material the electrons revolve in beer and in opposite sense that the net magnetic moment is zero. But when they are held in the magnetic field, the Lorentz Force supports the centripetal force of one electron and hence the magnetic moment of one electron increases and of other one decreases. And these become a net magnetic moment opposite to the magnetic field.