Explain the difference in the behaviour of a conductor and dielectric in the presence of external electric field.

There are charge carriers in conductor.

When a conductor is subjected to external electric field. The free charge carriers move and charge distribution in the conductor adjusts itself in such a way that the electric field due to the induced charges $\left(E_{i n}\right)$ opposes the external field $\left(E_{0}\right)$ within the conductor. This happen until the two fields cancel each other and the net electrostatic field in the conductor is zero.

$\therefore \mathrm{E}_{0}+\mathrm{E}_{\text {in }}=0$

In a dielectric free movement of charges is not possible but the external field induces dipole moment by stretching or reorienting molecules of the dielectric.

The collective effect of all the molecular dipole moments is net charges on the surface of the dielectric which produce a field that opposes the external field. Hence external electric field reduces.

$\therefore \mathrm{E}_{0}+\mathrm{E}_{\mathrm{in}} \neq 0$

The extent of the effect depends on the nature of the dielectric.

The behaviour of a conductor and dielectric in the presence of external electric field are shown as in below.

Dielectric : "Dielectric is such a substance that it does not allow the charges to pass through it but allows the electric force on charged to each other.

Actually is an insulator that can be polarized by limited displacement of charges.