Dielectrics and Dielectric Polarization

Dielectrics are insulating materials, which transmit electric effects without conducting. Dielectrics are of two types:

1. Non-polar
2. Polar

Non-polar Dielectrics

In the molecules of non–polar dielectrics, the centre of positive charge coincides with the centre of negative charge. Each molecule has zero dipole moment in its normal state. These molecules are mostly symmetrical such as nitrogen, oxygen, benzene, methane, CO₂, etc.

Polar Dielectrics

Polar dielectrics have asymmetric shape of the molecules such as water, NH₃, HCl, etc. In such molecules, the centres of positive and negative charges are separated through a definite distance and have finite permanent dipole moment.

When a non-polar dielectric is held in an external electric field, the centre of positive charge in each molecule is pushed in the direction of E and the centre of negative charge is displaced in the direction opposite to E. Because of external electric field, centres of positive and negative charges in the non-polar dielectric molecules are separated. Dielectric is then said to be polarized and a tiny dipole moment develops in each molecule.