Dielectric materials

Any materials that do not allow the electric charges to easily pass through the materials is called insulator or dielectric material.
Any material is made up of molecules but the molecules have symmetric charge distributions. So, such kind of molecules are called non-polar molecules. In the absence of external electric field, non-polar molecule has its centre of positive charge conincides with the centre of negative charge.
But, when the dielectric placed in an external electric field Eo, in each molecule the centre of positive charge will be displaced in the direction of the field, and the centre of negative charge will be displaced in the opposite direction. We called it as molecule gets polarized.



In the electric field Eo existing between the plates, each molecule in the dielectric gets polarized. Therefore, the entire dielectric gets polarized. Due to this reason, there become opposite charges to the charges on molecules of dielectric are induced. Inside the volume of the dielectric, the near by positive and negative charges cancel each other. Altogether, dielectric becomes neutral. Due to induced charges on the surface of the dielectric, the electric field Ei appears in the opposite direction to the actual electric field direction Eo.

So that, the net electric field E=Eo-Ei. Therefore, the potential difference Vo(without dielectric) reduces to V(with dielectric)

E=Eo/K
V=Vo/K
The capacitance of the capacitor with dielectric will be

C=Q/V=Q/(Vo/K)=K(Q/Vo)=KCo