plz explain what is electric polarisation vector . plz define the term electric susceptibility.

Electric polarization is a process in which the charges in an insulator get separated by certain distance due to the presence of external electric field. This separation of charges by certain distance acts as a dipole in the material. It is just when we will place the material in between charged plates then the positive and negative charges which are in the material will be separated by some distance, there by dipoles are formed. 

The separated positive and negative charges lead to an internal electric field in the material which is in the opposite direction to the external electric field. This leads to reduction in the field inside dielectric. The reduced value of electric field is given by