A polarised dielectric is the equivalent of two charged surfaces (polarization charges). Induced surface charges (polarisation charges) oppose the external electric field, weakening the original field within the dielectric.
A dielectric, an insulator, or a very poor conductor of electric current When placed in an electric field, dielectrics conduct almost no current because, unlike metals, they have no loosely bound, or free, electrons that can drift through the material. Instead, electric polarization takes place.