Separation of charges due to polarisation. The separation of charges induced by an electric field generates polarisation charges on the surface of a dielectric object, e.g., (a) a rectangular slab of dielectric material and (b) a dielectric sphere. In turn, the presence of the polarisation charges contributes to the overall electric field inside the dielectric material, reducing it relative to the total external field by the relative dielectric permittivity εr.
Fig. 3.4 — Separation of charges due to polarisation