Depolarization Factor

When a dielectric body is placed in a field, the induced polarization charges always act to decrease the average field in the dielectric from the value it had before the material was introduced. The polarization charges produce a non-uniform field. So the original field is modified differently at different regions in the dielectric body.

Let us limit the original field to a uniform one, choosing the special case of ellipsoidal dielectric bodies with a principal axis along the field direction. The polarization charges produce in an isotropic dielectric a field which is uniform and exactly opposed to the original external field. In such cases, it is helpful to discuss the average fields in terms of the original field less a depolarizing field, E_dep . E_dep depends on a geometric factor (L) and on the magnitude of the polarization. P. We can write.

            E_dep = 1/ε₀ LP

L is called the depolarizing factor. It varies from 0 to 1, depending on the shape of the dielectric.