4.1 Basic Properties: Dielectrics in DC Electric Field

Upon application of a dc or static electric field, there is a long range migration of charges. However, there is a limited movement of charges leading to the formation of charge dipoles and the material, in this state, is considered as polarized. These dipoles are aligned in the direction of the applied field.
The applied field can also align the dipoles that were already present in the material i.e. material containing dipoles without application of the field.

Of course, both these effects may be present in a single material i.e. dipoles can be aligned as well as be induced by the applied field.

The net effect is called Polarization of the material.