Dielectric loss:

 It can be shown that the imaginary part of the dielectric constant  is a measure of the absorption of energy by the dielectric from the alternating field. The electric current density in the material due to the external alternating field.

This imaginary part of the dielectric constant  is related to the component of the current which is in phase with the applied field. This component of the current gives rise to absorption not the other component which is900 out of phase with the field. The energy absorbed by the dielectric per m3 per second is given by