Electrical energy storage and dissipation in materials

Using a simple classical approach, we consider where and how electrical energy is stored in lossy dispersive materials. We argue that the material contribution to the electrical energy density is simply the sum of the kinetic and potential energies of the charges present under the influence of the applied electric field. It follows that the stored energy density must be positive. We provide simple expressions for the stored and dissipated energy densities; in the lossless case, our expressions reduce to the standard results of Brillouin and Landau.