The Drude model explains the electrodynamic properties of metals. The simple approach is to regard the conduction band electrons as non-interacting electron gas.

We solve the problem of a spherical capacitor with (almost) arbitrary permittivity of the dielectric.

The electrostatic potential of a dielectric sphere subject to an external field is calculated.

The capacitance of a coaxial capacitor with two embedded dielectrics is calculated.

In a vanishing-thickness limit, the surface conductivity of graphene can be interpreted as permittivity.