A dielectric material is a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic field s. If the flow of current between opposite electric charge poles is kept to a minimum while the electrostatic lines of flux are not impeded or interrupted, an electrostatic field can store energy. This property is useful in capacitor s, especially at radio frequencies. Dielectric materials are also used in the construction of radio-frequency transmission lines. It is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced toward the field and negative charges shift in the opposite direction. The electric susceptibility χe of a dielectric material is a measure of how easily it polarizes in response to an electric field.It is defined as the constant of proportionality (which may be a tensor) relating an electric field E to the induced dielectric polarization density P such that
The electric susceptibility χe of a dielectric material is a measure of how easily it polarizes in response to an electric field.
P = e0XeE
where ε0 is the electric permittivity of free space.The susceptibility of a medium is related to its relative permittivity εr by
So in the case of a vacuum,
Xe = 0