Gevoeligheid, diëlektrische constante en diëlektrische constante

In a polarized dielectric, the total charge density is the sum of the bound and free charge densities. Recalling the expression for bound charge density and rewriting the total charge density in terms of the total electric field gives the expression for electric displacement in terms of polarization.

In the case of linear dielectrics, the polarization is proportional to the total electric field. The constant of proportionality is called the electric susceptibility of the material, and the permittivity of free space makes the electric susceptibility dimensionless.

For an applied electric field, if electric susceptibility increases, the polarization increases.

Substituting the expression for polarization implies that the electric displacement is also proportional to the total electric field.

The new constant of proportionality is the permittivity of the material. The ratio of the material's permittivity to the permittivity of free space gives the relative permittivity, also known as the dielectric constant.

This estimates the ability to store charge for a given electric field. Materials with higher dielectric constants are used in capacitors to increase energy storage.