# What is the unit of relative permittivity

## Dielectric constant

In contrast to the dielectric constant of the vacuum is the relative dielectric constant εr, the dielectric constant, carrier of physical information: in it the behavior of dielectric material (dielectric) in an external electric field is parametrized. The dielectric displacementD. when an electric field is applied E. to a dielectric

D. = εrε0E..

Is in a vacuum εr equal to one; the different numerical value in dielectric materials is due to the fact that an external electric field E. shifts the electrical charges in the atoms or molecules of the dielectric, which in turn changes the electrical field inside the dielectric; the medium is thus electrically polarized (electrical polarization). The following applies: D. = εrε0E. = ε0E. + P, in the isotropic medium too D. = ε0(1 + χe)E. (P: electrical polarization, χe = εr – 1: electrical susceptibility).

In isotropic media is εr for some materials an approximately constant scalar (see table), but mostly a complex function that depends on the frequency of the electric field (complex dielectric constantε *(ω)); in anisotropic media, however, are E. and D. often no longer parallel, εr thus has a tensorial character (dielectric tensor). This is particularly important in crystal optics.

Dielectric constant: Relative dielectric constant of some substances.