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The relative permittivity of a medium is related to its electric susceptibility, χ e, as ε r (ω) = 1 + χ e. In anisotropic media (such as non cubic crystals) the relative permittivity is a second rank tensor. The relative permittivity of a material for a frequency of zero is known as its static relative permittivity.
Another common term encountered for both absolute and relative permittivity is the dielectric constant which has been deprecated in physics and engineering [2] as well as in chemistry. [ 3 ] By definition, a perfect vacuum has a relative permittivity of exactly 1 whereas at standard temperature and pressure , air has a relative permittivity of ...
The Lorentz–Lorenz equation is similar to the Clausius–Mossotti relation, except that it relates the refractive index (rather than the dielectric constant) of a substance to its polarizability. The Lorentz–Lorenz equation is named after the Danish mathematician and scientist Ludvig Lorenz , who published it in 1869, and the Dutch ...
physics, engineering (Damping ratio of oscillator or resonator; energy stored versus energy lost) Relative density: RD = hydrometers, material comparisons (ratio of density of a material to a reference material—usually water)
A similar parameter exists to relate the magnitude of the induced dipole moment p of an individual molecule to the local electric field E that induced the dipole. This parameter is the molecular polarizability (α), and the dipole moment resulting from the local electric field E local is given by: =
where R is the molar refractivity, is the Avogadro constant, is the electronic polarizability, p is the density of molecules, M is the molar mass, and = / is the material's relative permittivity or dielectric constant (or in optics, the square of the refractive index).
In terms of relative permeability, the magnetic susceptibility is χ m = μ r − 1. {\displaystyle \chi _{m}=\mu _{r}-1.} The number χ m is a dimensionless quantity , sometimes called volumetric or bulk susceptibility, to distinguish it from χ p ( magnetic mass or specific susceptibility) and χ M ( molar or molar mass susceptibility).
In materials with relative permittivity, ε r, and relative permeability, μ r, the phase velocity of light becomes =, which is usually [note 5] less than c. In addition, E and B are perpendicular to each other and to the direction of wave propagation, and are in phase with each other.