Permittiviteitsconstante

Permittiviteitsconstante, in electromagnetism often referred to simply as the permittivity, is the property of a material that relates the electric displacement field D to the electric field E: D = ε E. The absolute permittivity ε has units of farads per meter (F/m). In vacuum, the vacuum permittivity ε0 is a fundamental constant, approximately 8.854187817×10^-12 F/m. For a homogeneous, isotropic dielectric, ε = εr ε0, where εr is the relative permittivity (the dielectric constant) of the material and is dimensionless.

The permittivity determines how electric fields interact with a medium. It appears in Coulomb’s law for charges in a medium as F = (1/(4π ε)) q1 q2 / r^2, and in the electric energy density as u = 1/2 ε E^2. In capacitors, the capacitance scales with ε: for a parallel-plate capacitor, C = ε A/d. The speed of light in vacuum is linked to ε0 and the magnetic permeability μ0 by c^2 = 1/(μ0 ε0); in a medium, the effective permittivity is ε = εr ε0, and the propagation speed is reduced accordingly.

In general, ε can be frequency-dependent and, in anisotropic materials, represented by a tensor εij. Materials exhibit a wide range of relative permittivities, from near 1 in air to tens or hundreds in some liquids and solids. The permittivity constant is a central quantity in Maxwell’s equations for media and in the design of electrical and electronic devices.