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By definition, a perfect vacuum has a relative permittivity of exactly 1 whereas at standard temperature and pressure, air has a relative permittivity of ε r air ≡ κ air ≈ 1.0006 . Relative permittivity is directly related to electric susceptibility (χ) by = otherwise written as
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.
Vacuum permittivity, commonly denoted ε 0 (pronounced "epsilon nought" or "epsilon zero"), is the value of the absolute dielectric permittivity of classical vacuum. It may also be referred to as the permittivity of free space , the electric constant , or the distributed capacitance of the vacuum.
In electromagnetism, the Clausius–Mossotti relation, named for O. F. Mossotti and Rudolf Clausius, expresses the dielectric constant (relative permittivity, ε r) of a material in terms of the atomic polarizability, α, of the material's constituent atoms and/or molecules, or a homogeneous mixture thereof.
is the speed of light (i.e. phase velocity) in a medium with permeability μ, and permittivity ε, and ∇ 2 is the Laplace operator. In a vacuum, v ph = c 0 = 299 792 458 m/s, a fundamental physical constant. [1] The electromagnetic wave equation derives from Maxwell's equations.
Relative permittivity = electrostatics (ratio of capacitance of test capacitor with dielectric material versus vacuum) Specific gravity: SG (same as Relative density) Stefan number: Ste = Josef Stefan
This (volumetric) energy density is given by = + where E is the electric field, B is the magnetic field, and ε and µ are the permittivity and permeability of the surroundings respectively. The SI unit is the joule per cubic metre.
Pressure can be achieved by simple materials (e.g. regular steel) and positive displacement vacuum pumps; viscous flow regime for gases <100 Pa to 0.1 Pa medium (fine) vacuum Pressure can be achieved by elaborate materials (e.g. stainless steel) and positive displacement vacuum pumps; transitional flow regime for gases <0.1 Pa to 1 × 10 −6 Pa