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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.
μ 0 ≈ 12.566 × 10 −7 H/m is the magnetic constant, also known as the permeability of free space, ε 0 ≈ 8.854 × 10 −12 F/m is the electric constant, also known as the permittivity of free space, c is the speed of light in free space, [9] [10] The reciprocal of Z 0 is sometimes referred to as the admittance of free space and ...
The vacuum permittivity ε o (also called permittivity of free space or the electric constant) ... and therefore so is the new 2019 definition of ε 0 ...
The permeability of vacuum (also known as permeability of free space) is a physical constant, denoted μ 0. The SI units of μ are volt-seconds per ampere-meter, equivalently henry per meter. Typically μ would be a scalar, but for an anisotropic material, μ could be a second rank tensor .
Historically, the constant μ 0 has had different names. In the 1987 IUPAP Red book, for example, this constant was called the permeability of vacuum. [12] Another, now rather rare and obsolete, term is "magnetic permittivity of vacuum". See, for example, Servant et al. [13] Variations thereof, such as "permeability of free space", remain ...
ε 0 is the permittivity of free space; E is the electric field intensity; and; P is the polarization of the medium. Differentiating this equation with respect to time defines the displacement current density, which therefore has two components in a dielectric: [1] (see also the "displacement current" section of the article "current density")
The relative static permittivity, ε r, can be measured for static electric fields as follows: first the capacitance of a test capacitor, C 0, is measured with vacuum between its plates. Then, using the same capacitor and distance between its plates, the capacitance C with a dielectric between the plates is measured.
In free space the wave impedance of plane waves is: = (where ε 0 is the permittivity constant in free space and μ 0 is the permeability constant in free space). Now, since = = (by definition of the metre),