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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.
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.
The linear permittivity of a homogeneous material is usually given relative to that of free space, as a relative permittivity ε r (also called dielectric constant, although this term is deprecated and sometimes only refers to the static, zero-frequency relative permittivity).
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 ...
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 ...
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),
The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field.
The Bohr radius is defined as [3] = =, where . is the permittivity of free space,; is the reduced Planck constant,; is the mass of an electron,; is the elementary charge,; is the speed of light in vacuum, and