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The change of name had been made because μ 0 was a defined value, and was not the result of experimental measurement (see below). In the new SI system, the permeability of vacuum no longer has a defined value, but is a measured quantity, with an uncertainty related to that of the (measured) dimensionless fine structure constant.
The value of the electron charge became a numerically defined quantity, not measured, making μ 0 a measured quantity. Consequently, ε 0 is not exact. As before, it is defined by the equation ε 0 = 1/( μ 0 c 2 ) , and is thus determined by the value of μ 0 , the magnetic vacuum permeability which in turn is determined by the experimentally ...
Values shown above are approximate and valid only at the magnetic fields shown. They are given for a zero frequency; in practice, the permeability is generally a function of the frequency. When the frequency is considered, the permeability can be complex , corresponding to the in-phase and out of phase response.
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 ε ...
However, many tables of magnetic susceptibility give the values of the corresponding quantities of the CGS system (more specifically CGS-EMU, short for electromagnetic units, or Gaussian-CGS; both are the same in this context).
Lorentz force on a charged particle (of charge q) in motion (velocity v), used as the definition of the E field and B field. Here subscripts e and m are used to differ between electric and magnetic charges. The definitions for monopoles are of theoretical interest, although real magnetic dipoles can be described using pole strengths.
By definition, the linear relative permittivity of vacuum is equal to 1, [19] that is ε = ε 0, although there are theoretical nonlinear quantum effects in vacuum that become non-negligible at high field strengths. [20] The following table gives some typical values.
That value is also the standard formation energy (∆G f °) for an Fe 2+ ion, since e − and Fe(s) both have zero formation energy. Data from different sources may cause table inconsistencies.