Vacuum permittivity - Wikipedia
https://en.wikipedia.org/wiki/Vacuum_permittivity
WEBVacuum 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.
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