ISO 31-5
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ISO 31-5

ISO 31-5 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to electricity and magnetism. It is superseded by ISO 80000-6.

Some of its definitions are below, with values taken from NIST values of the constants:

Name Symbol Definition Value
Speed of light in vacuum c0 299 792 458 m s-1 299 792 458 m s-1
Magnetic constant ?0 4? × 10-7 N A-2 12.566 370 614... x 10-7 N A-2
Electric constant ?0 ${\displaystyle {\begin{matrix}{\frac {1}{\mu _{0}{c_{0}}^{2}}}\end{matrix}}}$ 8.854 187 817... x 10-12 F m-1
Characteristic impedance of vacuum Z0 ?0c0 376.730 313 461...?