ISO 31-5

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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 It is superseded by ISO 80000-6 .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 c 0 299 792 458 m s ?1 299 792 458 m s ?1
Magnetic constant μ 0 4π × 10 ?7 N A ?2 12.566 370 614... x 10 ?7 N A ?2
Electric constant ε 0 8.854 187 817... x 10 ?12 F m ?1
Characteristic impedance of vacuum Z 0 μ 0 c 0 376.730 313 461...Ω