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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 It is superseded by ISO 80000-6.[1]
Some of its definitions are below, with values taken from NIST values of the constants:[2]
| Name | Symbol | Definition | Value |
|---|---|---|---|
| Speed of light in vacuum | 0 | 299 792 458 m sโ1 | 299 792 458 m sโ1 |
| Magnetic constant | 0 | 4ฯ ร 10โ7 N Aโ2 | 12.566 370 614... x 10โ7 N Aโ2 |
| Electric constant | 0 | ๐ {\displaystyle {\begin{matrix}{\frac {1}{\mu _{0}{c_{0}}^{2}}}\end{matrix}}} |
8.854 187 817... x 10โ12 F mโ1 |
| Characteristic impedance of vacuum | 0 | 0 0 | 376.730 313 461...ฮฉ |
References
[edit]- ^ "ISO 31-5:1992 Quantities and units". International Organization for Standardization. November 1992. Retrieved 14 June 2025.
- ^ "Fundamental Physical Constants from NIST". physics.nist.gov. Retrieved 14 June 2025.
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