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ISO 31-5 is the part ofinternational standardISO 31 that defines names and symbols forquantities andunits related toelectricity and magnetism. It is superseded byISO 80000-6.[1]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 | c0 | 299 792 458 m s−1 | 299 792 458 m s−1 |
| Magnetic constant | μ0 | 4π × 10−7 N A−2 | 12.566 370 614... x 10−7 N A−2 |
| Electric constant | ε0 | 8.854 187 817... x 10−12 F m−1 | |
| Characteristic impedance of vacuum | Z0 | μ0c0 | 376.730 313 461...Ω |
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