ISO 31-5
Encyclopedia
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.
Some of its definitions are below, with values taken from NIST values of the constants:
International standard
International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...
ISO 31
ISO 31
International Standard ISO 31 was the most widely respected style guide for the use of physical quantities and units of measurement, and formulas involving them, in scientific and educational documents worldwide...
that defines names and symbols for quantities
Physical quantity
A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.-Definition of a physical quantity:Formally, the International Vocabulary of Metrology, 3rd edition defines quantity as:...
and units related to electricity and magnetism.
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 | μ0 | 4π × 10−7 N A−2 | 12.566 370 614... x 10−7 N A−2 |
| Electric constant Electric constant The physical constant ε0, commonly called the vacuum permittivity, permittivity of free space or electric constant is an ideal, physical constant, which is the value of the absolute dielectric permittivity of classical vacuum... |
ε0 |  |
8.854 187 817... x 10−12 F m−1 |
| Characteristic impedance of vacuum | Z0 | μ0 c0 | 376.730 313 461...Ω |