SI unit
SI unit
The SI unit (pronounced as /ɛs aɪ juːnɪt/), also known as the International System of Units, is the modern form of the metric system and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, which are the ampere, kelvin, second, metre, kilogram, candela, and mole.
Etymology
The term SI unit is derived from the French Système international (d'unités), which translates to "International System of Units" in English. The system was first proposed in 1960 by the General Conference on Weights and Measures (CGPM) as a comprehensive system of units of measurement for all physical quantities.
Related Terms
- Ampere: The SI unit of electric current, named after the French physicist André-Marie Ampère.
- Kelvin: The SI unit of thermodynamic temperature, named after the Scottish physicist William Thomson, 1st Baron Kelvin.
- Second: The SI unit of time, it is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.
- Metre: The SI unit of length, it is defined as the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second.
- Kilogram: The SI unit of mass, it is defined by setting the Planck constant h exactly to 6.62607015×10−34 J⋅s.
- Candela: The SI unit of luminous intensity, it is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
- Mole: The SI unit of amount of substance, it is defined as exactly 6.02214076×10^23 elementary entities.
External links
- Medical encyclopedia article on SI unit
- Wikipedia's article - SI unit
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