Earlier, different countries were using different systems of measurement like CGS, FPS (or British) and MKS system
- CGS: centimetre, gram, second
- FPS: foot, pound, second
- MKS: metre, kilogram, second
Now, there is an internationally accepted system of measurements known as Systeme Internationale d' Unites (French for International System of Units) abbreviated as SI. It was developed by General Conference on Weights and Measures in 1971 for international usage.
Length | metre | m | Distance travelled by light in vacuum during 1/299,792,458 second |
Mass | kilogram | kg | Mass of international prototype of kilogram at international Bureau of Weights and Measures |
Time | second | s | duration of 9,192,631,770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133 atom |
Electric current | ampere | A | that constant current which if maintained between two straight parallel conductors of infinite length, placed 1 metre apart in vacuum would produce a force 2 × 10–7 newton per metre of length |
Thermodynamic temperature | Kelvin | K | 1/273.16 of the thermodynamic temperature of the triple point of water |
Amount of substance | mole | mol | amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12 |
Luminous intensity | candela | cd | 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 |
When mole is used elementary entities must be specified.
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