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Base units

Base units
Base units

There are seven mutally independent base units, from which all other physical units are derived. They are based on the definitions of some universal constants of nature, such as, among others, the speed of light in vacuum, the constants of Avogadro, Boltzmann and Planck, and the electron charge.

unit symbol quantity definition
second s time ground-state hyperfine transition frequency νhf of 133Cs = 9,192,631,770 Hz *)
meter m length speed of light c in vacuum = 299,792,458 m/s
kilogram kg mass Planck's constant h = 6.626,070,15×10-34 J·s **)
ampere A current electron charge e = 1.602,176,634×10-19 A·s
kelvin K temperature Boltzmann's constant kB = 1.380,649×10-23 J/K **)
mole mol matter Avogadro's constant NA = 6.022,140,76×1023 particles per mole
candela cd luminous intensity

luminous intensity of radiation source with frequency of 540×1012 Hz *) emitting an energy of 1/683 J **) per second and per steradian = 1 candela

*) 1 Hz = 1 s-1
**) 1 J = 1 kg·m2·s-2

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Last modified:10 April 2024 09.44 a.m.
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