<span title="Home" class="fa-solid-900 icon"></span> Home

Ciro Santilli's Homepage

Science

Natural science

Physics

System of units

List of systems of units

International System of Units

Versions of the international System of Units

{wiki}

https://web.archive.org/web/20181119214326/https://www.bipm.org/utils/common/pdf/CGPM-2018/26th-CGPM-Resolutions.pdf gives it in raw:
> * the unperturbed ground state hyperfine transition frequency of the <caesium-133> atom $\Delta v_{Cs}$ is 9 192 631 770 Hz
  * the speed of light in vacuum c is 299 792 458 m/s
  * the <Planck constant> h is 6.626 070 15 × $10^{-34}$ J s
  * the elementary charge e is 1.602 176 634 × $10^{-19}$ C
  * the <Boltzmann constant> k is 1.380 649 × $10^{-23}$ J/K
  * the Avogadro constant NA is 6.022 140 76 × $10^{23}$ mol
  * the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, is 683 lm/W,
The breakdown is:
* actually use some physical constant:
  * > the unperturbed ground state hyperfine transition frequency of the <caesium-133> atom $\Delta v_{Cs}$ is 9 192 631 770 Hz

    Defines the <second> in terms of <caesium-133> experiments. The beauty of this definition is that we only have to count an integer number of discrete events, which is what allows us to make things precise.
  * > the speed of light in vacuum c is 299 792 458 m/s

    Defines the <meter> in terms of <speed of light> experiments. We already had the <second> from the previous definition.
  * > the <Planck constant> h is 6.626 070 15 × $10^{-34}$ J s

    Defines the <kilogram> in terms of the <Planck constant>.
  * > the elementary charge e is 1.602 176 634 × $10^{-19}$ C

    Defines the <Coulomb> in terms of the <electron charge>.
* arbitrary definitions based on the above just to match historical values as well as possible:
  * > the <Boltzmann constant> k is 1.380 649 × $10^{-23}$ J/K

    Arbitrarily defines temperature from previously defined energy (J) to match historical values.
  * > the Avogadro constant NA is 6.022 140 76 × $10^{23}$ mol

    Arbitrarily defines the mol to match historical values. In particular, the <kilogram> is not an exact multiple of the weight of an atom of <hydrogen>.
  * > the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, is 683 lm/W

    Arbitrarily defines the Candela in terms of previous values to match historical records. The most useless unit comes last as you'd expect.


2019 redefinition of the SI base units

2019 redefinition of the Kilogram

 Tagged (1)

 Ancestors (8)

 Incoming links (6)

 Discussion (0)

 Articles by others on the same topic (0)