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New SI (formally implemented on May 20, 2019)

new si card for english version

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International System of Units (SI) have been defined by physical constants since May 20, 2019, as following:

  • the caesium hyperfine frequency (ΔνCs) 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 × 1023 mol-1;
  • the luminous efficacy of a defined visible radiation (Kcd) is 683 lm/W.
  • Last Updated:2020/08/10
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