Kilogram, ampere, kelvin and mole: units of measurement that evolve after a decision of the General Conference of weights and measures. Explanations.
Farewell “big K”! the new global definition of the kilogram , independent of any physical object, came into effect Monday 20th May, 2019.
The new international measurement system which also concerns the ampere, the kelvin and the mole was recorded in November 2018 in Versailles , near Paris , by the General Conference of Weights and Measures (CGPM) created at the end of the 19th century and which meets every 4 to 6 years.
The standard kilogram lost weight
Representatives from 60 countries voted in a “landmark decision” to redefining the International System of Units (SI), forever changing the global definition of the kilogram, the ampere, the kelvin, and the mole .
Until now, a kilogram was defined as being equal to the mass of the “Big K”, a platinum and iridium cylinder carefully preserved since 1889 at the International Bureau of Weights and Measures (BIPM) in Sèvres, near Paris.
However, the scientists realized that the mass of the international prototype had slightly varied compared to those of the six control copies made at the same time.
This variation is obviously anecdotal for the common man when it comes to making his market. But may become problematic: science and industry have entered the era of the infinitely small with the development of quantum technologies.
The kilogram will now be defined from the Planck constant (h) of quantum physics.
Other changes recorded: the kelvin, measured from water, will be redefined from the Boltzmann constant (k), related to the measurement of the thermal agitation of the fundamental constituents of a body.
The ampere will be connected to the elementary charge (e), the electric charge of a proton. The mole, the unit of quantity of material, used mainly in chemistry, will be defined directly by fixing the Avogadro constant (NA).