The Planck Constant for the Definition and Realization of the Kilogram

Abstract

On May 20, 2019 the values of the Planck, h, and Avogadro, N A , constants will be fixed, revising our measurement system, the International System of Units (SI), and providing a new way to get mass traceability. While the famous energy relations mc 2 and hf may remind many that the Planck constant is indeed related to mass, it is less recognized how this is also true for the Avogadro constant. These concepts are reviewed in the context of the upcoming revision of the SI. How the fixed values were chosen and how mass traceability will be maintained with the smallest uncertainty are also discussed.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/andp.201800308 ν Cs = 9 192 631 770 Hz hyperfine transition frequency of 133 Cs c = 299 792 458 m s −1 speed of light in vacuum h = 6.626 070 15 × 10 −34 J s Planck constant e = 1.602 176 634 × 10 −19 C elementary charge k = 1.380 649 × 10 −23 J K −1 Boltzmann constant N A = 6.022 140 76 × 10 23 mol −1 Avogadro constant K cd = 683 lm W −1 luminous efficacy of 540 × 10 12 Hz radiationThe values and use of c, ν Cs , and K cd are already established within the SI and this has made the change more manageable.

Understanding the Revised SI: Background, Consequences, and Perspectives

“…One example is the Planck constant. The conceptually completely different approaches of the so‐called X‐ray crystal density (XRCD) and Kibble balance methods connect h with a reference mass using different underlying equations . Another example is provided by electrical units: A specific current that is realized by a combination of a Josephson voltage standard and a quantum‐Hall can be compared with a single‐electron current source.…”

New Eras in Physics

“…[1] With this, the French metrology institution BIPM will give up its traditional role as host of the famous "Grand K", the kilogram prototype, which is to be replaced by a fixed value of the Planck constant h. [2] At the same time, also the elementary charge e, [3] the Boltzmann constant k, [4] and the Avogadro constant N A [5] received new definitions so that in the future all seven SI units will be defined in terms of physical constants. [1] With this, the French metrology institution BIPM will give up its traditional role as host of the famous "Grand K", the kilogram prototype, which is to be replaced by a fixed value of the Planck constant h. [2] At the same time, also the elementary charge e, [3] the Boltzmann constant k, [4] and the Avogadro constant N A [5] received new definitions so that in the future all seven SI units will be defined in terms of physical constants.…”

“…On 16 November 2018, the 26th meeting of the General Conference on Weights and Measures in Versailles adopted a resolution on the revision of the International System of Units (SI). [1] With this, the French metrology institution BIPM will give up its traditional role as host of the famous "Grand K", the kilogram prototype, which is to be replaced by a fixed value of the Planck constant h. [2] At the same time, also the elementary charge e, [3] the Boltzmann constant k, [4] and the Avogadro constant N A [5] received new definitions so that in the future all seven SI units will be defined in terms of physical constants. These changes will come into effect on 20 May 2019, and on this occasion Annalen der Physik will publish a special issue "The Revised SI: Fundamental Constants, Basic Physics and Units", edited by our Editorial Advisory Board member Klaus Blaum (Max Planck Institute for Nuclear Physics Heidelberg), Dmitry Budker (Johannes Gutenberg University of Mainz), Andrey Surzhykov (Technical University and Physikalisch-Technische Bundesanstalt -PTB, Braunschweig), and Joachim H. Ullrich (President of the PTB, the National Metrology Institute of Germany) (Figure 1).…”

Design of sorption and buoyancy artefacts made of silicon

“…The best-known spheres have a nominal weight of one kilogram, and an uncertainty of 1.1 × 10 -8 kg. They are made of highly enriched monocrystalline silicon of isotope 28 ( 28 Si) [1]. However, their use is very limited due to the rare availability of the material, its sophisticated manufacturing process and the very high price.…”