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Dr. Bryan Kibble: Mass from Energy ? A Unit for a Quantum World

25 Nov 2015   14:30-15:30

Abstract: The watt balance is so good because it involves virtual work and because the size of the measured quantities is so favourable. It provides a direct link to Planck?s constant, h. Its present claimed accuracy of about 1.9 x 10-8 is adequate for the proposed re-definition of the kilogram, and the result is consistent with the alternative approach of the silicon atom-counting measurement.
We can now start to think about what needs to be done after the expected re-definition in 2018. Probably dissemination of the kilogram will continue as before with high-density artefacts and hence work started should continue on better handling and storage of 1 Kg masses of Platinum-Iridium alloy or alternative materials, e.g. silicon spheres or tungsten. There will be a need for simplified, routine watt balance or silicon atom-counting realisations of 2x10-8 accuracy for periodic re-establishment of the unit and I will describe a suggestion for a simplified watt balance.

Bio: Dr. Bryan Kibble has reshaped the SI system through his determinations and definitions of the ampere, volt, ohm and kilogram, and his principles have become the established methods for generations of metrologists who have followed him. Dr. Kibble measured the gyromagnetic ratio of the proton, which improved the realization of the SI definition of the ampere. This work was significant in uncovering a substantial error in the traditional realization of the ampere with current balances. Subsequently, his best-known work involved the development of what would become known as the ?watt balance? and resulted in worldwide acceptance of the Josephson and von Klitzing constants to represent the conventional values of the volt and ohm. Prior to this, major industrialized nations had different representations for these units, presenting a trade barrier to the sale of electrical measuring instruments. Watt balances are now playing a role in redefining the kilogram.

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Contact person
doc. Ing. Jan Holub, Ph.D., holubjan@fel.cvut.cz
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