# Physics Colloquium by Barry Wood

- This event is offered only in English.

**Speaker**: Barry Wood, National Research Council Canada, Ottawa, Canada

**Title**: Redefinition of the SI and Planck Constant Determinations at NRC

**Abstract**: In November of this year, in Versailles France, the 58 countries that make up the member states of the Metre Convention are expected to approve a revision of the world’s measurement system, the SI [1]. This will be the most sweeping change in the SI in 130 years. In essence the change is based on assigning fixed values to seven reference constants and deriving measurement units from those constants using the laws of physics [2]. Those seven constants include five fundamental constants of nature; the speed of light, the elementary charge, the Planck constant, the Boltzmann constant and the Avogadro constant. In the first part of this lecture I will outline these changes in the SI and their impact. In the second part of the lecture I will describe the NRC determination of the value of the Planck constant using a Kibble balance [3]. This experiment includes measurements of mass in air, mass in vacuum, velocity, the acceleration of gravity, voltage and resistance, all to parts in 109. The link between the macroscopic quantity of mass and the Planck constant is achieved through the use of the Josephson and quantum Hall effects as references for the voltage and resistance measurements. To date our measurements of the value of the Planck constant have a relative uncertainty of 9.1 10 9 which is the most accurate every published and has the most weight in determining the fixed value set by the CODATA Task Group on Fundamental Constants [4]. I will also summarize the Planck results of other Kibble balances, as well as those of the International Avogadro Cooperation.

Coffee and cookies at 14:15