[time-nuts] Re: Realization of electrical units (was: What everyday uses are there for accurate clocks?)

[Dr. David Kirkby]

On Wed, 30 Nov 2022 at 09:21, Attila Kinali via time-nuts <
time-nuts at lists.febo.com> wrote:

> On Tue, 29 Nov 2022 22:02:19 +0000
> Andy Talbot via time-nuts <time-nuts at lists.febo.com> wrote:
>
> > The volt isn’t an SI unit. The amp is, and volts will be derived from
> amps
> > via power which itself comes from mass, length and time.
>
> While it is true that the SI unit is Ampère, the mise en pratique
> for electrical units is done using a Josephson junction for the Volt
> and a fractional Hal effect system for the Ohm. The Ampère is then
> realized using a calibrated voltage and resistance.



The volt is not one of the 7 base SI units, but  it is one of the 22
derived SI units with special names. See section 2.3.4 of

https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf

Dave





Why? Because
> the Volt and Ohm can be accurately realized by quantum mechanical
> systems that are impervious to small changes in their environment.
> While the old definition of the Ampère was very hard to realize and
> thus was never really used that way. This is also reflected in the
> redefinition of 2019, which allows Volt and Ohm to be precisely calculated
> using quantum mechanical relations and thus allow the for an exact
> realization of the Ampère when going backwards.
>
> But this is going into volt-nuts territory. Please ask there if
> you want to know more.
>
>                         Attila Kinali
>
> --
> Science is made up of so many things that appear obvious
> after they are explained. -- Pardot Kynes
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