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Re: TC Electrosattics Revisited II




From: 	Greg Leyh[SMTP:lod-at-pacbell-dot-net]
Sent: 	Saturday, September 13, 1997 7:25 PM
To: 	Tesla List
Subject: 	Re: TC Electrosattics Revisited II

Edward V. Phillips wrote:


> "> leaving ke to be determined empirically. By international agreement:
> >
> > "A constant current of one ampere maintained in two parallel, infinitely long,
> > straight conductors of negligible cross-section separated by one metre in
> > vacuum, produces a force between these conductors of 2 x lO-7 newtons per metr
> e
> > of length."
> 
> John,
> 
> So is it correct to conclude that, under the SI unit convention, the Ampere is
> determined empirically, and the Coulomb is defined as one ampere-second?
> 
> -GL
> "
>         NO.  The force is defined independently and the ampere, by
> international agreement, is as defined.  Not empirical at all.  As
> I remember, the value so defined differs by some parts per million
> from the value defined by electro deposition of Ag.  Bureau of
> Standards has measured current with a force balance for a very
> long time.

Sorry -- by empirically, I meant that it was measured (by a force balance
or other suitably pre-calibrated device) rather than simply defined.
In any case, it appears that under the SI convention a coulomb is defined
as one Ampere-second, without requiring any further physical measurement
once the Ampere is exacted.

-GL