Re: OT: volt and current (ALSA sound recording frustration)

[Andrew Reid <reidac@bellatlantic.net>]

On Friday 28 November 2008 16:28, lee wrote:
> On Fri, Nov 28, 2008 at 04:13:21PM -0500, Andrew Reid wrote:
> > On Friday 28 November 2008 14:10, lee wrote:
> > > Is it even possible to measure a mere potential?
> >
> >   You mean, in principle?  Of course.
> >
> >   Put your two wires of unknown potential difference at
> > opposite ends of an evacuated tube.  Arrange the geometry
> > so that the electric field between them is linear in space.
> > You can do this by hooking them up to big plates and putting
> > the plates close enough together, making basically a
> > vacuum capacitor.
> >
> >   Then, shoot charged particles into the space between
> > the electrodes.  
>
> It takes energy to defect particles or to change the shape of a
> crystal, doesn't it? You would be observing/measuring effects and
> *deduce* that there is a potential, but that is different from
> observing/measuring the potential itself, isn't it?

  It needn't -- if the deflection is purely elastic,
then the particle comes out with the same energy as when
it went in, and there's no energy transfer.  There is a 
momentum transfer, of course.

  Then again, "deducing that there is a potential" is 
a pretty good definition of measurement, I think.

				-- A.
-- 
Andrew Reid / reidac@bellatlantic.net