Re: Toward the equilibrium

[brian whatcott <inet@INTELLISYS.NET>]

[Bob]
> > > Note the similarity with the decay of a charged capacitor through a
> > > resistor - would a small time constant for an RC circuit imply
> > > superluminal effects?

[Brian]
> > I arrange one kilometer of copper wire in a straight line, and
> > measure its resistance as five ohms.
> > Along side it, I arrange a series string of capacitors whose aggregate
> > capacitance value is 0.001 microfarad, and whose series resistance
> > is also five ohms.  (These are practical possibilities, given
> > the necessary resources).
> >
> > I charge the string to a terminal voltage of 10,000 volts
> > and connect the ends of the capacitor string and the wire (resistor)
> > together.
> > How long will it be before the terminal voltage has fallen
> > to 1/e X 10000 volts?
> >
> > ... it will not be accomplished in  one time constant of
> > ten nanoseconds

At 14:17 1/5/01 -0500, you wrote:
> Brian,
> Your example is a strawman - it is the 1 kilometer length
> which brings in superluminal considerations.
>
> Bob Sciamanda (W3NLV)

It is indeed, and if a spatial extension of 1 km demonstrates
electric field changes on a timescale of 15 microseconds,
 [which it will...] why would one demur at a verbal picture of
 effects on a timescale one thousand times shorter, when the
characteristic length in question is also one thousand times
smaller?

 Electrostatic effects are well described and well documented.
Dynamic effects which could well be explored in a non mathemetical,
experimental way, typically are not.

 I advocate the early exposure of students to a simple
experimental rig consisting essentially of a battery driven
relay arranged to tremble between on and off states like
an electric bell, so that a resistor of about 50 ohms
can be repetitively connected from the battery to a coaxial
cable of 30 meters or so.

 Describing an electric wave travelling down the cable to a
short circuit at the far end between central conductor and braid,
followed by a returning wavefront which cancels the outgoing
field is easily displayed on an ordinary oscilloscope as a pulse
of more than two hundred nanoseconds.
 I have shown this demonstration.  It is well received.
Removing the short at the far end, shows the other striking case:
the *identical* pulse, followed by its doubled amplitude after
the wave's round trip.
brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!