Re: copper rods

[William Beaty <billb@eskimo.com>]

On Tue, 29 Jul 1997, Chuck Britton wrote:

> William Beaty wrote
> > Regardless, I'd better make my rods a million KM long, so that it takes a
> > few seconds for my "work" done on the generator shaft to appear on the
> > distant motor shaft. 
>
> The electrons themselves will move surprisingly slowly. A few mm/s for 
> several amps in common lab sized wires! But the electromagnetic 
> disturbance will move at a speed comparable to that of light.

Yep!  I recently found yet another way to express this.  If we could move
electrons at a few cm per second, the wire would heat up a rate of
kilowatts per cubic mm, it would glow white hot and melt, if not vaporize. 
Or conversely, if we could grab the electron-stuff of a wire and shove it
along, it would take kilo-newtons force to make it move at cm per second
rate (and of course it would smoke and melt.)  The "electric fluid" within
wires is not like water.  It behaves more like cold tar being pumped
through a sponge!  Amazing that electrical devices work at all.

> In this case the wave of 'work' is probably sometime refered to as a 
> 'voltage' pulse.

But in transmission lines (and circuits), the voltage pulse is accompanied
by an in-phase current pulse, so either "voltage pulse" or "current pulse"
would serve.  Which makes sense, since "work" should have a "force" part
and a "motion" part. 

> (I might be tempted to define voltage as Work/charge but 
> somebody might take umbrage.)

Is this last part controversial?  It's one I haven't encountered. 
However, I do recall seeing voltage defined this way (In Hewitt, I think.) 
I think it's very strange, and doesn't connect very seamlessly with what I
understand of electrical physics.  Voltage is a feature of the e-field, it
exists whether charges are present or not (or are there some who insist
that fields do not exist except when they interact with matter?)  I'd
agree that work could be defined in terms of charge transported across a
voltage, or that the relationship between voltage, work, and charge could
be stated.  But to me, expressing voltage as being "made of" work per
unit charge seems quite alien.  I see "voltage" as being the stuff that
appears in the space around a balloon which has been rubbed on my head
Actually, nowdays I would have to rub it on my arm!   ;)

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