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Re: Capacitor charge, were is it?

Subject: Re: Capacitor charge, were is it?
  
On 11/01/96 22:26:04 you wrote:
>
>>From sroys-at-umabnet.ab.umd.eduFri Nov  1 21:44:18 1996
>Date: Fri, 1 Nov 1996 09:53:14 -0500 (EST)
>From: Steve Roys <sroys-at-umabnet.ab.umd.edu>
>To: tesla-at-pupman-dot-com
>Subject: Re: Capacitor charge, were is it?
>
>On Thu, 31 Oct 1996, Tesla List wrote:
>
>> >A vacuum diode passes charge when the heated cathode boils electrons off
>> >and they are drawn towards the anode.  If you turn the filament off, the
>> >vacuum diode stops conducting and becomes a vacuum capacitor.
>> >
>>   
>> Makes sense to me.  But the vacuum is still a conductor of electrons when 
>> the electrons are freed from the cathode.
>
>To preface this, I'm not a physicist, and so I'm probably as confused as 
you
>are, but...
>
>Yes, electrons travel through a vacuum, but not in the conventional sense
>of conduction of electricity through matter.  The way I understand it, the
>conduction of electricity through matter is more of a field phenomenon
>where electrons actually move at a very small fraction of the speed of
>what we consider to be "current.  The individual electrons only make short
>jumps between atoms, but the disturbance that one electron has on the next 
>travels from one end of the wire to the next at nearly the speed of light
>Sort of like a crowded highway at rush hour...a disturbance at one end of
>the line of traffic can propagate back through the line of cars much
>faster than the cars can actually move.

You are correct in this analogy.  However, since current is defined as 
charge transfer over time (dQ/dT), any electron flow regardless of the 
medium can be considered a current flow.  Take an electron beam.  Is this 
not a current flow?  Beta radiation is electrons flowing from a radioactive 
material.  Is this not also current flow?

>
>Conductors pass the electrons on easily between atoms, insulators hold
>onto their electrons and don't let them go as easily.  The better the
>insulator, the stronger the hold on the electrons.  Vacuum has nothing to
>retard the electrons.  Once the electron breaks free, it's free to go,
>governed only by it's initial momentum and the surrounding electric and
>magnetic fields.
>
>So in a sense, it seems like once an electron breaks away from a conductor
>into the vacuum, a perfect vacuum could actually be considered a perfect 
>conductor. I guess what makes a vacuum an "insulator" is the fact that the
>only way the electrons get launched into it is by outright emission from
>the surface, which is a function of the applied voltage, the work function
>of the electrode, the temperature of the surface, etc... and is in NO way
>related to the properties of the vacuum itself?  Help, Mr. Wizard!
>
>Steve (looking for support) Roys.
>



Phil Gantt (pgantt-at-ix-dot-netcom-dot-com)
http://www-dot-netcom-dot-com/~pgantt/intro.html