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Re: Capacitor charge, were is it?
>Date: Mon, 11 Nov 1996 11:21:45 PST
>From: "Fred W. Bach, TRIUMF Operations" <music-at-triumf.ca>
>To: tesla-at-pupman-dot-com
>Cc: music-at-triumf.ca
>Subject: Re: Capacitor charge, were is it?
>
[routing snip to save chip]
>>"Now what would happen if we cut that rod in two, put a very tiny
>> microammeter between the two half-rods and connected the leads of
>> the microammeter to the two half-rods such that the ammeter was now
>> in series with the rods, and then we turned on the field V. We
>> agree that in the steady state there is no current flow in the rod.
>> But what would the meter read if we started with the field off and
>> the we turned it on? Would the meter ever read any current? Would
>> the current start and flow in one direction and stop, or would the
>> current turn around and flow back the other way? Would there be
>> any net charge transferred through the microammeter if we left the
>> voltage on?"
>> At the time the field was applied there would be a
>>transient current through the microammeter, since the two
>>ends of the rod to which it is connect are, in effect, small
>>capacitors coupled to the two plates. After the initial transient
>>those two capacitors are charged, so a net current had to flow.
Now break the circuit between both rod halves, move them apart and
discharge them inside a faraday cage. You've just made an "influence
machine" (electrostatic generator) ala Wimhearst(sp) , Dirod and
probably several others whose names I've forgotten with time. In each
case, 2 electrodes are connected, an electric field is applied across
them to move electrons from one electrode to the other, the connection
is removed (leaving the electrodes charged) and the charged electrodes
are moved to a new position for discharge.
Now, contrast this method with a Van DeGraff electrostatic generator
where a charge is placed/deposited/stored on/in a dielectric which is
then moved to a new location for discharge. Both work by moving
electrons (charge if you will) from a point of low concentration to a
point of high concentration but the Van DeGraff does it by dielectric
charge movement and shows the Q=C*V relationship as V=Q/C directly.
(sorry, about an hour ago I was attacked by 6.75 year old "bomber
plane" by the name of Stuart and lost my train of thought. I WAS going
to tie this into a relationship with TCs but, alas, some nights I have
the attention span of a 6 year old ;)
The influence machines move charge (as extra electrons) directly from
a point of low concentration to a point of high concentration.
> So my question is, where are the extra electrons on the half of the
> rod nearest to the V+ ? They are still associated with/ attached
> to that half of the bar. What is the nature of this bond?
>
Fred,
Electrons in a metal are closer to a gas floating in the
crystal lattice (who says that crystal energy is "new age fru-fru" ?
everything I design with uses a crystal of some type; resistors,
capacitors, crystals, ICs, tubes, LCDs, CRTs, wire ... the only
exceptions I can come up with are glass: a supper cooled liquid and
polymers: a supper sized lattice 8;) and can be pumped between places
with the application of an electromotive force or pulled between
places with an electric field.
The "electron gas" has flowed toward the positive influence to create
a system of lower potential energy.
Regards,
jim