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Re: Isotropic Capacitance
Tesla List wrote:
>
> >From brzozoww-at-rchland.vnet.ibm-dot-comWed May 22 22:32:12 1996
> Date: Wed, 22 May 1996 11:01:21 -0400 (EST)
> From: Wesley Brzozowski <brzozoww-at-rchland.vnet.ibm-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Isotropic Capacitance
>
> Richard Hull <hullr-at-whitlock-dot-com> Writes:
>
> > Basically, Space is a dielectric, in that it has a quality called
> > permittivity (8.8 picofarads/meter) It is thru this good office and the
> > rest of the matter in the universe that a single terminal in outer space
> > has capacitance. The equations for this value are all screwed up as are
>
> Greetings, Richard!
>
> I'm a faithful reader, but very sporadic contributor to this list (mostly
> because there's rarely enough time to quickly read through everything; I'd
> contribute more if I could but find the time). In any case, I think my last
> contributions were before you joined here, so I thought I'd put in the little
> intro. Also, we met at Ed Wingate's Teslathon last summer, but who's gonna
> remember that far back?
>
> Anyway, I thought I'd put in a really minor addition to your comments on
> the subject. They're excellent, but they also can be read in two ways;
> only one of which is correct. I'm sure you had the right one in mind when
> you wrote your note, but this may clear up any confusion among some who
> read it.
>
> While a sphere, or any shape for that matter has capacitance, it does not
> require "the rest of the matter in the universe" in order for that
> capacitance to exist. In any first semester fields text, the capacitance of
> an isolated sphere is the first thing derived when they get to the subject of
> capacitance, because the math is so straightforeward. But in this derivation,
> no extra matter in the universe is assumed; in fact the implicit assumption
> is that there's absolutely no extra matter in existence. They usually say
> that there're no other bodies close enough to influence it, but without
> quantitatively defining what constitues "influence", they're really assuming
> that there's nothing else there, or perhaps that any other matter is
> infinitely far away. (Same difference, I guess.)
>
> In any case, an arbitrary charge q on the body produces an electric field
> which can be predicted. The electric field is integrated from the surface of
> the sphere to a point infinitely far away, giving the potential (voltage)
> between the sphere and that point, and then the familiar old C = q/V is
> applied to get the capacitance between the sphere and the point infinitely
> far away. This is the equation we tend to (ab)use for a spherical capacitor.
>
> Now, I don't expect that you implied that extra matter in the universe was
> required to greate a capacitance on the isolated sphere, but a quick reading
> of your note could give that impression. Since you immediately followed the
> portion I quoted with a comment that the equation for the capacitance of a
> sphere doesn't work perfectly in the Real World, I suspect you were referring
> to the fact that additional matter in the vicinity will affect the value of
> the sphere's capacitance, and the capacitance we measure won't match up to
> that nice, idealized equation, becaue we've violated the assumptions that
> made it so easy to derive.
>
> Predicting the real capacitance in such a situation would take lots
> more work that just might not be worth the effort. Using a computer
> with decent number-crunching power along with the Method of Moments
> should yield pretty accurate results, but if the idealized equation
> is already within 20% of the actual as you seem to have measured,
> there would seem to be better things to do with our time. Do the
> equations for toroid capacitances come this close too?
>
> Anyway, I thought I'd put in my two cent's worth. Hope that's okay.
>
> Wes B.
Wes,
I didn't want to snip any of your text due to the nice format you
supplied above. Others may wish to reread your full text. I agree in
principal to the statement about all the rest of the matter in the
universe being a poor terminology on my behalf and an outright mispeak.
However, I have of late been questioning a number of sacred tenants
regarding the very definition of what constitutes electrostatics and
electrodynamics and the shadowy zone that constantly shifts about in the
demarcation between the two. Many scientists, physicists researchers,
etc. disagree on a number of different "fine points"! I am not a loose
canon or a maverick, but believe the right to question is paramount in
science.
The charge figured relative to a point infinitely distant is a nice
concept. But, to aquire a charge, anywhere in the real world, work must
be performed in a dielectric (space in this case) by sparating this
charge relative to something (the point far off). Metals can't have
charge separated within them -(they are not permitive, only permeable).
They may have a charge depositied on them, however. It is the insulator
(space)/ metal inferface where the charge is developed due to some work
being performed in the dielectric (space). This should have a reaction
point (universe) to have the work performed against (second plate),
separating the charge. Naked monopolar charges are suppossedly not
allowed anymore than magnetic monopoles. Theory is great, but it must be
self-consistent when viewed from every angle.
Again I do not question the math or the concept, just the physical
embodiment.
A fantastic book I am currently wading through calls into question some
aspects of Maxwell's equations especially as regards displacement
currents and their hypothesized attendant magnetic fields and further
points up and mathematically proves that some of his equations have no
demostrable causal relationships. This is a very well done piece of work
by Dr. Oleg Jefmenko, professor at West Virginia State Univ. If anyone
is a guru on electrostatics/ electrodynamics, it is he. (has written two
text books on the subject). In short, grave doubts about what we were
taught at the core level are starting to bubble to the surface.
Thanks and I welcome any response,
Richard Hull, TCBOR