alt.sci.physics

On Sep 13, 1:15 pm, ...@ wrote:
> On Sep 12, 5:04 am, "Don Kelly" wrote:
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> > > Considering the above-mentioned material it is shown that, contrary
> > > to the current belief, capacitance of a capacitor does not at all
> > > depend on the dielectric used in it and depends only on the
> > > configuration of its conductors.
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> > > ....
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> > > it is shown that
> > > contrary to what the current theory predicts, resonance frequency of
> > > a circuit of RLC will increase by inserting dielectric into the
> > > capacitor (without any change of the geometry of its conductors).
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> > > ....
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> > > That actually whether or not the resonance frequency of the circuit
> > > increases with inserting dielectric between the plates of the
> > > capacitor (without any change in the plates' configuration) is a
> > > quite practical test for establishing the validity of the theory
> > > presented in this article and invalidity of the current belief in
> > > this respect, or vice versa. Recently this experiment has been
> > > performed with a briliant success for the theory presented in this
> > > article showing specifically increase of the resonance frequency when
> > > inserting the dielectric. Here is the report of an electronics
> > > engineer who could not believe the result of his experiments in
> > > this respect:
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> > > | Oh, yes, indeed the resonant frequencies do change as
> > > | drastically as you suggest if you put a dielectric with high
> > > | dielectric constant between the parallel plates of a capacitor.
> > > | I've put an example at the end of this posting.
> > > |
> > > | Example of capacitor with high-K dielectric...
> > > | You can buy "disc ceramic" capacitors with about capacitance.
> > > | These are nominally 1cm diameter, with nominally plate
> > > | separation, with dielectric only between the conductive plates.
> > > | The dielectric has a very high dielectric constant. If you resonant
> > > | such a capacitor with, say, a 5mH inductor, you will find its
> > > | resonant frequency will be about 70kHz. You can replace that
> > > | capacitor with one with the same plate size and spacing but air
> > > | dielectric, resulting in roughly capacitance. Then you will
> > > | find that the measured resonant frequency depends on the self-
> > > | resonance of the inductor, because you will be very hard-pressed to
> > > | make a 5mH inductor with self-capacitance as low as . If you
> > > | choose an inductor of, say, 1uH, properly constructed, then you
> > > | might reasonably see the effects of , but now you will be
> > > | dealing with much more awkward (especially if you have limited
> > > | access to good test equipment) resonant frequencies in the hundreds
> > > | of MHz. You will indeed find that the resonant frequency of that
> > > | inductor with the nominal ceramic-dielectric capacitor will
> > > | be on the order of 5MHz. The Q in each case should be high enough
> > > | (with a well-constructed inductor) to give an easily measured
> > > | resonant frequency. I _could_ do the experiment to specifically
> > > | demonstrate the _dramatic_ shift in resonance, and even use other
> > > | dielectrics less extreme, but I feel no need to: as I told you
> > > | before, I _routinely_ design resonant circuits and filters, even
> > > | taking into account the effects of stray capacitance and inductance
> > > | and the resistances of things like circuit board traces where
> > > | appropriate, and within my understanding of the tolerances of the
> > > | parts and the effects of the strays, I'm never surprised. I am
> > > | CERTAINLY never surprised by a resonance shifting higher as I
> > > | increase capacitance, so long as I'm within the practical range of
> > > | the parts I'm using.
> > > |
> > > | Note on 1uH coil: If you make a coil with #18AWG wire, which is
> > > | about diameter, and make that coil with uniformly spaced
> > > | turns, about diameter turns, spaced out total coil
> > > | length, it will have an inductance about , and its first
> > > | parallel self-resonance at about 190MHz. That implies about
> > > | effective self-capacitance. Adding an external capacitance
> > > | would drop the resonant frequency to about 145MHz.
>
> > > Regards,
> > > Hamid V. Ansari
>
> > ----------------------
> > The quoted material indicates a higher frequency with a smaller
> > capacitor-look at the numbers-
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> I'm eager to know if there is any demonstration of any lower frequency
> with big capacitors. Understand me; I'm not saying that this won't be
> the case, but I'm saying that I want to know if this is the case to
> modify the theory.
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> >(resonance shifting higher as capacitance
> > increased is probably either a typo or a factor due to the coil internal
> > capacitance )-guess what- that doesn't contradict present theory.
> > May I also point out the the relation of capacitance to the dielectric
> > material was established from experiments carried out over the last 100 or
> > so years. It's been tested. In fact putting a dielectric in a parallel
> > plate capacitor and measuring the change in capacitance is one way to
> > measure relative permittivity.
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> The capacitance of the capacitor will not increase but the dielectric
> will act as a source of potential to gather charge on the capacitor.
> And these two ways are not equivalent to each other and for
> example as I've shown will cause the capacitance to incrtease rather
> than decrease when only dielectric is inserted.
Excuse me, a lapse of me. I mean "will cause the resonance frequency
to increase ..."
> If you are intrested to know more in this respect see: /hvansari/
>
> Regards,
> Hamid V Ansari- Hide quoted text -
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> - Show quoted text -