alt.sci.physics

On Sep 12, 5:04 am, "Don Kelly" wrote:
>
> > 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.
>
> > ....
>
> > 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).
>
> > ....
>
> > 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:
>
> > | 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-

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.

>(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.

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.
If you are intrested to know more in this respect see:
/hvansari/

Regards,
Hamid V Ansari