# Re: Variable Capacitance and Inductance

```Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

Jan: A good posting. I can place two wites side by side in a test fixture
and measure the rap/rap capacitance of the wire. Now if I wind the wire into
a coil I have the action of inductance 180o out of phase with capacitance
and wire resistance  90o from that. Now I coat the mess with assorted
coatings and put it all in an enviorment of rain snow and salt water sea
mist and wonder why my measurements are not consistant. Your dish water is
no cleaner than the dishes you clean. What I mean is the variables are
beyond our ability to sort them all out in a field of garage research.
Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Thu, 23 May 2002 00:25:35 -0600
> To: tesla-at-pupman-dot-com
> Subject: RE: Variable Capacitance and Inductance
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Thu, 23 May 2002 00:26:46 -0600
>
> Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jwagner-at-cc.hut.fi>
>
>
>> Wow! And until a couple weeks ago nobody seemed to care that Wheeler's
>> formula was outputting 1000 inches (and many probably still don't care.)
>> It was a point clearly made by some that we just don't have any formulas
>> that give direct capacitance or direct inductance.
>
> Well, we do have, but it gets to iterative solving of rather ugly
> formulas. Not anything one would do by hand. For example microstrip
> antenna design for slightly more complicated antennas... no-one would
> calculate that by hand.
>
> But, all accuracy won't help for real-life situations where the object
> under measurement is not really in free space. Different surroundings
> affect the result differently. How much the error will be depends on a lot
> of things...
>
>> Why can't our "better instruments since then" give us exact inductance
>> and capacitance measurements?
>> Could it be because inductance and capacitance are variable;
>> just as Tesla noted?
>
> Yes, L and C do vary, if the surroundings of the place of measurement are
> changed. If the surroundings remain absolutely fixed, exactly, L and C
> won't change.
>
> Here's an experiment for your (maybe for others too!):
> take a small metal box that can be closed completely and tightly, mount a
> plate capacitor inside (firmly!), maybe  even fill up the box with some
> for of resin or other hardening material so that nothing will move/rattle
> around, and have a connector on the box wall (so that you can connect your
> measurement equipment from the outside).
>
> Then make a second plate capacitor similar to the first one, but not
> enclosed. Maybe mount it on top of the box? There's no need for
> capacitances to be exactly equal...
>
> Then do a long simultaneous measurement series with both capacitors,
> at least over a few days, and at various locations / "measurement sites".
> Does the capacitance of the enclosed cap change? And how about the
> non-enclosed cap?
>
> I'll probably have to try that out myself too, once I get the time.
>
> cheers,
>
> - Jan
>
> --
> *************************************************
> high voltage at http://www.hut.fi/~jwagner/tesla
>
>
>
>

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