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Re: 50%
ATesla List wrote:
>
> >From kg7bz-at-whitemtns-dot-comSat Nov 9 21:23:06 1996
> Date: Fri, 08 Nov 1996 19:35:47 -0700
> From: "August H. Johnson" <kg7bz-at-whitemtns-dot-com>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: 50%
>
> I've been reading this thread about the 50% energy loss and it reminded
> me of a experiment I'd done about 15-20 years ago. I'd just been given
> a neat 5,000pF 10,000V Jennings variable vacuum capacitor. I wish I
> still had it now! I'd made a calibrated turns counting dial on it so I
> could adjust it to whatever capacitance I wanted.
>
> I set it to 5,000pF and charged it to 5,000 volts. Then I cranked it
> out to 2,500pF and used one of those neat 1000:1 40KV Tektronix scope
> probes to measure the voltage. It was about 10,000 volts. The
> measurement was a bit hard to make since the time constant was only a
> couple seconds when I connected the probe to measure the voltage but a
> storage scope helped. I also did the reverse of this, charge the
> 2,500pF capacitor to 10,000 volts and then adjust it in to 5,000pF. It
> then measured about 5,000 volts. My readings weren't the most accurate
> due to things like leakage on the glass and likely some corona discharge
> in the air but I got in the ballpark. Now do the math on the two:
>
> (5000V)**2 x (5000pF/2) = 0.0626j
> (10000V)**2 x (2500pF/2) = 0.125j
>
> Same charge, but the capacitance of the capacitor was changed. Now,
> if the mechanics were frictionless I could have extracted mechanical
> energy when I let the plates of the capacitor move closer together
> (5000pF) since the plates have opposite charge and are attracted to each
> other, and it would have taken mechanical energy to move them farther
> apart (2500pF) for the same reason. Is this mechanical energy equal to
> the energy change from 0.0625j to 0.125j? I've often wondered about
> this but don't know how to do the conversions.
>
> Now that I think about it, due to the actual mechanical construction
> of that capacitor (many concentric cylinders with alternate ones
> connected together) I don't think the actual attraction between the
> plates is all that well translated to the actuator.
>
> August
> --
> August Johnson KG7BZ AMI 733 http://www.whitemtns-dot-com/~kg7bz
> P.O. Box 795
> Pinetop, AZ 85935
August,
To separate the plates in a charged cap, regardless of orientation, work
must be done to overcome the coulomb force. My large .01ufd discetable
capacitor requires quite a bit of strength to separate even when charged
to a rather whimpy 7KV. Once the plate is spearated, the charged
dielectric can be removed, rolled up, and mailed to my friend in
Alabama. He can reassemble down there with his own plates and ...POW!
The electrophorous gets its power to repeatedly charge a single plate, by
the work done by the arm in separateing the plate from the dielectric
which charges the air around the now isotropic plate as it is pulled
away from the cake.
I can actually turn the second (removable) plate of my fully discharged
disectable capacitor into an electrophorous by grounding the removable
plate just before lifting it off and the plate will appear to retain a
charge as the air pulled to the proximity of it at separation is charged
by induction.
Richard Hull, TCBOR