Re: capacitance formula

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "robert & june heidlebaugh by way of Terry Fritz <teslalist-at-qwest-dot-net>" <rheidlebaugh-at-desertgate-dot-com>

PL: let me show the flaw , In par 1 you separate the two sheets with a plate
of Al. Now to show the problem .Capacitance is directly proportional to the
area and inverse to the spacing. YES you now have two capacitors, BUT
spacing is now 1/2 and capacitance is double in each half to give C total
the same. Ie . now 200 pf and 200pf gives Ct= 100  same, NOW change the
dialectric constant of one series capacitor and you now have 200 pf in
series with 210 pf and the total is not the same it is 102pf for Ct. Your
illistration dose not take account of the fact that you changed the spacing.
In a real capacitor with mixed dialectric the effect is parallel not series
because the spacing is not changed only the total dialectric constant even
if powdered mica is added to oil  the effect is parallel not series.
--         Robert   H


 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > Date: Wed, 04 Jun 2003 15:01:53 -0600
 > To: tesla-at-pupman-dot-com
 > Subject: Re: capacitance formula
 > Resent-From: tesla-at-pupman-dot-com
 > Resent-Date: Wed, 4 Jun 2003 15:13:11 -0600
 >
 > Original poster: "Peter Lawrence by way of Terry Fritz 
<teslalist-at-qwest-dot-net>"
 > <Peter.Lawrence-at-Sun.COM>
 >
 > Robert,
 > I came to my conclusion by thinking about the physics of the situation.
 >
 > Imagine a one-layer capacitor with one thick sheet of dialectric, now think
 > of building the dialectric from two sheets half as thick. You get the same
 > resulting capacitance in the end. Now imagine placing an aluminum sheet
 > between the two half-thick dialectric sheets - result is same overall
 > capacitance, but you've got what can also be considered as two capacitors
 > in series. Now imagine that one of the half-sheets is replaced with oil,
 > again you've got two capacitors in series.
 >
 > I think this logic is correct, so if you claim "NO: That is not correct."
 > you'll have to give a supporting argument based on physics.
 >
 > You're answer "it is somewhere between the capacitance that would result
 > in all plastic verses all oil" is consistent with the mathematical
 > formula C = 1/(1/c1 + 1/c2), so I'm not sure how your observational
 > evidence contradicts what I and others are saying.
 >
 > One thing I am not claiming is that if the space between the conductive
 > plates is filled with materials of two different dialectric constants
 > that are not essentially flat (plastic sheet and oil are both essentially
 > flat, but powered or granular material suspended in oil or glass fibers
 > in an epoxy or polyester matrix for example are not) then the simple formula
 > still holds, in fact it probably fails in this case. In this case the lines
 > of the electrostatic field are not straight and parallel, and the two
 > different dialectrics can no longer be (conceptually) separated into
 > two independent capacitors.
 >
 > -Pete Lawrence.
 >
 >
 >>
 >> Original poster: "June Heidlebaugh by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>"
 > <rheidlebaugh-at-desertgate-dot-com>
 >>
 >> NO: That is not correct. I can not give you an answer that is definite. The
 >> value is somewhere between the max capacitance of the dielectric of a given
 >> spacing and the min capacitance of the other dielectric of the same 
distance
 >> of separation.I have the same problem with PE sheets and oil capacitors. so
 >> I say use the limits and measure the results. In my case the difference is
 >> not very great. If I was using something like paper and oil the difference
 >> would much greater, but the results would still have to be measured to 
know.
 >> Robert  H
 >> ----- Original Message -----
 >> From: Tesla list <tesla-at-pupman-dot-com>
 >> To: <tesla-at-pupman-dot-com>
 >> Sent: Tuesday, June 03, 2003 7:55 PM
 >> Subject: capacitance formula
 >>
 >>
 >>> Original poster: "Peter Lawrence by way of Terry Fritz
 >> <teslalist-at-qwest-dot-net>" <Peter.Lawrence-at-Sun.COM>
 >>>
 >>>
 >>> I've been wondering what the capacitance between two conductive plates
 >>> separated by some distance that is filled with both a sheet of plastic
 >>> and some oil, where the plastic and oil have different dialectric
 >>> constants, and the thickness of each is different.
 >>>
 >>> I've come to the conclusion that it will be the same as if it were two
 >>> capacitors in series, one purely the plastic, the other purely the oil,
 >>> each with their own individual thicknesses. Then use the series
 >> capacitance
 >>> formula C = 1/ (1/c1 + 1/c2).
 >>>
 >>> Is this correct?
 >>>
 >>> -Pete Lawrence.
 >>>
 >>>
 >>
 >>
 >
 >