Re: capacitance formula

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

Original poster: "harvey norris by way of Terry Fritz <twftesla-at-qwest-dot-net>" <harvich-at-yahoo-dot-com>


--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Dr. Wolfram Steinkamp by way of
> Terry Fritz <twftesla-at-qwest-dot-net>"
> <Wolfram-Steinkamp-at-gmx.de>
> 
> yes my dear, so it is.
Caution is the order of the day here folks: I am
fairly certain that (ENGLISH OR METRIC) distance units
MUST be used for the measurement units, or this gives
an incorrect answer. Found this out a long time ago
when my capacities didnt jive using inches for the
length and area factors. Although it sounds a little
illogical, we CANNOT ASSUME that just because we have
converted BOTH the numerator and denominator to a
different ratio of length standard, (ie 2.54 cm = 1
inch); that converting both the top and bottom length
factors will also convert the ratio answer to be
identical. This can easily be shown for a case example
of A=1 inch^2 and d= 1/2 inch which easily computes
that A/d ratio to be 2. Now convert to metric and find
the A/d ratio; this becomes 2.54^2/1.27 using cm or
A/d = 5.08, not the no 2 that was arrived at using
inches as the length factor. Thus this formula was
derived SPECIFICALLY FOR METRIC MEASUREMENT LENGTHS,
and if it were derived specifically for inches, it
would be an entirely different formula. Maybe this was
obvious to most of us, but since I made this kind of
mistake in the past, I thought it would be notweworthy
to mention so that other folks dont make the same kind
of mistake, and wind up scratching their noggins tryin
to figure out what went wrong?  HDN
> regards
> 
> stone
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Sunday, September 15, 2002 9:41 PM
> Subject: capacitance formula
> 
> 
> > Original poster: "colin.heath4 by way of Terry
> Fritz <twftesla-at-qwest-dot-net>"
> <colin.heath4-at-ntlworld-dot-com>
> >
> > hi all
> >         my ee is rusty and im trying to build
> homemade caps what is the
> > formula
> > is it
> > Eo x Er x A
> > -------------
> >         d
> > where EO = 8.85E-12
> > Er of polyethylene 3
> > A area of plate
> > d distance between plates
> > cheers
> > colin heath
> >
> >
> >
> 
> 
> 
> 


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