Re: capacitance formula

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 9/16/02 4:17:23 PM Pacific Daylight Time, tesla-at-pupman-dot-com
writes:


>
> The problem is that one cannot plug numbers blindly into a formula without
> regard to what they represent. However, many of those who were raised with
> calculators tend to ignore dimensional analysis. If one considers the
> dimensions and not just the numbers, it is immediately obvious that you get
> the
> same VALUE for A/d in both your examples.
>
>       1 in x 1 in / 0.5 in =2 in. likewise, 2.54 cm x 2.54 cm / 1.27 cm =
> 5.08
> cm
>
> While 2 does not equal 5.08, nevertheless and A/d ratio of 2 inches is
> IDENTICAL to an A/d ratio of 5.08 cm. One would expect the ratios to be the
> same number IF AND ONLY IF they were pure, dimensionless numbers, not numbers
> with dimensions attached. Crunching numbers without regard to dimensions will
> almost always lead to problems. Even Einstein's famous E=mc^2 looks funny if
> mass is in slugs and c is in furlongs per fortnight, but it can be done and
> the
> answer even expressed  in "heat of equivalent standard cartloads of buffalo
> chips" ;-) It's all in knowing how to PROPERLY handle the dimensions.
>
> Matt D.



Then there is the formula using inches:
C (pf) = .224 K A / d
K = dielectric constant
A = plate area in square inches
d = distance between plates in inches

Ed Sonderman