Re: New Inductance Formula

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "David Thomson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
> 
> Well guys, get out your flame torches.  I've got my first practical
> breakthrough from the energy pulse model, earlier known as the c^2 theory.  I
> was working on my flat spiral/solenoid combination coil today and was working
> with the Wheeler formula for inductance on MathCAD Pro 2000.  When I put the
> Wheeler formula into MathCAD it confirmed my earlier observation that the
> formula was incorrect.  The units in Wheeler's formula results in meters, not
> henries.

	Wheeler's formulae (there are several) are usually known as Wheeler's
approximations, and were developed during "slide rule days" as a
convenient and simple tool for radio engineers, who seldom need an
accuracy of as great as 1%.  Handbooks usually state the range of
accuracy of each formulae as a function of the coil shape.  The exact
formulae for self inductance and mutual inductance were worked out
toward the end of the 19th century and the solutions involve small
differences between the values of elliptic integrals, a messy business
at best. 

	Much more accurate expressions and tables are given in Bureau of
Standards Circular 74, written in 1917 and still the "bible" for such
things.  Quite recently a guy named Lundin (?) worked out fairly simple
expressions giving an accuracy of better than a part in 300,000.  I've
compared the inductance he gets with the inductance calculated by the
Wheeler formulae and put it into an Excel spread sheet for fun.  Wheeler
did good work and I see no reason for the average engineer to use
anything more accurate.

	By the way, I believe the dimension of inductance is indeed length,
(centimeters in the old cgs system) though don't have time to look that
up right now.

Ed