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*To*: tesla-at-pupman-dot-com*Subject*: RE: Variable Capacitance and Inductance*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Sat, 25 May 2002 22:56:26 -0600*Resent-Date*: Sat, 25 May 2002 22:56:33 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <goPgZD.A.1-D.8rG88-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org> Hi Ed, >one thing which is evident is that he is assuming that the capacitance of his bottle primary capacitor is constant. Perhaps someone who had played with bottle capacitors could comment on their stability. You can see Tesla's own concern for the accuracy of his primary capacitors on page 242. >He makes no mention of the sharpness of tuning This is on page 211. Tuning was "very sharp" at least on October 5. >As far as Wheeler's formulae (there are several), it IS NOT based on empirical measurements, but on fitting simple expressions to the more exact solutions over limited ranges of geometry. Does this not have the same effect as being empirically based? You may be correct on the terminology, but the end result is that Wheeler's formula is not based on first principles. It has a fudge factor built into it. And as far as I know, the nature of what is being fudged has not been determined. Wheeler's formula is just a bunch of seemingly relevant variables and numbers that happens to put out a close approximation of an air coil's inductance. Is it OK to question why Wheeler's formula seemingly has a fudge factor built into it? >> 4 pi^2 N^2 R^2 >> L = -------------- >> H >> >> Where L is in 1000 inches. > What does H stand for in this expression? The same as Wheeler's formula. H is the winding length, R is the radius, N is the number of turns. R and H are in inches. >What do you mean by "Where L is in 1000 inches". If you strictly solve for R, H and N the units of the answer is 1000 inches. >Is L the inductance or the length or what? I'm told that L is the inductance expressed in length of 1000 inches. My improvement to this formula (that I posted in another lifetime) corrects the units and outputs inductance as henry. But I don't post that here as correct units seem to be forbidden by the experts on this list. >Wheeler's formula is not empirical. I've never seen Wheeler's paper. All I can go on is the word of those who post to this list. Several people in a recent discussion on Wheeler's formula referred to the formula as being empirically based. If you can provide some kind of solid answer to resolve this it would be much appreciated. But regardless of whether the formula is empirical or derived from picking good numbers from a hat, it isn't based solely on the physical characteristics of the coil and the permeability of the medium. >I've read through these pages several times and I can find NO statement implying that the thought the inductance was a function of the voltage across the coil. His statement "Small corrections should have been made for the e.m.f. making it smaller..." seems to tie in with the statement at the bottom of page 271 where he says "To ascertain approximately their inductances readings were taken etc.". In other words, he might be saying that the inductance should be corrected by using the results of the e.m.f. measurement (he was measuring the voltage due to a measured current which would give the reactance from which the inductance can be calculated). Like I said in my post, I have no conclusions but this caught my attention and I'll research the notes closer for a clearer understanding. I'm not in a position to agree or disagree on this at this time. >> This would imply that the closer to earth, the lower the inductance. The >> further from the earth, the closer the coil gets to its unbiased inductance >> value. > I can't find the implication. If it can be assumed that the true inductance of an air coil in free space - and not affected by a large body such as the earth - is represented as the product of the permeability of free space times the physical characteristics of the coil; and it can be further assumed that Wheeler's formulas for inductance use fudge factors that compensate for a uniform electrostatic? effect by the earth on air core coils; then it would follow that the closer one gets to a large charged body the lower the inductance will be and the further away from said body, the closer the inductance will be to coil's calculated inductance of permeability of free space times the physical characteristics of the coil. The implication is based on the assumptions. Dave

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