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*To*: tesla-at-pupman-dot-com*Subject*: Re: New Inductance Formula*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Sat, 04 May 2002 18:11:11 -0600*Resent-Date*: Sat, 4 May 2002 18:14:54 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <8A0r2B.A.O2H.3lH18-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>" <scepp-at-mts-dot-net> Hey dave, Yup, way off. The reason is that is the equation L = N^2*u*A/l is for a long solenoid, where length is 10x or more larger that radius, your example was for a short fat coil, there are equation specially for this, but I can't find them right now. I tried both equation, this one and wheelers for a solenoid using my tesla secondary as an example. r = 2.125 " l = 22 " N = 1400 turns convert valued to metric for the non wheeler equation and I get: L = 40.3 mH from the above equation and, L = 37.01mH from wheelers equation, and the same from my metric version. I see you included units again, I think that Webers/amp is a much more meaningful unit for electrical/magnetic measurements that the base units that you have been using. All the best, Shaun Epp, goin' for another round 8 - ) ----- Original Message ----- From: "Tesla list" <tesla-at-pupman-dot-com> To: <tesla-at-pupman-dot-com> Sent: Saturday, May 04, 2002 1:36 PM Subject: RE: New Inductance Formula > Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org> > > Hi Shaun, > > >And Dave, the reason that inductance formula is way off is because it is > missing a "pi", see below: > >> In the book Physics, by Edward R. McCliment, Univ of Iowa, the formula > for > >> self inductance is given as: > >> > >> 4pi * km * R^2 * N^2 > >> Lself = -------------------- > >> l > >Should read: > > > > 4 * pi^2 * 10^-7 * R^2 * N^2 > >Lself = ---------------------------- > > l > >which is the expanded version of that physics text inductance formula for a > long selenoid. I expanded u and area. > > You are correct that I missed the pi. But the actual expanded formula is: > > 4 * pi^2 * 10^-7 *tesla * m * R^2 * N^2 > Lself = --------------------------------------- > l * amp > > And this formula, while it gives the correct units, is 356% greater than > Wheeler's when: > > R = .61m > l = .305m > N = 411.5 > > Dave >

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