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*To*: tesla-at-pupman-dot-com*Subject*: RE: New Inductance Formula*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Fri, 03 May 2002 17:20:04 -0600*Resent-Date*: Fri, 3 May 2002 17:42:17 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <_C2m.A.IcC.WBy08-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 Jim, >>>The inductance of a long solenoid is given, theoretically, by: >>> eq1 >L=u0*a*N^2/l H >> Where did you find this formula? >This is sort of the fundamental definition of inductance of a coil... from first principles. You'll find it in any first year physics text. 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 where km is a magnetic force constant equal to 10^-7 tesla*m/amp. This formula is way off in calculating the inductance, but at least it has the right units. Ahhh, there's the formula with permeability, it is in University Physics by Sears Zemansky. Thanks for pointing this out. In the Sears/Zemansky book the denominator only has the length of the windings and also neglects to add the length of the radius. I would expect that if inductance were as well understood as some indicate, then these university level physics texts would have a formula for inductance that gives accurate values. In the Physics book by McCliment, the self inductance formula is supposed to work for a solenoid coil. This is all the more reason why I will continue to research inductance. Dave

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