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*To*: tesla-at-pupman-dot-com*Subject*: Re: New Inductance Formula*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Thu, 02 May 2002 19:55:56 -0600*Resent-Date*: Thu, 2 May 2002 19:56:04 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <yxXnR.A.2jC.x4e08-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br> Ok, I will enter this discussion too... It's interesting to see what is Wheeler's formula for the inductance of a solenoid in metric units. The inductance of a long solenoid is given, theoretically, by: L=u0*a*N^2/l H where u0=4*pi*10^-7, a is the area of a cross-section, and l is the length of the coil. Using a=pi*r^2: L=u0*pi*r^2*N^2/l H Add a "correction factor" to the denominator, replacing l by l+0.9*r: L=u0*pi*r^2*N^2/(l+0.9*r) H This is Wheeler's formula. To put it in the familiar shape for measurements in inches, multiply r and l by 2.54/100, or simply multiply the formula by this factor: L=u0*pi*2.54/100*r^2*N^2/(l+0.9*r) H Substituting u0, multiplying numerator and denominator by 10, and putting the result in uH: L=4*pi^2*2.54/100*r^2*N^2/(10*l+9*r) uH L=1.0028*r^2*N^2/(10*l+9*r) uH So, the multiplying constant ~1, in the Wheeler' formula is just: 4*pi^2*2.54/100 uH/inches. Antonio Carlos M. de Queiroz

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