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RE: New Inductance Formula

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Antonio,

>The inductance of a long solenoid is given, theoretically, by:
eq1 >L=u0*a*N^2/l H

Where did you find this formula?  It is interesting in that it uses metric
units and gives inductance as henry.  The values are not very accurate, but
it can be modified to give better results.

eq2 >L=4*pi^2*2.54/100*r^2*N^2/(10*l+9*r) uH

It is better to use eq1.  Both formulas have similar (but inaccurate) values
but eq1 produces the correct units.

Also, if you take eq1 and add radius to the denominator:

eq3 henry = ---------------

you get a much more accurate formula for metric that also has the correct
units.  This is comparable to the formula:

eq4 henry = --------------------
               (R + H)coul^2

Where eq4 is just a little closer to Wheeler than eq3.