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Re: Re: [TCML] Spark models, revisited



On 30/10/2012 10:07, Jim Lux wrote:

Using the formula from E.B. Rosa's 1907 NBS work... a 100 cm long wire that is 0.04 cm in diameter has an inductance of 1.55 uH..

=2*(B9*LN((B9+SQRT(B9^2+C9^2))/C9)-SQRT(B9^2+C9^2)+B9/4+C9)
B9 is length
C9 is diameter
gives resulting inductance in cm (Yeah, back at the turn of the century, they didn't always use MKS or SI units).. divide by 1000 to get microhenries.
Using the formula implemented in the Inca program, tested by direct solving of the numerical integral, I get 1.692 uH. Using then the speed of light as propagation speed:
c = 1/sqrt(L*C)
C = 1/(c^2*L) = 1/(3e8^2*1.692e-6) = 6.57 pF
Quite close to the measurements.
A complication with this calculation is that the inductance of 1 m of wire is not exactly the inductance per meter of the wire for small lengths. But my calculation is not giving a constant L/m for small lengths. Something to verify.

Antonio Carlos M. de Queiroz

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