Wire length (fwd)

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---------- Forwarded message ----------
Date: Tue, 12 Dec 2006 09:45:33 -0500
From: Jared Dwarshuis <jdwarshuis@xxxxxxxxx>
To: Pupman <tesla@xxxxxxxxxx>
Subject: Wire length

Hello Jared,



I was wondering why wirelength is so important to you ?



Your level of math and physics knowledge is way beyond probably all but a
few on the tesla list.  I have never even heard of the Neumann equation (but
I looked it up), it's advanced level quantum physics.



I did look up inductance in my university level physics text book and it
states:



for  L = u N^2 A
     ------------
         l



"This shows that L depends on geometric factors and is proportional to the
square of the number of turns. "



Serway Physics for Scientists & Engineers



Why then do you quote wirelength?







I wish had your level of education!



Shaun Epp



Hi : Shaun



Most of the coils that my friend Larry and I have built are multiple
wavelength. The speed of light and frequency determine the location of
voltage and current nodes along the wires length.



The Neumann equation can be found in many electromagnetic textbooks.



L does depend on geometric considerations and the equation that you have
shown is correct (in the abstract).



Visualize a long piece of wire being like a wet noodle. We have a collection
of jars, and when we place the noodle in a long skinny jar it coils up
against the walls of the jar giving us a large number of turns. (but a low
inductance) Now we take the wire and place it in a short jar and it coils up
to give us far fewer turns then before. But the inductance is much larger
then with the skinny jar.



  L = u (wire length)sqrd / 4pi H



The wire length remains constant but the Height of the solenoid has
decreased with the short jar. Can you now, see why the inductance is greater
even though we have less turns?



Now there is a practical matter. In real life a short solenoid departs
significantly from a uniform magnetic field, (a condition of the derivation)
So the inductance is not really as large as the equations would suggest. But
is very close to true for long solenoids where the bulk of the magnetic
field is uniform.



I still poop in my calculus diapers, you should envy someone else.



Sincerely: Jared Dwarshuis