Re: Wire length (fwd)

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Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Tue, 12 Dec 2006 14:29:42 EST
From: Mddeming@xxxxxxx
To: tesla@xxxxxxxxxx
Subject: Re: Wire length (fwd)

 
Hi Shaun, Jared, et.al.
 
    IIRC, back in Nov 2002, a paper was posted to the  list which showed that 
for any given length of wire and turns/inch there is  a unique solenoid and a 
unique flat spiral which give maximum inductance  for each configuration. 
While it was an interesting mathematical  derivation, I'm not sure that anyone 
ever found it practical for TC  building. If it's not there any longer, I'll be 
happy to re-post it or send an  off-list copy on request.
    It is also possible to express power input of a  coil in "equivalent 
standard cartloads of buffalo chips per fortnight" instead  of kilowatts, or the 
surface area of memory chips can be expressed in nanoacres.  Again, interesting 
exercises but it seems no one has recognized their great  theoretical value 
yet. ;^)
 
Matt D.
 
 
In a message dated 12/12/06 10:15:32 A.M. Eastern Standard Time,  
tesla@xxxxxxxxxx writes:

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