# Re: Wire length (fwd)

Original poster: List moderator <mod1@xxxxxxxxxx>

---------- Forwarded message ----------
Date: Tue, 12 Dec 2006 21:50:27 -0600
From: Shaun Epp <scepp@xxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Wire length (fwd)

Jared,

The problem is not my understanding of the 'inductance for a solenoid
equation'!  I realize that that equation is only for a long selenoid.  The
problem is why do you still use "wirelength" in you equations when both of
us have shown that the coil geometry is the factor that determines
inductance?

Do you think that in your multi-wavelegth coils that you make that
wirelength is the determining factor for its resonant frequency?   The
coupling in your multi-wave must be very low as your solenoid gets longer,
it would be a waste of time making one that long...... what's the point?

Shaun

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, December 12, 2006 9:13 AM
Subject: Wire length (fwd)

> Original poster: List moderator <mod1@xxxxxxxxxx>
>
>
>
> ---------- 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?
>
>
>
>
>
>
>
>
>
>
> 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
>