Re: My first TC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Scott Fulks by way of Terry Fritz <twftesla-at-uswest-dot-net>" <darkthing-at-earthlink-dot-net>

William wrote:
> I have found that the outer turns do
> in fact have more inductance per square inch than the
> inner turns of wire. It must be some sort of coupling
> effect, since I can't think of any other logical
> reason.

I believe the reason for this is that the magnetic field inside a loop is
stronger than the field outside.  A long straight wire has a magnetic field
which is equal in all directions away from the wire, but when bent into a
loop the field inside the loop is reinforced, and the field outside the loop
diminished.  In a flat spiral coil, each turn strongly affects the turns
inside it, and weakly affects the turns outside.  The inner turns will only
induce significant current in a few of the turns outside their radius,
whereas the outer turns induce a current in all of the turns inside them.
So, the inductance per unit area is larger in the outer turns.

Regards,
Scott Fulks (darkthing-at-earthlink-dot-net)