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Re: Skin Effect Re: [TCML] Q,,question



I believe that ac current seeks the path of least magnetic field encircling it.
For tubes and solid conductors that is the outer most skin.
For coax with a return current in the center conductor,
it's the inside of the outer conductor, because of field cancellations.
from the inner return current.
Terman argues that in a flat strip the max current is at the outer
edges leaving the middle less current dense. how ever I've
read arguments to the contrary.

Dave
----- Original Message ----- From: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, December 20, 2007 7:02 PM
Subject: Re: Skin Effect Re: [TCML] Q,,question


Dave Pierson wrote:
I do not see why current would pass on a flat strips both sides but not
both sides of a copper tube.

   Like charges repel.
   The concept of an inside and an outside to a conductor is not
   commonly taught.

   Consider, as a tubular example, a piece of coax cable.
   Whats inside (in this case) STAYS inside:
   minimal current on the outside.

   In the case under discussion: a 'typical solenoid primary'
   (or secondary, come to that) the current is applied to the outside.

   Thought will lead to experiments, which will demonstrate
   the effect.

It's really weird that skin effect applies only to the outer surface of a tube, but this happens. The reason is not the repulsion of charges, as the tube can be at zero potential and the effect still happens. The reason is the (ideal) absence of magnetic field inside the tube. Current is always associated with a magnetic field around it. No field at the inner surface = no current too.

Antonio Carlos M. de Queiroz


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