Re: I need help.

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

On Fri, 22 Feb 2002, Ludwik Kowalski wrote:
> If it is true that surface charges are necessary in wires to
> bend electric lines locally then they are also necessary to
> bend the E lines in a conducting sheet. Is this a reasonable
> expectation? If not then why not? It is a separate answer
> worth discussing under the Chabay/Sherwood thread.
> Ludwik Kowalski
I suspect there is some misscommunication going on here.  The reason lines
of E bend is because of superposition...you have two essentially point
charges whose electric fields add.  The resulting tangent lines are
curved.
That is not at all the issue in the current in a wire and the need for
surface charges.  In that case, the electric field obtained by adding the
two contributions from the battery plates cannot account for the
complicated field configuration which most occur if you are going to argue
that electrons in the wire move because of the electric field caused by
the battery plates.  Therefore there most be other charges present to
create the complex fields configuration needed.  Hence one appeals to the
existence of charged regions which are induced by the original field and
the shape of the conductor.  These are the surface charges.

One does not have to appeal to surface charges to get curved field lines.

Finally, why in heavens name are you considering such a complicated
geometry to decide  whether the conducting sheet is 2D or 3D?

Or have I missed something?


cheers


Joseph J. Bellina, Jr.        219-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556