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Re: I need help.



What I said was that I looked at a much simpler system, a dot and a
concentric ring. It this were a 2D situation, the field would fall off
as 1/r, if it were a 3d situation, it would fall off as 1/r squared.
The data clearly indicated 1/r. Conclusion it is a 2D situation, which
is what I would expect.

joe

On
Wed, 20 Feb 2002, kowalskil wrote:

Hi Joseph:
Two "theories" were tried: (a) charged spheres and (b) charged
rods. Neither of them matched the equipotential line on the sheet.
My understanding was that, according to you, the "two rods"
theory should be appropriate. Perhaps you did not mean this.

That is why I wrote:

And, consequently, you would expect the theoretical curve
(b) to match the experimental line. ...
Ludwik Kowalski
********************************************
Joseph Bellina wrote:

I'm not sure what your response means. The theory for a charged rod
would predict a 1/r dependence of the field, whereas for a charge sphere
you would expect 1/r squared. The experiment gave a result of 1/r,
hence my conclusion that the sheet is a 2D space, and represents the
field in a plane perpendicular to the rod.

Could you explain your concern more fully?

joe

On Wed, 20 Feb 2002, kowalskil
wrote:

Joseph Bellina wrote:

Since the flow lines all lie in the plane of the paper, it seems to me
that the situation is a 2 dimensional one.
Let me describe an experiment I did some time ago which supports this
claim.
Construct a ring of conducting paint, and put a dot of conducting paint
in the center. Measure the potential as a function of distance from the
center, plot the curve, differentiate it by drawing some tangent lines,
and then plot the slopes as a function of distance on log-log paper. Of
course now you would do it with a computer. The slope of the resulting
line is -1, so the electric field falls off as 1/r, which is the
characteristic of an infinite rod. In this sense the paper can be
seen as a perpendicular cut in the space around a charged rod.

And, consequently, you would expect the theoretical curve (b) to
match the experimental line. But this did not happen. Why?
Ludwik Kowalski


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


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