Re: I need help.

[kowalskil <kowalskil@MAIL.MONTCLAIR.EDU>]

But what is wrong with my claim that the finite size of the sheet
has a negligible effect for the geometry chosen? Is it not true that
rho calculated from your formula, David, and rho calculated from
the narrow strip would be different if a sizable fraction of the total
flux was prevented from going through regions outside the paper?
The two values of rho turned out to be practically identical. How
can you ignore this argument?

I will ask students to locate the experimental curves for a geometry
in which circles are closer than 10 cm. If the discrepancy between
what is observed and what is predicted is reduced then I will also
start blaming the paper size effect. We will see. For the time being
I will blame surface charges. I know that such blaming has no value
unless some theoretical or experimental evidence is produced. I think
I do have some evidence against the paper size effect. Where am I
wrong with it?

David Bowman wrote:

> It seems to me that the problem you are having with this, Ludwik, is
> that your measurements are compomised (when trying to confirm the
> exact theoretical solution) by the fact that your carbon paper is
> a finite sized rectangle, rather than an infinite plane.  Please
> go back and look at the numerically calculated equipotential curves
> calculated at Noah Gintis's URL that Brian W. mentioned:
>
> http://www.nova.edu/~gintis/vlabs/overview/ef.html  .
>
> These calculations are *precisely* for the case of a finite
> sized rectangular conducting region.  Notice the shape of the
> equipotential curves around the outside of the circle electrodes.
> They are *not* circles.  Instead they are flattened along the
> directions parallel to the paper sides, and have the symmetry of
> the paper itself.  My exact solution for the infinite sheet problem
> has no such finite size boundary effects, and its equipotential
> curves outside a conducting circle are all exactly circular in
> shape whether or not there are one or two charged conducting
> circles present.
>
> > The most important contribution, at this time is to check
> > my conclusion; no experiment can be taken seriously
> > unless it is confirmed by others. Spend 15 minutes after
> > the lab is set for students and report your findings. (But
> > make sure R of the voltmeter is at least ten megaohms.)
> > Ludwik Kowalski
>
> Or you can just look at the calculation (Gintis's) that is
> appropriate for the actual geometry of the actual experimental
> situation.