FW: equipotentials

["Zajac, Richard" <rzajac@SAL.KSU.EDU>]

Equipotentials corresponding to different values of the electric potential
cannot intersect, since no point can have two differevent values of electric
potential.
Equipotentials corresponding to the same value can cross.

As an example, consider two equal positive charges separated by some
distance.  Close to either charge, the equipotentials are nearly circular.
As you move away from either charge, these "circles" expand.  At a point
midway between the equal charges, the "circle" around one charge intersects
the "circle" around the other charge.  (The circles aren't very circular by
this point).

The net effect is what appears to be two equipotentials crossing.  At that
point, the electric field is of course zero.  Since the equipotentials in
question have the same value, it can be argued, I suppose, that these aren't
really different equipotentials.
You can see this by playing with EMField from Physics Academic Software.

Richard Zajac

> ----------
> From:         Forum for Physics Educators[SMTP:PHYS-L@lists.nau.edu] on
> behalf of Justin Parke[SMTP:FIZIX29@AOL.COM]
> Reply To:     Forum for Physics Educators
> Sent:         Friday, February 20, 2004 10:32 AM
> To:   PHYS-L@lists.nau.edu
> Subject:      equipotentials
>
> Can equipotential surfaces cross?  If so then in what direction does the
> electric field point at the line of intersection?
>
> (This is another disagreement between me and the "back of the book" answer
> for a textbook question)
>
> Justin Parke
> Oakland Mills High School
> Columbia, MD