Re: [Phys-L] Field Lines and charges

["LaMontagne, Bob" <RLAMONT@providence.edu>]

________________________________________
From: phys-l-bounces@mail.phys-l.org [phys-l-bounces@mail.phys-l.org] on behalf of John Denker [jsd@av8n.com]
Sent: Tuesday, July 03, 2012 9:25 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Field Lines and charges

On 07/03/2012 09:06 AM, LaMontagne, Bob wrote:
> > Here is a pair of field lines that do not follow the usual maxim of
> > starting and stopping on a charge.

I don't buy it, for a reason nobody has mentioned yet:  in addition to the
lines flowing out from the origin in the plane of symmetry, there are also
lines flowing *into* the origin along the axis of symmetry.

Just because we didn't mention them doesn't mean they are not there.  I'm
kicking myself for not mentioning them earlier.  The inflowing lines have
just as much significance (i.e. not much) as the outflowing lines.  These
lines have virtually no significance because the density of lines is zero
at the origin.

--------------------------------
[LaMontagne]
Thanks - that appears to be a good resolution of the apparant paradox. If the density of field lines is zero at the origin, then the starting and stopping of lines there simply becomes an ill posed question.

Bob at PC