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Re: [Phys-L] Field Lines and charges

Yes - that is why I added the caveat of "little deep significance" - there is no contribution to the Gauss's Law integral. It was the maxim that I was really thinking of.

Bob at PC

-----Original Message-----
From: phys-l-bounces@mail.phys-l.org [mailto:phys-l-bounces@mail.phys-
l.org] On Behalf Of John Mallinckrodt
Sent: Tuesday, July 03, 2012 12:54 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Field Lines and charges

The phenomenon occurs at all X-type neutral points. As Bob points out, it's
modestly amusing, but these field lines don't really so much "end" as they do
simply "disappear" and Gauss' law is certainly not violated.

John Mallinckrodt
Cal Poly Pomona

On Jul 3, 2012, at 9:06 AM, LaMontagne, Bob wrote:

A little something to get us away from politics - I found it amusing - with
little deep significance:


Consider a configuration of two point charges of value +q, one placed on
the x axis of a standard x-y-z coordinate system at +a and the other at -a.
Now look at the electric field vectors - specifically along the y axis.

For any position along the positive y axis the field vector points in the
positive y direction. The field magnitude is zero at y = 0, and as y increases,
grows and forms a maximum at y = 0.707 a, and then gradually goes to zero
as y increases further in value. One could trace a field line starting at y=0, x=0
and follow it along the positive y axis to positive infinity.

For any position along the negative y axis the field vector points in the
negative y direction. The field magnitude is zero at y = 0, and as y decreases,
grows and forms a maximum at y = -0.707 a, and then gradually goes to zero
as y increases further in value. One could trace a field line starting at y=0, x=0
and follow it along the negative y axis to negative infinity.

Here is a pair of field lines that do not follow the usual maxim of starting
and stopping on a charge.

Bob at PC
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