[Phys-L] Re: Elecric Field Lines

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

At 09:11 AM 2/8/2006, you wrote:
> David Abineri's question about electric fields reminded me of a problem I have
> always had in visualizing the field surrounding two equal positive charges.
>
> Consider two equal positive charges on the x-axis where q1 is at -1m and q2 is
> at +1m.  clearly the field is zero at the origin and the field lines are
> directed straight up on the +y axis and straight down on the -y axis.
>
> The electric field "lines" are also linear on the x axis; to the left from -1m
> to infinity; to the right from +1m to infinity; to the right from -1m to zero;
> to the left from +1m to zero.
>
> I am concerned with the region between the vertical lines x = -1m and x = +1m.
>
> I had mistakenly thought that lines in this region would always approach the y
> axis; in other words, if a line set out from a charge toward the y axis it
> would never eventually curve away from the y axis.
>
> This clearly cannot be the case, since if we consider any point on,
> say line y =
> -1, (other than 0,-1) the x component of its electric field is negative,
> meaning it is part of a field line headed (somewhat) to the left.  Since the
> field line originated on q1 it must have started out headed to the right.
>
> My question is: Are there any lines that approach the y axis
> asymptotically, or
> do all lines that begin between x = -1 and x = +1 eventually curve away from
> the y axis (and eventually cross my vertical boundary lines)?
>
> Thank you in advance for any insight.  I look forward to reading the responses
> in the list serve digest tomorrow.
> --
> Stuart Leinoff
> Professor of Physics
> Adirondack Community College
> (518) 743-2256

Without much consideration, I looked around for other helpful analogs.
   I visualized two water sources in an elliptical  tray with a
peripheral sink.
I visualized placing the potassium permanganate crystals round each
source and imagined the stream lines.
Then, from symmetry considerations, I imagined a wall placed on the y axis
which would have no effect on the resulting streamlines.
  I could see in my mind's eye, that the outflow from the left source would
be radial to the left, and asymptotic up and down to the right.

Having said this, I am deeply aware of the drawbacks of gedanken
experiments.



Brian Whatcott    Altus OK    Eureka!
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