Re: Electric Field Lines

[Rick Tarara <rbtarara@SPRYNET.COM>]

Maybe this is too simple, but it seems to me that in the construction
process you create the 'correct' density at the charge and therefore it
should not be surprising that the process yields the 'correct' density
elsewhere.  I've used this basic algorithm in the E&M package of the
Animated Chalkboard and it does seem to work.  When I programmed this, I
setup a test charge that I place at equal angular displacements around a
fixed charge and then calculate the force due to the all the fixed charges.
I move the test charge a small increment--showing the path on the
screen--and then repeat.  This is just the prescription we teach and it does
work!  I was surprised (the first time I programmed this) that it works well
and is relatively simple to code.  [It also helps that today's computers are
so fast.  I remember doing this on a Commodore 64!  In the potential mapping
program I actually calculate the potential at every pixel on the screen
(786,432) from up to ten charges and then use color to indicate the
strength.  While this routine takes a few minutes to run, it wasn't long ago
that it would have taken hours.]

Rick

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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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www.saintmarys.edu/~rtarara/software.html
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> At 05:26 10/25/01 -0400, Ed Schweber wrote:
> > Hi:
> >
> >    Yesterday I posed a question about the standard algorithm for
> > constructing electric field lines, using a dipole as a paradigm.
> >
> >   " What has recently begun to perplex me is that we have only paid
> > explicit
> >    attention to the direction of the field and the correct
proportionality
> >     between the density of the field lines and the strength of the field
> > seems
> >      to have appeared by magic."