Re: Electric fields and points of stability

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

I didn't make my concerns clear.  It seemed to me before (and it does
even more so now that I've had a chance to look more carefully) that
the drawing does not properly represent the field of four *point*
charges.  If it did, many of the field lines that head *toward* the
center would actually *go* to the center rather than curving back
outwards as they do in your diagram.  The field of four infinite line
charges, on the other hand, *does* look like your drawing which makes
me think that your program may actually be calculating the fields of
line charges rather than point charges.  This is commonly done in
two-d representations so that the resulting field obeys Gauss' law in
two dimensions since the field due to point charges does not!

> The way the generator works is how we explain field lines.  I place a
> positive test charge at equally spaced (angularly) positions around each
> charge and then using all the charges in place, calculate the path that the
> test charge would move.  That is what is traced.  The number of initial
> charge positions is fixed and may not be properly chosen in this example to
> show all the details.  This is really designed just to introduce the idea of
> field lines to the class.  The way the lines are drawn, one can actually
> watch them being generated.  With today's really fast machines, it happens
> pretty fast, but not too fast (yet) to see.
>
> Rick

--
John Mallinckrodt        mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.