[Phys-L] Re: Electric Field?

[Bernard Cleyet <bernardcleyet@REDSHIFT.COM>]

I don't understand the complication.  JD and others have described
numerical solns. of LaPlace's eq.  Several text's  describe the method
in detail, Eisberg and Lerner in particular.

As I earlier posted, the algebraic method is rather easy.

Or am I missing the point?

bc

Rick Tarara wrote:

> Turns out I was smarter 5 or 6 years ago than I am now--having forgotten how
> I actually did the fields lines.  What I actually do (and clearly I must
> have understood this better at the time) was to do exactly what I say
> below--calculate the force on the test charge, the acceleration, the
> velocity and the new position--all for a small time increment, BUT THEN I
> reset the velocity to zero before doing the calculation again.  To the
> accuracy of the small time interval then, this (I think) should work
> reasonably well.  As John alluded to earlier, there are probably easier ways
> to generate the field lines, but I wanted to animate them based on the idea
> of a test charge--and ended up with what's described.
>
> Rick
>
> ----- Original Message -----
> From: "Bob Sciamanda" <trebor@WINBEAM.COM>
> To: <PHYS-L@LISTS.NAU.EDU>
> Sent: Wednesday, February 08, 2006 11:08 AM
> Subject: Re: Electric Field?
>
>
>
>
> > This procedure will not generate a field line unless the test particle
> > never
> > develops a velocity component perpendicular to the direction of the local
> > electric field vector.
> >
> > A (gravitational) example where this procedure does work is that of a test
> > gravitational mass dropped with zero horizontal initial velocity component
> > in the purely vertical gravitational field near the surface of the (flat)
> > earth.  Here the field lines are vertical.  The test particle will then
> > follow a vertical field line.  But if the particle ever gets a horizontal
> > velocity component, it will follow a parabolic path, not the path of a
> > vertical field line.
> >
> > Bob Sciamanda
> > Physics, Edinboro Univ of PA (Em)
> > http://www.winbeam.com/~trebor/
> > trebor@winbeam.com
> > ----- Original Message -----
> > From: "Rick Tarara" <rtarara@SAINTMARYS.EDU>
> > To: <PHYS-L@LISTS.NAU.EDU>
> > Sent: Wednesday, February 08, 2006 7:26 AM
> > Subject: Re: Electric Field?
> >
> >
> > | I'm not too sure of what John writes below.  I have written a program
> > (part
> > | of the E&M Animated Chalkboard package) to map electric field lines in 2
> > | dimensions.  The way it works is that I place a test charge near one of
> > the
> > | charges that makes up the charge distribution.  I then calculate the
> > force
> > | on the test charge due to all charges in the distribution, the
> > acceleration,
> > | the velocity, and the new position taking a very small time interval.  I
> > | move the test charge to that position plotting the path to get there and
> > | then repeat until the charge either gets far off the visible screen or
> > ends
> > | up at a second charge.  This method produces the field line patterns we
> > all
> > | know.  Of course, to do this one 'nails down' the original charges.
> > Another
> > | animation allows up to 6 charges to be 'released' and now they all
> > scramble
> > | around.
> > |
> > | Rick
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