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[Phys-L] Re: Electric Field?



Rick,
In order to follow a field line, the principle is not to follow the path of
a test particle, even over a small ds and even re-beginning with zero
velocity. Instead, one calculates (eg, in two dimensions) the field vector
components Ex and Ey and advances a vector displacement ds whose components
satisfy dy/dx = Ey/Ex. The motion of a particle is not the quantity of
interest, rather we seek to move in the direction of the local field vector
E. After all, we might be plotting some other abstract vector field which
might have nothing at all to do with the motion of a test particle.

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 2:31 PM
Subject: Re: Electric Field?


| 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
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