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Re: Potential of a point charge

Sorry to jump in late in the afternoon - just got out of
two back to back classes. I'm a little confused following
this thread. Isn't the minus sign coming from the dot
product? I can't really believe that the dr = -ds because
you're moving toward the charge. That directional sign
would be taken care of in the limits of integration.

Bob at PC

*********** REPLY SEPARATOR ***********

On 2/26/2004 at 1:12 PM Rick Tarara wrote:

----- Original Message -----
From: "John Denker" <jsd@AV8N.COM>
That dr = -ds is always my stumbling block because
most texts don't
spell it out. HR&K just jump from E dot ds to Edr.

Probably their limits of integration are swapped
relative to yours.

No, actually my confusion was dumber than that. I looked
at the picture
showing ds pointed towards the point charge and just
mentally replaced it
with dr -- not thinking that pointed that way would make
it -dr.