Re: wrong divergence?!?
- To: mathgroup at smc.vnet.net
- Subject: [mg6378] [mg6378] Re: [mg6346] wrong divergence?!?
- From: seanross at worldnet.att.net
- Date: Fri, 14 Mar 1997 14:54:30 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
peter wrote:
>
> hi all
>
> when i take the divergence of:
>
> e = {q/r^2, 0, 0}
>
> i get zero. i remembered to load VectorAnalysis and SetCoordinates to
> Spherical.
>
> this is the electric field due to a point charge at the origin. even
> though MMA doesn't know maxwell's equations, if we strip all the physical
> meaning from this vector field, shouldn't the divergence be something other
> than zero at the origin?
>
> thanks!
>
> peter
I don't have my copy of Classical Electrodynamics in front of me, but as
I recall, the divergence of 1/r^2 is something like 4 Pi diracdelta(r)
which means that it is identically zero everywhere but the origin. As I
recall from doing that derivation once, it is a little tricky and I
wouldn't expect a program to catch on to something that subtle. Once
again, as wonderful as Mathematica is, there is no substitute for pencil
and paper.