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.