Delta function representation from EM theory

pellman

Claim:

[tex]\nabla \cdot \frac{\hat{e}_r}{r^2}=4\pi\delta^3(\vec{x})[/tex]

Anyone know of a proof of this? (or a reference which covers it?) We need to show that

[tex]\frac{1}{4\pi}\int_0^R{(\nabla \cdot \frac{\hat{e}_r}{r^2})f(r)dr=f(0)[/tex].



The claimed identity can be seen in the solution for the electric field of a point charge in EM theory, where

[tex]\vec{E}=\frac{q}{r^2}\hat{e}_r[/tex]

is the solution to

[tex]\nabla \cdot \vec{E}=4\pi q\delta^3(\vec{x})[/tex]

It is easy to show in this case that [tex]\nabla \cdot \vec{E}=0[/tex] everywhere but the origin, but I don't know how to show that the delta function relation holds at the origin.