# Electrostatic problem

by dingo_d
Tags: electrostatic
 P: 211 1. The problem statement, all variables and given/known data I'm looking at Y.K.Lim's Problems and solutions in Electromagnetism and there's one thing that's confusing me: 2. Relevant equations Where does the square in r comes from? When in the beginning it says that the electric field is: $$E=A\frac{e^{-br}}{r}e_r$$ not$$E=A\frac{e^{-br}}{r^2}e_r$$ What am I missing? And what should $$e_r$$ stand for? Charge?
 P: 802 This E-field is not due to a single charge. It is due to a distribution of charges, so it needs not be proportional to r^2. For example, a uniformly charged plane produces uniform E-field on each side of the plane, obviously not proportional to distance^2, correct? $$e_r$$ is the unit radius vector.
 P: 211 Ok it needs not be proportional to r^2, but why did he put it then? When taking the divergence of the field?
P: 802

## Electrostatic problem

Oh I see. Then it seems to me that it's a typo
 P: 211 Oh, I thought it's something new I didn't know XD

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