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: [tex]E=A\frac{e^{-br}}{r}e_r[/tex] not[tex]E=A\frac{e^{-br}}{r^2}e_r[/tex] What am I missing? And what should [tex]e_r[/tex] stand for? Charge?
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? [tex]e_r[/tex] is the unit radius vector.
Ok it needs not be proportional to r^2, but why did he put it then? When taking the divergence of the field?