# Help for density of charges in electric field [closed]

This is for a homework assignment so it would be great to have a hint or an explanation of how to do it. In a certain region in space, the electric field is given by

$\vec{E}(r) = \dfrac{A}{r} \hat{r} + \dfrac{B \sin{\theta} \cos{\phi}}{r} \hat{\phi}$

What is the charge density in the region?

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## closed as too localized by David Z♦Feb 10 '13 at 5:04

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Hello user1992214, I've edited your question to format the $E(r)$ equation in TeX in order to make it more clear to people. I hope I haven't changed its content. If I have, let me know. – Wouter Feb 10 '13 at 0:43
Nope, It's exact. I was unaware of TeX formatting, i'll try to use it for future questions. Thanks! – user1992214 Feb 10 '13 at 0:46
No problem, I also posted an answer which I think goes as far as the rules of Physics.SE allow for homework questions. Good luck. – Wouter Feb 10 '13 at 0:58
Hi user1992214, and welcome to Physics Stack Exchange! This is a site for conceptual questions about physics, not general homework help. We prefer questions to be about the specific physics concept that is giving you trouble, so keep that in mind for the future. See our FAQ and homework policy for more information. – David Z Feb 10 '13 at 5:05

## 1 Answer

You will probably find Gauss's law useful, and in particular the differential form. It relates the electric field to the distribution of electric charge, as is also stated on the wikipage.

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I should have though of that, thanks! – user1992214 Feb 10 '13 at 1:04
Just FYI this is just the right kind of answer to post for a homework question. (Although personally I wouldn't have posted it at all.) – David Z Feb 10 '13 at 5:06