# Homework Help: Testing for Charges in X-Y Plane Given Field Lines

1. Apr 1, 2013

### trevor51590

1. The problem statement, all variables and given/known data
The Electric field lines in an X-Y plane are given in the attached image. The field is defined as E=αi(vector)y at x=0 and x=some distance along the positive X axis. α is a positive constant.

Test for charges in the X-Y plane

2. Relevant equations
N/A

3. The attempt at a solution
The diagram is attached below showing the field lines in the X-Y plane. I understand that the electric field is dependent upon the y axis only, but am having a tough time figuring out the "test for charges" Perhaps there is a way to describe the charge in equation form?

I already solved the "more difficult" 2nd part of the question - go figure :rofl:

A hint I was given was to "draw field lines from a charge". I feel like this is ridiculously simple and I'm missing something silly.

Thanks as always!

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2. Apr 2, 2013

### ehild

The field lines originate at charges and end at charges. The differential form of Gauss' Law says that the divergence of the electric field vector is equal to the charge density/ε0. Determine the divergence of the given electric field.

If you haven't learnt divergence yet, you can apply the integral forms of Gauss' Law. Considering any closed surface, what is the net flux?

ehild