# Line Charge

1. Nov 26, 2006

### swain1

A line charge of liner charge density lambda=4.5 nC/m lies on the x axis and extends from x=-5cm to x=5cm. Derive an expression for E_y.

I have started with this question and it seems that I have to sum the electric fields in the y direction caused by each dx along the line with a charge dq. I think I understand how to do the integral but I just don't know what the field in the y direction is? Thanks for any help.

2. Nov 26, 2006

### winwizard3k

Just imagine that the apparent charge, when 'felt' from test charges away from the rod convene to a equidistant point on both sides of this rod. Consider this to be the y-distance away from the x-axis (rod). Since this rod is of finite length, then you should approximate the greatest electric field to be at x=0, and then at some distance y from the bar. Now, all you have to do is find how far away from y=0 the electric field maximizes. You can simply triangulate to find this point, and then use vector addition of the j-components from the two integrals.