# Electric field of a line of charge

1. Jan 26, 2009

### Oblivion77

1. The problem statement, all variables and given/known data

Find the magnitude of the electric field these wires produce at point P, which is 60.0cm from each wire
2. Relevant equations

E = kQ/r^2, $$\lambda$$=Q/L

3. The attempt at a solution

I am not exactly sure how to set up the integral, I have the formula of a general case (with no numbers, just letters). But I am confused how to do it with actual numbers, I don't just want to plug numbers into the formula. I want to know how to derive it. Thanks.

2. Jan 26, 2009

### Oblivion77

Ok I might have figured it out, last thing that is confusing me is the limits of integration. I need to integrate over the length of the rod but not sure what the lower and upper limits should be? Would it be 0 for lower and 1.20 for upper for both of the rods?

3. Jan 27, 2009

### xboy

Have you tried working it out for a single finite rod? What difference do you think will be there between the fields due to the two line charges? It would help if you said how you are setting about solving the problem.

4. Jan 28, 2009

### turin

Essentially, you decide. The only condition is that the difference between the limits is equal to the length of the rod. However, there are "good" choices and "not-so-good" choices. Typically, you want to set up an integral in order to make full use of symmetry.