# What is the electric field at this point?

1. Feb 21, 2017

### Luke0034

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

A charge -3.2 micro-coulombs is spread evenly throughout a rod of length (a). At a distance (b) from the rod, what is the electric field?

a = 1.2 m
b = 3.4 m

So basically, you start at zero and then there's a line of charge horizontally to the right from 0 to 1.2 meters, and then at 3.4 meters to the right of the origin there is a point that is distance b away from the end of (a), and I need to find the electric field there.

2. Relevant equations

E = kq/r^2

charge density = dq/dx

3. The attempt at a solution

I used E = kq/r^2

I knew that the charge density = dq/dx

So I set up the integration like this: E = integral(k/r^2)dq

Then I switched to terms of dx... E = integral((k * charge density)/r^2)dx

Then I plugged in 3.4 + x for r... E = integral((k * charge density)/(3.4 + x)^2)dx

k and the charge density were constants for I pulled the out of the integral and integrated 1/(3.4+x)^2dx from 0 to 1.2. I did used u substitution to do this.

I was wondering if I used the correct method here, and if my answer was correct.

I got -1840 N/C

2. Feb 21, 2017

### BvU

Hi Luke,
I think you're doing just fine. Why the hesitation ?

3. Feb 21, 2017

### Staff: Mentor

This is rather vague. You need to specify the geometry more precisely. From where on the rod is (b) measured and in what direction?