What is the electric field at this point?

[Luke0034]

Homework Statement

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.

Homework Equations

E = kq/r^2

charge density = dq/dx

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

 

[BvU]

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

 

[gneill]

At a distance (b) from the rod, what is the electric field?

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