# Homework Help: Calculating potential from a nonuniform linear charge distribution.

1. Sep 13, 2012

### r0wbrt

1. The problem statement, all variables and given/known data
The thin plastic rod has length L, and a nonuniform linear charge density λ = cx. With V = 0 at infinity, find the electric potential (in V) at point P1 on the axis, at distance d from one end.
c = 28.9 pC/m^2
L = 12.0cm
d = 3.00 cm

Now, from what I can tell the left side of the rod is placed at the origin, and p1 is a distance of d from the left end.
2. Relevant equations

V = (kq)/r (potential of the point charge).

$V = \int \frac{kcx}{x+d} dx$.

k is the Coulomb constant.

3. The attempt at a solution

Now I assumed using the above equation to integrate the potential over 0 to L would give the solution. However, when I checked the back of the book I was mistaken. Is it possible I missed something? I am treating cx dx as an point charge and summing over the potential each one produces at the point in question.

I get using the equation 156Volts while the book claims the answer to be 18.6mV.

2. Sep 13, 2012

### voko

Why is c C/m^2? It should be C/m.

Apart from this, I think your approach is correct. Without seeing how you integrated the thing, I can't say more.

3. Sep 13, 2012

### r0wbrt

Okay, yes disregard my question. I was using a computer algebra system (Microsoft Mathematics) to solve the integral. I tried it on my TI-84 Plus and I got .01863 Volts.

(This is what I get for being lazy).