# Solve Charge Density (rod) Homework Problem

• jesuslovesu
In summary, the conversation is about finding the electric potential at point A on a rod with nonuniform charge density. The attempt at a solution involves using the equations V = kq/r, E = kqq/r^2, and V = - $\int_a^b E dot dr$ and integrating to solve for a constant a in terms of the rod's length and total charge Q. The question also mentions a similar problem involving a rod with nonuniform linear charge density along the y-axis and asks for help with finding the constant a in terms of L and Q.

#### jesuslovesu

Never mind, i got it, whew

## Homework Statement

http://img137.imageshack.us/img137/6250/chargqg0.th.jpg [Broken]
The rod has a nonuniform charge density lambda = ax (a is a positive constant). Find electric potential at point A.

## Homework Equations

V = kq/r
E = kqq/r^2
V = -$$$\int_a^b E dot dr$$$

## The Attempt at a Solution

I am pretty close to the answer, I'm just not quite there.
If I'm not mistaken it is something like:
$$\[ \int_d^{L+d} kax*r/r^2\,dr$$
but I'm not quite sure what to do with the 'x', from the answer, I know that it has to end up being the integral of 1/r, so x can't be r because it would end up being just the integral of dr

Maybe the limits are incorrect?

Last edited by a moderator:
Hi! I have a similar problem...

A rod of length L lies along the y-axis with its center at the origin. The rod has a nonuniform linear charge density lambda =a | y | , where a is a constant with the units {\rm C}/{\rm m}^{2} . Determine the constant a in terms of L and the rod's total charge Q.

I know that for uniform charge its lambda=L*Q and then integrate but what do I do in this case?

Thanks!