# Homework Help: Electric field expression problem

1. Apr 8, 2009

### Cakiemmatdo

So here is the problem, there is thin rod of length L with total charge Q. The rod was placed so it is along the y-axis. From the rod a distance x is point P
1. The problem statement, all variables and given/known data
Find an expression for the electric fields E at distance x from the end of the rod. Give your answer in component form

2. Relevant equations
F= qE
Delta Q= Lambda* Delta L (linearly charged density)
E= integrate of delta E

3. The attempt at a solution
I integrate and found the x-component of the electric fields but haven't been able to figure the y-component.....I'm not sure what is the limit for the y-component (my limit for x-component was 0 to L)

Thanks for all the helps

2. Apr 8, 2009

### rl.bhat

In this problem point P is fixed at a distance x from one end of the rod.
Consider a small element dl on the rod. Charge on it will be Q/L*dl. Line joining P and dl make an angle theta with the rod. Due to this element field at P is given by
dE = k*Q/L*dl/(x*2 + l*2)
Its x-component is dE*sin(theta) = dE*x/(x^2 + l^2)^1/2 and limit will be 0 to L
Its y-component is dE*cos(theta) = dE*l/(x^2 + l^2)^1/2 and limit will be 0 to L