# Homework Help: Thin Rod + Poncual Charge Find Vb-Va

1. Oct 1, 2008

### co_life04

Thin Rod + Poncual Charge.... Find Vb-Va

1. The problem statement, all variables and given/known data
A thin "rod" of 10 m is located between (0m,4m) and (0m,14m). Its linear density is 50*10^-9C/m. Also, there is a ponctal charge of Q=10*10^-9 located at (-1m,0m).
Given 2 points:
A at (0m,-5m)
B at (0m,0m)
Find Vb-Va.

2. Relevant equations
E=k|Q|/r^2
E*d=V
some integrals...

3. The attempt at a solution
Okay, this seems like a tricky one, does it not?
I know I could use Vb-Va = Integral of : E*s, possibly with s=5
But then, I would have a Vb-Va for the rod, would I have to also calculate the Vb-Va due to the poncyal charge and then sum these 2? This is what I would have done during an exam, though I'm really not sure it'd be good, would it?

Thanks for any help you can provide... belive me, I,ve tried it a couple of times before posting here.

2. Oct 1, 2008

### co_life04

Re: Thin Rod + Poncual Charge.... Find Vb-Va

Ok, so i've tried something, not sure though...
I could separate the question in finding :
-Vb : Vb-from the rog + Vb from the charge
-Va : Va-from the rog + Va from the charge
And then simply substract...is this it? Im not sure but i just think it could...

Thanks for helping

3. Oct 2, 2008

### co_life04

Re: Thin Rod + Poncual Charge.... Find Vb-Va

I managed to find a number, but as I do not have the answer key, i can't tell if it's good. So if somebody is able to do it, maybe then we could compare our answers :)
this would be really appreciated