# Homework Help: Electric Potential and Charges Problem

1. May 11, 2010

1. The problem statement, all variables and given/known data

Point P is at the origin. Charge A is at (-3,0) and Charge B is at (4,0). What is the electric potential at point P. Lets assume they are both positive charges for now, but I am interested to know if and how it changes if either/both of the charges are negative.

2. Relevant equations

I assume I will need to use V=kq/r but I could be mistaken.

3. The attempt at a solution

Once I get both the potentials using V=kq/r can I simply add them together to get the potential at P? If one charge was negative do I subtract the potential from that one from the positive charge to get the potential at P?

Thank you

2. May 11, 2010

### zachzach

Yes, you can use Kq/r to calculate the potential due to each charge at P. The great thing about using potentials is that it is a scalar and you can just add them. If you were using the E-field you would have to add the vectors which is more difficult. If charge is negative then it makes the potential negative since v = kq/r, so if q is negative then v will be negative as well.

3. May 11, 2010