# What is the resultant vector electric field at the point P?

1. Feb 26, 2015

### Freya

1. The problem statement, all variables and given/known data
There are 3 charges, each denoted q, the first at (0,a), the second at (0,0) and finally one at (b,0). What is the resultant electric field at point P, (b,a)?

2. Relevant equations
E
=q/(4πεo r2) for a point charge

3. The attempt at a solution
So I know I need to use the superposition principle and sum the fields caused by the individual charges but I'm not sure whether I need to consider the fact that their fields wont necessarily be in the same direction.

My attempt gave me
E= q/(4πεo (1/a2 + 1/b2 + 1/(a2 + b2)) in the direction the same as sqrt(a2 + b2).

Thanks for any help, I've been debating this with friends.

2. Feb 26, 2015

### BvU

Hello again,

You really need to make a drawing. $\vec E$ is a vector, as is $\vec F = q\vec E$. Fields add up, so you can calculate the forces separately and then add them up. Vector-wise, as is the habit when dealing with forces !

Oh, and $\sqrt{a^2+b^2}$ has no direction! It's a number, a scalar.

Oh, and E $\propto$ 1/r2, not 1/ ( 1/r2 )