# Find the electric field at the origin

1. Jul 15, 2017

1. The problem statement, all variables and given/known data
Given two charged particles:

1) 5x10^-9 C, (-.03 m, 0 m)
2) -20x10^-9 C (.04 m, .02 m)

find the electric field at the origin.

2. Relevant equations
F = (kQq)/r^2
E = (kQ)/r^2

3. The attempt at a solution

So I know since 1)'s charge is plus, its field vector is

$( (8.99x10^{-9}) (Q) ) / (.03)^2$ i hat, meaning its going to the right

I use arctan to find the angle between the origin and 2), it is 26.57 deg, and pathagorean theorem to find the distance r to be .045m

since 2) is - charged, its electric field is going away from the origin at 26.57 degrees.

$( (8.99x10^{-9}) (Q) ) / (.045)^2$

Now I can break it down in to components, but how am I suppose to find Q, the charge of the origin?

If they gave me a value for the electric force between the origin and one of the particles I can find Q, but with this information I dont see any way I can find it?

Last edited: Jul 15, 2017
2. Jul 15, 2017

### TSny

There is no charge at the origin. In the formula E = kQ/r2, Q is the charge that is producing the electric field. Each of the two charges that are given in the problem is producing electric field at the origin.

3. Jul 16, 2017