# Find the electric field at the origin

## Homework Statement

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.

F = (kQq)/r^2
E = (kQ)/r^2

## 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:

## Answers and Replies

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TSny
Homework Helper
Gold Member
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.

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.
Thank you sir. I was wasting my time on this question for 2 hours already.. now my answer matches my books answer. TY.

TSny
Homework Helper
Gold Member
OK, good work.