# Electric Field and charge location

## Homework Statement

A 6.0mC charge experiences a force of 2.0x10^-3 N in the +x-direction at a certain point in space.
A. What was the electric field at that location before the charge was placed there
B. What would be the force if the 6mC charge were replaced by a -2.0mC charge?[/B]

## Homework Equations

E=F/Q
F=(kQ1Q2)/r^2[/B]

## The Attempt at a Solution

I'm actually quite clueless as I think that the given problem lacks information.

I've tried having to use E=F/Q to try and solve for [/B]

gneill
Mentor
I've tried having to use E=F/Q to try and solve for

It got cut off, sorry. :)
To solve for the R but it just wouldn't work. So I've got no more ideas for this. I couldn't think of any other solution.

gneill
Mentor
It got cut off, sorry. :)
To solve for the R but it just wouldn't work. So I've got no more ideas for this. I couldn't think of any other solution.
You don't need R to find the field. You were on the right track with E = F/Q.

Yeah I got the electric field but how do i get the electric field BEFORE the charge was placed there?

Sorry, this is really confusing me. :/

gneill
Mentor
The value that you got will be the field before the new charge is placed. The new charge reacts to the field that is due to other charges, not to its own field. Of course, if another charge were to be brought into the picture, then the new charge would feel the effects of the previous field plus the that of the field due to the original Q, and Q would also feel the new charge.