Determining the magnitude of unknown charges

[crazuiee]

Homework Statement

A positive charge +q1 is 3.00m to the left of a negative charge -q2. The net electric field is zero 1.00m to the right of the negative charge. Determine the relative magnitude of the charges in a ratio q1/q2

Homework Equations

E=kQ/r^2

The Attempt at a Solution

I set it so that kQ1/r1^2=kQ2/r2^2 but I'm not sure how to solve for the ratio? would the k's cancel out and it'd just be a ratio of the distances? Are the distances r1=4.00m and r2=1.00m?

 

[rl.bhat]

Your distances are correct.
Find Q1/Q2.

 

[crazuiee]

would the ratio just work out to be the ratio of the distances? so 4/1?

 

[rl.bhat]

No. It should be square of the distances.

 

[crazuiee]

So q1= +16 and q2= -1 ? Also there's a part of the question that asks to locate two spots where the potential is zero, in relation to the negative charge, any ideas how to find it?

 

[rl.bhat]

In between the charges you can get zero potential. Similarly out side the charges near the smaller charge you can get another spot where then potential is zero.
If x is the distance where the potential is zero, then
kq1/(d-x) - kq2/x = 0