# Where is the electric field zero?

1. The problem statement, all variables and given/known data

Two point charges are placed 1.00m apart.
q(1) = -2.50 x 10^(-6) C
q(2) = +6.00 x 10^(-6) C
Task is to find where along the line, other than at infinity, the electric field will be equal to zero.

2. Relevant equations

E = (k * q) / r^2

3. The attempt at a solution

I let E(1) + E(2) = 0 and substituted the above formula in, which, after simplifying gives me a quadratic (I let ‘x’ equal the first radius, and ‘1.00 – x’ equal the second, so q(1) is at zero on the axis, and the solution for x will give me the point on the axis with respect to q1 at which the two fields cancel out and the net field equals zero).

I solved the quadratic and came up with:

x = 0.39m (0.39m to the right of q(1) ) and
x = -1.83m (1.83m to the left of q (1) )

The answer is -1.83m, but I am wondering if someone can explain why +0.39m isn’t correct also? I think my conceptual understanding is lacking here, and my textbook hasn’t quite revealed the answer.

Thanks very much in advance, folks.

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