# Electric Field and the position of a charge

#### dalson

1. Homework Statement

A -10.0nC charge is located at position (x, y) = (2.0cm, 1.0cm) . At what (x, y) position(s) is the electric field - 225,000i N/C?

2. Homework Equations
E = (Kq/r^2)*r(hat)

3. The Attempt at a Solution

r = sqrt(Kq/E) = .02m = 2cm
So coordinates are (0,-2)

I tried putting this answer into mastering physics online and it says it is incorrect. I can't seem to find what I have done wrong. Any help please?

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#### cepheid

Staff Emeritus
Gold Member
Right away without calculating anything, I can tell you that since the electric field of a negative point charge points radially inward in all directions, the only way for the field to be pointing in the x-direction is if the point at which you are measuring the field is somewhere along a line that runs parallel to the x-axis and passes through the charge. Your answer cannot be right, because your point lies on the y axis.

Hint: r only tells you the distance of the point away from the charge...it does not specify in which direction.

#### merryjman

Yeah, you've got the right distance but the wrong location. You've even got the right idea, using the negative sign, but like cepheid says, the field points in the i direction.

#### dalson

Ah, I get it now! Thank you very much!

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