# Electric field between two charges in 1D

1. Feb 22, 2010

### Tekee

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

Two identical positive charges of +Q are 1 m apart. What is the magnitude and direction of the electric field at point A, 0.25 m to the right of the left-hand charge?

2. Relevant equations

E = kQ/r^2

3. The attempt at a solution

I summed up kQ+/(.25^2) and kQ+/(.75^2) and what I got was one of the answer choices, but apparently it was wrong. Evidently you have to subtract the .75 charge from the .25 to get the right answer. I also am unsure of which direction the electric field points.

2. Feb 22, 2010

### dacruick

okay tekee, imagine that the point of interest is a positive charge. Which should be the default. A positive charge to the righthand side of it pushes it left. and a positive charge to the lefthand side of it will push right. So you will have to make appropriate changes to your answer due to that.

3. Feb 22, 2010

### willem2

point A is between the charges. The direction of the electric field is the direction of the force on a positive test-charge.
What is the magnitude and direction of the field due to the positive charge 0.25 m to the left of A?
What is the magnitude and direction of the field due to the positive charge 0.75 m to the right of A?
Now you can add those fields like vectors.