Consider an electric dipole in the attached document. At point P, the fields E+ due to q+ and E- due to q- are:
E+ = kq/(r-a)2, E- = -kq/(r+a)2
Then total field at P is:
E = E+ + E- = kq [ 1/(r-a)2 - 1/(r+a)2] y-hat
See question 1.
The Attempt at a Solution
So this post is just trying to comprehend the example problem above. I don't believe I'm fully understanding electric field. In the problem above, they have a point P without a charge given. They say that the impact of the electric field of +q occurs at a distance of r-a which makes sense if P is a postive charge. But then for -q, it takes place at a distance of r+a. What I don't understand for this, shouldn't it take place at a distance of 2a+r? It seems like it'd be a distance of 2a from Point P. Or are we considering that the electric field is moving towards -q? I'm not sure I understand this problem...