1. The problem statement, all variables and given/known data Two equal and positive point charges Q1 and Q2 are a distance d from each other on the x-axis. Find the electric potential at the point P which lies a distance z on the z-axis from their centre. Then find the Electric field at the point, and then find the force F on a charge q placed there. 3. The attempt at a solution Since the charges are equal, and the distance to the point is the same for both of them, I figured I could just find the potential due to one of the charges, and multiply it by 2. When it comes to the second part, I just took the derivative of the potential and multiplied it times a unit vector. Then I tought the unit vector should point in the z-direction, because the horizontal components of the field will cancel each other out. But thinking about it, I don't think that will give the correct answer, as some part of the field as stated will disappear... I've attached a picture of my described attempt at a solution. Would appriciate any help on this one!