Say we have two charges in a closed spherical universe, of radius R, a distance r apart. If the charges are close, r<<R, we might guess that the force would go as 1/r^2? Let the two charges move away from each other till they are as far apart as possible. At this point the force between charges is zero? How might we modify the 1/r^2 force to fit the above criteria? Thank you for any help.