Chapter 19, Problem 70GP

CE Predict/Explain In Conceptual Example 19-9, suppose the charge to be placed at either point A or point B is +q rather than −q. (a) Is the magnitude of the net force experienced by the movable charge at point A greater than, less than, or equal to the magnitude of the net force at point B? (b) Choose the best explanation from among the following:

1. I.                    Point B is farther from the two fixed charges. As a result, the net force at point B is less than at point A.
2. II.                  The net force at point A cancels, just as it does in Conceptual Example 19-9. Therefore, the nonzero net force at point B is greater in magnitude than the zero net force at point A.
3. III.               The net force is greater in magnitude at point A because at that location the movable charge experiences a net repulsion from each of the fixed charges.