Que:

Consider two identical tiny metal balls one having a charge of +1 micro-coulombs and the other having a charge of +3 micro-coulombs. The balls are separated from each one other by 15 cm. Each one exerts a force F on the other. The balls are brought in to momentary contact with each other (assume each ball is on the end of its own non-conducting rod for handling purposes) and then separated such that the distance between them is once again 15 cm. At this point each one exerts a force F' on the other. How does F' evaluate with F?

Feedback:

Given that the separation is the similar in the two cases the only variable that the force depends on is the product of the charges. In the case of F this is 1μC × 3μC which is 3 (μC)². While the two balls are touched together the charge redistributes itself such that each ball has a charge of 2μC. For F' the product of the charges is therefore 2μC × 2μC which is 4 (μC)².  Seeing as this product is greater F' > F.