Chapter 17, Problem 12Q

To determine

What is the significance of the sign of the potential energy in each case?

Answer to Problem 12Q

Solution:

In case of like charges work must be done to move the charges together

Explanation of Solution

We have potential energy between two charges, $PE=k\frac{Q_1{Q}_2}{r}$

In first case charges are unlike, so if we substitute in PE equation we will get $PE=-ve$, in second case charges are like, when substitute in PE equation we will get $PE=+ve$.

In case of unlike charges work must be done to separate them, in case of like charges work must be done to move the charges together. This is the significance of the sign of the potential energy.