Question

True or false: Consider two parallel plates, one with a uniform positive charge and the other with a uniform negative charge. The plates are initially very far apart. The potential energy of the plates increases when you bring the plates close together.

Answer 1

When the plates are brought close together, the distance between the plates decreases and as a result the capacitance of the parallel plates increases. As the potential energy of parallel plates is directly proportional to its capacitance, the potential energy increases due to increase in capacitance. But, at the same time the potential difference decreases proportionally. As potential energy is proportional to the square of potential difference, the net effect will be a decrease in total potential energy. Therefore, the statement is false.