Day 47: Electrical Potential Energy

Today in AP Physics 2, we began to investigate the concept electrical potential energy. It is important that students have a strong understanding in electrical potential energy before we start to investigate the concept of electric potential. While students are familiar with other forms of potential energy (gravitational, elastic), a couple of aspects of electrical potential energy provides a challenge. One, unlike gravitational potential energy, the electrical potential energy depends not only on the position of the particle in the field but on the sign of the charge of the particle as well. Two, negative electrical potential energies are quite common. While “zero” gravitational potential energy could be defined such that negative gravitational potential energies are considered, students rarely encounter this in their first-year course.

Students spent most of class today, thinking through the following nine scenarios (from Knight’s Five Easy Lessons) and whether the electrical potential energy of the particle increases, decrease, or stays the same from the initial point to the final point; first individually, then among their groups, and finally as a whole class. It was fantastic to hear students justify their answers in terms of energy conservation, work done on the particle, and the relationship between the direction of displacement and force.



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