A2L Item 140
- Description: Indicate which charge configuration contains least potential energy.
- Goal: Link potential energy with work needed to assemble a charge configuration.
- Source: 283-460 Lowest potential energy
- Keywords: Electromagnetism, Energy, Potential Energy
The question for students:
Which of the following charge distributions has the lowest potential energy?
Commentary for teachers:
Answer
(2) Encourage students to reason to the answer rather than write formal expressions for each case. They should be able to perceive that cases #1, #3 and #5 all have positive PE. Situation #4 has zero energy as can be seen by assembling subunits, then moving the two positive charges along the zero equipotential of the charges on the y-axis. Finally, situation #2 is clearly negative.
A good follow-up question is to ask students to order the cases according to increasing potential energy.