EField was designed to model the Coulomb interaction between particles. It is used here to reinforce the operational definition of charge ("opposites attract, likes repel"). The first simulation shows charges with arrows represents the total force acting on each charge. The second simulation shows the potential energy of each charge. As you move the charges, these visual clues change appropriately. The accompanying question asks you to determine the sign of each charge. This task is more complex than it first seems. Students are comparing each charge with a reference charge of their choice. One strategy is to put one charge in each of the four corners of the screen and then bring one to the middle next to be the test charge. Other strategies can be deployed. This exercise allows you to show some creativity in solving a physics problem.
Problem by Wolfgang Christian
Script by Wolfgang Christian