I had students answer some questions from the end of a PHeT lab on capacitors after the test today. The most interesting conversation came from the first picture above. How do places of "more than typical amount of charge" interact with other areas with "more than typical amount of charge"? With areas with "less than typical amount of charge"? We had no good model, but more than one student came up with more than one circuitous way to draw the forces on the bottom right negative spot like in the picture above. We're sure it's the right answer; we just don't like it.
We also figured out how capacitors add in series and in parallel from first principles today. It was quick and not a focus of the lesson; I don't think it's essential to the curriculum, but it's good practice of Kirchhoff's Laws.