(Note: I believe this was either 10/16/12 or 10/17/12)

Due to some timing things, only about a third of the groups got through the whole problem by the end of class on one day. I wrapped up that day by having one student articulate the symmetry arguments for the cylindrical case and one for the spherical case. The next day, instead of asking the groups to finish the problem so that we could compare, I decided to go a different direction. I asked the groups to come up with a list of everything that they needed to do in order to solve this kind of problem. Then, I acted as a scribe as different students listed different things. This produced some really nice discussions about when is the order necessary (e.g., solving for E before making symmetry arguments) and when it is not (e.g., do you have to choose your coordinate system or draw your picture first?). It also forced them to explicitly articulate several things that they did implicitly while solving the problem (e.g., defining their Gaussian surface).

This allowed for some really nice back and forth among the students, I got several to stand up and articulate, and it was a good exercise for thinking about the kind of sense-making they need to be doing while they are problem-solving. It should also hopefully help them on their upcoming homework. All in all, I think it was a good choice given the awkwardness of the timing.