Homework 3 solutions

Find them here.

UPDATE 7 Feb 08: Here are the results:


I can draw a couple of conclusions from this plot (and the massive amounts of grading it entailed). Before that: very well done! The overall average (87.7%) was honestly much higher than I was expecting on what was a fairly punishing problem set.

First, while finding an equivalent capacitance didn't cause much trouble, working backwards to get the charge and voltage on each capacitor was very tough for you collectively. We should probably work some more of those problems.

Second, on the first question many of you ran into trouble by using the wrong distances and charges setting up the problem. It is important that you read the solutions to the homework - all of the information you needed was in the HW2 solution!

Third, on the last question many of you calculated the potential energy of the system of charges, rather than the electric potential at the center of the arrangement. This, combined with question 1 leads me to believe I have not made careful enough distinction between electric potential and potential energy.

Finally, number 7 seems to have caused trouble for two reasons: first, mathematical difficulties , and second, not taking into account that the capacitor was held at a fixed voltage. I don't think there are serious conceptual difficulties here as a whole.