HW2 solutions

They are done, though probably not without errors. (UPDATE: a few stray typos fixed.)

In particular, in problem 11 showing that Coulomb's law is recovered in the limit of small lengths of the rods is stupidly difficult. I think it can be done much more quickly (or at least in many fewer steps) than I took in the solutions, but I wanted to try and make it as clear as I could. Given that it is not trivial to take the small length limits, you will be given a wide berth on that part of the question ...

Now, for HW3: tomorrow we'll set up several of the problems in lecture, I will post some hints tonight. If you did HW2 in a reasonably general way (or at all, really), you will save yourself some work on HW3. In particular, you can re-use the solution for the electric potential due to a line charge and a number of geometric insights.