Student "edition" found at [csi dot journalspace dot com].

Maybe I shouldn't have started this blog now, not with everything that's been going on.

In my Introduction to Electricity and Magnetism lecture class on the first day of the sixth week of the first term, I gave the shortcut equations for cylindrical and planar symmetry in Gaussian surfaces (for a uniform charge on a rod and on a sheet respectively), having started with the spherical symmetry on a point charge last meeting.

I showed that for the rod it is dependent only on the distance of the surface from the rod but not the length enclosed in the imaginary surface, while for the plate it is dependent on the area but not on the distance of the measured surface from the plate. For spherical symmetry it was just a verification of the relationship between the electric field and the electrostatic force.

At this point Deiv asked, practically, if it was only the final expression that would be used in the exams, and (he left unsaid) not the whole long derivation, so he can just concentrate on memorizing and practicing the application of fewer equations (damn, I read minds GOOD). I had to answer yes.

After that I gave the special case of two conducting spheres of equal but opposite charge, where the electric field exists only between the two plates at double the intensity but has a value of zero outside the plates.

Lastly I gave an example for two parallel plates that did not have the same surface charge density, and thus had electric field that “leaked” out from between the plates to the left and the right side.

As there seemed to be some confusion still on how we arrived at our answers for that one, I gave them a seatwork with three plates and four areas to solve the electric field for.

For this class and the previous one, by the way, their problem sets which are the same questions as in their first exam were due, the one for the earlier taken INTRELM exam having been moved back one meeting because they had no idea what they were supposed to do.

“Keep your questionnaire when you submit your test booklet,” I said near the end of the exam. “That will be your problem set due next week.”

“Sir,” asks one of the students, “Are we going to answer them?”

Just like in the seatwork I was talking about in the previous post. “Work on these problems by pairs,” I instructed.

“Sir,” threatened the same student, “Do we put our answers in one paper, or separately?”

Session 631 will have to say its goodbyes at this point. Class dismissed for today.