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

I started on the chapter on Gauss’ Law in my electricity and magnetism lecture today. I introduced the quantities flux and charge per unit area, which are represented by the Greek letters phi and rho respectively.

Then I had some simple examples demonstrating how to look for the enclosed charge in the given Gaussian surfaces.

This was a trick that was not performed easily, especially since I had to take into consideration the fact that at least a third of the class had not yet taken up integral calculus. But I’m more or less still on track with the syllabus.

That was during the first half of the session, because at that time there were still some students who had not submitted their problem sets, despite my admonition that I would start the period with the answers to their quiz/problem set and would not accept any late papers after that.

I also determined that I would discuss the problems in order of difficulty instead of in the numerical order they were segregated in their questionnaire. I discussed the two direct substitution problems first, one for electrostatic force and one for electric field. In the quiz when I checked their papers I found out there were some who were able to answer this, except for their mistake in getting the proper value of the prefix micro for given charges in coulomb.

Then I discussed the four problems on net forces or net electric field for two particles in one dimension. We already had one or two examples of this in class, although the fact that no one got any of these correctly in the quiz may mean they need more. Or, maybe it’s just that they let themselves be intimidated by the problems again.

After that I discussed the only two-dimensional problem, which had an electron and a proton (of equal charge but opposite in direction) on two points of an equilateral triangle. I showed how the free body diagram of the electric field would look like at the third point, and how the y components of the fields would cancel out at that point. This meant that the magnitude of the net field is only equal to twice the x component of the electric field of either charge.

Second to the last was the problem where the combined charge and force of two charges were given. This used the quadratic formula, and I wasn’t surprised that they already knew how to answer this because one of the students was able to get this correctly in the quiz.

The last question was the one that had two spheres of differing charge attracting each other, then repelling each other after the spheres are momentarily connected. The only given were the distance and the magnitudes of the forces before and after connection, and they had to get the original charges.

This I’m sure we only had one example about. So I was also expectant that they wouldn’t get that the differences between the two original charges would be the total charge of both spheres after connection, and that each sphere would then have the same equal charge afterwards. What made the solving stretch out was I realized I made a mistake in my earlier answer, so I had to redo the last two thirds from scratch on the board.

When I announced that they could get their test papers from the faculty room afterwards, they were also reluctant, anticipating their low scores.