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

Since I only spent a few minutes today at the recruitment drive (before the first classes of the day, then before and after lunch: having breakfast, looking for my cousin and seeing the two highest officers put up the Tinig booth respectively), I wll catch up on what I did in my classes for the past two days first.

Last Monday was the electricity and magnetism class. I finished the third chapter, Number 24, on Gauss’ Law. First I introduced the linear charge density, which was represented by the Greek letter lambda. I also told them that it was the same as charge per unit length of a conductor, and equal to the total charge divided by the length of the conductor. After this I used lambda to give them the charge of a conducting ring given its radius and the distance of the electric field.

I recalled surface charge density (using the Greek letter rho), which I had used on the past meeting, and gave them the equation for the charge of a conducting ring, again given the radius and the distance of the charge.

Afterwards I applied Gauss’ Law to cylindrical symmetry of the enclosed surface (using lambda) for a length of wire. Then I showed them the electric fields generated by one, next two, conducting plates, and the vector addition involved.
I mentioned the special cases of when the plates have equal charges which are opposite in sign and when they have the same sign.

Lastly I recalled for them the charge of a hollow conducting sphere when the Gaussian surface is inside and outside the shell.

I gave them two exercises they called ‘trick questions, one for ranking four points between two conducting plates of the same charge with another similar point charge nearby, and how the flux changes when the Gaussian surface is increased in radius or changed to a cube with length of one side equal to the radius.

For the first problem the charge from the plates equaled zero (one of the special cases) so the points were just ranked according to increasing distance from the point charge. Second, the fluxes of all four cases are equal because the equation from flux is not dependent on the size of the surface but the charge enclosed.

I just hope they retain that information in the exam.

For the Trig class yesterday we discussed how to computer for the depth of a hole using two angles of depression, and how in application there has to be an adjustment made in both cases for the height of the person doing the measurement. For getting the height, the eye level to ground distance is added. For getting the depth, it is subtracted.

Just like in my previous class last term, I made it into a class activity for them to measure the depth of the quadrangle below from the third floor hallway outside. A few months ago though, we were on the second floor and I provided a meter stick.

There were some groups who measured the distance as 20 feet or 6 meters. I told them to see if the height per floor given by those results was realistic. I also told them that the two angles of depression they measured from sighting the same point had to be as far apart as possible for their results to be more accurate. So those who used two angles just a meter apart had to repeat the procedure. With the first point against the railing, the second point was already inside the door to the room.