# Day 104: I’ll RC Your Circuits, Bub

Friday, March 16

Physics: Review questions! There’s an exam on Monday (which I supremely dislike, but am a slave to the syllabus). We reviewed the labs, the review questions, and whatever other questions the students asked.

Honors Physics: Strangely enough, we are still doing circuits. It was time for them to move to building series and parallel circuits to discover those patterns. We’ll continue on Monday and probably start aggregating class data so they have more places to look for patterns considering this lab tends to have a WHOLE lot of measurement mistakes, but once everyone’s data is put together you can see where the pattern is MOSTLY followed and often make an educated guess as to what mistake was made in taking the wonky data.

AP Physics: Today students practiced solving problems with capacitors. Lots of solving exponentials and using natural logs, which is the easy part. I can tell some started out still not really understanding how capacitors worked, but eventually they seemed to figure it out and be able to turn the ideas in the problems into mathematical representations. Monday we are going to have a quiz where students draw the graphs of current and voltage for both the capacitor and resistor in RC circuits both series and parallel. Whether they memorize it or understand it, I’m ok with it. I would prefer the latter, obviously, but if they can only work from memorized material, once they have the graphs the math pretty much falls out. I also gave them 2004Q2 released FR for practice, so we’ll see how that goes.

One of the students pointed out that there HAS to be a resistor in series with a capacitor in order for the time constant not to be zero. Fair point, although technically the time constant is just really, really, really small because the wire itself does have some resistance, and what I cared about was understanding that the current decreased over time through the capacitor while increasing through a branch parallel to the capacitor during charging. I’ll make that point on Monday after the quiz so it doesn’t cause any confusion beforehand, but they still get that point.