# Gas station without pumps

## 2013 February 3

### Chapter 20 homework

Filed under: home school — gasstationwithoutpumps @ 21:27
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We finished Chapter 19 last week, about 4 weeks behind our original schedule.  The problem was not that Chapter 19 was difficult—it was that the chapter was too boring to hold our interest—I couldn’t even come up with any labs to make it interesting.

We had a bit of digression, spending a little time reviewing old F=ma exams, in preparation for my son taking the F=ma exam for the first time last Tuesday (2013 Jan 29). We had his consultant teacher at the homeschool umbrella proctor the exam, which required a bit of a mess in the registration.  The AAPT allows homeschoolers to take the exam, but hasn’t figured how to make the registration procedures make sense for them—they assume that the teacher and the proctor are identical, and they don’t distinguish between them on the registration forms (even though parents are not permitted to be proctors).  Maybe next year they’ll have thought through their registration procedures a bit better, but I wouldn’t bet on it.

We did finally polish off the chapter 19 despite the tedium and the distraction of the F=ma exam, and my son has already read Chapter 20.  I’ve not read it yet, but it seems to be about capacitors and RC time constants, so we should at least be able to do some data logging of capacitors charging and discharging through various resistors, fitting the $e^{-t/(RC)}$ model to the data.  Perhaps we could even measure some “unknown” capacitors by using known resistors.  They also have an RC low-pass filter in Section 20.8, so we could do a little filter design and Bode plots (the same stuff I did recently in the circuits course).

Homework for Chapter 20:  20P53, 20P58, 20P59, 20P60 (the principle behind capacitance and electret microphones!),  20P73 (I was going to complain to Bruce Sherwood about not specifying the wire gauge for the copper wires, but instead will add to the exercise: at what wire gauge does it start to matter), 20P75, 20P80, 20P82,  20P94, 20P95, 20P97.

I hope that we can finish these problems by 12 Feb, as well as doing some RC labs. I’d be willing to take an extra week if we throw in Bode plots.