Circuit Fun

128 I had promised the AP class “Circuit Fun” on the last day before spring break. To me, this means making different circuits to light up light bulbs in various configurations!


Loop Rule

127 (Tuesday, March 26th) I love this question in Chapter 27 of Halliday, Resnick, and Walker. We spent a while in class talking about which conservation of energy loop or loops you should choose to write loop equations for in order to determine the current through resistor R. There is one loop where you can solve for the unknown with one equation. If you don’t choose that loop, you will have multiple unknowns and will need multiple loops and multiple equations to answer the question. (All batteries are ideal and have emf = 4 V and all resistors are identical and have resistance = 4 Ω.)


126 (Monday, March 25th) This video demonstrates the difficulty some groups had in collecting data from the squishy circuits lab. The conductive dough they made never gave consistent readings. When we got frustrated with trying to measure ΔV and I for their dough, we tried measuring R directly using the digital multimeters. The video shows the readings for a given chunk of dough measured in MΩ, fluctuating between 1.02 MΩ in the first frame and 0.55 MΩ in the last frame. There will be a lot of experimental uncertainty to write about in the lab report!


125 The AP class is investigating the resistivity of conductive dough. I was going to make it myself, but then I had jury duty and I had to ask the kids to make it and bring it in. Which they did! It seemed to work pretty well for some groups, but not for others. I will be experimenting on my own at home to troubleshoot some of the issues. Mostly, it had nothing to do with kids using the digital multimeters incorrectly to measure current, though if they did things wrong yesterday they may have blown a fuse and I could not tell. So that is another thing I need to check.

Sticky Tape

124 The conceptual classes are now starting to study static electricity using sticky tape! I love this activity!


IMG_20130319_205852123 I’m on a jury, for the first time ever. So I’m out of school. Garrgh.

Poster Project

IMG_20130315_142007121 My conceptual classes had to make a poster explaining how to solve projectile problems. The idea was that in the process of creating the posters, they would cement the ideas more firmly in their own minds. We shall see, as they do assessments over the next couple of weeks. I do plan on leaving the posters up while they do in-class assessments.


Pi Day!

pie120 The AP class had a test today, on potential and capacitance. Then we ate pie! The choices were: pumpkin, apple, blueberry, blackberry, chocolate, chocolate pudding, chocolate cream, and oreo/peanut butter ice cream pie!


fusion119 I have been working on solving old US Physics Team Semifinal exams with my semifinalist student. This is a scratch paper in which I was trying to figure out a solar fusion problem. Something I didn’t remember from my undergraduate education is that in addition to energy conservation, charge conservation, and momentum conservation, nuclear processes include baryon number conservation and lepton number conservation. So solving this type of problem requires remembering which particles are of which type, as well as knowing what the types of particle are. I find it a little crazy that this test for high school students involves this kind of physics, but the test is supposed to select students to compete against other students who have been picked out of their countries as the best physics students, so it has to be hard enough to winnow out the top 20 high school physicists in the country!


118 I am reviewing projectile material with my conceptual classes, and for fun I pulled out this old VHS recording of a Paul Hewitt lecture. The first half of the lecture is pretty good, and the kids are happy with how much they understand. We have fun playing along with “ask your neighbor” and “what’s the answer? It starts with ‘t’…” and the kids are amazed that it is a college-level class. Then there is a long bit where he goes on and on about how to impress an attractive young person at a church picnic by determining the height of a cliff from how long it takes a stone to hit the water. At the end, there is another good bit where Hewitt talks about orbits. I wish it were as easy to edit VHS as it is to edit digital video!