Van de Graaf


142 Friday 4/19 was a day when it was nice to forget all the things going on in the world and have some fun. Despite the rainy weather, the Van de Graaf generator was working up a nice electric potential, and we successfully made a number of students’ hair stand away from their heads. I love the Van de Graaf generator. (It was also the day of the spring pep rally. My students usually do not wear glitter on their faces.)




140 On Wednesday 4/17 I tried to forestall difficulties with calculations using scientific notation with the conceptual class by using several different calculator examples. This is one of those times when I am so happy that I have a document camera! Perhaps you recognize the number in the display of each calculator.



139 This was Tuesday, 4/16. The AP class was determining the relationship between the magnetic field strength and distance from a long current-carrying wire. Almost all of my photos turned out blurry. I am not sure what I had messed up in my phone’s camera settings.


134 The conceptual classes are playing with this sim today. It is one of my favorites. I love watching the charges in the wall when you bring a charged balloon nearby. Nicely done, PhET!

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!


106 Some of my kids are missing today’s (Friday, 2/22) lecture on electric potential. So I had three kids video it, and I am trying to edit it into one video. Tiring! But here is a small clip.