One of my demonstrations has been published in the December 2010 issue of The Physics Teacher magazine! (And I owe a big thank you to Dan MacIsaac of Buffalo State University for encouraging me to submit the demo for consideration.)
It’s called The Tin Foil Capacitor — and it’s one of the few articles available as a free download for non-AAPT members not free anymore.
In the demo, an electroscope is connected to a rolled up sheet of aluminum foil with an alligator clip wire. The purpose of the demo is to illustrate: (1) excess charges on a conductor reside on the surface of the conductor; and (2) the charges spread out over as large a surface area as possible. The electroscope is charged up and then the aluminum foil is unrolled and then rolled back up again. Here’s a video of the demonstration in action:
I also have a simple interactive lecture demonstration (ILD) worksheet to use with students before and after doing the demo: Tinfoil Capacitor ILD Sheet.
Update: A new and improved ILD sheet from physics teacher Michael Sivell — TinFoilCapILD_Sivell
More Interactive Lecture Demonstrations from the University of Maryland PER Group.
Action-Reaction 