I would like to call your attention to an article in the current (Feb. '04) issue of Nuts & Volts magazine, page 40, entitled "Harvesting Electricity From The Environment." It describes an easy experiment that produces some attention-getting (as well as educational) results, and your teacher clients might be interested in it. Copies are for sale at Barnes & Noble and at Borders magazine racks, or if you click on the website, "back issues" can be ordered. The graphics for the article can be clicked on to enlarge it, at
I wrote the article, and a summary of it appears below (not copyrighted), but much more is communicated by the article itself.
Best wishes, Dan Shanefield, Princeton, NJ, retired sci. prof., Rutgers U.
------------------------------------------------------------ Easy Demo of EMFs by Dan Shanefield
(This is an uncopyrighted summary of my article in Nuts & Volts magazine, Feb. 2004,page 40 --- see
With cell phones, wi-fi, and microwave heating becoming commonplace, the electromagnetic fields ("EMFs") going through all of us are beginning to get scary. You can see for yourself by doing an easy experiment. Just run a 15 foot wire (an extension cord will do) out along the floor of your building. This will be your antenna. Outside, pound a metal rod (a curtain rod will do) into the ground, and run a wire from that in through an open window (thin enameled magnet wire will do). Now hook up a voltmeter with a high input impedance (any modern digital multimeter will do) to measure the voltage between one end of your antenna wire and the grounding rod.
You are probably expecting to see a few microvolts, as I was. But I saw 3 volts of ac. (On an oscilloscope, it's mostly 60 and 120 Hz noise, but with lots of higher frequency "hash" riding on top of it.) Putting the antenna outside in the back yard, horizontally draped over beach chairs, I only got about 100 millivolts, but near a telephone pole and power line in the front yard, there was at least a whole volt.
Putting a rectifier diode in series, I charged up a 1,000 mfd capacitor with that dc for about an hour, inside my house. It got up to 5 volts, so I attached a tiny tungsten incandescent bulb that will run on as little as 25 ma (Radio Shack cat. no. 272-1139). It flashed briefly but quite visibly.
(Note: there are lots more easy experiments and explanations in the Nuts & Volts article.)
Other writers have also worried about the increasing EMFs, and bad interference with computers and TVs has been reported --- see for example, the item in PC Magazine, visible at
Yes, you have to make sure electronic equipment is well shielded, nowadays. (And maybe our brains will have to be shielded in the future!) Some devices have to be "guarded" in addition to being "shielded," and an explanation of the difference is in the electronics textbook that I wrote, which includes many other simplified experiments. You can find (very complimentary!) descriptions of this easy-to-read book on amazon.com by searching my name (Shanefield) and then clicking on the blue "Customer Reviews" line.