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Easy demo. exper. about strong EMFs all around us

Discussion in 'Misc Electronics' started by Dan Shanefield, Feb 3, 2004.

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  1. 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

    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,4149,1382851,00.asp ,
    especially the second and third paragraphs.

    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 by searching my name (Shanefield) and
    then clicking on the blue "Customer Reviews" line.
  2. CWatters

    CWatters Guest

    What ONLY 3V.
  3. Yeah, a tinfoil hat!
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