Connect with us

Easy demo of powerful EMFs around us

Discussion in 'Electronic Basics' started by Dan Shanefield, Feb 3, 2004.

Scroll to continue with content
  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
    http://www.nutsvolts.com/toc_Pages/feb04toc.htm

    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.
    http://homepage.mac.com/shanefield/Resume1.html

    ------------------------------------------------------------
    Easy Demo of EMFs by Dan Shanefield

    (This is an uncopyrighted summary of my article in Nuts & Volts
    magazine, Feb. 2004,page 40 --- see
    http://www.nutsvolts.com/toc_Pages/feb04toc.htm .)

    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
    http://www.pcmag.com/article2/0,4149,1382851,00.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 amazon.com by searching my name (Shanefield) and
    then clicking on the blue "Customer Reviews" line.
     
  2. Zipperhead

    Zipperhead Guest

    So don't take off your tinfoil hat.
     
  3. Bob Masta

    Bob Masta Guest

    On 3 Feb 2004 09:25:22 -0800, (Dan Shanefield)
    wrote:

    I suspect much of this was simple transformer action, with
    the house wiring as the primary and the "antenna" as the
    secondary. (At least for the 60-120 Hz stuff.)

    Another eye-opening thing you can do is to use a small
    telephone pickup coil and monitor amp/speaker, like
    those sold by Radio Shack. Bring the pickup near
    various water pipes and you'll find all sorts of interesting
    "ground" currents, due to household loads and/or
    transformer coupling.




    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
     
  4. John Larkin

    John Larkin Guest


    Since the wire was insulated ("an extension cord") there was no DC
    path for the diode return current. So how can it charge the cap?

    John
     
  5. Roy McCammon

    Roy McCammon Guest

    That nice warm sunlight is a powerful em field.

    Heck, we are mostly an em field.
     
  6. The insulated antenna (just an extension cord) went to one terminal of
    an ac voltmeter, and the other terminal went to the ground (a rod
    poked into the earth, outside). There was up to 3 volts ac, and with
    a diode in series, a capac. was charged up. Then the capac. had as
    much as 5 V of dc.
    Dan
     
  7. I certainly had nothing to do with the fact that "EMF" is written to
    mean "RF e'mag. fields" these days. (Pretty dumb acronym, especially
    since it used to mean electromotive force in the older physics
    textbooks.) But that's the way it appears in IEEE and other
    literature, lately, ignoring lightwaves and other such fields (even
    ignoring static fields). Anyhow, it's RF.
    Dan Shanefield
     
  8. My biggest surprise was with a straight wire (extension cord) out in
    the backyard, far from the house and from telephone poles. Another
    surprise was measuring 20 volts of as, between the outside ground rod
    (poked into the earth) and the green safety ground wire in my house,
    even with no big appliances running. (It wouldn't have surprised me
    if there had been a clothes drier going, but there wasn't --- at least
    not in my house.)
    Dan Shanefield
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-