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LED lights up when touched

  1. Jan 31, 2012 #1
    An LED lights up when i touch it.
    One leg is attached to a piece of metal, other is the one i touch.
    Polarity does not matter.
    Amount of metal maters - table frame makes it full bright, half-meter steel ruler makes it dim, a piece of wire makes it just visible.
    Touching that piece of metal makes the light go off.

    This only happens when there are power main wires nearby, which suggest an induction effect.
    I want to reproduce that light without touching the LED.
    The question is - what am i in the circuit?

    I tried attaching the second leg to several coils, with not a slightest result.
    I also tried a 680pF capacitor, also without a result.
    Peculiarly, the LED is lit if i touch the side of the capacitor, which is ceramic.
    Combing the hair to make static charges does not affect the brightness.
    And that exhausts my familiarity with electricity.

    What is going on here?
    How can i get the LED to light up like that without touching it?
  2. jcsd
  3. Feb 1, 2012 #2
    Hook it up to a battery.
  4. Feb 2, 2012 #3


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    Science Advisor

    "This only happens when there are power main wires nearby".
    There is an electric field outside a power wire.
    That could provide the EMF.
  5. Feb 5, 2012 #4
    That would be boring.
    As i suspected.
    The question is, what kind of circuit part me touching it is?
  6. Feb 7, 2012 #5
    i doubt your induction theory . because if the induction is due to the ac supply then the led should be ON and OFF very rapidly . it should not glow continuously (@reverse bias of a diode ). of course that blink might not be tangible but its still a thought .......... i can not explain the capacitor effect but i think referring to your original question you are the ground.
  7. Feb 7, 2012 #6
    Maybe it's your electric personality? :-)

    If you are in an area where there's a strong electric field from a local source (so the field drops sharply with distance), your body could act as a crude antenna, while the metal plate could be acting as a capacitor coupling it to ground. Then when you touch the LED, one half of the cycles conduct current thru the LED to illuminate it. If it's an AC mains field at 50 or 60Hz, it's too fast to detect the on/off blinking so it looks like it's on continuously. Just a guess!
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