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Electricity device help

  1. Feb 20, 2008 #1
    i need to make a device but dont know how
    it is 2 lightbulbs, when they are far away, (more than 2 feet), then one or both of them should light up. if they are close, they should both turn off.
    any idea how i can do this?
  2. jcsd
  3. Feb 20, 2008 #2
    Since both light bulbs need to be connected to a power source anyway, you can connect them linearly and add a string and pin, two feet in length, which would short circuit the two. If the light bulbs move to more than the length of the string from each other the string would disconnect and thus there will be light!

    Of course you meant, without direct contact between the two, but I couldn't resist the obvious solution. You can also use positioning devices that works on sound, which would calculate the distance by measuring the time under a constant velosity. You can also use a common lazer and a small mirror and mesure the shift. Are these good for you?
  4. Feb 20, 2008 #3


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    Gold Member

    Welcome to PF, Umaga.
    You could simply place a conductive plate on the table. When both lamps are in contact with it, the circuit is closed; when one isn't, darkness.
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