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Experiment: my like charges didn't repel

  1. Nov 28, 2014 #1
    i had a battery powered device that outputted 5kV DC . i hooked up one of the output leads to two long pieces of Al foil. i was expecting a repulsion but nothing happened, why? is the voltage not high enough?
     
  2. jcsd
  3. Nov 28, 2014 #2

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    A few more details might help --- are you arranging the foil as the leaves in a leaf electrometer? Or, just hanging off a terminal of the power supply? What's the configuration of your "ground plane?" (What's connected to the other terminal to "shape" the electric field?)
     
  4. Nov 28, 2014 #3
    previous setup
    QyOOXNe.png
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    i hooked up each foil to the opposite ends of the device and the foils were attracted to each other, which is good news but i was going for a repulsive effect. charge should be accumulating at the ends of both terminals of the device so i figured either end should have half the amount of ΔV.
    anyway, in the first setup (image), i didn't notice the foils moving at all and i don't know why.
     
  5. Nov 28, 2014 #4

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    How heavy is the foil?
     
  6. Nov 28, 2014 #5
    judging from your reply i take it the foils should have repelled, they were probably just too massive?
     
  7. Nov 28, 2014 #6

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    That would be my guess --- hit Wiki, or Google around a bit for capacitance formulae, and you'll find the capacitance between your leaves and the ground plane is going to be in the neighborhood of hundredths of picofarads, times the 5kV is a charge of a few picocoulombs on the leaves; split that charge, tuck it into coulomb repulsion, and it's not going to be enough to noticeably deflect the leaves from each other in the earth's gravitational field. The foil wrap that used to be on Nestles bars was around 0.0005" and just barely moved for carpet static on a nice dry winter day.
     
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