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Homework Help: Electric force and free electrons

  1. Oct 23, 2008 #1
    Two point charges of -1.0 micro C and +1.0 micro C are fixed at opposite ends of a meterstick. Where could a) a free electron and b) a free proton be in electrostatic equilibrium?

    I'm guessing the answer is nowhere since there have to be opposite charges to be in equilibrium?
     
  2. jcsd
  3. Oct 23, 2008 #2

    Dick

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    I think you are right. The forces don't balance anywhere.
     
  4. Oct 24, 2008 #3
    is there any way I can prove it with the formula kq1q2/r^2?
     
  5. Oct 24, 2008 #4

    Dick

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    Put one charge at r=(1/2) and another at r=(-1/2). Then the magnitude (ignoring direction) of the force on the third charge located at x due to one charge is k/(x-1/2)^2 and the other is k/(x+1/2)^2. If you set those equal you find the only possible position is x=0. But at x=0 you know the directions of both forces are the same. So they can't cancel.
     
  6. Oct 24, 2008 #5
    yes! that's what I thought... thank you!
     
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