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Horizontal parallel

  1. Feb 5, 2013 #1
    1. A proton is suspended in a vacuum between two oppositely charged horizontal parallel plates. The separation between the plates is 2.60mm



    2. I assume it uses E=vd/d, but I dont really know



    3. what is the sign of the charge on the lower plate?
    what is the voltage across the plate?
     
    Last edited by a moderator: Feb 5, 2013
  2. jcsd
  3. Feb 5, 2013 #2

    mfb

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    What does that mean?

    Some hints how to start:
    Can you identify the forces acting on the proton?
    If the proton stays at rest between the plates, can you identify the direction of those forces?
     
  4. Feb 5, 2013 #3

    berkeman

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    Welcome to the PF.

    You are required to show your work toward a solution before we can offer much tutorial help.
     
  5. Feb 5, 2013 #4
    since gravity pulls the proton downward so the lower plate should be the positive charge to repel the proton.
    F=mg=qE
    E=mg/q=v/d, m=1.673x10^-27kg, g=9.8m/s2, q=1.602x10^-19 and d=2.60x10^-3m
    so we just need to solve q to get the voltage across the plates?
     
  6. Feb 5, 2013 #5

    mfb

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    You know q, I think you mean V? Right.
     
  7. Feb 5, 2013 #6
    yes, I solved V= 2.66x10^-10...not positive sure it's correct tho
     
  8. Feb 6, 2013 #7

    mfb

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    Gravity is weak, and you can check your calculations in WolframAlpha, for example. If the units match, it should be right.
     
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