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Point Charge help?

  1. Jul 8, 2008 #1
    1. The problem statement, all variables and given/known data

    A point charge of mass 0.069 kg and charge q = +5.89 µC is suspended by a thread between the vertical parallel plates of a parallel-plate capacitor.

    If the angle of deflection is 22°, and the separation between the plates is 0.025 m, what is the potential difference between the plates?



    2. Relevant equations

    U = .5C*V^2

    3. The attempt at a solution

    I know the left has a higher potential energy because the mass is attracted toward the right?
     
  2. jcsd
  3. Jul 8, 2008 #2

    Hootenanny

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    Welcome to PF,

    If the charge is displaced to the right, then the left would indeed be at a higher potential.

    Can you start by determining the tension in the string?
     
  4. Jul 8, 2008 #3
    The tension of the string is m*g= .68

    I am still lost at how to find the the force that attracts it to the side.

    would it be 5.89E-6 cos 22?
     
  5. Jul 8, 2008 #4

    Hootenanny

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    That would be correct if the string was hanging vertically, but that isn't the case is it?
     
  6. Jul 8, 2008 #5
    no its not hanging vertically so mg=cos22???

    I am sorta lost...
     
  7. Jul 8, 2008 #6

    Hootenanny

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    You're getting closer:

    [tex]T\cos22 = mg[/tex]

    Now since the mass is in equilibrium, what can you say about the horizontal forces acting on the mass?
     
  8. Jul 8, 2008 #7
    alright so the force acting on the mass is the same as the tension force which is 0.729.

    so would you use F=q(v/x)?
     
  9. Jul 8, 2008 #8

    Hootenanny

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    Remember that you want the horizontal component of the force, not the vertical.
     
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