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Homework Help: Potential difference between the plates?

  1. Mar 16, 2009 #1
    1. The problem statement, all variables and given/known data

    A small electrically charged object is suspended by a thread between the vertical plates of a parallel-plate capacitor. The acceleration of gravity is 9.8 m/s^2.
    What is the potential difference between the plates? Answer in units of kV.

    Given: tetha = 14 degrees
    mass of the object = 152 mg
    q = 15 nC
    distance between the two plates = 5.6 cm

    2. Relevant equations

    I used the following:

    delta V = U/Q
    U = F x d

    3. The attempt at a solution

    I got U = 0.0000834176 Joules
    and I got V = 5561.1733333 V
    which is V = 5.561173333 kV

    but it's wrong.

    could someone please please tell me how to do it?
  2. jcsd
  3. Mar 16, 2009 #2


    User Avatar
    Homework Helper

    Welcome to PF.

    How did you resolve the force of gravity and the electrostatic force to determine your E field?
  4. Mar 16, 2009 #3
    Thank you.

    I got it.
    It took forever to finally get a reply from someone, so I asked someone else.

    What I did was Tcos(tetha) = (152x10^-6)(9.8)
    then, F=Tsin(tetha)

    Then I used, E=F/q
    Then I used, V=Ed, V/1000 (conversion from V to kV)

    My final answer is V = 1.386556241 kV

    And it's correct! :smile:
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