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Homework Help: Parallel plates with a mass m at an angle

  1. Apr 15, 2008 #1


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    1. The problem statement, all variables and given/known data

    An object of mass m carries a charge q and is supsended by a thread between the vertical plates of a parallel plate capacitor. The plate seperation is d. If the thread makes an angle [tex]\theta[/tex] with th evertical, what is the potential difference between the plates?

    2. Relevant equations
    [tex]E = \frac{\sigma} {\epsilon_0}= \frac{Q} {\epsilon_0 A}[/tex]

    [tex]C=Q/ \Delta V[/tex]
    3. The attempt at a solution

    I know that for a capacitor without the mass in between it it, the potential difference is:

    [tex]E = \frac{\sigma} {\epsilon_0}= \frac{Q} {\epsilon_0A}[/tex]

    [tex]\Delta V= Ed = \frac{Qd} {\epsilon_0 A}[/tex]

    The thing is that I'm not sure what difference would the mass at an angle would make in the potential difference.

    I do know that the mass at an angle has an electric force (if the mass is angled toward the right) force pulling it to the right at an angle, the gravitational force is pulling it down, and tension force in the string. And thus mass stays stationary in the field.

    Thank you
  2. jcsd
  3. Apr 15, 2008 #2


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    Science Advisor

    So, you say you know the object is in equilibrium? Why don't you try drawing a diagram, labeling forces, and finding out what has to equal what.
  4. Apr 15, 2008 #3


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    http://img151.imageshack.us/img151/4862/84586505yl8.th.jpg [Broken]

    I drew it but I still don't know hwat the mass has to do with the potential difference.

    can ANYONE help me out with this? Please?
    Last edited by a moderator: May 3, 2017
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