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Changing the distance between capacitor plates

  1. Sep 15, 2014 #1
    1. The problem statement, all variables and given/known data

    1. The distance between two parallel plates is increased while they remain hooked to a battery. Which one of the following statements is true?

    The voltage between the plates will decrease.
    The electric field between the plates will increase.
    The charge on the plates will decrease.
    The capacitance of these two plates will increase.
    None of the above.

    2. Relevant equations

    3. The attempt at a solution

    So for question one,
    What does the battery have to do with anything!? That just means that the voltage is constant?

    C = εA / d

    So if distance is increased the answer is supposed to be that the charge will decrease. What?! Doesn't make any sense. What does the charge have to do with anything? I thought the charge came from the electrons moving around, so why would moving the plates affect the electrons at all?
  2. jcsd
  3. Sep 15, 2014 #2
    Think about what other equation relates capacitance, charge and voltage
  4. Sep 15, 2014 #3
    C = Q/V

    I'm trying to get the physical picture. What exactly is going on here?

    I've googled and searched for videos on youtube. I can't find anything that explains it.
  5. Sep 16, 2014 #4


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    Homework Helper

    If d changes then c changes. Now think about the second eqn.
  6. Sep 16, 2014 #5


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    Perhaps think what would happen if the plates were moved with and without the battery connected. What can and can't change with or without the battery connected and why.
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