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Homework Help: Charge en energy on capacitor

  1. May 28, 2009 #1
    I guess this is a simple question and I can't find clarification on it any where

    If the total charge on each plate of a parallel plate capacitor is 1200 joules then is the total energy stored in that capacitor 2400 joules. Lol might seem dumb but I just want to make sure this was correct

  2. jcsd
  3. May 28, 2009 #2


    Staff: Mentor

    Re: Capcitor

    Charge is measured in units of coulombs, not joules.
  4. May 28, 2009 #3
    Re: Capcitor

    k then does the charge on each plate = total charge

    so 1200 on one plate 1200 on the other = 2400
  5. May 28, 2009 #4
    Re: Capcitor

    Capacitor charge Q is defined so that there is charge separation with +Q on the positive plate and also -Q on the negative plate, when we say that the capacitor voltage is V=Q/C and the energy stored is (1/2)CV^2.

    (Note that a total for +Q and -Q would always be zero.)
    Last edited: May 28, 2009
  6. May 28, 2009 #5
    Re: Capcitor

    total energy stored in a capacitor is split between the 2 plates. So say the capacitor stores 2 joules of energy does each plate hold 1 joule of charge.
  7. May 28, 2009 #6
    Re: Capcitor

    Don't think of each plate holding half of the energy. Think of the energy being in the fact that +Q and -Q are attracted to each other but not allowed to move toward each other because of the insulation in the spacing.
  8. May 28, 2009 #7
    Re: Capcitor

    The question I have is a parallel plate capacitor holds a charge of 1200 joules on each plate. It has a potential difference of 110 volts applied to it what is the capacitance of the capacitor in farads
  9. May 28, 2009 #8
    Re: Capcitor

    What DaleSpam said above. If the question says "a charge of 1200 joules" the question is incorrectly worded. I would ask the writer of the question if they mean "a charge of 1200 coulombs." If they say yes, then Q is 1200 coulombs.

    I have never heard anyone refer to energy per plate.
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