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Homework Help: Why Capacitors Store Half The Charge They Are Given

  1. Feb 22, 2012 #1
    I have been studying capacitors this week and learned two equations. One is Q=CV and the other is Q=0.5CV. The latter equation is derived from C-V graph. From this it shows that half the charge delivered is stored. I am very curious to know where the other half of the charge go and why is the charge stored exactly half of the charge supplied? How is the half of the charge which is not stored used?
  2. jcsd
  3. Feb 22, 2012 #2


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    The charge stored in a capacitor of capacitance, C, with a potential difference, V, across its plates is Q = CV .

    The energy stored in such a capacitor is (1/2)CV2. That doesn't mean that the charge is (1/2)CV.
  4. Feb 22, 2012 #3


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    Replace the word 'charge' in this paragraph with the word 'energy' and you will then have a good question. As Sammy was implying, all of the charge delivered is stored.

    P.S. you have an awesome name. and welcome to physics forums!
  5. Feb 22, 2012 #4
    You have your terms mixed up
    C = Q/V or Q = C x V or V = Q/C....these give the relationships between Q, C and V.
    The graph I think you are talking about is Q against V (not C ~ V)
    This graph enables you to calculate the ENERGY stored on the capacitor, the ENERGY equations are
    E 0.5QV...or 0.5CV^2 or 0.5Q^2/C
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