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Capacitor charge question

  1. Nov 10, 2008 #1
    1. The problem statement, all variables and given/known data
    A circuit composed of 2 capacitors of .40MF and .50MF are connected in series to a 9V battery. Calculate the charge on each

    I just have a general question. I know that capacitors in series have the same charge.
    I found Q to be 2MC and I was wondering if 1.8MC is the charge on both caps or is it .9MC charge on both caps.
     
    Last edited: Nov 10, 2008
  2. jcsd
  3. Nov 10, 2008 #2

    LowlyPion

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    Capacitors in parallel have the same voltage but not necessarily the same charge unless the capacitances are the same.

    Q = v * C

    As for your question about the 1.8 mC - that is what is across the "equivalent" capacitor.

    If you were to figure the voltages of the 2 capacitors and know they are supposed to add to 9 v, you will be able to answer your own question about how the charges are distributed.
     
  4. Nov 10, 2008 #3
    Oops sorry my bad i mean capacitors in series have same charge. But I can't solve for V w/o finding out the capacitance on each capacitor. So what im trying to say is does the both of the capacitors get 1.8mC of charge or do they each get .9mC?
     
  5. Nov 10, 2008 #4

    LowlyPion

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    What voltage do you get across each capacitor for both of those possibilities?

    Which possibility adds up to 9 v adding the voltages of both capacitors? Because that's the one that's your answer.

    Btw, where did the 1.8 mC come from? Didn't you calculate the equivalent capacitance and multiply by the voltage?
     
    Last edited: Nov 10, 2008
  6. Nov 10, 2008 #5
    round errors and I figured it out. 1.8mC gets dumped on both of the caps.
     
  7. Nov 10, 2008 #6

    LowlyPion

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    Well if you had used 2 mC it would have maybe been a little more obvious?

    Cheers.
     
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