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Final charge on capacitor

  1. Sep 26, 2016 #1
    1. The problem statement, all variables and given/known data
    In the circuit shown in the figure, C1 = 1.0 µF, C2 = 1.9 µF, C3 = 2.8 µF, and a voltage Vab = 30 V is applied across points a and b. After C1 is fully charged the switch is thrown to the right. What is the final charge and potential difference on each capacitor?

    24-33.gif

    2. Relevant equations

    Q=CV

    3. The attempt at a solution

    I found everything (V1, Q2, V2, Q3, V3) except for Q1. I tried doing Q1 = CeffV1, but the answer was wrong.
     
    Last edited: Sep 26, 2016
  2. jcsd
  3. Sep 26, 2016 #2
    Ok so since V1=V2+V3, I did Q1/C1 = Q2/C2 + Q3/C3. Solving for Q1, I get Q1 = C1[ Q2/C2 + Q3/C3].

    Q2=Q3=q

    Q1=C1*q[1/C2 + 1/C3]

    Plugging in the numbers, when q = 15.9μC, I get Q1 = 1.4*10-5 C. Does that look right?
     
    Last edited: Sep 26, 2016
  4. Sep 26, 2016 #3

    gneill

    User Avatar

    Staff: Mentor

    That looks right for the final charge on C1, yes.
     
  5. Sep 26, 2016 #4
    Thank you!
     
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