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Homework Help: Capacitors in a circuit

  1. Mar 16, 2008 #1
    1. The problem statement, all variables and given/known data
    http://img512.imageshack.us/img512/6864/59797183jd5.png [Broken]

    (capacitance in micro farads).

    Initially the switch is at the left position and capacitors C_2 and C_3 are uncharged. Then the switch is flipped to the right position. Afterward, what are the chard on and the potential difference across each capacitor?

    3. The attempt at a solution

    First I turned C_2 and C_3 into a capacitor with equivalent capacitance 12 uF.

    Before the switch flip, C_1 is charged to 100V and has 1.5 mC of charge. I'm not sure what happens after the switch flips though. Does C_1 still affect the circuit? If not, then its charge and voltage won't change from before it flipped. And then the voltage and charge on C_2 and C_3 are completely unaffected by the presence of C_1?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Mar 16, 2008 #2
    Since the switch is flipped to the right, the circuit loop doesn't connect to both terminals of the battery, so what you could do is ignore the battery in the system. I'm thinking that C1 does affect the other 2 capacitors, in which it provides a current to the capacitors for a short interval of time. At some point, the current should approach 0 effectively enough and the capacitors should approach some steady charge and voltage. What you could use is Kirchoff's rules for the particular loop of C1, C2, and C3, in which you come up with an arbitrary current and set the net voltage along the loop to 0V.
  4. Mar 16, 2008 #3
    Oh I didn't even notice that the battery wouldn't connect to the other two capacitors... doh!
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