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Capacitors and a Switch

  1. Feb 15, 2015 #1
    1. The problem statement, all variables and given/known data
    The switch is initially open and the capacitors are uncharged. The applied potential difference Vab = +210V.
    a.) What is the potential difference Vcd?
    b.) What is the potential difference across each capacitor when the switch is closed?
    c.) How much charge flowed through the switch when it was closed?

    2. Relevant equations
    I'm thinking this will be all I need:
    Q=CV

    3. The attempt at a solution
    I can't even visualize what happens when the switch closes, so I'd like to start there. When the switch closes, more current will divert to the bottom capacitor since it will offer less resistance, but my solution manual says it changes the entire circuit setup.
    I've attached the problem statement and the solution manual setup statement. Screenshot_2015-02-15-14-58-00.png Screenshot_2015-02-15-14-59-26.png
     
  2. jcsd
  3. Feb 15, 2015 #2

    gneill

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    Staff: Mentor

    You do realize that this is a DC setup with capacitors as the load, right? So any current that flows will be a momentary transient while the capacitors charge or change charge to a new steady-state. There are no resistances in the circuit.

    Have you worked out the initial voltages and charges on all the capacitors prior to the switch closing? It doesn't make sense to start at part (b) if you haven't established the initial conditions for part (b) to take place.
     
  4. Feb 15, 2015 #3
    Okay so, heeding your advice, I solved part (a). I got a potential difference of +70 V from point c to point d.

    Now, closing the switch, what happens? I still can't picture it.
     
  5. Feb 15, 2015 #4

    gneill

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    Staff: Mentor

    You won't picture it until you've labelled the diagram with the charges on each capacitor. I haven't seen your values for those charges.
     
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