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Homework Help: Finding voltages across capacitors under DC conditions

  1. Sep 3, 2010 #1
    1. The problem statement, all variables and given/known data
    Find the voltage across the capacitors in the circuit given under DC conditions.

    2. Relevant equations

    3. The attempt at a solution
    The solution is already given (the picture attached was obtained from the solution manual. I have a difficult time understanding how they arrived to that answer. V1 and V2 are really capacitors, but since this is in DC conditions, they are treated as open circuits.

    I think I understand why V1 is 30v - since this circuit is essentially 3 resistors in series on the left side, all I'd need to do is find the current, then use that current across the 30 ohm resistor to find voltage, and since that resistor is in parallel with the capacitor, the voltage would be the same.

    The right side is what I do not understand. Why would the voltage V2 be equal to 60-20*I1?


    Attached Files:

    • cap.jpg
      File size:
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  2. jcsd
  3. Sep 3, 2010 #2


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    Homework Helper

    Current I1=1A flows through the 20 ohm resistor, causing a potential drop of 20 V across it.
    The potential at the positive terminal of the battery is 60 V with respect to the 0 point. Across a resistor, the current flows from the positive end towards the negative one, so the potential Ua is 20V lower than U+: Ua=60-20=40V. As no current flows through the 50 ohm resistor, the potential V2 is the same as Ua.

    Attached Files:

  4. Sep 3, 2010 #3
    I understand what you are saying. Thank you very much for the help!
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