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Homework Help: Conceptual RC Circuit questions

  1. Oct 24, 2011 #1
    1. The problem statement, all variables and given/known data

    After a long time after the switch is closed.

    1) Rank the current of each component.
    2) What is the voltage across each component?

    2. Relevant equations

    3. The attempt at a solution

    1) The current across B is the same as the capacitor C because the capacitor is fully charged. There is no current across Vbattery and A because the capacitor now has positive charges on the top and negative charges on the bottom so there is no potential outside the parallel part (B and C).

    2) 0 V for A and Vbattery. But B and C have the total voltage across each.

    Is this right?

    I'm thinking that the parallel part creates it's own self powered loop and blocks out the rest, the battery and A.

    Thanks for any help.

    Attached Files:

  2. jcsd
  3. Oct 24, 2011 #2


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    Staff: Mentor

    Current flows THROUGH. Voltage appears ACROSS.

    After a long time the capacitor voltage settles to whatever the circuit around it dictates. In this case it won't be equal to the battery voltage because the lamps are creating a voltage divider. To see this, use the rule of thumb that says that at steady state the capacitor current will be zero and its voltage fixed, so for all intents and purposes you can simply ignore it (remove it from the circuit entirely). What does the remaining circuit look like?
  4. Oct 24, 2011 #3


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    Homework Helper

    Sorry, this is totally wrong.
    The capacitor is parallel connected to B. Why should the same current flow through both? What is the same across them?
    The voltage of the battery is given, Vbat. Is there a closed path between the terminals through A and B? Can current flow from the positive pole of the battery to the negative one?

    No. The voltage of the battery is constant, Vbat.

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