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Homework Help: Diffifult RC Circuit

  1. Oct 16, 2014 #1
    • Warrning: Posting template must be used for homework questions
    Find the potential of point a with respect to point b in the figure (Fighttps://s.yimg.com/hd/answers/i/1ffe0f8aeaf145679cde38f7812b1c7f_A.png?a=answers&mr=0&x=1413484693&s=0943630e47eb74ae023909f7d39f74e3 [Broken] ure 1) .

    If points a and b are connected by a wire with negligible resistance, find the magnitude of the current in the 10.0V battery.

    V=IR, Req=R1+R2, 1/Re = 1/R1+1/R2

    So basically added up the resistors in series on the side getting 4 ohm and 3 ohm respectively. Im stuck because the a-b is disconnected which is something i haven't seen until this problem. also i cant seem to simplify the circuit into a single "line" if you know what i mean.
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Oct 16, 2014 #2
  4. Oct 16, 2014 #3


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    Staff: Mentor

    Or just write the KCL equations for the circuit. I would put ground at the middle right of the circuit, between the 3 resistors. For the open-circuit case, there is no current flowing in the middle branch (obviously).

    Can you show us the KCL equations?
    Last edited by a moderator: May 7, 2017
  5. Oct 16, 2014 #4


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    Gold Member

    Incidentally, this is not an RC circuit because there are no capacitors.

    When you do have to find the transient voltages and currents in a RC circuit in DC by using differential equations, you will then realize a new level of "difficult".
    Finding voltages and currents in an RC circuit in AC has challenges as well, but is not as difficult as the dreaded DC transient RC circuits.
    Both of these will be coming to you soon assuming you are in an engineering program.

    A hint to solve the problem....there is ZERO current thru that middle branch as suggested above.
  6. Oct 18, 2014 #5
  7. Oct 18, 2014 #6


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    Staff: Mentor

    Kirchoff's Current Law (KCL). I'm guessing by your response that you haven't covered that yet in class. It's a very easy and useful technique to learn -- maybe check it out at Wikipedia, and you will be ahead of the rest of your class! :-)
  8. Oct 22, 2014 #7
    Ahh i see now. Thanks
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