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Homework Help: Series parallel combination circuit

  1. May 21, 2013 #1
    1. The problem statement, all variables and given/known data

    In the attached circuit diagram, I have to find the Total resistance of the cicuit, the current at I1, the voltage over R6 and the current through I5.

    2. Relevant equations

    V = IR

    3. The attempt at a solution

    Rt = 12Ohms
    I1 = 1A
    R6 = 6v
    I5 = 1A
    1. The problem statement, all variables and given/known data

    Attached Files:

    Last edited: May 21, 2013
  2. jcsd
  3. May 21, 2013 #2
    Figure out which resistors are in series and which are in parallel. Then,try using a combination of kirchoff''s loop and junction rules to come up with a few linearly independent equations from which you can solve for the various I's. Also, Ohm's law is V = IR. See where that gets you.
  4. May 21, 2013 #3

    I re-attached my attempt, please have a look. I need to solve for the total resistance, current through I1, voltage over R6, and current through I5. I made an attempt by reducing the circuit to a simpler circuit. What confuses me is the current through I5, and whether R3 actually makes any difference to the total resistance of the circuit, because in my eyes it is as if it is bypassed by the wire carrying current I5.

    Meant V = IR, sorry about that.

    Help will be much appreciated. Thanks
  5. May 21, 2013 #4
    Could you tell me what the resistance of the top right resistor is? It's not included in the diagram.
  6. May 21, 2013 #5
    Its 24 Ohm, I re-scanned the diagram, has all info now..
  7. May 21, 2013 #6
    Well, are you familiar with Kirchoff's loop rule?
  8. May 21, 2013 #7
    I know his First law(current law), and Second law(Voltage law). Are you talking about one of them?

    Just another question, if Resistor three is short circuited, does it add to the total resistance of the circuit or do I just ignore it?
  9. May 21, 2013 #8
    Well, the loop rule states that the sum of all the potential differences around a closed circuit is zero (For a conservative electric field that is). Have a think about that in relation to the total resistance of your circuit.
  10. May 21, 2013 #9
    Uhhh... I think I am a little confused now. But ill try to figure it out.. Thanks for the help
  11. May 21, 2013 #10
    Wait, I've totally jumped the gun here with using the rules. My apologies for any confusion!
  12. May 21, 2013 #11


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    Hint: R4 the 10Ω resistor is shorted, it does not contribute anything. Remove it from the circuit all currents and voltages will remain the same.
  13. May 21, 2013 #12


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    Actually that's R3.
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