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Homework Help: DC Circuit - Total Resistance

  1. Dec 30, 2011 #1
    1. The problem statement, all variables and given/known data

    Breakdown, and find the total resistance for this circuit.

    2. Relevant equations

    Parallel Circuits - 1/Rtot = 1/R1 + 1/R2 ...

    Series Circuits - Rtot = R1 + R2

    3. The attempt at a solution

    http://img696.imageshack.us/img696/4176/centralkootenayj2011122.jpg [Broken]

    Please dont mind the resistor units, they're all in kΩ.

    Basically, I try to breakdown the circuit into its most simple form. I feel however that in my 3rd recreation I'm doing something wrong.

    In the first circuit diagram, I took the two resistors on the right and made them one (as they're in series). I then considered the two resistors on the far right in parallel, finding the new resistance. However --- is this correct, as there is the 6 ohm resistor just before it. Must I include this in the Rparallel equation? I have tried this but still I get an incorrect answer, of 2.67kΩ.

    My answer as done in the picture is 2.5kΩ. However the supposed answer is 3kΩ.

    And no there isn't supposed to be a rounding of the answer.

    Please help!
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Dec 30, 2011 #2
    Your method is fine but in your 3rd diagram the 12 resistor immediately to the right of the battery should not be there.
    You will then get the correct answer.
  4. Dec 30, 2011 #3


    User Avatar

    Staff: Mentor

    3.0 k
  5. Dec 30, 2011 #4
    I'm sorry but I do not understand. In the preceding diagrams the 12 resistor is there... why should it no longer be there? I must be missing something.
  6. Dec 30, 2011 #5


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    Staff: Mentor

    You have drawn two of them, should be one. An extra one materialized from nowhere!
  7. Dec 30, 2011 #6
    oh my god! i'm such an idiot.

    I saw he 12V battery and wrote in an extra resistor.

    Thanks. hahaha.
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