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Urgent Circuit Analysis (Req in Parallel and Series)

  1. Oct 15, 2012 #1
    1. The problem statement, all variables and given/known data
    http://puu.sh/1faG5 [Broken]


    2. Relevant equations



    3. The attempt at a solution
    http://puu.sh/1faFD [Broken]

    I labelled the nodes ^^.

    I redrew the circuit based on the nodes, I ignored the 10 ohm resistor because it short circuits. (Note: I drew the series resistors in reverse order, 80 ohms should be between Node A and Node B, instead, I drew it between B&C. However, the result should be the same.)

    http://puu.sh/1faFh [Broken]
    Based on this, the resistance is:
    20 || 30 || (80+8)

    Req = 10.56 ohms.

    But that is not the answer, I'm not sure where I am going wrong, could someone please help me out please. Thanks a lot! Exam tomorrow :(
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 15, 2012 #2

    gneill

    User Avatar

    Staff: Mentor

    In your second drawing you have NODE C directly connected to terminal B. This is not how it is in the original drawing. I think you need to think a little more about how to redraw the circuit so that all the nodes and connections are preserved.

    Eliminating the 10k resistor is fine; as you say, it's shorted out. The same short puts the top of the 20k resistor in contact with the bottom of the 30k resistor...
     
  4. Oct 15, 2012 #3
    I got 16 kilo-Ohms, I think I understand what mistake I made now. I didn't follow the current from the negative terminal, I was just trying to make them connect. Makes sense now. :) THanks
     
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