Equivalent resistance

Discussion in 'Homework Help' started by gicode0823, Feb 19, 2012.

  1. gicode0823

    Thread Starter Member

    Feb 8, 2012
    31
    0
    [​IMG]
    (a) Find equivalent resistance respect to terminals A and B.
    (b) Find equivalent resistance respect to terminal A and C.

    redrew the diagram using iCircuit app
    [​IMG]

    First I counted the all the node (8 nodes)

    In series:
    31 + 25 = 56Ω
    38 + 29 = 67Ω

    then I redrew the diagram
    [​IMG]

    parallel:
    67//26//39//23 = 6.65Ω
    26//30 = 13.93Ω
    32//34 = 16.48Ω

    I redrew again
    [​IMG]
    21 + 6.65 = 27.65
    24//32//27.65 = 9.17

    Now I saw that the 16.48 resistor is shorted

    I redrew again
    27//32 = 14.64
    13.93 // 56 = 11.15

    11.15 + 37 = 48.15

    48.15//14.64//9.17 = 5.04 Ω

    But the answer for part (a) is 13.07Ω.

    I can't seem to find the error in my computation...
     
  2. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    It looks like you have a typo in your first schematic. The 34 ohm resistor was written as a 31 ohm resistor. I'm guessing that's not the only mistake, but I'll look further.
     
  3. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    The 16.48 ohm resistor shouldn't be shorted.
     
  4. gicode0823

    Thread Starter Member

    Feb 8, 2012
    31
    0
    I understand now that 16.48 ohm resistor shouldnt be shorted... but still not getting the right answer. Will redo this problem again...
     
  5. gicode0823

    Thread Starter Member

    Feb 8, 2012
    31
    0
    31 + 25 = 56

    38 + 29 = 67

    23//36//39//26//67 = 6.65

    26//30 = 13.93

    32//34 = 16.48

    33//27 = 14.85

    [​IMG]
    R1 = 24
    R2 = 21
    R3 = 6.65
    R4 = 16.48
    R5 = 14.85
    R6 = 37
    R7 = 13.93
    R8 = 56
    R9 = 35

    14.85 + 37 = 51.85

    51.85//13.93 = 10.98

    10.98 + 56 = 66.98

    16.48//66.98 = 13.23

    21 + 6.65 = 27.65

    13.23 + 24 = 37.23

    10.92 as answer.

    Other two tries, I got 53.02550844 ohms...

    Can't find the error...
     
    Last edited: Feb 20, 2012
  6. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Almost correct.

    Rab=24||(13.23+(35||27.65))=13.065Ω
     
    gicode0823 likes this.
  7. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
    326
    It looks to me like Rac is not going to work out so nicely. I think a delta-wye transformation may be necessary. Anyway, for reference, I get Rac = 26.2607
     
    gicode0823 and t_n_k like this.
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