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Homework Help: I need help with resistance question

  1. Mar 23, 2013 #1
    I don't know how to find the total resistance in the circuit i've attached.

    Anybody please help me, Thanks in advance.

    Attached Files:

    • q1.jpg
      File size:
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  2. jcsd
  3. Mar 23, 2013 #2
    Look at the circuit for what share the same start and end nodes and what don't. Those that do share the same start and end nodes add in parallel and those that don't add in series. So the 2 ten ohm resistors on the very right are in series, but that 20ohm resistor adds in parallel to the total of the 2 ten ohm resistors added in series.

    To get you started, the right hand "upper triangle" should look like this...

    10 ohms + 10 ohms = 20 ohms

    and 20*20/(20+20) = R total

    (or.. 1/Rtotal = (1/20) + (1/20))

    R total for that very right "upper triangle" being 10 ohms.
  4. Mar 23, 2013 #3
    From quick rough working.. I got 17.5 ohms for the total of the circuit.

    So, starting from right to left... I got.

    10 ohms in parallel with 20 ohms.

    This gave me 6.666667 ohms in parallel with another 20 ohms

    which gave me 5 ohms, which is in series with 20 ohms.

    This gives 25 ohms, which is now in parallel with 25 ohms.

    This gives 12.5 ohms, which is now in series with the 5 ohm resistor, and totals 17.5 ohms.
  5. Mar 23, 2013 #4
    I don't know if the 20 ohm resistor is parallel or series, the one i highlighted in the attachment.


    Attached Files:

    • q2.jpg
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  6. Mar 23, 2013 #5
    np! (Don't quote me as I'm only a third year college student haha, but I do quite well on electrical papers)

    That depends, just start from right to left as I outlined in my post previously. And reduce the circuit down resistor by resistor.

    That resistor though, is in series with the 5 resistors on the right as they don't share the same start and end nodes because of that 25 ohm resistor.
    Last edited: Mar 23, 2013
  7. Mar 23, 2013 #6
    The answer is right man, thanks heaps for the help :)
  8. Mar 23, 2013 #7

    Excellent. I hope you learnt! Make sure you try see circuits as nodes rather than just the way they're orientated.
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