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Homework Help: Thevenin Equivalent Circuit

  1. Feb 17, 2014 #1
    1. The problem statement, all variables and given/known data
    Problem located in attachment.

    2. Relevant equations
    Parallel, series and wheatstone bridge equations for resistors

    3. The attempt at a solution
    Converted the circuit to look less confusing. Work shown in other attachment.
    I am simply using the equations relating to simplifying circuits to get R total or th, but the book I am using is telling I am wrong. Thoughts?


    Attached Files:

  2. jcsd
  3. Feb 17, 2014 #2


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    Science Advisor
    Homework Helper

    hi maximade! :smile:

    hmm … i get the same as you (1.5 Ω) :confused:

    anyone else? :smile:

    btw, it might be easier if you started with a different diagram …

    put it all inside a triangle with edges 3 3 and ab, and you should see a symmetry that makes it a lot easier :wink:
  4. Feb 17, 2014 #3


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    Staff: Mentor

    It's a talking book? :tongue:

    I'd say you're half right. A Thévenin equivalent involves a voltage source together with a series resistance. So, what's your voltage?
    Last edited: Feb 17, 2014
  5. Feb 17, 2014 #4
    Yes, it is a talking book haha. (Don't know how to do that quote thing you did)

    Correct me if I am wrong but because the current source is the load, I thought I just turn it into an open circuit then solve for resistance from there.

    I could just be not understand the whole process.

  6. Feb 17, 2014 #5


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    Staff: Mentor

    Use the "Quote" button on the post in question to start your reply with that post's text included as a quote.

    Ah, but the current source is not the load; it's part of the circuit. It just happens to lie across the output nodes. If you think about the network of resistors "behind" it being reduced to a single resistor, then what would the current source and resistor look like (in terms of circuits you might be familiar with)?
  7. Feb 17, 2014 #6


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    Staff: Mentor

    It may look like a bridge arrangement, but no one says it can't be used in an exercise where you just need a jumble of resistors. :smile:

    The question asks that you find the Thévenin equivalent of the circuit as it appears at terminals (a,b). The source is, in this question, part of that circuit. At terminals (a,b) you will see a source feeding into a resistance. You have correctly determined the equivalent single resistance, now imagine that source connected across that resistance. How much current will be flowing? What voltage will be measured at the terminals (a,b)?

    Describe what you have so that it fits the classic Thévenin circuit.
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