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D/C Circuit with one current and voltage source

  1. Sep 18, 2014 #1
    1. The problem statement, all variables and given/known data

    A circuit problem and I think a picture could do a much better job than anything I could type.
    Picture should be attached below if I didn't screw it up.

    2. Relevant equations

    I'm allowed to use Ohm's Law, resistor series/parallel combinations, superposition, Thevenin's theorem, KCL/KVL, voltage and current division.

    3. The attempt at a solution

    The only thing that really jumps out at me here is Thevenin's theorem. Unfortunately that's probably the concept I'm the least comfortable with so I'm a little unsure here.

    My thought process so far was to open up the resistor R and calculate the Thevenin voltage and resistance.

    I tried out the voltage first since it's usually the hardest and started off by combining the two resistors to the right because from my understanding (not 100% sure here) they're in parallel.

    I'm unsure of how to treat the two remaining resistors though because of the mysterious current source in the middle between them. Since it's pushing current upwards, would it be okay to consider the two resistors in series?

    Attached Files:

    • ee.png
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    Last edited: Sep 18, 2014
  2. jcsd
  3. Sep 18, 2014 #2

    Simon Bridge

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    Which two? The 6Ohm and 30Ohm? Actually it doesn't matter - none of them are in parallel.

    You should be able to just apply kirkoffs laws directly without worrying about combining resistors.

    I'd be tempted to find the equivalent voltage-source circuit for the current source and the 30Ohm resistor - or just look for the thevinin equivalent circuit for everything left of R.
  4. Sep 18, 2014 #3


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    The current of the current source is needed, it must have been given.

  5. Sep 18, 2014 #4
    My goal in combining resistors was to try to get a value for current somewhere and see where that would take me since I don't really see how I can apply KVL without any value for current.

    As for the value of the current source, what's shown on the picture is all I know...
  6. Sep 18, 2014 #5

    Simon Bridge

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    Then you should probably go complain: there is not enough information.
  7. Sep 18, 2014 #6


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    The problem can be solved symbolically in terms of the unknown current.
  8. Sep 18, 2014 #7

    Simon Bridge

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    Sure, you can find an expression for VR but not the value of it.
    Which is a point - do we have the actual problem statement?
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