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Circuit Theory - Basic

  1. Sep 7, 2006 #1
    Hey,

    I'm having a bit of difficulty with this specific circuit theory problem... We understand the basics, Ohm's law, Kirchoff's voltage and current laws, voltage and current division... I'm just confused about what to do with this problem:

    Find the value of Vx in the circuit below such that the power supplied by the 5-A source is 60W.

    [​IMG]

    I mean, I figure I'd start with the 5A current source... P=IV, so the potential over that current source would be 12v? I don't know, I'm really confused. The shape of this thing has me confused as well, what's in parallel with what and what's in series?

    I'm completely stumped. Any pointers on how to go about this problem?
     
    Last edited: Sep 7, 2006
  2. jcsd
  3. Sep 7, 2006 #2
    You didn't mentioned superposition, so I'll assume that it is part of the course too.

    You could try to use superposition (of the 4 sources) to work out to the 12V across the 5A source. From there, it should be possible to know what value Vx is.
     
  4. Sep 7, 2006 #3
    haven't been introduced to superposition yet...
     
  5. Sep 8, 2006 #4
    In which case, is it possible that you learn about the method and apply it on the problem? Here is a good place to start:
    http://www.allaboutcircuits.com/vol_1/chpt_10/6.html

    You could, of course, use something in the like of KVL or KCL to solve the problem, but I don't think it will be any easier than superposition.
     
  6. Sep 8, 2006 #5
    we haven't learned superposition yet, this is an exercise to teach us how to use KCL KVL current division, voltage division and ohm's law to find values

    i just don't know how to start this problem using KCL KCL current division, voltage division and ohm's law... not superposition... i'm confused with where to start
     
  7. Sep 8, 2006 #6
    If the picture is confusing you, begin by redrawing it with all of the shorts gone, so the element ends touch each other and there are no straight segments of wire connecting nodes.

    If you do that you should get a triangle at the bottom because everything at the bottom is touching so you can pinch that together to one node. Then since you have a voltage source on the left and you figued out V through the 5 amp source, you can use KVL to find the voltage drop across the 4Ohm resistor. Now you should know the voltage and current for every element below the 3A current source, and I won't spoil the rest for you but do similarly to the remaining pieces and you should be able to find Vx easily.
     
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