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Homework Help: Superposition and Circuits

  1. Mar 1, 2009 #1
    1. The problem statement, all variables and given/known data

    hello Everyone, I've attached the Circuit to this post. We are suppose to solve it using superposition. we are suppose to find the current through the 9 ohm resistor.

    2. Relevant equations

    Some relevant equations I thought were the basic ones to solve circuits, for example: Ohm's law, which stats V=IR

    3. The attempt at a solution

    The thing that is throwing me off with this particular question is that there is a circle thing that has 5A, with an arrow going up. I have NO idea what that arow means, I even googled. The way I thought we would solve this would be to find the Rseries, so would I just add up all the resistances to find that? i.e would I add 4+6=10, then i'd do 1/10 +1/9 (because they are parallel) and then inverse it to equal 4.74, which we would then add to 3, and then do 1/7.74+1/20 (because they are parallel) to obtain 5.58 as a final resistance? I know that superposition means we have to answer the question from both sides. But i don't understand how we solve it from the side of the 5A.

    for the 10V part, do we just do V=IR and then do 10V= 5.58I so obtain I=1.79?

    thanks for the help!!!

    Attached Files:

  2. jcsd
  3. Mar 2, 2009 #2
    The "circle thing" is a constant current power supply and the arrow gives the direction of the current.
  4. Mar 2, 2009 #3
    ooh ok...so is my work correct then?
  5. Mar 4, 2009 #4
    By using current nodes and voltage loops, superposition is utilized. Finding the equivalent resistance of the circuit is not using superposition. Keep in mind the constant current source and constant voltage source when using node analysis and voltage loops.
  6. Mar 4, 2009 #5


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    Homework Helper

    There is a convenient way to solve this problem using Norton and/or Thevinin equivalents (a total of two), and then using superposition.

    BTW, that circle with the + and - and the arrow next to it is NOT the symbol that is typically used for an ideal current source. The ideal current source is typically a circle with an arrow inside, and the ideal voltage source is typically a circle with a + and -. However, the arrow next to the circle would suggest that this is supposed to be an ideal current source, OR that they have given you the resulting current but expect you to treat it as a voltage source - THERE IS A DIFFERENCE.
  7. Mar 4, 2009 #6
    wow thanks so much for your help. is it ok if i post my entire solution down? this person help me do it but i feel like it's such a complex way and there are wayy too many steps, could anyone possibly tell me if i could do this in a more simple way? i feel like 3 pages of work is too much for this problem :S
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