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Homework Help: Basic circuits and ohm's law

  1. Sep 27, 2014 #1
    1. The problem statement, all variables and given/known data
    Determine the power absorbed by the 15 ohms resistor, see circuit below.(the ix, i1, and i2 are things i added)
    http://puu.sh/bQyEk/5f47888b03.png [Broken]

    2. Relevant equations

    the KCL law
    the KVL law
    the ohm's law
    power = voltage * current

    3. The attempt at a solution
    I calculated the whole resistance of the second branch first. then I found the relationship between current ix and current i since the voltage of a loop = zero. I then calculated the current using the KCL current law. i then found a relationship between current i1 and current i2. I calculated current i2 and used the power = resistance * current * current.
    My answer is way off from the answer key, and I would like to know what I did wrong??

    http://puu.sh/bQyK1/715544a6a1.png [Broken]
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Sep 27, 2014 #2
    Your approach looks good. It looks like you miscalculated ix = 36/51*(.425).
  4. Sep 27, 2014 #3
    ops!! that was a minor mistake on my part, but the answer is still not right with the answer key......
    here is the answer key
    http://puu.sh/bQDw6/e03756b3b0.jpg [Broken]
    Last edited by a moderator: May 7, 2017
  5. Sep 27, 2014 #4
    The answer key is wrong. It comes up with v = -19 when solving for -2 - 2*v/6 = v/8.5 + v/6 + v/6, which is clearly incorrect (I calculate v = -2.55).
  6. Sep 27, 2014 #5
    OH!!! thank you so much for clearing this up for me. aw, never thought the answer key would be wrong. I guess I should believe in my methods more often. thank you again.
  7. Sep 27, 2014 #6
    You're welcome! It's always unnerving when the answer key is wrong, but it's nice when you can spot the mistake so you know for sure.
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