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Homework Help: Basic Ciruits , dependent sources

  1. Feb 7, 2013 #1
    1. The problem statement, all variables and given/known data

    https://www.diigo.com/item/image/2sb3i/1svo [Broken]

    Why don't we flip the signs of VA like this :

    https://www.diigo.com/item/image/2sb3i/g2a4 [Broken]

    because the current must flow from + to - of the resistor.

    2. Relevant equations

    3. The attempt at a solution
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Feb 7, 2013 #2


    User Avatar

    Staff: Mentor

    The "+ -" tags on the 15Ω resistor tell you which way to "measure" the potential VA; It's like specifying how to orient the positive and negative leads of a voltmeter on the component.

    You could change the tags as you suggest IF you also reverse the polarity of the controlled voltage source 2VA, since its output depends on how VA is "measured".
  4. Feb 7, 2013 #3
    and the KvL equation changes from :
    -120+V30+2VA-VA = 0

    to :
    -120+V30-2VA+VA = 0
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