1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Find voltage across resistor using mesh current analysis

  1. Mar 17, 2016 #1
    • Thread moved from the technical forums, so no Homework Help Template is shown
    tZmlcM7.jpg

    I'd like to find Vth by mesh current analysis.

    Mesh A and B share a current source, so they're treated as one supermesh.

    What's the equation for this supermesh? Also, do I ignore the loop with the open circuit? Since there's no current flowing there...

    2A = ib - ia

    Anyway, is this the right equation:

    +12V + ia(6Ω) + ib(6Ω + 4Ω) = 0?

    if yes, then my ia ends up being -32V/(4Ω) = - 8A

    ib = 2A + 8A = 10A

    And the Voltage across 4Ω (Vth) = ib * 4Ω = 40 V!

    But that's not correct, Vth should be 6V!
     
  2. jcsd
  3. Mar 17, 2016 #2

    NascentOxygen

    User Avatar

    Staff: Mentor

    With currents marked clockwise, the voltages across all resistors here sum clockwise as voltage falls, and you could pencil in a small + and - sign on each resistor as a reminder.

    So summing in a clockwise path the voltage rises around the loop:
    +12 - ia(6) - ib(6+4) = 0
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted