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!

Homework Help: Thevenin's theorem

  1. Apr 6, 2015 #1
    can you tell me please which solution is correct:


    We need to find the Vth and Rth. Rth is easily 4Ohms, but what about Vth???

    1st solution:
    Calculate Vth, by doing 10A=I1+I2 and 4V+2xI1=2xI2, where you find I1=6A and I2=4A, so Vth=12V

    2nd solution:
    Calcullate Vth, by transforming the voltage source into current source and then apply KCL, so Vth=8V

    which is the correct?

    Last edited: Apr 6, 2015
  2. jcsd
  3. Apr 6, 2015 #2


    User Avatar
    Gold Member

    Perhaps, in this case, it's good to apply the theorem thrice, in 3 easy steps... - that would help to choose the values of the resistors if you're doing a real practical circuit.
  4. Apr 6, 2015 #3


    User Avatar

    Staff: Mentor

    Hi sciman.

    In future be sure to use the homework template when you post a problem here in the homework sections! It's in the rules.

    I can see by the result that your first method is incorrect, but it is also incorrect because you haven't defined I1 and I2 so your equation doesn't mean anything!

    Your second approach is much better, but you need to be careful about the polarities of things. What direction will the net current be flowing through the combined resistance?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted