What is the best way of solving the circuit?

Discussion in 'Homework Help' started by pyler, Oct 9, 2012.

  1. pyler

    Thread Starter New Member

    Oct 9, 2012
    Nodal analysis
    Mesh analysis
    Source transformation thevenin equivalence
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    "Sudoku style". ;)

    Start by deducing the bits you can do, and that will give you more info on what the other bits are doing.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Mesh analysis, final answer.

    Make 4 current loops clockwise. I1 is where marked, then continuing around to the right then up for I2 (thru 24 ohm), I3 (thru 4 ohm) and I4 (thru 20 ohm).

    By inspection:

    I1 - I3 = 3A

    -I2*24 + (I3-I2)*15 = 100V

    I3 - I4 = 3*I1

    6*I1 + 24*I2 + 4*I3 + 20*I4 = 0

    That's 4 equations in 4 unknowns.
    justtrying likes this.
  4. WBahn


    Mar 31, 2012
    I'd say it's a toss up between mesh, node, and ad-hoc. I don't see any obvious source transformations.

    If you use nodal analysis, note that there are five nodes. You always get to declare on of them to be 0V. I'd pick the center node. Then you immediately have the bottom node since it is tied to the reference node via a voltage source. So now you only need three equations. Dealing with current sources is easy in nodal analysis, but in this case it is even easier to go ad-hoc noting that you can write equations for the left node in terms of i1 and the bottom node (and the resistor between them). So you only have to do node equations for the other two.
  5. mlog


    Feb 11, 2012
    Toss up. Good answer. That's what I thought too. Nothing is obviously simple, or is that simply obvious? Never mind. :D
  6. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    The first equation is incorrect; it should be:

    I4 - I1 = 3A
    ErnieM likes this.
  7. panic mode

    Senior Member

    Oct 10, 2011
    i would start by naming nodes and currents, rest is .... toss up
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011

    Here's how I was defining the loop currents and resistor voltages:


    The first equation is in error. The constant current source 3A is the combination of I1 and I4. I4 is in the direction of the source, while I1 is in opposite direction. Thus the correct equation should be:

    I4 - I1 = 3A

    As the Electrician correctly pointed out. While I trust he checked the other equations as thoroughly, it's not *my* assignment, and the ultimate answers calculated should be verified. :D
  9. panic mode

    Senior Member

    Oct 10, 2011
    totally agreed :D