(easy) Mesh analysis problem on mit ocw

Discussion in 'Homework Help' started by inkyvoyd, Nov 15, 2012.

  1. inkyvoyd

    Thread Starter New Member

    Dec 6, 2011
    25
    0
    Hi, I am trying to learn as much as I can about DC circuits for an upcoming Science Olympiad competition about circuits - I found out about node analysis, but I also started learning about mesh analysis. I did a quick google search and came up with some nice practice problems, and did the first few ones, but had a little trouble with a specific problem.

    http://ocw.mit.edu/courses/electric...pring-2006/lecture-notes/nodal_mesh_methd.pdf

    I'm curious about the setup of the equations of the first problem on page 17.
    my equations are
    6i_a+4(i_a-i_b)=12
    2(i_b-i_c)+4(i_b-i_a)=6
    2(i_c-i_b)+2i_c=2
    which simplifies down to

    10i_a-4i_b=12
    -2i_a+6i_b-2i_c=6
    -2i_b+4i_c=2
    The only problem is that this gives incorrect answers.
    (i_a=44/21, i_b=47/21, and i_c=34/21)
    Note - i_1=i_a,i_3=i_b,i_5=i_c

    Thanks in advance!
     
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
    326
    You've got a sign error in your second equation. It should be:

    2(i_b-i_c)+4(i_b-i_a)=-6

    Also, the second equation in the second group of equations should be:

    -4i_a+6i_b-2i_c=-6
     
    inkyvoyd likes this.
  3. inkyvoyd

    Thread Starter New Member

    Dec 6, 2011
    25
    0
    That. Is so helpful - thank you very much :D
     
Loading...