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Homework Help: Mesh Current Analysis

  1. Feb 18, 2014 #1
    1. The problem statement, all variables and given/known data

    I need to find the Current through short circuit wire (between a and b).

    2. Relevant equations

    All the resistor values are same, 100 Ohms
    V1 = 5V
    V2 = 10V

    3. The attempt at a solution

    Loop A
    ia*(R2+R4+R1) - ib*(R4) = 5

    Loop B
    10 + (ib-ia)*R4 + ib*R3 = 0
    ib*(R4+R3) - ib*R4 = -10

    After plugging in all the values,

    300ia - 100ib = 5
    -100ia + 200ib = -10

    ia= 0, ib= 0.05 Amps

    Current through the circuit is same as ib because the current is not going to flow through R5.
    But the problem is I don't think it is possible for ia to be 0...

    Attached Files:

    • mesh.jpg
      File size:
      10.2 KB
  2. jcsd
  3. Feb 18, 2014 #2


    User Avatar

    Staff: Mentor

    That looks right.

    If V2 were much higher, say 60v, it would be forcing current into source V1, similar to charging a battery. So there is some point where V1 ceases to supply current, but before its current goes negative. This point occurs when V2=10v here.

    Yes, the current in the s/c is that current in R3.
  4. Feb 18, 2014 #3
    Thanks. But how does V1 stop supplying current?
  5. Feb 18, 2014 #4


    User Avatar

    Staff: Mentor

    When it finds itself connected to a voltage that's exactly equal to its own voltage. Current can flow neither IN nor OUT.
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