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Homework Help: Basic Electric Circuit Analysis

  1. Apr 23, 2014 #1
    1. The problem statement, all variables and given/known data

    From this circuit diagram assume Vs and R1 through R2 are known.
    Find the following:
    a) How many unknown currents are there?
    b) How many independent equations can be written using KCL?
    c) How many independent equations can be derived from KVL equations?

    2. Relevant equations
    KCL: Current in - Current out = 0
    KVL: Voltage drop around loop should be zero
    Ohm's Law: V = iR

    3. The attempt at a solution

    This problem should not be that difficult but the part that is tripping me up is the middle wire with no resistance in it. Am I correct in assuming that no current will be flowing through it? If so these are the answers I got.

    a) 3 unknown currents
    b) 1 KCL equation
    c) 2 KVL equation

    I got (a) from just drawing currents on diagram.

    I got (b) from node-voltage which says:
    # of KCL eqns = (essential nodes - 1)

    Lastly, (c) from mesh-current which says:
    # of KVL eqns = branches - (nodes - 1)
  2. jcsd
  3. Apr 23, 2014 #2


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    Science Advisor

    Why do you think the currents through R2 and R3 are equal?
  4. Apr 23, 2014 #3


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    Science Advisor
    Homework Helper

    You can draw the circuit diagram without that piece of wire. Just join the ends of R2 R3 R6 and R7 together.

    If you solve that circuit to find the currents in those four resistors, count the number of essential nodes, etc, you can answer your own question.
  5. Apr 23, 2014 #4


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    Staff: Mentor

    Unless, of course, that wire happens to represent an actual wire in a physical actualization of the circuit. In which case you could think of it as a resistor with value ~0 Ohms for purposes of analyzing the circuit.
  6. Apr 23, 2014 #5
    Thank you! I can solve it from there
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