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Homework Help: Defining current in a circuit

  1. Nov 30, 2008 #1
    1. The problem statement, all variables and given/known data

    I just had a general question for solving for an unknown current(s) in single or multi-loops circuits. How exactly do we know how many arbitrary currents we need to define for solving the for the currents in the circuit? do we define a current for each loop that is present? for each voltage source? this always confuses me when i'm solving problems like these. any help is appreciated.

  2. jcsd
  3. Nov 30, 2008 #2

    Doc Al

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    Staff: Mentor

    You won't go wrong if you first assign each branch its own current. Those currents are not all independent, as they are related by Kirchhoff's law.
  4. Nov 30, 2008 #3
    Al is right. Concentrate not on how many currents you worry about, but rather the fact that every circuit analysis problem you get is based on:
    (a) V=IR for various components
    (b) Kirchoff 1: the total voltage is equal to the sum of the voltages of each component in sequence. (V_T = V_1 + V_2 + ... + V_n)
    (c) Kirchoff 2: the total current entering a junction is precisely equal to the total current exiting a junction. (I_in =I_out)

    Then brace for epic win on your next circuits problem:grin:
  5. Dec 1, 2008 #4


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    Homework Helper

    Or maybe (a) V=IZ, depending on your level.
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