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Homework Help: Current in multi-loop circuit

  1. May 13, 2007 #1
    1. the problem
    In Figure 27-69 (see attached), the ideal each resistance is 4.50 and V1 = 11.0 V.


    (a) What is the size and direction of current i1? (Take upward to be positive.)
    (No Response)[-2.44] A
    (b) What is the size and direction of current i2? (Take upward to be positive.)
    (No Response)[-1.33] A
    (c) At what rate is energy being transferred at the 4.00 V battery and is the battery supplying or absorbing energy?
    (No Response)[5.33] W (No Response)[ supplying ]
    (d) At what rate is energy being transferred at the 11.0 V battery and is the battery supplying or absorbing energy?
    (No Response)[41.6] W (No Response)[ supplying ]


    Attempted Solution

    Help needed with part b.

    for part a: we ignored the right hand part of the cirucuit, and just did the left-most loop. Then we summed the voltages and set them to zero, and got the correct answer.

    for part b: We looked at the two right loops and combined them by saying that there are two resistors in parallel which can be replaced by [tex]R_{eq}=\frac{1}{R}+\frac{1}{R})^{-1}[/tex]. Then we tried ignoring the left loop and summing the voltages in the middle loop (with the top right resistor replaced by R_eq) and setting everything equal to zero. That's the wrong answer.
    Frankly, I don't understand why [tex]i_2\neq i_1[/tex].
    And the bloody final is tomorrow:cry:
     

    Attached Files:

  2. jcsd
  3. May 13, 2007 #2
    Here's a better diagram, I think, which hopefully will be approved a little more quickly. :wink:

    In the new diagram, the two resistors being combined are R3 and R4.
     

    Attached Files:

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