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Homework Help: Current and Voltage values using Ohm's Law

  1. Feb 1, 2010 #1
    1. The problem statement, all variables and given/known data
    In the circuit above given that Vg is 55 V, R1 is 3 Ohm, R2 is 12 Ohm and R3 is 90 Ohm. Using the polarity shown in figure answer the following questions.

    (A) Find the value of i3?
    (B) What is the value of i2?
    (C) What is the value of V3?
    (D) Calculate the power dissipated in R1?
    (E) Calculate the power delivered by the source Vg?

    2. Relevant equations
    Ohm's Law (I = V/R)
    Parallel Resistance Formula (R1 + R2*R3/R2+R3)

    3. The attempt at a solution
    I was able to configure the Parallel Resistance Formula correctly (I think) using the figure drawn with this problem. After that, I did the following:
    Total V = 55 V (Vg... Given)
    Total R = R1 + R2*R3/R2+R3 = 1083/102 = 10.62 Ohm (Formula Above)
    Initial I = V/R = 55/10.62 = 5.18 A (Or I1)

    then V=(I1)*(R1) across the first resistor to find V at the node = 15.54 V
    I2 = that V/R2
    I3 = I1-I2
    and V3 = I3R3

    And so forth. My I2, however, is not showing up as the right answer. I feel like I am either missing a step, or did not setup the resistance formula correctly. Help?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 1, 2010 #2


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    Homework Helper

    Welcome to PF!

    Hi Kas0988! Welcome to PF! :smile:

    (try using the X2 tag just above the Reply box :wink:)
    erm :redface:

    you've added the 3 in the wrong place! :cry:
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