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Homework Help: Where did I go wrong while solving for R_L?

  1. Jul 5, 2011 #1
    Hi, :smile:

    I was finding the value R_L for which maximum power takes place. Maximum power takes place when R_L = R_Th. Please have a look on the following link; you can see my answer is different: http://img215.imageshack.us/img215/7743/imgtb.jpg

    Where did I go wrong?:confused: Please help me out. Many thanks.
  2. jcsd
  3. Jul 5, 2011 #2


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    Staff: Mentor

    Your loop 1 equation looks to be incorrect. I see -9I1 rather than -7I1.
  4. Jul 5, 2011 #3
    Thanks a lot, gneill. You are correct. I have made an error.

  5. Jul 6, 2011 #4
    Hi again, gneill

    Please help me!

    1: I have also used nodal analysis to solve the problem. Please have a look here: http://img838.imageshack.us/img838/1970/prob1x.jpg

    What is your answer to "Ref 1"? Is my answer correct?

    2: I have tried nortonized the circuit and tried to find I_N using I_sc. Please have a look here: http://img39.imageshack.us/img39/3187/prob2s.jpg

    My answer is not correct as you can see. The V_Th and R_th found previously in previous posts produce different value for I_N than the one found using I_sc. What did go wrong?

    Please help me out. Many, many thanks.

  6. Jul 6, 2011 #5


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    Staff: Mentor

    Looks good.
    After you substituted for I2 in the loop 1 equation, you went on to clear the 5 in the denominator by multiplying through by 5. Unfortunately, you overlooked multiplying the 9V on the RHS of the equation by 5 also.
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