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Maximum Power Transfer Question

Discussion in 'General Electronics' started by Mrs. Kerchief, Nov 15, 2003.

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  1. I've posted theorem-related questions on this newsgroup that are
    honest (ungraded homework problems) and don't plan to dishonor a
    take-home examination that deals with all the theorems.

    But a question on an examination regarding maximum power transfer,
    which I answered, or attempted to answer, by thevenizing the circuit
    gave a Rth with a decimal. I doubt its accuracy for that reason.
    Barring the fact that this *is* a "make-believe" classroom question
    employing Thevinin's Theorem, am I wrong in being concerned that my
    Rth has a value with a decimal? (Don't answer if you think I'm wrong
    for asking this or feel free to tell me I shouldn't be asking.)

    Second, our instructor asked for the Efficiency of the circuit once we
    found the value of the load. I assume, because he and the textbook
    claim it, that the value of the load must equal Rth. He also asked
    for the Power of the load; and, using P(out)/P(in), I arrived at an
    infinitesmal difference. I employed the equations he did for
    computing Efficiency--i.e., Pout/Pin, or (according to him) I^2 x
    R(load)/Eth x I.

    Since this is a maximum power transfer question, am I wrong in
    assuming the proportion of the value of the numerator to the
    denominator *must* be 2:1 to arrive at an efficiency rating of 50%?

    Thanks in advance for any responses and apologies if I stated any of
    this in an uninformed or crude way.
  2. Value of resistance can come in decimal, so don't worry about it.
    Its ok. You will get 50% efficiency after calculation.
    Ratio should be 1:2 to get efficiency of 50%.
    Animesh Maurya
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