Maximum power transfer theorem???

Discussion in 'General Electronics Chat' started by dogar sahab, Sep 8, 2008.

  1. dogar sahab

    Thread Starter Active Member

    Mar 15, 2008
    116
    0
    I performed practical for finding maximum power transfer theorem on a simple circuit having one load reistance in series to another resistance!!!
    the practical was performed ok and it gave maximum power transfer when load resistance becomes equal to series resisatnce...
    but u all know the general curve of power transfer theorem and my readings also gave the perfect curve!!!
    but the problem is that my teacher says that
    THE CURVE FOR THE MAXIMUM POWER TRANSFER IS NOT SYMMETRICAL???
    i want to ask the reason as he has not told us!!!!
    so my humble Q is about the unsymmetry of the curve??
    any1 plz help me out as I ahve thought a lot but I am not getting the reason behind that!!!!??
     
  2. dogar sahab

    Thread Starter Active Member

    Mar 15, 2008
    116
    0
    this is the standard graph..and my graph is in close proximation with that!!!!
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    For a symmetrical graph, you must pick a number exactly halfway between zero and infinity. :)
     
  4. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    dogar sahab,

    Because the equations that determine the curve are not symetrical. The definition of symmetry of that the value of the equation is the same for each equal distance value from the line of symmetry. Since the equation for power transfer involves ascending square values of voltage and nonlinear increases in current, it is no wonder that the graph is not symetrical. It is symetrical, however, if you look at the output resistance in a relative way. For instance, 50 ohms is your center point. Doubling and halving the output resistance, 100 ohms and 25 ohms are the same. Quadrupling and quartering, 200 and 12.5 are the same, etc.

    By the way, many folks do not realize that you can output more power if you reduce the source impedance, if that is possible, instead of trying to match the output impedance to the source impedance. Even if you don't change the output impedance. In your example, if you changed the source impedance to 25 ohms and kept the load impedance at 50 ohms, you would output more power.

    Ratch
     
    Last edited: Sep 8, 2008
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