Simple Op-Amp question

Discussion in 'Homework Help' started by aashish, Mar 17, 2010.

  1. aashish

    Thread Starter New Member

    Feb 17, 2010
    13
    0
    I want to solve the following problem,
    Q. Assuming the op-amp to be ideal, what is the voltage gain of the amp. Shown below ?
    [​IMG]
    My soln. The pot. at inv. terminal = pot. at noninv. terminal = 0 (due to the virtual ground conditian)
    Then KCL at the node a gives,
    (V1-0)/R1 = (0-Vo)/R2 (as the op-amp is ideal no current will flow inside it)
    So, Vo/V1 = voltage gain = –(R2 / R1)
    But the correct ans. is –(R2 || R3) / R1 (I found this in more than five books but none have it solved)
    Please help me and please show me the step by step solution.
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    It is very strange because voltage gain don't depends on the load resistance.
    So correct answer is Vo/V1 = voltage gain = –(R2 / R1).
    Can you give as the names of this books with the wrong answer, because it is very interesting. [​IMG]Wyświetl tekst transliterowany na alfabet łaciński
     
  3. Bychon

    Member

    Mar 12, 2010
    469
    41
    Jony130 is right. Gain is -R2/R1
    R3 is not in the feedback loop.
     
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