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Op-Amp: Find Vout

  1. Oct 14, 2012 #1
    1. Please refer to attached image.



    2. The attempt at a solution.

    I noted that Vb was grounded and would therefore be equal to 0 and because one of the two op-amp rules states that Va = Vb, both will be equal to 0.

    I wrote an equation at node Va:

    [Va - Vin]/R1 + [Va - Vout]/R2 = 0

    Because Va is 0, the equation simply became:

    -Vin/R1 - Vout/R2 = 0

    And plugging in the given values for part (a), I acquired - 5V. I'm not sure if this is correct or not as the book does not have a solution manual available yet.
     

    Attached Files:

  2. jcsd
  3. Oct 14, 2012 #2

    lewando

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    Gold Member

    -5V is right. In this configuration, the circuit is an "inverter".
     
  4. Oct 14, 2012 #3
    Thanks! I was just wondering :)
     
  5. Oct 14, 2012 #4

    CWatters

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    Science Advisor
    Homework Helper

    Just for completeness....

    Take your equation...

    -Vin/R1 - Vout/R2 = 0

    then rearrange it to give..

    Vout/Vin = -R2/R1

    where Vout/Vin is known as the Gain.

    a) R2 = R1 so Gain = -1
    b) etc
     
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