1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar
    Homework Helper
    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook