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Homework Help: An omp amplifier example

  1. Mar 16, 2012 #1
    i came across an example in my text book as shown :

    http://img593.imageshack.us/img593/8444/img1314i.jpg [Broken]

    if we used KCL and In = 0 :

    In = I_100 + I_25

    => I_25 = -I_100

    but as being written in the answer , I_25 = I_100 !

    could anyone explain it for me ? thanks
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Mar 16, 2012 #2
    No current flows into or out of the + or - inputs of an ideal op amp.
    Hope this helps
  4. Mar 16, 2012 #3
    Wouldn't the technical answer be [itex]i_{25}=-i_{100}[/itex] since the direction in the diagram is opposite to the actual direction? My textbooks take into account the assumed direction, and if the final answer is supposed to be opposite to the assumed direction, you merely place a minus sign in front of it to indicate that it is in the opposite direction to the supposed direction.
  5. Mar 16, 2012 #4
    Completely agree with Sandy Bridge
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