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Homework Help: Ok how do they got this ?

  1. Jun 14, 2013 #1
    1. The problem statement, all variables and given/known data
    I am following book and they got this equation but i dont know how they got it ??

    2. Relevant equations

    3. The attempt at a solution
    I know they use kirchoff's voltage law but at which point they are choosing and how they are going and acquire this equation.?
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jun 15, 2013 #2

    Simon Bridge

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    You don't apply the voltage law at a point - you apply it to a loop.
    They tell you which loop they applied it to - the one containing R4 and R3.

    Redraw the circuit diagram so the loop containing R4 and R3 looks like a loop and do the mesh analysis - don't forget to appropriately model the op-amp.
  4. Jun 15, 2013 #3
    Hint: Remember that all ground symbols are connected to each other.
  5. Jun 17, 2013 #4


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    I find it helps by writing a KVL sum so it adds to zero. Then rearrage it. Don't start by writing "Vo = "

    eg start with an equation of the form...

    (v1) + (v2) + (v3).... = 0

    Remembering that v1,v2, or v3... might be negative depending on which direction is defined as positive current.
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