# 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 ?

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)

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2. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,513
1,272
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. 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.