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An operational amplifier as shown below has a poor open loop voltage gain of 45 but otherwise it is ideal. Find the closed loop gain of the amplifier.


41. An operational amplifier as shown below has a poor open loop voltage gain of 45 but otherwise it is ideal. Find the closed loop gain of the amplifier.


 
[Non-inverting op-amp configuration. Feedback resistor Rf = 20kฮฉ, ground-side resistor R1 = 5kฮฉ. Input voltage Vin at the non-inverting terminal.]
A. 5
B. -4
C. 4.5
D. 4
Answer: Option C
Solution: Non-inverting op-amp = 1+ 20/5 = 5
Open loop gain 45 (given)
closed loop gain = 5/(20+5) = 1/5
Closed-loop gain of the OPamp is 45/(1+(1/5).45) = 4.5
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