Question

While performing an experiment to determine the gain for an ideal operational amplifier having finite gain, a student mistakenly used the equation 1 + R2/R1 where R2 is the feedback resistance. What is the percentage error in his result? Given A is the finite voltage gain of the ideal amplifier used.

(a) (R2/R1)/(A+ R2/R1) X 100%

(b) (1+R2/R1)/(A+R2/R1) X 100%

(c) (1+R2/R1)/(A+1+R2/R1) X 100%

(d) (R2/R1)/(A+1+R2/R1) X 100%

This question was addressed to me in an interview.

This intriguing question originated from The Non Inverting Configuration in division Operational Amplifiers of Electronic Devices & Circuits

Answer 1

Right option is (c) (1+R2/R1)/(A+1+R2/R1) X 100%

Easiest explanation: The correct formula is (1+R2/R1)/(1+((1+R2/R1)/A)).