2.12 (a) Show that if the op amp in the circuit of Fig. 2.12 has a finite open-loop gain A, then the closed-loop gain is given by Eq. (2.11). (b) For R1 = 1 kΩ and R2 = 9 kΩ find the percentage deviation ϵ of the closed-loop gain from the ideal value of (1 + R2/R1) for the cases A = 103, 104, and 105. For vI = 1 V, find in each case the voltage between the two input terminals of the op amp.
ϵ = −1%, −0.1%, −0.01%; v2 − v1 = 9.9 mV, 1 mV, 0.1 mV