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GATE 2025 IN – Question 20

Analog Electronics · Operational amplifiers and applications · 1 mark · Multiple choice

For the ideal-opamp circuit shown, the ratio $V/I$ is

Diagram for GATE 2025 IN question 20
  1. $R_1\frac{R_3+R_4}{R_1+R_3}$
  2. $R_3\frac{R_2+R_4}{R_1+R_3}$
  3. $R_1+R_3$
  4. $R_3+R_4$

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Correct answer: (A) $R_1\frac{R_3+R_4}{R_1+R_3}$

Explanation

The noninverting input is $V_+=VR_4/(R_3+R_4)$.

Ideal negative feedback gives $V_-=V_+$, and both input currents are zero.

The source current is $I=(V-V_-)/R_1+(V-V_+)/R_3=V(R_1+R_3)/[R_1(R_3+R_4)]$.

Hence $V/I=R_1(R_3+R_4)/(R_1+R_3)$, **A**.