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GATE 2014 EC (EC1) – Question 48

Analog Circuits · Op-amp Circuits · 2 marks · Multiple choice

The op-amp in the circuit has finite input impedance, infinite voltage gain and zero input offset voltage. Find Vout.

Diagram for GATE 2014 EC (EC1) question 48
  1. $-I_2(R_1+R_2)$
  2. $I_2R_2$
  3. $I_1R_2$
  4. $-I_1(R_1+R_2)$

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Show answer and explanation

Correct answer: (C) $I_1R_2$

Explanation

Infinite gain and zero offset under negative feedback make the inverting node equal to the grounded non-inverting node,0V. Thus no current flows through R1. The current I1 entering the inverting input must be supplied through R2 from the output, so Vout/R2=I1. Hence **Vout=I1R2,C**. Finite input impedance prevents assuming I1=0.