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The Output voltage for the circuit shown below is: Input voltage 
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+ 1 when S open, 1 + R2 when S closed R1 -
R4 – R2 when S open, + 1 when S closed R3 R1 -
– 1 when S open, 1 + R3 when S closed R4 -
+ 1 when S open, –R2 when S closed R1
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Correct Option: D
When switch S is open. Circuit becomes
i2 = 0 becomes op-amp draws negligible current.
Vd = 0, since VA = VB = Vi
| i1 = | = 0 (Vi = VA) | |
| R1 |
| At node A, i1 = | = 0 or | = 1 | ||
| R1 + R2 | Vi |
When S is closed, it functions as inverting amplifier
| with gain = – | ||
| R1 |
Hence alternative (D) is the correct choice.
