GATE 2024 IN – Question 51
In the circuit shown, $R=4.5$ kΩ, $\Delta R=1.5$ kΩ, and the instrumentation amplifier INA is ideal. The equivalent resistance between A and B is ______ kΩ (nearest integer).
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Correct answer: 4 to 4
Explanation
Suppress the ideal excitation voltage source to find equivalent resistance. Each midpoint then sees $(R+\Delta R)\parallel(R-\Delta R)=6\parallel3=2$ kΩ to the common source node. The ideal INA draws no current, so the two midpoint resistances add: $R_{AB}=2+2=\boxed4$ kΩ.