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GATE 2026 IN – Question 25

Sensors and Industrial Instrumentation · Resistive capacitive and inductive sensors · 1 mark · Multiple choice

Active strain gauges are connected in a half-bridge configuration to measure strain in a cantilever element. When powered by a voltage source of $10\ \mathrm V$, the voltage at the output of the bridge is $1\ \mathrm{mV}$. If the gauge factor is 2.5, the strain in the cantilever element is ________ microstrain.

  1. 40
  2. 80
  3. 20
  4. 160

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Correct answer: (B) 80

Explanation

For a half bridge with active gauges experiencing equal tensile and compressive strains, $V_o/V_{ex}\approx GF\,\varepsilon/2$.

Hence $\varepsilon=2V_o/(GF\,V_{ex})=2(0.001)/(2.5\times10)=8\times10^{-5}$. Multiplying by $10^6$ gives **80 microstrain (B)**.