ITPEC FE Morning October 2022 Question 21
By using a sensor that detects changes in shape, the condition of infrastructure such as elevated highways can be monitored and maintained. Which of the following is a sensor that is used for this purpose?
Explanation
Strain gage — a sensor whose electrical resistance changes as the surface it is bonded to stretches or compresses, so it measures deformation directly.
A strain gage is a thin metal foil or wire pattern glued to a structure. When the structure deforms, the foil lengthens or shortens with it, and its resistance changes in proportion to the strain. A bridge circuit turns that small change into a voltage. Gages bonded to girders and piers of elevated highways or bridges reveal deformation from loads, fatigue or cracking over time, which is exactly "changes in shape".
Answer (c)
Why not others:
- •(a) Gyro — measures angular velocity (rotation), used for orientation in phones, drones and vehicle stability control; it does not sense a structure bending
- •(b) Hall element — outputs a voltage proportional to a magnetic field, used for position, rotation speed and current sensing
- •(d) Thermistor — a resistor whose resistance changes with temperature; it measures heat, not shape
Key rule: Match the sensor to the physical quantity: deformation → strain gage, rotation → gyro, magnetic field → Hall element, temperature → thermistor, acceleration → accelerometer.
Hardware · AI-written, may contain errors
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