Question

Choose the option that correctly pairs the given measurement devices with the quantities they measure. 
\[ \begin{array}{c c c c} \underline{S\ No} & \underline{\text{Measurement Device}} & \underline{S\ No} & \underline{\text{Measured Quantity}} \\ \text{I} & \text{Bourdon Gauge} & \text{A} & \text{Temperature} \\ \text{II} & \text{Orifice Plate meter} & \text{B} & \text{Concentration} \\ \text{III} & \text{Pyrometer} & \text{C} & \text{Pressure} \\ \text{IV} & \text{Colorimeter} & \text{D} & \text{Flow rate} \\ \text{V} & \text{Pirani Gauge} & \text{E} & \text{Liquid level} \\ \end{array} \]

• A. I-E II-C III-D IV-B V-A
• B. I-C II-D III-A IV-B V-C
• C. I-C II-D III-E IV-A V-D
• D. I-D II-C III-A IV-E V-C

Hint:

Many measurement devices can be identified by remembering the physical principle they are based on—mechanical deformation (pressure), optical absorption (concentration), radiation detection (temperature), and differential pressure (flow rate).

Answer 1

The Correct Option is B

To match the devices with the quantities they measure, we must understand how each instrument works and what physical principle it uses. This ensures that the pairing is based on scientific reasoning rather than memorization.
1. Bourdon Gauge (I):
A Bourdon gauge is a mechanical pressure-measuring device. It uses a curved metallic tube that tends to straighten when internal pressure increases. The movement of this tube is converted into a readable scale. Since its operation relies on mechanical deformation due to applied pressure, it clearly measures Pressure (C).
2. Orifice Plate Meter (II):
An orifice plate meter is used in fluid flow measurement. It works on the principle of differential pressure created when a fluid passes through a restriction (orifice). This pressure drop is directly related to the flow rate using Bernoulli's equation. Hence it measures Flow Rate (D) and not pressure, temperature, or concentration.
3. Pyrometer (III):
A pyrometer is a non-contact temperature-measuring instrument used especially for very high temperatures where thermocouples cannot be used. It detects thermal radiation emitted by a body and converts it into a temperature reading. Therefore, it measures Temperature (A).
4. Colorimeter (IV):
A colorimeter is an analytical device used in chemistry to measure the concentration of a solute by evaluating how much light of a specific wavelength is absorbed by the solution. Beer–Lambert law governs this measurement. Hence Colorimeter measures Concentration (B).
5. Pirani Gauge (V):
A Pirani gauge is used to measure very low pressures (vacuum levels). It operates by monitoring the rate of heat loss from a heated filament to the surrounding gas; heat loss changes with pressure. Therefore, a Pirani gauge measures Pressure (C), specifically low pressures.
Final Matching:
I–C, II–D, III–A, IV–B, V–C, which exactly corresponds to option (B).