What instrument is commonly used to measure pressures or forces in boilers?

• A. Strain gauge
• B. Thermocouple
• C. Manometer
• D. Flow meter

Answer: (C)

The main idea here is directly measuring pressure, which is a force per unit area inside boiler systems. A manometer works by balancing the pressure you want to measure against a known reference pressure using a liquid column. The height difference of the liquid translates to a pressure value via ρgh, so it provides a direct readout of pressure or pressure differences. This makes it the appropriate instrument for gauges of pressure or force-related measurements in boilers. The other tools measure different things: a strain gauge detects deformation from force but not pressure itself, a thermocouple measures temperature, and a flow meter measures flow rate.