Barometer is used to measure ..........
Try it first: pick an option, then read the explanation.
Asked in SSC JE 2 MARCH 2017 Evening Shift
Detailed Explanation
The barometer is a dedicated meteorological and laboratory instrument whose sole primary function is the measurement of ambient atmospheric pressure.
1. Operating principle of mercury barometer:
The atmospheric pressure acting on the open cistern surface supports a vertical mercury column inside an evacuated glass tube:
\[ p_{\text{atm}} = \rho_{\text{Hg}} \cdot g \cdot h \]
2. Comparison of pressure measuring instruments:
- Barometer: Atmospheric pressure.
- Piezometer / Pressure Gauge: Pressure inside pipes and vessels.
- McLeod gauge / Pirani gauge: Very low pressures (high vacuum).
- Differential manometer: Difference of pressure between two points.
Why “atmospheric pressure” Is Correct
By definition and universal engineering practice, a barometer is used specifically to measure ambient atmospheric pressure.
Why the Other Options Are Wrong
- A. pressure in pipes, channels etc.: Pressure in pipes and channels is measured using piezometers, manometers, or Bourdon dial gauges.
- C. very low pressure: Very low pressures (high vacuum) are measured using McLeod gauges, Knudsen gauges, or Pirani gauges.
- D. difference of pressure between two points: Difference of pressure between two points is measured using differential manometers.
Key Point
A barometer measures ambient atmospheric pressure.
Key Concepts for Students
- Torricellian barometer uses mercury with a near-perfect vacuum above the column.
- Fortin's barometer includes an adjustable leather cistern base to set the zero datum accurately.
- Aneroid barometers use an evacuated corrugated metallic capsule to operate without liquids.
Practice more: this is question 26 in Measurement of Pressure MCQs – Part 2. Try the whole set and check every answer instantly.