Which of the following is measured with the help of barometer?

Asked in SSC JE 29-01-2018 (Evening Shift)

Detailed Explanation

Invented by Evangelista Torricelli in 1643, the mercury barometer is the classic instrument designed to measure local ambient atmospheric pressure.

1. Working principle of a barometer:

• A glass tube sealed at one end and filled with mercury is inverted into a mercury cistern.
• The mercury column drops until its downward weight balances the atmospheric pressure pushing on the cistern surface.
• The space above the mercury is a Torricellian vacuum.
• The height of the column directly indicates the atmospheric pressure: \(p_{\text{atm}} = \rho_{\text{Hg}} g h\).

2. Purpose of other instruments:

• Velocity: Measured by Pitot tube, current meter, or anemometer.
• Discharge intensity: Measured by flumes, notches, or weirs.
• Surface tension: Measured by stalagmometer, capillary tube, or du Noüy ring method.

Why “Pressure” Is Correct

The barometer is universally defined and employed as the standard meteorological and laboratory instrument for measuring ambient atmospheric pressure.

Why the Other Options Are Wrong

• A. Velocity: Fluid velocity is measured with a Pitot-static tube or current meter.
• B. Discharge intensity: Discharge intensity (flow per unit width, q = Q/b) is measured using weirs or flumes.
• D. Surface tension: Surface tension is measured using a capillary tube or stalagmometer.

Key Concepts for Students

• Torricelli invented the barometer in 1643 using a column of mercury.
• Mercury is chosen for its high density (compact 760 mm height) and extremely low vapor pressure.
• Aneroid barometers use an evacuated corrugated metallic capsule to measure atmospheric pressure without liquids.

Practice more: this is question 10 in Measurement of Pressure MCQs – Part 1. Try the whole set and check every answer instantly.