Measurement Of Air Pressure

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Measurement of air pressure and volume




Description of Apparatus Used2

Experimental method used7

Tabulated Data9






Objective: To measure pressure and volume of enclosed mass of air at constant temperature using manometers and to compare measurements with the equation of state for a perfect gas.


In this experimental report the techniques of measuring pressure and volume of certain mass of air which is encapsulated in a tube at constant temperature had been discussed and analyzed. The two instruments which are commonly used for the measurement of pressure and volume were being used to take the readings of pressure and volume and calculations were performed on the basis of experimental data using slopes of graphs as well as from theoretical formulas and the comparison of two was performed.

Description of Apparatus Used

Construction of U-tube Manometer:

This manometer consists of a U shaped tube in which the manometeric liquid is filled. The manometer is used to measure the pressure which is unknown by the balancing gravity force and acceleration due to gravity, g = 9.81 m/sec2.

The manometer consists of a steel, brass and aluminum material. It has a glass tube made up of pyralex glass. The graduations are made on the tube in terms of mm or in some condition it is graduated in kilo Pascal.

U- tube Manometer used in the experiment

Working of U-tube Manometer:

The unknown pressure is applied in the one arm of the tube and the mercury in the tube or manometeric liquid filled in the tube moves in the tube or rises to the constant region and then the movement is stopped. The height of the liquid is measured and noted. The pressure is calculated by using the formula,

  P1-P2 = Pmhg

The above equation is arrived by 

P1 = Pthg = P2+Pmhg

P1-P2 = hg(Pt - Pm)

P1 = applied pressure

P2 = 0

Pt = specific gravity of the liquid or water

g = acceleration due to gravity.

P1 - P2 is approximately equal to Pmhg.

Advantages of U-tube Manometer:

Simple in construction

Low cost

Very accurate and sensitive

It can be used to measure other process variables.

Disadvantages of U-tube Manometer:

Fragile in construction.

Very sensitive to temperature changes.

Error can happen while measuring the h.

Characteristics of liquid used in U-tube Manometer:

Viscosity should be low.

Low surface tension is required.

The liquid should stick on the walls.

Should not get vaporized.

Fortin Barometer


Barometric pressure, a measure of the force of air, is frequently used in forecasting the weather. It is usually measured with a Fortin barometer, in which mercury is enclosed in glass, and travels up and down a metal tube in response to air pressure changes. A scale helps to match the mercury levels with the barometric pressure at the time a reading is taken. The Fortin barometer is generally used in meteorological stations as well as in laboratories and schools. In 2007, the primary manufacturer of the barometer discontinued production as mercury can be harmful to the skin and generally toxic to humans.

Fortin Barometer used to measure pressure and temperature


A Fortin barometer typically has a screw that allows the mercury level to be ...
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