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The Measurement of Expansion of Gases

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p- 264

2025-12-30

930

The Measurement of Expansion of Gases. The varying volume of the air in an air thermometer shows that a gas expands when heated, but it does not show the amount of the change in volume per degree. There are two conditions under which the effect of heat on a gas can be measured. If the gas is heated and the pressure kept constant, we can measure the change in its volume; and if the gas is heated and the volume kept constant, we can measure the change in its pressure. 

Measurements under both these conditions can be made by the use of an air thermometer such as is shown in Fig. 1.

In measurements under constant volume the mercury in the lefthand column is kept at a fixed height by raising or lowering the right-hand column, and in measurements under constant pressure the mercury level is kept at the same height in both columns by the same means.

As a result of such measurements, it is found that for each degree of change in the temperature of a gas under constant pressure there is a change in its volume equal to 1/273 of its volume at zero. Since this is true of all other gases as well as of air, we can write 1/273 or 0.003665 as the uniform coefficient of expansion of all gases.