Constant Volume Gas Thermometer - Absolute Zero


To determine the value of absolute zero.


Metal bulb (toilet plunger) with pressure gauge, ice water, boiling water on hot plate.



For being so simple this experiment is remarkably accurate, and generally gives a result within about 10 degrees. This demonstration helps students feel more comfortable with temperature scales.

Setup Time

5 min.




    With a constant volume of air in the chamber, measure the pressure P(B) at the boiling point and the pressure P(F) at the freezing point of water. If the pressure P is read at some arbitrary temperature T, then that temperature in degrees celsius is: T=100 [P-P(F)] / [P(B)-P(F)] For an ideal gas, the pressure should go to zero at the temperature of absolute zero. Setting P=0, the value of absolute zero in degrees celcius can be calculated. Another way to do this is to plot a graph of temperature as a function of pressure. Draw the line through the two points,◙determined at boiling and freezi


    Meiners, Section 25-2, 753-754, (Physics Demonstration Experiments, Vol. 2).