# Constant Volume Gas Thermometer - Absolute Zero

## Purpose

To determine the value of absolute zero.

## Equipment

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

## Suggestions

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.

5 min.

## Description

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

## References

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