PURPOSE: To determine the value of absolute zero.
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 freezing, and extend it so that it intersects the pressure axis, which is T=0 in celsius degrees.
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.
REFERENCES: (PIRA 4E30.20)
EQUIPMENT: Metal bulb (toilet plunger) with pressure gauge, ice water, boiling water on hot plate.
SETUP TIME: 5 min.
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