• Compression and expansion of an ideal gas

Relevant Publications :
"Measurement of a Thermodynamic Constant", A. McAlexander, The Physics Teacher, April 1988, 235/6.
How should this be referenced properly?

• adiabatic and isothermal expansion

Equipment needed :

• glass bottle (dewer)
• hoses
• glass valve
• hydrometer
• manometer

• Set up the apparatus as shown in the diagram.

• There is a worksheet available for this demonstration so that students can participate interactively in the lecture room.
• There is a report done as part of a fourth year project. Not quite ready yet

How to use the demonstration :

• Perform the demonstration, following the steps below, covering what happens in a qualitative manner.
• Establish that the liquid level indicates pressure. Ask for predictions from the class for each step of the experiment. For example
  
  1. pump up ?
  2. open valve ?
  3. why do the levels change in the manometer after the valve closes ?
• Record the results as you go and say these results will be used later in the demonstration.
• When the experiment is finished, cover it in a quantitative manner.

• Open the valve so that the pressure and temperature reach equilibrium with the room.
• Close the valve and blow air into it via the water removing hose. The pressure and temperature will both increase.
• Wait for the temperature of the air to return to room temperature
• Open the valve so that the pressure in the dewer comes into equilibrium with the atmosphere (adiabatic expansion). Close again quickly.
• Wait and observe that the pressure will slowly increase as the temperature of the air in the dewer rises to the temperature of the room.

• Opening a champagne bottle.

• Examine adiabatic expansion separately
• Examine isothermal expansion separately
• standardise equipment
• outline different uses
• Need more comprehensive documentation
• Improve stop corks, etc
• Provide a permanent board/mount for the manometer

• There are some difficult steps that rely on good technique.
• Lecturers should test the experiment to see they can make it work
• Use in tutorials
• This experiment could also be used to demonstrate "Fog formation by expansion".
  Liquid is the bottom of the manometer. Pressure increases/decreases (?) by opening the valve and the vapour in the manometer turns to liquid. The aim is to try to saturate the air with water (don't use a water filter). The experiment could be done using warm water.