The pressure in the dewer is increased by blowing into it via a tube. The bottle under pressure is then allowed to sit in order for the temperature to return to room temperature.

Experiment

The dewer is at room temperature but the pressure is greateer than atmospheric pressure.

1. Open the valve to let air out and when the manometer reads room pressure close the valve.
2. Record what you observe over the next few minutes.

The Model

Initially the gas is under pressure at room tempature. The variables are P1, T1 and V1.
NB T1 is room temeprature.
When the valve is opened the air escapes. There is an adiabatic expansion. When completed the variables are P2, T2 and V2.
NB T2 is lower than T1.
After a while the temparetare again rises to room temperature. The variables are now P2, T3 (=T1) and V3.

Theory

1. Going from P1 to P2 is an adiabatic expansion, therefore
   eqn(1) Using (eqn(2)) and substituting into the first equation it can be shown that
   eqn(3)
2. The ideal gas equation above can be used to describe the pressure change from P2 to P3. It can be shown that
   eqn(4) NB T1 = T3
   
3. Substituting equation 4 into equation 3 eqn(5) and when solved gives eqn(6)
4. Since then
   eqn(8)
5. Calculate gamma for the demonstration
   h1 =
   h2 =
   h3 =
   

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