 # Comprehension questions

## Andrews Experiment

1.  Sketch Andrew’s isothermal graph of pressure against volume for a real gas.

2.  Sketch Andrew’s isothermal graph of pV against p for a real gas

2.  Explain the term “isotherm”

3.  Describe and explain the shape of a high temperature isotherm on Andrew’s p vs v graph.

4.  An A-level text book suggests this information about carbon dioxide  – “it is virtually impossible to liquefy carbon dioxide by pressure alone if the temperature of the gas is above about 31oC” – explain the significance of this statement with reference to your sketch graph.

5.  Explain the terms “critical temperature”, “critical pressure” and “critical isotherm”.

6.  Annotate sketch graph 1 with the main features for Andrew’s isothermals for p against V for a real gas. (if you haven’t already)

7.  Explain the term “Boyle temperature”.  Explain the main feature of real gas behaviour with reference to pV against p curves for an Andrew’s isothermal that is above the Boyle temperature.

8.  Use the kinetic theory model to help describe and explain the main feature of the sketch graph in question 2 for an isothermal that is below the Boyle Temperature.

## Towards Absolute Zero

1.  Define absolute zero

2.  Explain how evaporation causes cooling.

3.  Explain how a refrigerator works – in principle

4.  What is the lowest temperature possible in a refrigerator determined by?

5.  Define adiabatic expansion – explain how it can cause cooling.

6.  Describe the Joule-Kelvin effect.  Draw a diagram of the apparatus to illustrate your answer.

7.  Sketch a graph of the results of a Joule-Kelvin investigation – and use this graph to describe the required conditions before the Joule-Kelvin effect can be used to cause cooling.  Explain the significance of the “inversion temperature”.

8.  Describe a practical arrangement that makes use of the Joule-Kelvin effect to liquefy hydrogen.  Explain the importance of the “countercurrent heat exchanger” and explain why Hydrogen needs to be pre-cooled.

## Superfluids and superconductors

1.  Below 2.17K Helium exhibits “superfluid behaviour”  describe some examples of this.

2.  Sketch a suitable graph to illustrate the lambda point of Helium.  Explain the significance of the lambda point.

3.  Sketch a graph to illustrate the variation of resistivity with temperature for a superconductor.

4.  Give examples of Metals, alloys and compounds as superconductors, and explain the terms critical temperature and current density for a superconductor.

5.  Describe the term “high temperature superconductor” and suggest possible applications.