1. 1
   A steel railway track is laid in sections during a cold winter. Engineers deliberately leave small gaps between consecutive sections of track.

   (a)

   Why do the engineers leave these gaps?

   [1 mark]

   • ATo allow the steel to expand in hot weather without buckling
   • BTo reduce the total mass of steel used
   • CTo allow the steel to contract further in cold weather
   • DTo make the track easier to transport in sections

   (b)

   On a very hot summer day, the gaps between the sections of steel track are observed to have become much smaller than they were in winter. Which explanation, in terms of particles, best accounts for this?

   [1 mark]

   • AThe increased temperature causes some of the steel to evaporate, reducing its length
   • BThe increased temperature makes the particles vibrate with greater amplitude, increasing the average separation between them
   • CThe increased temperature causes the particles themselves to become larger
   • DThe increased temperature reduces the number of particles in the steel

   (c)

   Explain, in terms of the arrangement and motion of particles in a solid, why the steel track becomes longer when its temperature rises.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A glass thermometer contains a thin column of liquid mercury in a narrow tube. As the temperature of the surroundings rises, the mercury column rises up the narrow tube.

   (a)

   Which statement correctly compares the thermal expansion of the mercury (a liquid) with the thermal expansion of the glass (a solid) for the same temperature rise?

   [1 mark]

   • ANeither the mercury nor the glass expands with temperature
   • BThe mercury expands considerably less than the glass
   • CThe mercury and the glass expand by exactly the same amount
   • DThe mercury expands considerably more than the glass

   (b)

   Why is the tube of the thermometer made narrow rather than wide?

   [1 mark]

   • ASo that the mercury cannot expand at all inside the tube
   • BSo that less mercury is required, making the thermometer cheaper to manufacture
   • CSo that a small expansion in the volume of the mercury produces a large, easily readable rise in the column
   • DSo that the glass expands more than the mercury

   (c)

   Explain, in terms of particles, why a liquid such as mercury generally expands more than a solid such as glass for the same rise in temperature.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A metal lid is stuck tightly on a glass jam jar. A cook runs hot water over the metal lid for a few seconds and finds that the lid then unscrews easily.

   (a)

   (a) Explain, in terms of particles, why running hot water over the lid makes it easier to remove.

   [3 marks]

   (b)

   Suggest what would happen if the cook instead poured the hot water over the whole sealed jar, including the glass, for a much longer time, and explain your reasoning.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hot air balloon is filled with air that is heated by a burner beneath the balloon envelope.

   (a)

   Explain fully, in terms of the kinetic particle model, why heating the air inside the balloon causes the balloon to rise, comparing the relative expansion of a gas with that of a solid or liquid for the same temperature rise, and explaining how this relates to the density of the air inside the balloon compared with the surrounding cooler air.

   [6 marks]

   (b)

   The pilot of the hot air balloon wants to descend gently. Explain fully, using the kinetic particle model and the relative expansion of gases, what the pilot should do to the air inside the balloon to make it descend, and explain the sequence of physical changes that would cause the balloon to lose height.

   [6 marks]

   Total for question 4: 12 marks

End of questions