1. 1
   A sealed rigid steel cylinder contains a fixed mass of nitrogen gas at room temperature. A heater wrapped around the cylinder is switched on and the gas inside is heated until its temperature has risen considerably, while the volume of the cylinder stays exactly the same throughout.

   (a)

   (a) Which statement correctly explains, in terms of particles, why the nitrogen gas exerts a pressure on the inside walls of the cylinder?

   [1 mark]

   • AGas particles are attracted to the walls of the cylinder and pull on them
   • BGas particles collide with the walls of the cylinder and exert a force on them
   • CGas particles are pushed towards the walls by gravity
   • DGas particles vibrate in fixed positions against the walls

   (b)

   (b) As the gas is heated at constant volume, what happens to the average speed of the gas particles?

   [1 mark]

   • AIt increases
   • BIt decreases
   • CIt stays the same
   • DIt increases then decreases back to its original value

   (c)

   (c) Explain, in terms of the motion of the gas particles, why the pressure inside the cylinder increases as the nitrogen gas is heated at constant volume.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student seals 60 cm³ of air inside a syringe at a pressure of 100 kPa and a constant room temperature. Keeping the temperature constant throughout, she slowly pushes the plunger in until the trapped air occupies a volume of 24 cm³.

   (a)

   (a) Which statement correctly describes what happens to the trapped air as its volume is reduced at constant temperature?

   [1 mark]

   • AThe air particles move further apart and collide with the syringe walls less often
   • BThe air particles move faster because they have gained kinetic energy
   • CThe air particles are squeezed into a smaller space and collide with the syringe walls more often
   • DThe number of air particles decreases as the volume decreases

   (b)

   (b) In which direction does the pressure of the trapped air act on the inner surface of the syringe?

   [1 mark]

   • AIn a single fixed direction determined by the plunger
   • BParallel to the surface, along its length
   • COnly downwards, due to gravity
   • DAt right angles (perpendicular) to the surface

   (c)

   (c) Calculate the new pressure of the trapped air once its volume has been reduced to 24 cm³, using $P_1 \times V_1 = P_2 \times V_2$.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A physics technician uses liquid nitrogen to cool a sample of gas in a sealed container from room temperature down towards absolute zero, monitoring the temperature on a Celsius thermometer throughout the experiment.

   (a)

   (a) Describe what is meant by the term "absolute zero", including its value in degrees Celsius and what it means for the motion of the gas particles.

   [3 marks]

   (b)

   (b) During the experiment, the technician records the sample's temperature falling from 27 °C to −73 °C. Convert both temperatures to kelvin, and calculate the fall in temperature in kelvin.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A cyclist uses a hand-operated pump to inflate a bicycle tyre. As she pumps the handle rapidly and repeatedly, she notices that the metal barrel of the pump becomes noticeably warm to the touch, even though no external heat source is applied to it.

   (a)

   (a) Explain, using ideas about particles and the work done on the gas, why the barrel of the pump becomes warm during pumping.

   [6 marks]

   (b)

   (b) The cyclist claims that if she pumped much more slowly, the barrel would not warm up as much, but the tyre would still reach the same final pressure either way. Evaluate this claim, using ideas about work done on a gas, particle motion and pressure.

   [6 marks]

   Total for question 4: 12 marks

End of questions