1. 1
   A technician has a 0.20 kg block of solid wax at room temperature. She places the wax in a beaker and heats it slowly and steadily using an electric heater, recording the temperature every 30 seconds until all the wax has melted and the liquid wax reaches 90 degrees Celsius. The heater supplies energy to the wax at a constant rate throughout.

   (a)

   Which row correctly describes the arrangement and movement of particles in a solid?

   [1 mark]

   • AParticles are close together in a fixed, regular pattern and only vibrate about fixed positions
   • BParticles are close together but randomly arranged and move freely past each other
   • CParticles are far apart, randomly arranged and move rapidly in all directions
   • DParticles are close together in a fixed pattern and move freely past each other

   (b)

   As the technician heats the solid wax towards its melting point, the temperature of the wax rises steadily. Which statement explains what is happening to the energy supplied by the heater during this stage?

   [1 mark]

   • AThe energy breaks the bonds between wax particles without changing their kinetic energy
   • BThe energy increases the kinetic energy of the wax particles, raising the temperature
   • CThe energy is used entirely to change the state of the wax from solid to liquid
   • DThe energy reduces the potential energy stored between the wax particles

   (c)

   The wax has a specific heat capacity of 2500 J/(kg degC) while it is liquid. Once the wax has fully melted, the technician continues heating the liquid wax from 65 degrees Celsius to 90 degrees Celsius. Calculate the thermal energy transferred to the liquid wax during this temperature rise.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student is investigating the densities of different metal samples as part of a core practical. She measures the mass of a small cube of aluminium on a digital balance and finds its dimensions using a ruler to calculate its volume. She repeats the process with a cube of copper of the same dimensions, which has a much greater mass than the aluminium cube.

   (a)

   A cube of aluminium has a mass of 54 g and a volume of 20 cm cubed. Which value, in kg/m cubed, is closest to the density of this aluminium cube?

   [1 mark]

   • A270 kg/m cubed
   • B0.37 kg/m cubed
   • C2700 kg/m cubed
   • D27000 kg/m cubed

   (b)

   The copper cube has the same volume as the aluminium cube but a much greater mass. Which statement correctly explains why copper has a higher density than aluminium, in terms of particles?

   [1 mark]

   • ACopper atoms are held together by stronger gravitational forces than aluminium atoms
   • BCopper atoms move faster than aluminium atoms, which pushes more mass into the same space
   • CCopper is a liquid at room temperature so its particles pack more tightly than solid aluminium
   • DCopper atoms have a greater mass and are packed at least as closely together as aluminium atoms, so more mass fits into the same volume

   (c)

   The copper cube has a mass of 178.2 g and the same volume as the aluminium cube, 20 cm cubed. Calculate the density of the copper cube in kg/m cubed, giving your answer to an appropriate number of significant figures.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A group of students set up an experiment to investigate how the temperature of a sample of ice changes as it is heated continuously and steadily from -10 degrees Celsius, using an electric immersion heater of known power placed in an insulated container, until it turns into steam at 100 degrees Celsius. They record temperature against time throughout the experiment.

   (a)

   Describe, in terms of the movement and arrangement of particles, what happens to a sample of solid ice as it is heated steadily until it becomes liquid water and then continues to be heated until it evaporates completely into steam.

   [3 marks]

   (b)

   The students notice that while the ice is melting at 0 degrees Celsius, the temperature stays constant for several minutes even though the heater continues to supply energy at a constant rate. Explain why the temperature does not rise during this time, and explain why the specific latent heat of fusion is defined using the amount of energy needed per kilogram of substance rather than a fixed total amount of energy.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A homeowner is comparing two types of loft insulation for reducing energy loss from a house during winter. Insulation X is a thick layer of mineral wool that traps pockets of air within its fibres. Insulation Y is a thin reflective foil sheet.

   (a)

   The homeowner wants to understand, in terms of particles and energy transfer, why adding loft insulation reduces the rate of unwanted thermal energy transfer from the house to the surroundings, and how the two named types of insulation each achieve this. Evaluate which type of insulation is likely to be more effective at reducing energy transfer by conduction through the loft space, and justify your answer using ideas about particles.

   [6 marks]

   (b)

   The homeowner also wants to reduce unwanted energy transfer through the walls of the house, which are made of solid brick. A builder suggests adding a layer of expanded polystyrene foam board to the inside of the brick walls, and separately points out that filling any gap between an inner and outer wall with foam (cavity wall insulation) is also common practice. Explain, using ideas about particles and energy transfer, how a layer of foam insulation reduces the rate of thermal energy transfer through a wall, and discuss what would happen to the rate of energy transfer if the thickness of the foam layer were doubled, justifying your reasoning.

   [6 marks]

   Total for question 4: 12 marks

End of questions