1. 1
   A cook places a copper saucepan and a wooden spoon on the same hot stove. Within a minute the copper handle becomes uncomfortably hot to touch, while the wooden spoon handle remains cool.

   (a)

   Which property of copper best explains why it heats up quickly?

   [1 mark]

   • ACopper has many free (delocalised) electrons that can transfer thermal energy quickly through the metal
   • BCopper has a lower density than wood
   • CCopper reflects thermal radiation better than wood
   • DCopper is transparent to infrared radiation

   (b)

   What term describes materials, like wood, that transfer thermal energy poorly compared with metals?

   [1 mark]

   • AThermal conductors
   • BThermal insulators
   • CRadiators
   • DConvectors

   (c)

   Explain, in terms of particles, why the wooden spoon handle stays much cooler than the copper handle even though both are on the same hot stove.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A double-glazed window consists of two sheets of glass with a thin layer of trapped air between them.

   (a)

   Which statement correctly explains why the trapped air layer improves the thermal insulation of the window compared with a single sheet of glass?

   [1 mark]

   • AThe trapped air layer increases the free electron density of the glass
   • BAir conducts thermal energy better than glass, so it warms the room more quickly
   • CThe trapped air layer reflects all light away from the window
   • DAir is a poor conductor of thermal energy because its particles are far apart and collide with each other much less frequently than particles in a solid

   (b)

   Which of these materials would generally be the best thermal conductor, based on typical particle structure?

   [1 mark]

   • AA block of dry, unstirred wool
   • BA trapped, still layer of gas
   • CA solid metal, due to its free (delocalised) electrons
   • DA vacuum with no particles present

   (c)

   Explain, in terms of particles, why gases such as the trapped air between the panes of glass conduct thermal energy poorly compared with solids.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An engineer is designing an insulated container to keep hot drinks warm for several hours. She is choosing between a container wall made from a single thick sheet of solid aluminium and a container wall made from two thinner layers of plastic with a thin layer of trapped air sealed between them.

   (a)

   (a) Explain which of the two designs would keep the drink warmer for longer, and why, referring to the particle structures involved.

   [3 marks]

   (b)

   The engineer decides to add a thin layer of foam plastic containing many tiny trapped air pockets, instead of a single large air gap, between the two plastic layers. Explain why using foam with many small trapped air pockets might improve the insulation even further compared with one single larger air gap of the same total thickness.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A blacksmith heats one end of a long iron rod in a furnace while holding the other end with a gloved hand. After some time, the gloved end of the rod becomes noticeably warm, even though it was never placed in the furnace.

   (a)

   Explain fully, in terms of the two mechanisms of conduction in a metal (lattice vibration and free electron movement), how thermal energy is transferred along the length of the iron rod from the heated end to the gloved end, and explain why metals such as iron are generally much better thermal conductors than non-metallic solids.

   [6 marks]

   (b)

   The blacksmith then compares two rods of identical length and diameter, one made of iron and one made of glass, both heated at one end in the same furnace for the same length of time. Explain fully why the gloved end of the glass rod stays much cooler than the gloved end of the iron rod, and explain what this comparison shows about the relationship between a material's structure and its ability to conduct thermal energy.

   [6 marks]

   Total for question 4: 12 marks

End of questions