1. 1
   An astronaut on a spacewalk outside the International Space Station feels the warmth of the Sun even though there is a vacuum of empty space between the Sun and the spacecraft, containing almost no particles at all.

   (a)

   Which type of thermal energy transfer explains how this warmth reaches the astronaut?

   [1 mark]

   • AThermal (infrared) radiation
   • BConduction
   • CConvection
   • DEvaporation

   (b)

   Why is thermal radiation the only method of thermal energy transfer that can cross the vacuum of space between the Sun and the astronaut?

   [1 mark]

   • ABecause convection currents can form even without any particles present
   • BBecause thermal radiation travels more slowly than conduction
   • CBecause a vacuum specifically increases the rate of conduction
   • DBecause thermal radiation does not require a medium of particles to travel through

   (c)

   The astronaut's spacesuit has a shiny, silver-coloured outer surface. Explain, referring to surface colour, why this design choice helps to reduce the amount of thermal radiation absorbed by the astronaut from the Sun.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A scientist compares two identical metal containers of hot water, one painted dull black and one painted shiny white, left to cool in the same room.

   (a)

   Which container is expected to cool down faster due to emission of thermal radiation?

   [1 mark]

   • ABoth containers cool at exactly the same rate
   • BThe shiny white container
   • CThe dull black container
   • DNeither container emits any thermal radiation

   (b)

   The scientist then fills two more identical containers with cold water and places them outdoors in bright sunshine, again one dull black and one shiny white. Which container is expected to warm up fastest due to absorption of thermal radiation from the Sun?

   [1 mark]

   • AThe shiny white container
   • BThe dull black container
   • CBoth containers warm up at exactly the same rate
   • DNeither container absorbs any thermal radiation

   (c)

   Explain why a dull black surface is both a good emitter of thermal radiation when hot, and a good absorber of thermal radiation when cold, whereas a shiny white surface is poor at both.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A solar hot water panel on a rooftop is designed with a dull black absorbing surface facing the Sun, behind a sheet of glass, to heat water flowing through pipes within the panel.

   (a)

   (a) Explain why the dull black surface is chosen for the absorbing panel rather than a shiny, reflective surface.

   [3 marks]

   (b)

   Explain fully why placing a sheet of glass in front of the black absorbing surface, rather than leaving it exposed directly to the air, improves the overall efficiency of the panel at heating the water, considering both radiation and other forms of thermal energy transfer.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A vacuum flask is used to keep a hot drink warm for many hours. It consists of a double-walled glass container with a vacuum between the two glass walls, and the inner surfaces of the glass facing the vacuum are coated with a thin, shiny, reflective silver layer.

   (a)

   Explain fully how each feature of the vacuum flask, the vacuum gap and the shiny silver coating, works to minimise thermal energy losses from the hot drink by each of the three methods of thermal energy transfer (conduction, convection and radiation).

   [6 marks]

   (b)

   A manufacturer proposes a cheaper alternative design in which the vacuum gap is replaced with an ordinary air gap of the same thickness, but the shiny silver coating is kept the same. Explain fully how this change would affect the flask's ability to keep the drink warm, discussing each of the three methods of thermal energy transfer and comparing this design directly with the original vacuum flask described in part (a).

   [6 marks]

   Total for question 4: 12 marks

End of questions