1. 1
   A student is investigating thermal radiation using two identical kettles, one with a matt black outer surface and one with a shiny silver outer surface. Both kettles are filled with the same volume of boiling water and placed on identical stands away from draughts. The student uses a temperature sensor connected to a datalogger to record the water temperature in each kettle every minute for 20 minutes as the kettles cool.

   (a)

   A matt black kettle and a shiny silver kettle, identical in shape and size, are both filled with boiling water and left to cool on a laboratory bench. Which kettle emits thermal radiation at the faster rate?

   [1 mark]

   • AThe shiny silver kettle, because shiny surfaces are better emitters of thermal radiation
   • BThe matt black kettle, because matt black surfaces are better emitters of thermal radiation
   • CBoth kettles emit thermal radiation at the same rate, because colour does not affect emission
   • DNeither kettle emits any thermal radiation, because they are not hot enough to glow

   (b)

   After 20 minutes, the student finds that the water in the matt black kettle has cooled to a lower temperature than the water in the shiny silver kettle. Which row correctly describes the surfaces in terms of absorbing radiation?

   [1 mark]

   • AMatt black surfaces are good absorbers; shiny surfaces are poor absorbers
   • BMatt black surfaces are poor absorbers; shiny surfaces are good absorbers
   • CBoth surfaces absorb radiation equally well
   • DAbsorption of radiation does not depend on surface type

   (c)

   Suggest two ways the student could improve the reliability of this investigation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A small metal cube is heated in a furnace to a series of increasing temperatures. At each temperature, the cube is removed briefly and a sensor measures the intensity and wavelength distribution of the radiation it emits, before the cube is returned to the furnace to be heated further.

   (a)

   Which statement about the radiation emitted by the metal block is correct?

   [1 mark]

   • AAs the block gets hotter, it emits radiation of lower intensity and longer wavelength
   • BThe block only emits radiation once it reaches its melting point
   • CThe intensity and wavelength distribution of the emitted radiation are independent of temperature
   • DAs the block gets hotter, it emits radiation of greater intensity and the distribution of wavelengths changes

   (b)

   The metal cube is eventually removed from the furnace and left in the laboratory at a fixed position with no further heating. It is found that the cube's temperature remains constant. Which statement explains this?

   [1 mark]

   • AThe cube radiates more average power than it absorbs
   • BThe cube absorbs more average power than it radiates
   • CThe cube radiates the same average power as it absorbs
   • DThe cube has stopped emitting and absorbing radiation entirely

   (c)

   The metal cube is later moved to a cold store. Explain what happens to its temperature and why, in terms of the power it radiates and absorbs.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician sets up four identical metal cans, differing only in their outer surface: one matt black, one matt white, one shiny black and one shiny silver. Each can is filled with the same volume of hot water at the same starting temperature. An infrared sensor can be placed at a fixed distance from each can to measure the radiation emitted.

   (a)

   Describe a method the student could use, with the equipment described, to investigate how the nature (colour/texture) of a surface affects the amount of thermal radiation it emits.

   [3 marks]

   (b)

   The technician's results show that the matt black can loses heat fastest, followed by the matt white can, then the shiny black can, with the shiny silver can losing heat slowest. Using ideas about absorption and emission of radiation, explain this ranking, and suggest one real-world application that makes use of this property.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Scientists monitor the Earth's average surface temperature and compare it with measurements of incoming solar radiation and outgoing radiation emitted by the Earth into space. Over recent decades, measurements suggest the amount of outgoing infrared radiation that escapes directly into space has decreased slightly, while incoming solar radiation has remained roughly constant.

   (a)

   Explain, using ideas about incoming and emitted radiation, how the balance between the radiation the Earth absorbs from the Sun and the radiation the Earth emits back into space determines the Earth's overall temperature, and describe what would happen to the Earth's temperature if this balance were disturbed.

   [6 marks]

   (b)

   The scientists' data shows that, over recent decades, average global temperatures have risen while the amount of outgoing infrared radiation escaping directly to space has decreased. Using your understanding of thermal radiation, explain a mechanism that could account for this trend, and evaluate why this evidence alone is not sufficient to prove the cause with certainty.

   [6 marks]

   Total for question 4: 12 marks

End of questions