1. 1
   A cook compares two frying pans on the same hob: one has a matte black outer surface and the other has a highly polished, shiny stainless steel outer surface. Both pans are heated to the same temperature and then left to cool.

   (a)

   Which pan cools down fastest, and why?

   [1 mark]

   • ABoth pans cool at exactly the same rate, because they reach the same temperature
   • BThe shiny pan, because shiny surfaces emit infrared radiation fastest
   • CThe matte black pan, because it is the better emitter of infrared radiation
   • DThe shiny pan, because it absorbs more radiation from its surroundings

   (b)

   The cook wonders what would happen if either pan were a 'perfect black body'. What is the definition of a perfect black body?

   [1 mark]

   • AAn object that is coloured black but does not emit any radiation
   • BAn object that only emits radiation when it is at a very high temperature
   • CAn object that reflects all radiation incident on it
   • DAn object that absorbs all of the radiation incident on it and is the best possible emitter

   (c)

   Explain, in terms of infrared radiation, why the matte black pan feels noticeably cooler to touch a few minutes after being taken off the hob than the shiny pan does.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A firefighter uses a thermal imaging camera to search a smoke-filled building for survivors. The camera detects radiation given off by objects and people in the room, even in complete darkness.

   (a)

   What type of radiation does the thermal camera detect?

   [1 mark]

   • AVisible light
   • BUltraviolet radiation
   • CInfrared radiation
   • DRadio waves

   (b)

   On the camera's display, the hottest parts of the room (such as a still-burning section of wall) appear brightest. What does this tell you about the relationship between temperature and infrared emission?

   [1 mark]

   • AHotter objects emit less radiation per unit time than cooler objects
   • BTemperature has no effect on the amount of radiation emitted
   • CHotter objects emit more radiation per unit time than cooler objects
   • DOnly objects above 100°C emit any infrared radiation at all

   (c)

   Explain how the thermal imaging camera is able to reveal the location of a survivor hidden behind thick smoke, even though the firefighter cannot see them with the naked eye.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A blacksmith heats an iron rod in a forge. As the rod gets hotter, it glows more brightly and feels increasingly warm to anyone standing nearby. Once heated, the blacksmith removes the rod from the forge and leaves it on a workbench to cool to room temperature.

   (a)

   Explain why the rod emits more radiation as its temperature increases.

   [3 marks]

   (b)

   (HT) After the blacksmith removes the rod from the forge, explain, in terms of the rates of absorption and emission of radiation, how the rod's temperature changes as it cools on the workbench until it reaches room temperature.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Climate scientists model the Earth as a body that absorbs radiation from the Sun and emits infrared radiation back into space, while some radiation is reflected straight back into space without being absorbed. Scientists have observed that greenhouse gases in the atmosphere, such as carbon dioxide, absorb infrared radiation emitted by the Earth's surface and re-emit some of it back towards the surface.

   (a)

   (HT) Explain, in terms of the rates of absorption and emission of radiation and reflection of radiation into space, how the Earth's average temperature depends on the balance between these processes.

   [6 marks]

   (b)

   (HT) Using the information above, evaluate how an increase in the concentration of greenhouse gases in the atmosphere could affect the Earth's average temperature, in terms of the balance between absorption and emission of radiation.

   [6 marks]

   Total for question 4: 12 marks

End of questions