Perfect black bodies and radiation — AQA GCSE Physics
Test yourself on Perfect black bodies and radiation with AQA GCSE practice questions.
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Perfect black bodies and radiation explained
This is Higher tier only. The standard diagram shows arrows whose widths represent rates of energy transfer: short wavelength radiation arriving from the Sun, part of it reflected straight back to space by clouds, snow and ice, the rest absorbed by the surface and the atmosphere.
Read the full explanation
The warmed surface then emits long wavelength infrared, some of which escapes and some of which is absorbed by greenhouse gases and re-emitted in all directions, including back down. To interpret a diagram, check each arrow for its direction, its wavelength label and its size, then total the energy in and the energy out: equal totals mean a steady temperature, and an excess arriving means the surface warms.
Your focus
- Label an energy flow diagram of the Earth with incoming short wavelength, reflected and outgoing long wavelength radiation.
- Use the values given on such a diagram to decide whether the Earth's temperature is rising.
- Explain from a diagram how greenhouse gases raise the surface temperature without any change in the Sun's output.
Perfect black bodies and radiation exam tips
Marking Points
- one mark for identifying incoming short wavelength solar radiation and outgoing long wavelength infrared on the diagram
- one mark for identifying radiation reflected back into space without being absorbed
- one mark for showing greenhouse gases absorbing infrared and re-emitting some of it back towards the surface
- one mark for using the values on the diagram to state whether the temperature will rise, fall or stay constant
Examiner Tips
- 💡Label every arrow with its direction and whether it is short or long wavelength.
- 💡Add up the values entering and leaving before writing any conclusion.
- 💡This is Higher tier only; diagrams are often marked for arrow direction as much as for wording.
Common Mistakes
- drawing the outgoing radiation at the same wavelength as the incoming radiation
- drawing re-emission from greenhouse gases only downwards, never upwards
- leaving the reflected arrow out when totalling the energy arriving and leaving
- concluding the temperature is constant when the numbers on the arrows do not balance