AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
(HT only) Students should be able to explain how the temperature of a body…
Full specification wording
Perfect black bodies and radiation: (HT only) Students should be able to explain how the temperature of a body is related to the balance between incoming radiation absorbed and radiation emitted, using everyday examples to illustrate this balance, and the example of the factors which determine the temperature of the Earth.
This is Higher tier only, and it is one argument applied to many contexts.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 5 of 6
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This is Higher tier only, and it is one argument applied to many contexts. Always name the two rates, say which is larger, deduce the direction of the temperature change, and finish by saying what happens as the temperature changes. A person standing in sunlight warms because they absorb faster than they emit; a parked car reaches a steady temperature when the rates match; a hot drink cools because it emits faster than it absorbs. For the Earth, the mean temperature is steady while absorbed solar radiation equals emitted infrared. Add more greenhouse gas and less infrared escapes, so absorption temporarily exceeds emission and the surface warms until the balance is restored at a higher temperature.
What earns the marks
- Comparing the rate of absorption with the rate of emission in the situation described.
- Deducing the direction of the temperature change from that comparison.
- Explaining that the temperature becomes steady again when the two rates become equal.
- Applying the argument to the Earth, naming greenhouse gases absorbing the outgoing infrared.
Common mistakes and how to put them right
Describing temperatures rather than rates of absorption and emission.
Forgetting that the body keeps emitting radiation while it is warming.
Asserting that the Earth's temperature rises without saying which rate exceeds which.
Using the word heat loosely instead of naming the radiation absorbed and emitted.
Exam tips
- The word balance in a question is a signal to compare rates, not amounts.
- Finish the answer by saying what happens once the balance is restored.
- This is Higher tier only, and usually carries three or four marks, so write the full chain.
Try the lesson
The start of the Perfect black bodies and radiation: (HT only) Students should be able to explain how the temperature of a body is related to the balance between incoming radiation absorbed and radiation emitted, using everyday examples to illustrate this balance, and the example of the factors which determine the temperature of the Earth. lesson, made from checked teaching notes for this specification point.
Have a go first
A cup of hot tea is left on a table in a room. At first the tea cools quickly, but after several minutes its temperature stops falling and stays constant. What explains why the tea's temperature becomes constant?
Listen
This is Higher tier only, and it is one argument applied to many contexts. Always name the two rates, say which is larger, deduce the direction of the temperature change, and finish by saying what happens as the temperature changes. A person standing in sunlight warms because they absorb faster than they emit; a parked car reaches a steady temperature when the rates match; a hot drink cools because it emits faster than it absorbs. For the Earth, the mean temperature is steady while absorbed solar radiation equals emitted infrared. Add more greenhouse gas and less infrared escapes, so absorption temporarily exceeds emission and the surface warms until the balance is restored at a higher temperature. A strong answer earns marks for these points. comparing the rate of absorption with the rate of emission in the situation described. deducing the direction of the temperature change from that comparison. explaining that the temperature becomes steady again when the two rates become equal. applying the argument to the Earth, naming greenhouse gases absorbing the outgoing infrared. Exam tip: The word balance in a question is a signal to compare rates, not amounts.
Key words
Say what each word means before you turn the card.
radiation balance
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everyday examples
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See every definition
- radiation balance
- The balance between incoming radiation absorbed and radiation emitted, which determines the temperature of a body.
- everyday examples
- Examples used to illustrate the balance between incoming radiation absorbed and radiation emitted.
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