Question 1 (1 marks)
Knowledge
Which surface is generally the best infrared emitter: matt black or polished silver?
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Matt black (1).
Required Practical 21: Radiation and Absorption | AQA GCSE Science | The Science Department
About this practical and its aim
Aim
Investigate how infrared absorption or emission depends on the nature of a surface.
Introduction
So simple yet so important. By watching what happens with Leslie's cube, you get to see the variation of infrared heat given off from different colours. Most importantly, as the different colours are all getting their heat from the same place, it removes potential variation and makes the water temperature a control variable. This simple experiment is so fundamental, and it explains ideas from what colour clothes you should wear in which climate to why paramedics wrap patients in thin silver blankets.
The science behind the practical
Dark matt surfaces are generally better absorbers and emitters of infrared than shiny reflective surfaces.
Key things to remember
Compare surfaces while controlling temperature and measurement conditions; use a detector or measured temperature change.
Equipment and apparatus
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Leslie cube or matched cans
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hot water
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infrared detector or thermometer
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measuring cylinder
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timer
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heatproof mat
Method: How to carry out the experiment
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Setup the selection of test tubes in a test tube rack
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Add a thermometer into each test tube
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Using a measuring cylinder, add the same amount of hot water to each (not boiling, less than 80°C)
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Record the temperature of each thermometer
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Record the temperature every 30 seconds and record it for approximately 10 minutes
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Plot cooling curves and note the effects of different colour/texture has on the rate of cooling
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It is very important to see the demonstration involving Lesley's cube to support your result analysis
Variables and fair testing
| Type of variable | What is measured or controlled? |
|---|---|
| Independent variable | Colour or surface finish |
| Dependent variable | Infrared detector reading or temperature change |
| Control variables | Starting temperature; distance and angle; exposed area; observation time |
Safety and managing risks
Follow your teacher's instructions and your school's risk assessment. This page is not a substitute for a formal risk assessment.
| Hazard | Risk | Precaution |
|---|---|---|
Hot water and cube/cans |
Scalding or burns |
Use approved temperatures and heatproof mats; avoid overfilling. |
Infrared apparatus or hot lamps |
Hot surfaces |
Keep hands clear and let equipment cool. |
Results, calculations and analysis
Recording, presenting and interpreting results
Record surface type and corresponding detector reading or temperature change; repeat for each surface.
Calculations
Temperature difference = final temperature − initial temperature; compare means where measured.
Conclusions, accuracy and evaluation
Drawing a conclusion
At the same temperature, dull dark surfaces usually emit more infrared than shiny light surfaces.
Evaluating the investigation
Maintain equal initial temperature, distance and area; avoid inconsistent detector angles or reflections.
More to learn
Fair surface comparisons
Keep surface area, temperature, distance and detector angle constant when comparing infrared emission.
Common exam mistake
Infrared radiation is transferred by electromagnetic waves; shiny reflective surfaces are typically poor emitters and absorbers.
GCSE examination practice
Answer each question in full before opening the model answer. Check your work against the marking points and look for scientific key words.
Question 2 (2 marks)
Method
Why should compared surfaces start at the same temperature?
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Temperature affects infrared emission (1); keeping temperature the same makes surface type the main changing factor (1).
Question 3 (1 marks)
Evaluation
Give one reason infrared detector results might be unreliable.
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Distance or angle changes, surrounding reflections or unequal temperature (any one, 1).
Question 4 (2 marks)
Evaluation
Suggest one improvement to make the investigation more reliable and explain why it helps.
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Repeat measurements and calculate a mean (1), reducing the influence of random variation/anomalies (1). Alternative valid improvement specific to the experiment with explanation can gain both marks.
This page was updated on: 27th June 2026