Science required practicals
How do you do the infrared radiation required practical?
Fill a Leslie cube with very hot water. Its faces are all at the same temperature but have different surfaces, such as matt black and shiny silver. Point an infrared detector at each face from the same distance and record the reading. Matt black gives the highest reading and shiny silver the lowest, so the surface itself affects how much infrared is emitted. Show the results as a bar chart.
Last updated 23 September 2026 · Written and fact-checked by the GCSEwiz team
What does the infrared radiation practical investigate?
It investigates how the nature of a surface, its colour and texture, affects the amount of infrared radiation it gives out. Every object emits infrared, and hotter objects emit more, so the trick is to compare surfaces that are all at the same temperature. A Leslie cube does that: a hollow metal cube with a different finish on each side, filled with hot water.
AQA's wording covers infrared absorbed as well as emitted. This page follows the emission method with a Leslie cube. The same pattern holds for absorption, because a surface that is a good emitter is also a good absorber. It is a required practical on AQA GCSE Physics and on AQA GCSE Combined Science: Trilogy.
What equipment do you need?
You need a Leslie cube full of very hot water, and something that measures infrared.
- A Leslie cube, with a different surface on each side, such as matt black and shiny silver
- A kettle for very hot water
- An infrared detector, or an infrared thermometer
- A ruler, to keep the detector the same distance from each face
- A heatproof mat
What is the method?
You measure the infrared from each face in turn, as quickly as you can, while the water is still hot.
- Stand the Leslie cube on the heatproof mat.
- Fill it carefully with very hot water from the kettle and put the lid on.
- Wait about a minute, so every face warms up to the temperature of the water.
- Hold the detector a fixed distance from the first face, such as 10 cm, pointing straight at it, and record the reading.
- Turn the cube, or move the detector, and take a reading from each of the other faces at exactly the same distance.
- Repeat the set of readings, in a different order if you can, and work out a mean for each face.
What are the variables?
You change the type of surface and measure the infrared it emits. The temperature and the distance must stay the same, or they would change the readings too.
| Variable | In this practical |
|---|---|
| Independent variable | The type of surface (its colour and texture) |
| Dependent variable | The reading on the infrared detector |
| Control variable | The temperature of the surface: every face is heated by the same water |
| Control variable | The distance between the detector and each face |
| Control variable | The area of each face, which is the same on a cube |
How do you work out and present the results?
There is no equation here: you compare readings. Put them in a table with a column for each round of readings and a column for the mean.
Example: say the detector reads 8.1, 8.3 and 8.0 on the matt black face in three rounds, a mean of 8.1. The shiny silver face reads 1.2, 1.1 and 1.3, a mean of 1.2. The gap between the two means is far bigger than the spread in each face's own readings, so you can trust that the difference is real.
The type of surface is a category, not a number, so draw a bar chart with one bar per surface. A line graph would suggest there are values in between matt black and shiny silver, and there are not. Your conclusion: matt black surfaces emit the most infrared, and shiny silver surfaces the least.
How do you make it accurate and safe?
Keep the detector at the same distance and angle for every face. A ruler or a card spacer makes this easy. Work quickly, because the water cools as you go round the cube, and the last face you read would be slightly cooler than the first. Taking the next round in a different order evens this out.
On safety: the water is hot enough to scald, and the faces of the cube get hot too. Fill the cube while it stands on the heatproof mat, don't move it while it is full, and let it cool before you empty it.
What do exam questions ask about it?
Questions often give you a results table and ask which surface is the best emitter, and why the faces must all be at the same temperature. You may be asked why a bar chart suits the results. Some ask you to use the idea elsewhere, for example to say which surface would absorb the most infrared.
Here is one we wrote in the exam style: "A student measures the infrared emitted by each face of a Leslie cube, always in the same order. Explain why this could make the last face seem to emit less infrared than it really does. (2 marks)" A good answer says the water cools during the round, so the last face is cooler, and a cooler surface emits less infrared.
Common mistakes
- Drawing a line graph. The surfaces are categories, so use a bar chart.
- Changing the distance between the detector and the cube. Closer readings are higher, whatever the surface.
- Measuring before the faces have warmed up. Wait a minute after filling the cube.
- Writing that the black face is hotter. All the faces are at the same temperature; the black one emits more infrared at that temperature.