6.2.5Waves
Required Practical: Investigating Infrared Radiation — AQA GCSE Combined Science Trilogy 8464 - Physics Revision Notes & Topical Questions
5 min read 6 parts Lesson 11 of 15
Part 1 of 4Background ideas
Emission
- Emission All objects emit infrared radiation. The hotter the object, the more it emits.
- Dull black surfaces are the best emitters; shiny white or silver surfaces are the poorest.
Absorption
- Absorption Dull black surfaces are also the best absorbers of infrared;
- shiny light-coloured surfaces reflect more.
- Good absorbers are also good emitters.
Aim
- Aim To find how the type of surface affects the infrared emitted at the same temperature.
Part 2 of 4Method using a Leslie cube
1
Fill the Leslie cube, a hollow metal cube with four different faces (matt black, shiny black, matt white, shiny silver), with hot water from a kettle.
2
Place the cube on a heatproof mat and wait for the temperature to settle so all faces are at the same temperature.
3
Hold an infrared detector, or a thermopile, 10 cm from the first face. Keep the distance fixed with a ruler.
4
Record the detector reading. Rotate the cube and repeat for each face at the same distance.
5
Repeat each face three times and calculate the mean reading.
6
Compare the means for each surface.
Part 3 of 4Variables and safety
| Item | Detail |
|---|---|
| Independent variable | Type of surface (colour and finish) |
| Dependent variable | Infrared radiation detected, or temperature change |
| Control variables | Temperature of the cube, distance to the detector, time of measurement, same detector |
| Hazards | Hot water and a hot cube can scald; pour with care and keep the kettle away from the edge of the bench |
| Typical result | Matt black gives the highest reading; shiny silver gives the lowest |
Part 4 of 4Alternative: absorption test
1Prepare
- Prepare Take two identical metal containers, one painted matt black and one shiny silver, each with the same amount of water at the same start temperature.
2Heat
- Heat Place an equal radiant heater the same distance from each.
3Measure
- Measure Record the temperature every minute for 10 minutes.
4Compare
- Compare The black container warms faster because it absorbs more infrared.
Key terms
| Term | Meaning |
|---|---|
| Infrared radiation | Electromagnetic waves emitted by all objects, with a wavelength longer than visible light. |
| Emitter | A surface that gives out radiation. |
| Absorber | A surface that takes in radiation and heats up. |
| Leslie cube | A hollow cube with differently-treated faces used to compare how surfaces emit radiation. |
| Control variable | A quantity kept constant to make a test fair. |
Avoid these mistakes
1
Allowing the distance from detector to surface to change between faces, so the readings are not comparable.
2
Saying the shiny surface emits more because it looks hot. It emits least.
3
Using different starting temperatures for the containers in the absorption test.
4
Not repeating the readings, so one odd measurement cannot be spotted.
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