Required practical

Investigating absorption and emission of infrared radiation

There are different ways to investigate the amount of infrared radiation absorbed or radiated by a surface. It is important to:

  • use appropriate apparatus to measure and record temperature accurately
  • make observations regarding the effects of electromagnetic waves on different substances

The method described here uses a Leslie cube. This is a metal cube with four different types of surface. It is filled with hot water to increase its temperature.

A leslie cube on a heatproof mat. Next to the cube is an infrared detector, which is essentially a cylinder attached with two wires to a small reader with screen.

Aim of the experiment

To investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.


  1. Place a Leslie cube on a heat-resistant mat. Almost fill it with boiling water and replace the lid.
  2. Leave for one minute. This is to enable the surfaces to heat up to the temperature of the water.
  3. Use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. Make sure that the detector is the same distance from each surface for each reading.


Record results in a suitable table. The example below also shows some example results.

Surface typeInfrared intensity (W/m²)
matt black19.5
matt white5.1
shiny black14.2
shiny silver3.8


Plot a bar chart to show the results. Make sure each bar is the same width, and labelled clearly to show which surface it represents.

Bar chart showing the infrared intensities for different types of surface

Use your results to order the different surfaces from the best emitter to the worst emitter of infrared radiation.


Explain why the detector must be placed the same distance from each surface before taking a reading.

Hazards and control measures

HazardConsequenceControl measures
Boiling waterScaldsPour water slowly, using a funnel if necessary. Do not move the Leslie cube until it has cooled.