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.

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.

Method

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.

Results

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

Analysis

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.

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

Evaluation

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

Hazards and control measures