Radiation and absorption

Investigating the amount of infrared radiation radiated from different surfaces.

Students use a Leslie cube and an infrared detector to see how much heat radiation is emitted from the different surfaces of the Leslie cube. An Infrared thermometer is used in this example which determines the temperature of the Leslie cube through the emitted radiation.

Equipment (per pair of participants)

• Safety glasses
• Leslie cube
• Funnel
• Kettle
• 30cm ruler
• Stopwatch
• Infrared detector
• Heatproof mat

• Bench power supply
• Connecting leads
• Ammeter
• Voltmeter
• Electronic balance (2dp)
• Stopwatch
• Heatproof mat

Method

Students should place the Leslie cube on a heatproof mat.
The stopper should be removed from the top of the Leslie cube.
A funnel is placed into the top of the Leslie cube.
The Leslie cube is filled very carefully with hot water from the kettle using the funnel. The stopper is then replaced.
Students should allow a few minutes to pass, timing this with the stopwatch for the equipment to settle.
Students then use the infrared detector to measure the temperature of each surface of the cube, ensuring that the infrared detector is operated at the same distance away from each face of the cube, recording their values in a suitable table.
The values are plotted onto a graph to illustrate the amount of infrared radiation emitted from each surface of the cube. A conclusion can be drawn from their findings.

Technician tips

A number of kettles could be set up around the classroom for students to use. Great care should be taken by students when handling and dispensing the hot water.
If a Leslie cube for each group is unavailable, a set of boiling tubes painted with white, silver or black paint could be prepared. The boiling tubes are filled with hot water and the radiating temperature is taken in the same way.