10: Infrared

How much infrared is absorbed or radiated by different surfaces

The human eye cannot see infrared.

We can use a Leslie’s cube to see how much infrared is emitted from different surfaces.

A Leslie’s cube has:

Shiny metallic

White

Shiny Black

Matte Black

Surfaces.

1. Fill Leslie’s Cube with hot water.

2. Point an infrared detector at each 4 surfaces. Record amount of infrared emitted. It is important we keep the same distance between the Leslie’s Cube and the infrared detector. This means that the measurements are repeatable.

^ Matte Black

| Shiny Black

| White

Shiny Metallic

If we don’t have an infrared detector, we can use a thermometer with the bulb painted black.

The resolution of thermometer is less than the infrared detector.

The resolution is the smallest change that can be detected.

We may not be able to detect a large difference between surfaces using the thermometer, infrared is more likely to detect a difference.

To investigate infrared absorbance of different surfaces:

Infrared heater, on either side we have 2 metal plates. One plate has shiny metallic paint. The other has matte black paint. On both sides there is also vaseline used to attach a drawing pin.

Turn on heater and start timing.

The temperatures of the plates increase as they absorb the infrared.

Record the time it takes for the vaseline to melt and drawing pins to fall off.

The drawing pin should fall off of the matte black side first.

Matte Black surfaces absorb more infrared.

Infrared tends to be reflected from shiny surfaces instead of absorbed.