Infrared parctical

What do hot surfaces emit?

Infrared radiation. Human eye cannot see infrared.

What does this practical investigate?

How much infrared is emitted or absorbed by different substances.

What is a Leslie’s cube used for?

Used to see how much infrared is emitted from different surfaces.

What 4 different surfaces does a Leslie’s cube have?

• Shiny metallic surface

• white surface

• shiny black surface

• matte black surface

How do we find the amount of infrared emitted?

We point an infrared detector at each of the four surfaces and record the amount of infrared emitted.

What is important when using an infrared detector?

That we keep it the same distance between the Leslie’s cube and the infrared detector.

This makes the measurements repeatable.

What is the result of this investigation of how much infrared is emitted?

• Matte black emits the most infrared radiation

• Shiny black

• White

• Shiny metallic emits the least infrared radiation.

How would we find the infrared emitted without an infrared detector?

Then we can use a thermometer with the bulb painted black.

However, the resolution of a thermometer is less than the resolution on an infrared detector. Infrared detector is more likely to detect a difference.

What is resolution?

The smallest change that can be detected.

What equipment do we use to find how infrared is absorbed by different surfaces?

• We have an infrared heater

• On either side are 2 metal plates

What are the 2 metal plates painted with?

• Shiny metallic

• Matt black

What is on the side of the plates facing away from the infrared heater?

We have used vaseline to attach a drawing pin.

What do we do after we have attached the drawing pin?

Turn on the heater and start timing.

What happens when the heater is turned on?

The temperature of the metal plates increases as they absorb infrared.

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

What is the result for absorption of infrared radiation?

The drawing pin falls of the matt black plate first.

Matt black surfaces absorb more infrared than shiny metallic surfaces.

What is important about matt black surfaces?

They are much better at absorbing and emitting radiation than shiny metallic surfaces.

In fact, infrared tends to be reflected from shiny metallic surfaces.