GCSE PHYSICS - What are Infra-red Waves? - How are Infra-red Waves used for Cooking, Communication, Thermal Imaging and PIR?

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Electromagnetic Waves - What are Infra-red Waves?

Infra-red Waves are part of the electromagnetic spectrum.
Sir William Herschel discovered Infra-red waves in 1800.
This was the first discovery of any electromagnetic
waves that were outside the range of the visible spectrum.

Infra-red waves are sometimes also called
infra-red radiation or thermal radiation.

How are Infra-red Waves Used for Cooking?

Infra-red waves are easily absorbed by materials.
The energy of the wave causes the material to get hot.
We usually think of infra-red radiation as heat.
Ordinary ovens, grills and toasters use infra-red radiation
to cook food (ovens may also cook by convection).

Intense infra-red radiation will damage or kill living cells
(such as skin cells) by burning them.

How are Infra-red Waves Used for Communication?

Infra-red waves can transmit information through the air
to operate TV's and PVR's by remote control.
Information can also be sent through optical fibres.

What is Thermal Imaging?

Infra-red waves are used for thermal imaging.
In a thermal imaging device, a detector receives
infra-red waves and produces an image where
different colours show the intensity of the waves in
different places. This gives you a 'heat picture'
where hotter objects are orange / red
and colder objects are blue / green.
Thermal imaging is used by
fire fighters to see where the hottest part of the fire is.

What is a PIR?

A device called a PIR (passive infra-red) is used for security.
When a warm object such as a human or animal
approaches a house, the PIR can detect it against the
colder background and send a signal to switch on an outside light.

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