Behaviour and uses of electromagnetic waves

The behaviour of an electromagnetic wave in a substance depends on its frequency or wavelength. The differing behaviours of different groups in the electromagnetic spectrum make them suitable for a range of uses.

Radio waves

Radio waves are used for communication such as television and radio.

Radio waves are transmitted easily through air. They do not cause damage if absorbed by the human body, and they can be reflected to change their direction. These properties make them ideal for communications.

Producing radio waves - Higher

Radio waves can be produced by oscillations in electrical circuits. When radio waves are absorbed by a conductor, they create an alternating current. This electrical current has the same frequency as the radio waves. The conductor could be, for example, an aerial on a radio.

Information is coded into the wave before transmission, which can then be decoded when the wave is received. Television and radio systems use this principle to broadcast information.

Microwaves

Microwaves are used for cooking food and for satellite communications.

High frequency microwaves have frequencies which are easily absorbed by molecules in food. The internal energy of the molecules increases when they absorb microwaves, which causes heating. Microwaves pass easily through the atmosphere, so they can pass between stations on Earth and satellites in orbit.

Infrared

Infrared light is used by electrical heaters, cookers for cooking food, and by infrared cameras which detect people in the dark.

Infrared light has frequencies which are absorbed by some chemical bonds. The internal energy of the bonds increases when they absorb infrared light, which causes heating. This makes infrared light useful for electrical heaters and for cooking food. All objects emit infrared light. The human eye cannot see this light, but infrared cameras can detect it. This 'thermal imaging' is useful for detecting people in the dark.

Visible light

Visible light is the light we can see. It is used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver.

Ultraviolet radiation

Ultraviolet radiation can kill bacteria that are present in water - this sterilises the water and makes it safe to drink. Ultraviolet radiation is also good for the skin as it helps to make vitamin D. However, too much exposure to UV can cause skin problems.