The behaviour of an electromagnetic (EM) wave in a substance depends on its frequency. The differing behaviours of different groups in the electromagnetic spectrum make them suitable for a range of uses. With increasing frequency, EM waves become progressively more hazardous.
Radio waves are used for communication such as broadcasting television and radio, communications and satellite transmissions.
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.
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. 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 are used for cooking food, communications and for satellite communications. Intense sources of microwaves can be dangerous through internal heating of body cells.
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 (IR) light is used by electrical heaters, cookers for cooking food, short-range communications like remote controls, optical fibres, security systems and thermal imaging cameras which detect people in the dark. The heating effect of IR can cause burns to the skin.
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 is the light we can see, so is used in photography and illumination. It is also used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver.