Behaviour and uses of electromagnetic waves
The behaviour of an electromagnetic wave in a substance depends on its frequencyThe number of waves produced each second. The unit of frequency is hertz (Hz). or wavelengthThe length of a single wave, measured from one wave peak to the next, or one wave trough to the next. . 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 oscillationsThe repeated and regular fluctuations, above and below the same position, eg the pressure of a sound wave or the voltage of an alternating current. in electrical circuits. When radio waves are absorbed by a conductorA material which allows charge to move easily through it., they create an alternating currentAlso called ac. An electric current that regularly changes its direction and size.. 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 energyThe total kinetic energy and potential energy of the particles in an object. 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.