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Energy

Electromagnetic radiation

A microwave telecommunications towerA microwave telecommunications towerRadio waves, microwaves, light and X-rays have different characteristics, but they are all forms of electromagnetic radiation. Together with other forms, they make up a family called the electromagnetic spectrum. These forms of radiation can also be thought of as waves moving through space, in the same way as waves move across the surface of water. They all travel at the speed of light, but have different wavelengths—the distance between one wave crest and the next—and therefore different frequencies—the number of waves per second. Forms of electromagnetic radiation can be grouped according to their wavelengths—the distance between one wave crest and the next.


The electromagnetic spectrumThe electromagnetic spectrumA satellite receives and re-transmits radio waves A satellite receives and re-transmits radio waves

Radio waves

The longest waves of the electromagnetic spectrum are radio waves. They have wavelengths ranging from more than 100 kilometres down to less than a metre. Radio waves are produced when an electric current changes strength or direction. Radio waves are important in communications through air and space.


A wave varied by amplitude (top) or frequency (above)A wave varied by amplitude (top) or frequency (above)
Like all electromagnetic waves, radio waves have an amplitude and a frequency. Amplitude is the height or strength of a wave. Frequency is the number of wave crests that pass a point every second. To make a radio wave carry sound or TV pictures, it has to be modulated (varied). This can be done by modulating either the strength of a wave—amplitude modulation or AM—or the speed of a wave—frequency modulation or FM.

The wavelength at the left-hand end of the electromagnetic spectrum (radio waves) is a million million million times the wavelength at the right-hand end (gamma rays).

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