What are Electromagnetic Radiations?


Radio 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. Forms of electromagnetic radiation can be grouped according to their wavelengths – the distance between one wave crest and the next.

In reality, the wavelength at the left-hand end of the spectrum is a million million million times the wavelength at the right-hand end.


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. Microwaves are high-frequency radio waves also used in communications. Some microwave frequencies can be used in cooking.

Electromagnetic waves have 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, it has to be modulated. This can be done by modulating (varying) either the strength of a wave – amplitude modulation or AM – or the speed of a wave – frequency modulation or FM.


In the middle of the electromagnetic spectrum is a small group of waves that our eyes detect, which is called visible light. It has wavelengths of around a thousandth of a millimetre. Waves with slightly different wavelengths appear as different colours, which together make up the colour spectrum. Light and especially laser light is very important in modern communications. Where practical, it is used in place of electricity and radio waves, because it can carry far more information without problems of interference.



To the left of visible light on the spectrum is infrared (IR) radiation. This is the radiation you feel as heat from hot objects. It is one of ways in which heat energy travels. Infrared radiation is used for short-range communications, such as in television remote controls, video camera autofocus and remote locking in cars.

To the right of visible light on the spectrum is ultraviolet (UV) radiation. It carries more energy than visible light. Ultraviolet radiation from the Sun is mostly absorbed by the atmosphere, but it still causes tanning of the skin and sunburn.


To the right of ultraviolet radiation are two more forms of electromagnetic radiation – X-rays and gamma rays. They both have very short wavelengths (less than a millionth of a millimetre) and extremely high frequencies (more than a million million million cycles per second). This means that X-rays and gamma rays have extremely high energies, and they can pass right through some solids. This makes them useful for investigating what is inside solid objects, such as human bodies, or closed suitcases at an airport security checkpoint.

X-rays were discovered by the German physicist Wilhelm Rontgen in 1895. They have a wide range of applications. In medicine, they are used to see the structure of bones and other organs by placing the patient between an X-ray source and a photographic film or camera. X-rays and gamma rays are also used in radiotherapy for treating cancers. However, in high doses they can damage tissues. X-rays are given off by high-energy, distant objects in space. X-ray telescopes can detect them.

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