The Electromagnetic Spectrum

The spectrum of the radiation emitted by a hot body is continuous because there are many different kind of oscillators in any real lump of matter, so that in practice radiation exists at all frequencies.

The main components of the electromagnetic spectrum are gamma-rays, x-rays, ultra-violet, visible light, infra-red, microwaves and radio-waves.

Gamma-rays and X-rays are the highest-energy electromagnetic waves and able to penetrate matter easily. They have the shortest wavelengths and highest frequencies. Gamma rays may be emitted by radioactive substances, while X-rays may be produced by X-ray tubes.

Ultra-violet(UV) radiation is the next highest-energy. It may be produced by very hot bodies, such as the sun. The atmosphere filters most of the UV radiation from the sun. UV radiation also causes sun-burned skins.

The visible light is the only electromagnetic radiation that is visible to our eyes. It occupies a surprisingly small portion in the electromagnetic spectrum. Sun and other white-hot bodies emit white light, which is made up of violet, indigo, blue, green, yellow, orange and red colours. (in order of reducing frequencies)

Infra-red radiation (IR) may be produced by any hot bodies similar to white light, but with longer wavelengths. IR radiation is readily absorbed by matter and raises their temperature.

Microwave radiation is generated by special electronic devices known as klystron valves. Microwave receivers can be used to detect microwaves. They are reflected by metals and partly absorbed by non-metals.

Radio waves have the longest wavelengths, varying from a few centimetres to thousands of metres. These may be generated by oscillations in special electronic circuits and by electrical sparks and are detected by metal aerials.