the electromagnetic spectrum

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Electromagnetic radiation travels as waves and transfers energy from one place to another. An electomagnetic wave consists of electric and magnetic disturbances in the vacuum. Unlike other waves, it can travel through a vacuum.

White light can be split up into a spectrum of many different colours. You should know that visible light is just part of a continuous spectrum of electromagnetic radiation. Different types of electromagnetic radiation have different uses and hazards.

By 'electromagnetic spectrum', we mean the whole continuous range of wavelengths that electomagnetic waves can have.

The way an electromagnetic wave behaves when it meets matter depends upon its wavelength. Two electromagnetic waves with very different wavelengths will have very different properties. For convenience, we split the electomagnetic spectrum into different wavelength ranges and give each range a name, eg microwaves, ultra-violet etc.

Each wavelength range has different properties, uses and dangers. However, all electromagnetic waves travel at the same speed - 300 million m/s in a vacuum - regardless of their wavelength. This is about one million times faster than the speed of sound in air.

The only electromagnetic radiation that can we can see is what we call visible light. (Some animals can see well into the infrared and/or ultraviolet of the electromagnetic spectrum).

Generally, the only electromagnetic radiation that we can feel from objects on Earth is infrared, which we feel as heat. (Strange as it may sound though, most of the heat we feel from the sun - which is vastly hotter than the Earth - is the result of visible light.)

The complete electromagnetic spectrum comprises gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves and radio waves.

A beam of electromagnetic radiation delivers energy in photons. The more photons that are delivered per second, and the more energy each photon carries, the greater the intensity of the beam. The intensity decreases the further from the source you go.

Some types of electromagnetic radiation are ionising. Radio waves, microwaves and infrared light are all forms of non-ionising radiation. They heat up materials when they are absorbed. Visible light is also non-ionising.

Different types of electromagnetic radiation have different uses. While microwave radiation is used for cooking and telecommunications, there has been some concern that the use of mobile phones could be harmful, but there is no conclusive evidence for this. We do know, however, that ultraviolet light can damage the skin and eyes. It causes cataracts, sunburn, skin cancer and premature ageing of the skin.

»   What is a spectrum?
»   A simple model of electromagnetic radiation
»   Breakdown of the electromagnetic spectrum
»   Gamma radiation and X-rays
»   Ultraviolet radiation and infrared radiation
»   Microwaves
»   Radio waves
»   Uses of electromagnetic radiation
»   Transmitting information
»   Ionising EM radiation
»   Hazards of microwave radiation
»   Hazards of UV radiation
»   The intensity of a beam
»   Test on the electromagnetic spectrum


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