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Study Notes: Electromagnetic Radiation

Electromagnetic radiation (EMR) is a form of energy.

A small part of electromagnetic radiation is the visible light that we can see with our own eyes. The remaining parts of the electromagnetic spectrum cannot be seen but special analytical equipment can be used to detect these forms of EMR.

Electromagnetic radiation includes X-rays, ultraviolet light, visible light, infrared, microwaves and radio waves. The frequencies and wavelengths of these are shown below. Click on the visible light area to see an expansion of this range.Skip flash movie

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Spectroscopic analysis makes use of different parts of the electromagnetic spectrum:

  1. X-rays are produced when a stream of high-energy electrons hits a metal target. X-rays have short wavelengths and high energy. They can pass through thin solids and liquids. They can also pass through the body but are stopped by bones. Exposure to too much X-radiation can damage the body's cells.
  2. Ultraviolet (UV) radiation is produced by special lamps containing mercury vapour or deuterium gas. We cannot see UV light. Overexposure causes sunburn.
  3. Visible light is produced by normal light bulbs. White light from the sun is a mixture of all the different colours but we only ‘see’ the mixture instead of the individual colours.
  4. Infrared (IR) radiation is produced by hot objects such as a glowing metal wire in a heater. We cannot see IR light but we can feel its effects as it warms our skin.

The speed of light
All of the different forms of electromagnetic radiation travel through space (a vacuum) at a speed of 3 X 108 metres per second (ms-1).

The speed of light through a material is less than this. It varies for different substances.

The speed of light in air is a little below 3 X 108 ms-1 and in water or glass it is even lower.

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