Thursday, 10 February 2011

The Electromagnetic Spectrum : Infrared, Ultraviolet, & Visible Light, Radio Waves, & X-Rays

The Electromagnetic Spectrum - NASA
The Electromagnetic Spectrum - NASA

Electromagnetic Waves or Electromagnetic Radiation

Light, ultraviolet light, infrared light, radio waves, microwaves, X-rays, and gamma rays are all different forms of electromagnetic waves or electromagnetic radiation. But what are electromagnetic waves?
Electromagnetic waves are oscillations in electric and magnetic fields. Electric fields cause forces between electric charges such as protons and electrons. Magnetic fields cause magnetic forces such as those between a magnet and a piece of iron. Changing electric fields cause magnetic fields and changing magnetic fields cause electric fields.
In electromagnetic waves the electric and magnetic fields are perpendicular to each other and to the direction the wave is traveling. Both the electric and magnetic fields are oscillating between maximum positive and maximum negative values. Because of the way changing electric and magnetic fields each cause the other type of field both the electric and magnetic fields have maximum positive, maximum negative, and zero values simultaneously. Perpendicular electric and magnetic fields oscillate and the oscillations propagate in a direction perpendicular to both fields.

Properties of Waves
To understand wave properties visualize water waves at a beach. The waves have peaks and valleys moving towards the shore. The distance between two peaks, or between two valleys, is the wavelength. The number of wave peaks that hit a swimmer standing in the water each second is the frequency. If the wave peaks are further apart, fewer will hit the swimmer each second. Hence a longer wavelength corresponds to a lower frequency.

Electromagnetic waves are similar. The distance between two points where the electric and magnetic fields have maximum positive values is the wavelength. As the wave propagates, the number of times the maximum positive value passes a particular point each second is the wave's frequency, which is measured in Hertz. For all waves the frequency multiplied by the wavelength gives the speed at which the wave travels.
Make a wave in a rope by oscillating one end of the rope back and forth. A higher frequency wave will tire you faster than a lower frequency wave. Similarly, electromagnetic waves have more energy as the frequency increases and the wavelength decreases.

What Is the Electromagnetic Spectrum?

Visible light is the type of electromagnetic radiation that the human eye can detect. Different colors of light are simply different wavelengths and frequencies. Red light has a longer wavelength, lower frequency, and less energy than blue light. The visible light spectrum in order of decreasing wavelength is: red, orange, yellow, green, blue, indigo, and violet. Remember RoyGBiv.

The human eye can not detect all types of electromagnetic radiation. The electromagnetic radiation with shorter wavelength, higher frequency and more energy than violet light is ultraviolet light. Electromagnetic waves with even shorter wavelengths are X-rays and the shortest highest energy electromagnetic waves are gamma rays. At wavelengths longer than red light we have infrared light. Longer wavelength electromagnetic waves include all types of radio waves. Microwaves, AM waves, FM waves, television waves, and short-wave radio waves are examples of different types of radio waves.

Summary of the Electromagnetic Spectrum

The electromagnetic spectrum from the shortest wavelength, highest frequency, and highest energy to the longest wavelength, lowest frequency, and lowest energy is listed.
  • Gamma rays: energetic enough to damage cells and kill.
  • X-rays: enough energy to penetrate flesh and used for medical diagnostics.
  • Ultraviolet light: energetic enough to burn skin.
  • Visible light: detectable by the human eye.
  • Infrared light: feels warm on the skin as heat.
  • Microwaves: used for cooking and communications.
  • Radio waves: used for communications.

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