(Difference between revisions)
 Revision as of 17:01, 27 July 2010 (view source)Kwiggins (Talk | contribs)← Older edit Revision as of 17:03, 27 July 2010 (view source)Kwiggins (Talk | contribs) Newer edit → Line 1: Line 1: == Radio Waves
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When electrons move in a wire—that is, when there is an electric current in the wire—electric and magnetic fields are created around the wire. If the current is steady, then the electric and magnetic fields do not vary. But if the current varies, then the electric and magnetic fields vary. These variations in the electric and magnetic fields travel away from the wire, and because the electric-field variations and the magnetic-field variations are interrelated, the outward-traveling disturbances are called electromagnetic waves.

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[[Image:Radio_waves_hazard_symbol.png|thumb|left|Radio Waves Hazard Symbol]]When electrons move in a wire—that is, when there is an electric current in the wire—electric and magnetic fields are created around the wire. If the current is steady, then the electric and magnetic fields do not vary. But if the current varies, then the electric and magnetic fields vary. These variations in the electric and magnetic fields travel away from the wire, and because the electric-field variations and the magnetic-field variations are interrelated, the outward-traveling disturbances are called electromagnetic waves.

A wave is characterized by its wavelength—the distance from one crest to the next—and by its frequency—the number of crests per second. For any wave, the product of wavelength and frequency equals the speed of the wave. When electromagnetic waves have wavelengths in the range from 400 nanometers to 700 nanometers,(a nanometer is one billionth of a meter) they are visible to humans and are known as light. When electromagnetic waves have other wavelengths, they are known by other names, such as [[X-Rays|x-rays]], ultraviolets rays, microwaves, and radio waves. Thus, the definition of light is given by human physiology, but the other divisions of the electromagnetic spectrum are more arbitrary. The full range of wavelengths is known as the electromagnetic spectrum.

A wave is characterized by its wavelength—the distance from one crest to the next—and by its frequency—the number of crests per second. For any wave, the product of wavelength and frequency equals the speed of the wave. When electromagnetic waves have wavelengths in the range from 400 nanometers to 700 nanometers,(a nanometer is one billionth of a meter) they are visible to humans and are known as light. When electromagnetic waves have other wavelengths, they are known by other names, such as [[X-Rays|x-rays]], ultraviolets rays, microwaves, and radio waves. Thus, the definition of light is given by human physiology, but the other divisions of the electromagnetic spectrum are more arbitrary. The full range of wavelengths is known as the electromagnetic spectrum.

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