Speed of Light

The Physics Factbook
Edited by Glenn Elert -- Written by his students
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Bibliographic Entry Result
(w/surrounding text)
Serway, Raymond A., & Robert J. Beichner. Physics for Scientists and Engineers, Fifth Edition. USA: Saunders College Publishing, 2000. "The waves travel through a vacuum with the speed of light c, where " 3.00 × 108 m/s
"Light." World Book Encyclopedia. 2000 Edition. Chicago: World Book, 2000. "The speed of light in empty space- where atoms do not delay its travel- is 186,282 miles (299,792 kilometers) per second." 3.00 × 108 m/s
"Light, Electromagnetic Theory of." Macmillan Encyclopedia of Physics. New York: Simon & Schuster Macmillan, 1996. "… regardless of the motion of the observer, the speed of light always came out to be the same value, c = 3 × 108 m/s, with respect to the experimenter." 3.00 × 108 m/s
Fowler, Michael. The Speed of Light. University of Virginia, 1996. "… and a few years later Newton wrote in the Principia (Book I, section XIV): 'For it is now certain from the phenomena of Jupiter's satellites, confirmed by the observations of different astronomers, that light is propagated in succession (NOTE: I think this means at finite speed) and requires about seven or eight minutes to travel from the sun to the earth.'" 3.12–3.56 × 108 m/s
Historical Content of the SI: Unit of Length (Meter). National Institute of Standards and Technology. "The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second." 3.00 × 108 m/s

Light, which is a form of electromagnetic wave, is a phenomenon that has puzzled scientists for centuries. It was originally believed that the speed of light was not constant. Then in 1676 a Danish astronomer named Ole Romer made one of the first theories for a fixed value, c, the speed of light through free space. He theorized that, from watching the eclipse patterns of Jupiter and its moon, Io, that light travels at a finite speed due to the fact that the eclipses were seen from earth at different times than they actually occurred. The occurred latest when Io was furthest from earth and earliest when Io was closest to earth. This was due to the time required for the light to travel from Io to the earth's surface.

Presently, the speed of light has a fixed value of 299,792,458 m/s. Using Maxwell's equations, a relationship

can be derived that relates the speed of light to the fundamental constants ε0 and μ0, which are the vacuum permitivity and the permeability of free space. The speed of light can be defined as the speed it takes light to travel one meter in 1/299,792,458 of a second.

Johnny Alicea -- 2002

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