what is the speed of light ?

Article ID : 41
Created on 2007-07-20 at 9:39 AM
Author : Rahul Bhanot [rahulbhanot@yahoo.com]

Online URL : http://www.knowledge-gallery.com/question.php?ID=41


The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning "swiftness". It is the speed of all electromagnetic radiation in a vacuum, including visible light, and more generally it is the speed of anything with zero rest mass.

In metric units, c is exactly 299,792,458 metres per second (1,079,252,848.8 km/h) but 3×108 m/s is commonly used in rough estimates. Note that this speed is a definition, not a measurement. Because the fundamental SI unit of length, the metre, has been defined since October 21, 1983 in terms of the speed of light, one metre is the distance lightAAA+ 2015 New Fashion cheap replica watcheshttp://www.select.org.uk/image.php?p=Replica-Movado-watches.htmlhttp://www.cssa-unn.com/stall.phphttp://www.select.org.uk/image.php?p=breitling-replica.htmlAudemars Piguet replicareplica watches ukhttp://www.select.org.uk/image.php?p=swiss-replica-wtches.htmlPanerai Replica WatchesIWC Replica Watchesbreitling replicaPatek Philippe Replicacopy watcheshttp://www.select.org.uk/image.php?p=cartier-replica.htmlSWISS REPLICA WATCHES is Very Special In Our Store.
travels in a vacuum in 1/299,792,458 of a second. Thus, any further increase in the precision of the measurement of the speed of light will actually change the length of the metre; the speed of light will remain precisely 299,792,458 m/s. In imperial units, the speed of light is about 186,282.397 miles per second, that is about one foot per nanosecond.
 
A line showing the speed of light on a scale model of Earth and the Moon
A line showing the speed of light on a scale model of Earth and the Moon
 
When passing through a transparent or translucent material medium, like glass or air, light will have a slower speed than in a vacuum; the ratio of c to the observed phase velocity is called the refractive index of the medium. In general relativity, a gravitational potential can affect the speed of distant light in a vacuum, but locally light in a vacuum will always pass an observer at a rate of c.
 
 
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