Question
Wed May 23, 2012 By:
 

The metre is defined as the distance travelled by light in 1/299,792,458 second. Why didn't people choose some easier number such as1/300,000,000 second? Why not 1 second? please explain me nicely.

Expert Reply
Wed May 23, 2012
The meter (abbreviation, m; the British spelling is metre) is the International System of Units (SI) unit of displacement or length. One meter is the distance traveled by a ray of electromagnetic (EM) energy through a vacuum in 1/299,792,458 (3.33564095 x 10-9) of a second. The meter was originally defined as one ten-millionth (0.0000001 or 10-7) of the distance, as measured over the earth's surface in a great circle passing through Paris, France, from the geographic north pole to the equator.
 
The meter and its kin are used to specify the wavelengths of EM fields. The so-called radio spectrum occupies an informally defined range of wavelengths from roughly a millimeter (microwaves) to several tens of kilometers (myriametric waves). A 3-m radio wave falls near the middle of the standard FM (frequency modulation) broadcast band; a 300-m radio wave is near the middle of the standard AM (amplitude-modulation) broadcast band. The range of visible light wavelengths is from approximately 390 nm (violet) to 770 nm (red). The speed of EM-field propagation in a vacuum, to nine significant figures, is 2.99792458 x 108 meters per second. In this sense, the meter can be derived from the second if the latter unit has been previously defined in absolute terms; one meter is the distance a ray of light travels through a vacuum in 3.33564095 x 10-9 second.
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