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IMPERIAL UNIT MEASUREMENT [2 records]

Filter results by subject field Alphabetical list of terms

Filter results by subject field

Alphabetical list of terms

Record 1 2007-10-25

English

Subject field(s)
  • Electromagnetic Radiation
DEF

The speed at which light and other magnetic waves travel through empty space.

CONT

The velocity of light is 2.9979 x 108 m/s.

CONT

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 radiations, including visible light, in a vacuum. More generally, it is the speed of anything having zero rest mass.... In metric units, the speed of light is exactly 299, 792, 458 metres per second(1, 079, 252, 848. 8 km/h). The fundamental SI unit of length, the metre, has been defined since October 21, 1983, as the distance light travels in a vacuum in 1/299, 792, 458 of a second; any increase in the precision of the measurement of the speed of light would refine the definition of the metre, but not alter the numerical value of c. The approximate value of 3x108 m/s is commonly used in rough estimates. In imperial units, the speed of light is about 670, 616, 629. 2 miles per hour or 983, 571, 056 feet per second, which is about 186, 282, 397 miles per second, or roughly one foot per nanosecond. The speed of light when it passes through a transparent or translucent material medium, like glass or air, is slower than its speed in a vacuum. The ratio of c to the observed phase velocity is called the refractive index of the medium.

French

Domaine(s)
  • Rayonnements électromagnétiques
DEF

Vitesse de propagation de la lumière dans le vide.

CONT

La vitesse de la lumière est 2.9979 x 108 m/s.

Spanish

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Record 2 2003-10-23

English

Subject field(s)
  • Metrology and Units of Measure
DEF

A unit of measurement historically used in the United Kingdom and other English-speaking countries. Units include inch, foot, yard, mile, acre, ounce, pound, stone, ton, pint, quart and gallon.

OBS

Now largely replaced by metric units.

French

Domaine(s)
  • Unités de mesure et métrologie
CONT

Principales unités de mesure anglo-saxonnes. longueur : [...] pouce, pied [...] masse-avoir-du-poids (commerce) : once, livre, [...] capacité : gallon britannique [...]

Spanish

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