Units of Measurement/Length

Length l L metre m centimetre cm foot ft SI units The base unit of length in the SI system is the metre. This has had several definitions over time: 1889 The International Bureau of Weights and Measures defines the metre as the distance between two marks on a platinum-iridium alloy bar (the International Prototype Metre). This prototype is kept in a vault in Sèvres, near Paris. 1960 The 11th General Conference on Weights and Measures Conférence Générale des Poids et Mesures Compte rendu des séances de la 11e Conférence générale des Poids et Mesures 1960 Gauthier-Villars Paris 85 redefines the metre in terms of a specific number of wavelengths of light of a specific frequency in a vacuum. It is defined to be 1 650 763.73 wavelengths of the electromagnetic radiation emitted by an electron transitioning between the levels 2p10 and 5d5 of the krypton-86 (86Kr) atom in a vacuum. The metre is now defined in terms of reproducible physical effects, rather than a synthetic artifact. 1983 The 17th General Conference on Weights and Measures Conférence Générale des Poids et Mesures Compte rendu des séances de la 13e Conférence générale des Poids et Mesures 1983 redefines the metre in terms of the distance traversed by light (having a universally constant speed in a vacuum) in a specific time. It is defined as the distance traveled by a beam of light in a vacuum in 1/299 792 458 second. This is the current definition. This has the effect that the speed of light is defined to be exactly 299 792 458 m/s. +Conversion of metric units of lengthAfter Diem, K., Lentner, C. (ed.) Documenta Geigy Scientific Tables 7th ed. 1970 J.R. Geigy S.A. Basle Bold text Physics 200 ABUnitSymbolpmnmμmmmcmmkmpicometrepm 1 10-310-610-910-1010-1210-15ångström†Å10210−110−410−710−810−1010−13nanometrenm103 1 10−310−610−710−910−12micrometreμm106103 1 10−310−410−610−9millimetremm109106103 1 10−110−310−6centimetrecm1010107104101 1 10−210−5metrem1012109106103102 1 103kilometrekm10151012109106105103 1 1 A unit = b B units (b given in the table) † Ångström is accepted for use with, but not defined by the SI system. Its use is officially discouraged by the CIPM. Imperial units One international yard is defined as 0.914 4 m Astronomical units External links References