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PowerPedia:Meter

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The metre (or meter, see There was an error working with the wiki: Code[2]) is a measure of There was an error working with the wiki: Code[3] of There was an error working with the wiki: Code[4] below).

History

The word There was an error working with the wiki: Code[5] is from the Greek metron (There was an error working with the wiki: Code[1]), "a There was an error working with the wiki: Code[6]" via the French mètre. Its first recorded usage in English meaning this unit of length is from 1797.

In the eighteenth century, there were two favoured approaches to the definition of the standard unit of length. One suggested defining the metre as the length of a There was an error working with the wiki: Code[7] of one There was an error working with the wiki: Code[8] along a quadrant, that is the distance from the equator to the north pole. In 1791, the There was an error working with the wiki: Code[9] between There was an error working with the wiki: Code[20] and There was an error working with the wiki: Code[21]. This portion of the meridian, which also passes through There was an error working with the wiki: Code[22], was to serve as the basis for the length of the quarter meridian, connecting the There was an error working with the wiki: Code[23] with the There was an error working with the wiki: Code[24]. However, in 1793, France adopted the metre based on provisional results from the expedition as its official unit of length. Although it was later determined that the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the Earth, this length became the standard. So, the circumference of the There was an error working with the wiki: Code[25] through the poles is approximately forty million metres.

In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The There was an error working with the wiki: Code[26] (Convention du Mètre) of 1875 mandated the establishment of a permanent There was an error working with the wiki: Code[27] (BIPM: Bureau International des Poids et Mesures) to be located in There was an error working with the wiki: Code[28], France. This new organisation would preserve the new prototype metre and There was an error working with the wiki: Code[29] when constructed, distribute national metric prototypes, and would maintain comparisons between them and non-metric measurement standards. This organisation created a new prototype bar in 1889 at the first There was an error working with the wiki: Code[30] (CGPM: Conférence Générale des Poids et Mesures), establishing the International Prototype Metre as the distance between two lines on a standard bar of an alloy of ninety percent There was an error working with the wiki: Code[31] and ten percent There was an error working with the wiki: Code[32], measured at the melting point of ice.

In 1893, the standard metre was first measured with an There was an error working with the wiki: Code[10], the inventor of the device and an advocate of using some particular There was an error working with the wiki: Code[11] defined the metre in the new There was an error working with the wiki: Code[12]-There was an error working with the wiki: Code[33] There was an error working with the wiki: Code[34] in the There was an error working with the wiki: Code[35] of the There was an error working with the wiki: Code[36]-86 Atom in a There was an error working with the wiki: Code[37]. The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889.

To further reduce uncertainty, the seventeenth CGPM in 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of There was an error working with the wiki: Code[38] and the There was an error working with the wiki: Code[39]:

:The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.Resolution 1 of the seventeenth CGPM (1983): Definition of the metre

Note that this definition had the effect of fixing the speed of light in a vacuum at precisely 299,792,458 metres per second. Although the metre is now defined in terms of time-of-flight, actual laboratory realisations of the metre are still delineated by counting the required number of wavelengths of light along the distance. An intended byproduct of the 17th CGPM’s definition was that it enabled scientists to measure their lasers’ wavelengths with one-fifth the uncertainty. To further facilitate reproducibility from lab to lab, the 17th CGPM also made the iodine-stabilised Helium-Neon laser “a recommended radiation? for realising the metre.Reference: Time Line for the Definition of the Meter by the NIST. Today’s best determination of the wavelength of this laser is ?HeNe&nbsp=&nbsp632.991&nbsp398&nbsp22&nbspnm with an estimated relative standard uncertainty (U) of ± &nbsp2.5&nbsp×&nbsp10-11. This uncertainty is currently the limiting factor in laboratory realisations of the metre as it is several orders of magnitude poorer than that of the second (U&nbsp=&nbsp1&nbsp×&nbsp10-14). Consequently, a practical realisation of the metre is usually delineated (not defined) today in labs as 1,579,800.298&nbsp728 ±&nbsp0.000&nbsp039 wavelengths of Helium-Neon laser light in a vacuum.

Timeline of definition

There was an error working with the wiki: Code[13] decides that the length of the new metre would be equal to the length of a There was an error working with the wiki: Code[14] of one There was an error working with the wiki: Code[40].

There was an error working with the wiki: Code[15] along a quadrant through Paris, that is the distance from the equator to the north pole.

1795 &mdash Provisional metre bar constructed of There was an error working with the wiki: Code[41].

There was an error working with the wiki: Code[16], as the final standard.

There was an error working with the wiki: Code[42]There was an error working with the wiki: Code[43] &mdash The first There was an error working with the wiki: Code[44] (CGPM) defines the length as the distance between two lines on a standard bar of an alloy of There was an error working with the wiki: Code[45] with ten percent There was an error working with the wiki: Code[46], measured at the melting point of ice.

There was an error working with the wiki: Code[17], between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard There was an error working with the wiki: Code[18] and supported on two cylinders of at least one centimetre diameter, symmetrically placed in the same horizontal plane at a distance of 571 millimetres from each other.

There was an error working with the wiki: Code[19] corresponding to the transition between the 2p10 and 5d5 quantum levels of the There was an error working with the wiki: Code[47]-86 Atom.

There was an error working with the wiki: Code[48]There was an error working with the wiki: Code[49] &mdash The seventeenth CGPM defines the length as equal to the distance travelled by There was an error working with the wiki: Code[50] in There was an error working with the wiki: Code[51] during a time interval of 1/299 792 458 of a There was an error working with the wiki: Code[52].

SI prefixed forms of metre

There was an error working with the wiki: Code[53]es are often employed to denote decimal multiples and submultiples of the metre. The most commonly used factors of metre are listed below in bold.The term “most commonly used? is based on those with more than 5 million Google hits on the American spelling.

{| border="1" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0 background: #f5f5f5 border: 2px #525252 solid border-collapse: collapse font-size: 95%"

|-

|style="background:#d4d4d4" align="center"|Factor

|style="background:#d4d4d4" align="center"|Name

|style="background:#d4d4d4" align="center"|Symbol

|style="background:#d4d4d4" align="center"|

|style="background:#d4d4d4" align="center"|Factor

|style="background:#d4d4d4" align="center"|Name

|style="background:#d4d4d4" align="center"|Symbol

|-

|align="center"|10&minus1

|decimetre

|align="center"|dm

|

|align="center"|101

|decametre

|align="center"|dam

|-

|align="center"|10&minus2

|centimetre

|align="center"|cm

|

|align="center"|102

|hectometre

|align="center"|hm

|-

|align="center"|10&minus3

|millimetre

|align="center"|mm

|

|align="center"|103

|kilometre

|align="center"|km

|-

|align="center"|10&minus6

|micrometre

|align="center"|µm

|

|align="center"|106

|megametre

|align="center"|Mm

|-

|align="center"|10&minus9

|nanometre

|align="center"|nm

|

|align="center"|109

|gigametre

|align="center"|Gm

|-

|align="center"|10&minus12

|picometre

|align="center"|pm

|

|align="center"|1012

|terametre

|align="center"|Tm

|-

|align="center"|10&minus15

|femtometre (fermi)

|align="center"|fm

|

|align="center"|1015

|petametre

|align="center"|Pm

|-

|align="center"|10&minus18

|attometre

|align="center"|am

|

|align="center"|1018

|exametre

|align="center"|Em

|-

|align="center"|10&minus21

|zeptometre

|align="center"|zm

|

|align="center"|1021

|zettametre

|align="center"|Zm

|-

|align="center"|10&minus24

|yoctometre

|align="center"|ym

|

|align="center"|1024

|yottametre

|align="center"| Ym

|}

Equivalents in other units

{| border="1" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0 background: #f5f5f5 border: 2px #525252 solid border-collapse: collapse font-size: 95%"

|-

! SI value !! Other unit

|-

| 1 metre || 10000/254 ? 39.37 There was an error working with the wiki: Code[54]es

|-

| 2.54 centimetres || 1 inch

|-

| 1 nanometre || 10 There was an error working with the wiki: Code[55]s

|}

Related

There was an error working with the wiki: Code[56]

SI (International System of Units)

There was an error working with the wiki: Code[57]

There was an error working with the wiki: Code[58] for comparisons with other units

There was an error working with the wiki: Code[59]

There was an error working with the wiki: Code[60]

There was an error working with the wiki: Code[61]

External articles

References

Bureau International des Poids et Mesures. The BIPM and the evolution of the definition of the metre. URL accessed on There was an error working with the wiki: Code[62] There was an error working with the wiki: Code[63].

———. Resolutions of the CGPM. URL accessed on There was an error working with the wiki: Code[64] There was an error working with the wiki: Code[65].

Penzes, William B. at the U.S. National Institute of Standards and Technology Precision Engineering Division (There was an error working with the wiki: Code[66] There was an error working with the wiki: Code[67]). Time Line for the Definition of the Meter. URL accessed on There was an error working with the wiki: Code[68] There was an error working with the wiki: Code[69].

U.S. National Institute of Standards and Technology (October 2000). The NIST Reference on Constants, Units, and Uncertainty: International System of Units (SI):

SI base units. URL accessed on There was an error working with the wiki: Code[70] There was an error working with the wiki: Code[71].

Definitions of the SI base units. URL accessed on There was an error working with the wiki: Code[72] There was an error working with the wiki: Code[73].

Historical context of the SI: meter. URL accessed on There was an error working with the wiki: Code[74] There was an error working with the wiki: Code[75].

Other

Length—Evolution from Measurement Standard to a Fundamental Constant at U.S. NIST

The History of the Meter By Tibo Qorl (Translated by Sibille Rouzaud)

There was an error working with the wiki: Code[76]

There was an error working with the wiki: Code[77]

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