# 請問目前使用的各種單位分別是何時定義的？

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公尺(metre):

The 1889 definition of the metre, based upon the international prototype of platinum-iridium, was replaced by the 11th CGPM (1960) using a definition based upon a wavelength of krypton 86 radiation. This definition was adopted in order to improve the accuracy with which the metre may be realized. In turn, this was replaced in 1983 by the 17th CGPM (Resolution 1): "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. "Note that the effect of this definition is to fix the speed of light at exactly 299 792 458 m · s–1. The original international prototype of the metre, which was sanctioned by the 1st CGPM in 1889 (CR, 34-38), is still kept at the BIPM under conditions specified in 1889.

2006-01-18 12:43:15 補充：

秒(second):The definition of the second by the following: "The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom."

2006-01-18 12:44:32 補充：

續(秒):At its 1997 meeting, the CIPM affirmed that:"This definition refers to a caesium atom at rest at a temperature of 0 K."

2006-01-18 12:47:06 補充：

續(秒):"The definition of the SI second is based on a Cs atom unperturbed by black-body radiation, and that the frequencies of primary frequency standards should therefore be corrected for the shift due to ambient radiation" as stated at the meeting of the CCTF in 1999.

2006-01-18 12:48:23 補充：

公斤(kilogram):The 3rd CGPM (1901), in a declaration intended to end the ambiguity in popular usage concerning the word "weight" confirmed that: "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram."

2006-01-18 12:52:32 補充：

焦耳(J,joule)為導出單位(derived unit)代表的物理量:energy, work, quantity of heatExpressed in terms of SI base units: m^2 · kg · s^-2

Source(s): BIPM 國際度量衡局 http://www.bipm.fr/