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发表于 2010-3-3 15:52:24
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原帖由 井蛙 于 2010-3-3 07:28 发表 
谢谢你让俺们知道了什么是欧姆定律。俺你的说法，电流也应该是导出单位（俺依稀记得每秒流过一库伦的电量就是一安培）。还有一个疑问，如果电阻和电压“永远不可能找到基准”，生产相关测量仪表的部门是如何对仪表进 ...
偶没有提醒你什么是欧姆定律, 对不起!
FYI:
安培是電流的國際單位，簡稱為安，符號為A，定義為：在真空中相距為1米的兩根無限長平行直導線，通以相等的恆定電流，當每米導線上所受作用力為2×10-7N時，各導線上的電流為1安培。
Ampère's force law[4][5] states that there is an attractive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ampere which states that it is the constant current which will produce an attractive force of 2 × 10–7 newtons per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum.[1][6][7]
* http://www.bipm.org/en/si/si_brochure/chapter2/2-1/ampere.html
* The BIPM does not distinguish between quantum vacuum and free space.
* Paul M. S. Monk, Physical Chemistry: Understanding our Chemical World, John Wiley and Sons, 2004
online ( http://books.google.com/books?vi ... ymmLNYFMcXodwJZwvAM ).
The ampere is most accurately realised using a watt balance, but is in practice maintained via Ohm's Law from the units of electromotive force and resistance, the volt and the ohm, since the latter two can be tied to physical phenomena that are relatively easy to reproduce, the Josephson junction and the quantum Hall effect, respectively.[11]
http://www.bipm.org/en/si/si_brochure/appendix2/electrical.html
At present, techniques to establish the realisation of an ampere have a relative uncertainty of approximately a few parts in 107, and involve realisations of the watt, the ohm and the volt.[12]
http://www.bipm.org/en/si/si_brochure/appendix2/electrical.html
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The realization to high accuracy of the ampere (a base unit of the SI), the ohm and the volt (derived units of the SI) directly in terms of their definitions is difficult and time consuming. The best such realizations of the ampere are now obtained through combinations of realizations of the watt, the ohm and the volt. The watt realized electrically is compared by balance experiments with the watt realized mechanically. These experiments employ a coil in a magnetic flux and are devised in such a way that it is not necessary to know either the dimensions of the coil or the magnitude of the flux density. The ohm is realized using a Thompson-Lampard capacitor whose capacitance value can be changed by an amount that depends only on the magnitude of a linear displacement of a guard electrode. The volt is realized by means of a balance in which an electrostatic force is measured in terms of a mechanical force. The ampere may thus be deduced from combinations of any two of these units. The relative uncertainty in the value of the ampere obtained in this way is estimated to be a few parts in 107. The ampere, ohm and volt may also be determined from measurements of various combinations of physical constants. Laboratory reference standards for the volt and the ohm based upon the Josephson and quantum-Hall effects are, however, significantly more reproducible and stable than a few parts in 107. In order to take advantage of these highly stable methods of maintaining laboratory reference standards of the electrical units while at the same time taking care not to change their SI definitions, the 18th CGPM in 1987 adopted Resolution 6 which calls for representations of the volt and the ohm to be based on conventional values for the Josephson constant KJ and the von Klitzing constant RK.
这就是你要的答案, 现实当中的基准是怎么来的.
[ 本帖最后由 e3po 于 2010-3-3 15:57 编辑 ] |
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发表于 2010-3-3 07:27:22
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