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家园 请教 什么是三相点？水的固液分界点是0C，但是水蒸气在100C以下同样存在。三相点和绝对零度是否有关系？
- 复 请教
家园 水蒸气非气也 乃是液态水遇到冷空气形成的细小水滴悬浮在空气中，实质还是液态，所以用水蒸汽更合适些。
气态水要在摄氏100度以下存在，必须要减小气压。
- 复 请教
家园 三相点是物质气液固同时存在的点 需要特定的温度和压力。偏离了这个温度压力，就不是三相点了。
水的三相点不是水的冰点，也不是水的沸点。冰点和沸点都与压力有关系。
水的三相点是温度273.16K，压力0.611kPa。
由于水的三相点是水本身的性质决定的，这样就定义水的三相点就是273.16K，再加上绝对零度是已知的，有了两个点，就可以推导出1K究竟是多少。
家园 千克定义估计又要改了 Proposed future definitionSince a coulomb is approximately equal to 6.24150948×10^18 elementary charges, one ampere is approximately equivalent to 6.24150948×10^18 elementary charges, such as electrons, moving past a boundary in one second.
As with other SI base units, there have been proposals to redefine the kilogram in such a way as to define some presently measured physical constants to fixed values. One proposed definition of the kilogram is:
“ The kilogram is the mass which would be accelerated at precisely 2×10^-7 m/s^2 if subjected to the per metre force between two straight parallel conductors of infinite length, of negligible circular cross section, placed 1 metre apart in vacuum, through which flow a constant current of exactly 6 241 509 479 607 717 888 elementary charges per second. ”
This redefinition of the kilogram has the effect of fixing the elementary charge to be e = 1.60217653×10^-19 C and would result in a functionally equivalent definition for the coulomb as being the sum of exactly 6 241 509 479 607 717 888 elementary charges and the ampere as being the electrical current of exactly 6 241 509 479 607 717 888 elementary charges per second. This is consistent with the current 2002 CODATA value for the elementary charge which is 1.60217653×10^-19 ± 0.00000014×10^-19 C.
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家园 小白一下。千克 这两天咋了？
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