More precise
definition of a few metric (
SI) base units:
- s - second: One
second is 9 192 631 770 periods of the radiation corresponding to the transition between
the two hyperfine levels of the ground state of the cesium-133 atom.
- m - meter/metre:
One meter is the distance light travels in 1/299 792 458 of a second.
- A - ampere:
One ampere is the constant current which would produce a force of 2*10^-7 newton per meter of
length when the currant is maintained in two straight parallel conductors of infinite length
and neglectible circular cross section placed one meter apart in vacuum.
- K - kelvin:
The kelvin, unit of thermodynamic temperature, is the fraction of 1/237.16 of the
thermodynamic temperature of the triple point of water.
- kg - kilogram: A kg is equal to the mass of the international
prototype of the kilogram. (A particular cylinder of platinum-iridium alloy that is
preserved in a vault at Sevres, France.) (Duh!)
- cd - candela: The luminous intensity, in a given direction, of
a source that emits monochromatic radiation of frequency 540 * 10^12 hertz and that has a
radiant intensity in that direction of 1/683 watt per steradian.
- mol - mole: The amount of a substance that contains as many elementary entities as there are carbon atoms in 0.012 kg of carbon 12
And so on... most of the others are derived from these.
Sources:
- Tabeller og formelsamling / Gyldendal norsk forlag AS 2001
- University Physics / Young & Freedman / Addison-Wesley Publishing Company, Inc. 1996
(Thanks to
Professor Pi for correcting some horrible errors)