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Titelseite 页码，1/1 Electronic Automotive Handbook 1. Edition © Robert Bosch GmbH, 2002 Choose a chapter in the table of contents or start with the first page. file://D:\bosch\bosch\daten\eng\titel.html 2008-1-13 Basic principles, Physics 页码，1/9 Basic principles, Physics Quantities and units SI units SI denotes "Système International d'Unités" (International System of Units). The system is laid down in ISO 31 and ISO 1000 (ISO: International Organization for Standardization) and for Germany in DIN 1301 (DIN: Deutsches Institut für Normung – German Institute for Standardization). SI units comprise the seven base SI units and coherent units derived from these base Sl units using a numerical factor of 1. Base SI units Base quantity and symbols Base SI unit Name Symbol Length l meter m Mass m kilogram kg Time t second s Electric current I ampere A Thermodynamic temperature T kelvin K Amount of substance n mole mol Luminous intensity I candela cd All other quantities and units are derived from the base quantities and base units. The international unit of force is thus obtained by applying Newton's Law: force = mass x acceleration where m = 1 kg and a = 1 m/s2, thus F = 1 kg · 1 m/s2 = 1 kg · m/s2 = 1 N (newton). Definitions of the base Sl units 1 meter is defined as the distance which light travels in a vacuum in 1/299,792,458 seconds (17th CGPM, 19831). The meter is therefore defined using the speed of light in a vacuum, c = 299,792,458 m/s, and no longer by the wavelength of the radiation emitted by the krypton nuclide 86Kr. The meter was originally defined as the fortymillionth part of a terrestrial meridian (standard meter, Paris, 1875). 1 kilogram is the mass of the international prototype kilogram (1st CGPM, 1889 and 3rd CGPM, 19011). 1 second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state file://D:\bosch\bosch\daten\eng\physik\groessen.html 2008-1-10 Basic principles, Physics 页码，2/9 of atoms of the 133Cs nuclide (13th CGPM, 1967.1) 1 ampere is defined as that constant electric current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-sections, and placed 1 meter apart in a vacuum will produce between these conductors a force equal to 2 · 10–7 N per meter of length (9th CGPM, 1948.1) 1 kelvin is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point2) of water (13th CGPM, 1967.1) 1 mole is defined as the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of the carbon nuclide 12C. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles (14th CGPM1), 1971. 1 candela is the luminous intensity in a given direction of a source which emits monochromatic radiation of frequency 540 x 1012 hertz and of which the radiant intensity in that direction is 1/683 watt per steradian (16th CGPM, 1979.1) 1) CGPM: Conférence Générale des Poids et Mesures (General Conference on Weights and Measures). 2) Fixed point on the international temperature scale. The triple point is the only point at which all three phases of water (solid, liquid and gaseous) are in equilibrium (at a pressure of 1013.25 hPa). This temperature of 273.16 K is 0.01 K above the freezing point of water (27