preface to fifteenth edition

GENERAL INFORMATION, CONVERSION TABLES, AND MATHEMATICS 2.3
2.1 GENERAL INFORMATION AND CONVERSION
TABLES
TABLE 2.1 Fundamental Physical Constants
E. R. Cohen and B. N. Taylor, CODATA Bull. 63:1–49 (1986); J. Res. Nat. Bur. Standards, 92:85 (1987).
A. Defined values
Physical quantity
Name of
SI unit
Symbol for
SI unit
Definition
1. Base SI units
Amount of substance mole mol Amount of substance which contains as many
specified entities as there are atoms of carbon-12
in exactly 0.012 kg of that nuclide.
The elementary entities must be specified
and may be atoms, molecules, ions, electrons,
other particles, or specified groups
of such particles.
Electric current ampere A Magnitude of the current that, when flowing
through each of two straight parallel conductors
of infinite length, of negligible
cross-section, separated by 1 meter in a
vacuum, results in a force between the two
wires of 2 10 7 newton per meter of
length.
Length meter m Distance light travels in a vacuum during
1/299 792 458 of a second.
Luminous intensity candela cd 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.
Mass kilogram kg Mass of a cylinder of platinum-iridium alloy
kept at Paris.
Temperature kelvin K Defined as the fraction 1/273.16 of the thermodynamic
temperature of the triple point
of water.
Time second s 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 cesium-133 atom.
2. Supplementary SI units
Plane angle radian rad The plane angle between two radii of a circle
which cut off on the circumference an arc
equal in length to the radius.
Solid angle steradian sr The solid angle which, having its vertex in
the center of a sphere, cuts off an area of
the surface of the sphere equal to that of a
square with sides of length equal to the radius
of the sphere.