China
Africa
Explore chapters and articles related to this topic
Introduction
Published in Benjamin D. Shaw, Uncertainty Analysis of Experimental Data with R, 2017
Physical constants are present in almost all calculations in science and engineering, so it is crucial to have accurate numerical values for these constants. A source of values of physical constants is available [10]. Unless they are defined exactly, physical constants have uncertainties associated with them. For example, the standard acceleration of gravity and the speed of light in vacuum are defined exactly, but the universal gas constant is not. Current values (as of 2014) for a few physical constants and their relative standard uncertainties are listed in Table 1.3. The relative standard uncertainty of a quantity is the ratio of the standard deviation of the distribution of this quantity to its mean value. These uncertainties, which are typically very small, will be present in every calculation that uses these constants.
†
Published in Seán M. Stewart, R. Barry Johnson, Blackbody Radiation, 2016
Seán M. Stewart, R. Barry Johnson
Shortly after Canada’s paper appeared, news of the rule’s availability was quickly reported [5, 3, 43, 4] and it was not long before others started referring to his rule in the technical literature [222, 359]. The rule itself could be obtained postpaid for $0.75 from the General Electric Company, 1 River Road, Schenectady, New York. A revised rule designated the GEN-15A was released in April 1952. It is almost identical to the GEN-15 except in one important regard. The gauge mark of 1/(2π) on each of the emissivity scales have been replaced with a gauge mark of 1/π. Since the total radiance L for a blackbody is related to the total radiant exitance M by M = πL, the scale allowed for the determination of both total radiant exitance and total radiance and corrected the erroneous gauge mark of 1/(2π) printed on the GEN-15. An emissivity equal to one gives the total radiant exitance for a blackbody while at the gauge mark of 1/π the corresponding total radiance for a black-body in units of watts per square centimeter per steradian [W·cm−2·sr−1] at the particular temperature setting chosen can be found. Another difference, though only minor, is the removal of “General Engineering and Consulting Laboratory” from just below the rule’s name at the top left of the front of the rule and the shifting in the placement of the General Electric logo to a location slightly further down the front face of the rule. Values of all physical constants remained unchanged.
Extraction of spin-averaged rovibrational transition frequencies in HD+ for the determination of fundamental constants
Published in Molecular Physics, 2023
J.-Ph. Karr, Jeroen C. J. Koelemeij
Fundamental physical constants are determined from precision measurements, often performed on single particles or simple atomic quantum systems, by adjusting the values of the constants such that theoretical predictions match the experimental observations as closely as possible. Such adjustments, implemented via least-squares optimisation of the constants of interest with respect to large bodies of input data, are carried out by standards organisations such as the Committee on Data for Science and Technology (CODATA) and the Atomic Mass Data Centre (AMDC).