Category: Physics Dictionary

Absorption spectroscopy: Any of various spectroscopic techniques that measure the absorption of electromagnetic radiation due to its interaction with a sample. The sample absorbs energy, i.e. photons, from the radiating field. The intensity of the absorption varies as a function of frequency or wavelength, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.

Absolute zero : The theoretical lowest possible temperature, understood by international agreement as equivalent to 0 Kelvin or −273.15 °C (−459.67 °F). More formally, it is the theoretical lower limit of the thermodynamic temperature scale, at which enthalpy and entropy of a cooled ideal gas reach their minimum values and the fundamental particles of nature have minimal vibrational motion.

Absolute scale: Any system of measurement that begins at a minimum, or zero point, and progresses in only one direction. The zero point of an absolute scale is a natural minimum, leaving only one direction in which to progress, whereas an arbitrary or “relative” scale begins at some point selected by a person and can progress in both directions.

Absolute pressure: Is zero-referenced against a perfect vacuum, using an absolute scale, so it is equal to gauge pressure plus atmospheric pressure.

Absolute humidity: The ratio of the water vapor in a sample of air to the volume of the sample.

Absolute electrode potential : In electrochemistry, the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).

Abbe number:  Also called the V-number or constringence. In optics and lens design, a measure of a transparent material’s dispersion (a variation of refractive index versus wavelength). High values of V indicate low dispersion.

Ab initio: A mathematical model which seeks to describe atomic nuclei by solving the non-relativistic Schrödinger equation for all constituent nucleons and the forces that exist between them. Such methods yield precise results for very light nuclei but become more approximate for heavier nuclei.