Page 59 - The Illustrated Dictionary of Electronics

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44 atmospheric bending • atomic radiation

atmospheric bending The refraction or reflection
of electromagnetic waves by the troposphere or
ionosphere. See ATMOSPHERIC REFLECTION.
atmospheric duct A tropospheric stratum, often
associated with temperature inversions, lake ef-
fects, or weather fronts, through which electro-
magnetic energy at ultra-high and microwave
frequencies is efficiently propagated for long dis-
tances.

bending of radio waves in the ionosphere, result-
ing in long-range propagation at high frequencies.
atmospheric scatter 1. The scattering of very-high
frequency (VHF) and ultra-high frequency (UHF)
radio waves by the lower atmosphere. 2. Commu-
nication via scattering of VHF and UHF radio
waves in the lower atmosphere.
atmospherics See ATMOSPHERIC NOISE.
atom 1. The smallest material particle that dis-
plays the unique characteristics and properties of
an element. Atoms consist of a dense, positively
charged central nucleus, around which less-mas-
sive, negatively charged electrons “swarm” at def-
atmospheric electricity Static electricity present inite levels called shells. Also see BOHR ATOM
in the atmosphere, which evidences itself in dis- and RUTHERFORD ATOM. 2. In a computer-
turbance of radio communications and in dis- compiling operation, an operator or operand.
plays of lightning. atomechanics The physics of electron movement.
atmospheric noise Receiver noise resulting from atomic battery A battery in which atomic energy is
ATMOSPHERIC ELECTRICITY. Also called sferics converted into electrical energy.
or static. atomic charge The electrification (i.e., the electron
atmospheric pressure Abbreviation, atm press. 1. charge) exhibited by an ion.
The pressure exerted by the earth’s atmosphere, atomic clock Also called atomic time standard. A
as indicated by a barometer at sea level; normally highly accurate electronic clock, driven by the
between 29 and 31 inches of mercury. 2. A pres- characteristic oscillations of certain atoms.
6
sure of 1.013 × 10 dynes per square centimeter. atomic energy Energy released by the FUSION or
See ATMOSPHERE, 2. FISSION of atomic nuclei. Also see ATOMIC
atmospheric radio wave See SKYWAVE. POWER.
atmospheric radio window The band of frequen- atomic fission See FISSION.
cies (approximately 10 MHz to 10 GHz), including atomic frequency The natural vibration frequency
radio waves that can penetrate the earth’s tropo- of an atom.
sphere and ionosphere. atomic fusion See FUSION.
atmospheric reflection The return of a radio wave atomic pile See REACTOR, 2.
to earth, resulting from reflection by an ionized atomic mass unit Abbreviated amu. A unit that
portion of the atmosphere. expresses the relative mass of an elemental iso-
tope. One amu is equal to 1⁄12 of the atomic mass
of carbon 12 (C12). A neutron has a mass of
roughly one amu.
atomic migration The transfer or “wandering” of a
valence electron between or among atoms in a
single molecule.
atomic number The number of protons in the nu-
cleus of an atom. Also, the number of electrons if
the atom is electrically neutral. For example, the
atomic number for copper is 29, indicating 29
protons in the nucleus. An electrically neutral
atom of copper has 29 electrons. The atomic
atmospheric refraction 1. Downward bending of number uniquely identifies an element.
radio waves as a result of variations in the dielec- atomic radiation The emission of radiant energy
tric constant of the troposphere. 2. Downward by radioactive substances.