18WuD2x

380 involution • ionization time
involution Raising a number to a power: squaring,
cubing, etc. Compare EVOLUTION.
inward-outward dialing Also called direct dialing.
In a telephone system, a method of dialing in
which calls can be made to and from branch exchanges,
without operator assistance.
I/O Abbreviation of input/output (see INPUT/
OUTPUT EQUIPMENT).
Io Symbol for OUTPUT CURRENT.
iodine Symbol, I. A nonmetallic element of the
halogen family. Atomic number, 53. Atomic
weight, 126.905. Also see HALOGEN.
ion A charged atom [i.e., one that has gained one
or more electrons (a negative ion, or anion) or lost
one or more electrons (a positive ion, or cation)].
ion burn A spot burned on the screen of a cathoderay
tube by negative ions from the cathode striking
a single point on the faceplate with high
intensity for long periods.
ion concentration 1. The number of ions, expressed
as a percentage or as a number per unit
volume, in a substance. 2. Ionization density in
the atmosphere.
ion exchange resins Granular resins that contain
acid or base groups, and that trade ions with
salts in solutions. The resins play a part in the
purification of water for various industrial processes.
ionic binding forces In a crystal, the binding
forces that occur when valence electrons of one
atom are joined to those of a neighboring atom
whose outer shell they fill.
ionic bond In a solid, a bond between atoms,
formed as a result of the attraction between oppositely
charged atoms (ions).
ionic conduction Conduction, as in a gas or electrolyte,
by ion migration (positive to the cathode,
negative to the anode).
ionic crystal A crystal whose lattice is held together
by the electric forces between ions. Also
see IONIC BINDING FORCES and IONIC BOND.
ionic current Current caused by ion movement in
a gas or liquid. Also see ION, IONIZATION, and
IONIC CONDUCTION.
ionic semiconductor A semiconductor in which
the carrier is an ion, as opposed to an electron or
hole.
ionic switch See ELECTROCHEMICAL SWITCH.
ionization 1. The loss or gain of one or more electrons
by an atom. Also see ANION, CATION, and
ION. 2. The formation or existence of significant
numbers of ions in a gas, liquid, or solid (e.g., ionization
of the upper atmosphere).
ionization arc The electrical discharge resulting
from the ionization of a material because of high
voltage.
ionization chamber An enclosure containing a gas
and a pair of electrodes between which a high
voltage is applied. Radiation, such as X rays or
radioactive particles, passing through the walls of
the chamber ionize the gas, creating an ionization
current that is proportional to the intensity of the
radiation.
ionization current 1. Current in an ionized gas
(such as air). 2. Current flowing in an electrolyte.
3. Current in an ionization chamber, Geiger-
Mueller tube, or similar gaseous device. 4. In a
gas tube, current flowing after the ignition potential
has been reached. 5. Negative grid current resulting
from gassiness in a vacuum tube.
ionization density The extent to which ionization
exists in an ionized layer of the atmosphere. The
higher the ionization density, the greater the effect
on radio waves—especially at frequencies below
about 150 MHz.
ionization gauge A form of vacuum tube that can
be used to measure the hardness of a vacuum. It
consists of a cathode, an anode (plate), and a positively
charged grid. Plate current flows as a result
of ionization of the atoms within the tube.
The more nearly perfect the vacuum, the lower
the plate current.
To recorder
and measuring
circuits
Grid
Cathode
Anode
Electrons
ionization gauge
To vacuum system
Gas ions
Electrons
ionization potential The voltage at which a substance
(especially a gas) ionizes. Also called (for a
gas) ignition potential (see BREAKDOWN VOLT-
AGE).
ionization pressure In an ionized gas, the pressure
increase resulting from the ionization, as
compared with the same volume and mass of gas
when not ionized.
ionization resistance See CORONA RESISTANCE.
ionization smoke detector A device that senses
the presence of smoke or other particles as a result
of changes in the IONIZATION CURRENT
through the air. When the ionization current suddenly
changes, a signal is sent to an alarm circuit.
ionization time The interval, usually measured in
microseconds or milliseconds, between the instant
that an ionizing potential is applied to a
gas, and the instant at which the gas begins to
ionize. Compare DEIONIZATION TIME.
dc