The Illustrated Dictionary of Electronics - Loscha

380 involution • ionization timeinvolution 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 inwhich 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 thehalogen family. Atomic number, 53. Atomicweight, 126.905. Also see HALOGEN.ion A charged atom [i.e., one that has gained oneor more electrons (a negative ion, or anion) or lostone or more electrons (a positive ion, or cation)].ion burn A spot burned on the screen of a cathoderaytube by negative ions from the cathode strikinga single point on the faceplate with highintensity for long periods.ion concentration 1. The number of ions, expressedas a percentage or as a number per unitvolume, in a substance. 2. Ionization density inthe atmosphere.ion exchange resins Granular resins that containacid or base groups, and that trade ions withsalts in solutions. The resins play a part in thepurification of water for various industrial processes.ionic binding forces In a crystal, the bindingforces that occur when valence electrons of oneatom are joined to those of a neighboring atomwhose outer shell they fill.ionic bond In a solid, a bond between atoms,formed as a result of the attraction between oppositelycharged 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 togetherby the electric forces between ions. Alsosee IONIC BINDING FORCES and IONIC BOND.ionic current Current caused by ion movement ina gas or liquid. Also see ION, IONIZATION, andIONIC CONDUCTION.ionic semiconductor A semiconductor in whichthe carrier is an ion, as opposed to an electron orhole.ionic switch See ELECTROCHEMICAL SWITCH.ionization 1. The loss or gain of one or more electronsby an atom. Also see ANION, CATION, andION. 2. The formation or existence of significantnumbers of ions in a gas, liquid, or solid (e.g., ionizationof the upper atmosphere).ionization arc The electrical discharge resultingfrom the ionization of a material because of highvoltage.ionization chamber An enclosure containing a gasand a pair of electrodes between which a highvoltage is applied. Radiation, such as X rays orradioactive particles, passing through the walls ofthe chamber ionize the gas, creating an ionizationcurrent that is proportional to the intensity of theradiation.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 agas tube, current flowing after the ignition potentialhas been reached. 5. Negative grid current resultingfrom gassiness in a vacuum tube.ionization density The extent to which ionizationexists in an ionized layer of the atmosphere. Thehigher the ionization density, the greater the effecton radio waves—especially at frequencies belowabout 150 MHz.ionization gauge A form of vacuum tube that canbe used to measure the hardness of a vacuum. Itconsists of a cathode, an anode (plate), and a positivelycharged grid. Plate current flows as a resultof ionization of the atoms within the tube.The more nearly perfect the vacuum, the lowerthe plate current.To recorderand measuringcircuitsGridCathodeAnodeElectronsionization gaugeTo vacuum systemGas ionsElectronsionization potential The voltage at which a substance(especially a gas) ionizes. Also called (for agas) ignition potential (see BREAKDOWN VOLT-AGE).ionization pressure In an ionized gas, the pressureincrease resulting from the ionization, ascompared with the same volume and mass of gaswhen not ionized.ionization resistance See CORONA RESISTANCE.ionization smoke detector A device that sensesthe presence of smoke or other particles as a resultof changes in the IONIZATION CURRENTthrough the air. When the ionization current suddenlychanges, a signal is sent to an alarm circuit.ionization time The interval, usually measured inmicroseconds or milliseconds, between the instantthat an ionizing potential is applied to agas, and the instant at which the gas begins toionize. Compare DEIONIZATION TIME.dc