. 20
( 42)


horizontal wave See HORIZONTALLY POLARIZED horn speaker A loudspeaker using a horn in con-
WAVE. junction with an acoustic transducer. It generally
horizontal-width control See WIDTH CONTROL, produces sound of low fidelity, and is intended for
1, 2. use in marginal environments, such as outdoor
horn A radiating device that is essentially a cylin- public-address (PA) systems.
drical or rectangular pipe, whose surface flares horn throat The narrower (input) end of a horn an-
from a narrow entry to a wide exit. See, for exam- tenna or speaker. Compare HORN MOUTH.
ple, HORN ANTENNA, HORN SPEAKER, and horsepower Abbreviation, hp. A unit of power
MEGAPHONE. equal to 746 watts. It is generally used to express
horn antenna An antenna used for transmission mechanical power delivered by engines and elec-
and reception of signals at microwave frequen- tric motors.
cies. There are several configurations; most have horsepower-hour Abbreviation, hp-hr. A unit of
a square or rectangular cross section. The an- energy or work represented by the equivalent of
tenna provides a unidirectional radiation and one horsepower delivered for a period of one
response pattern, with the favored direction hour; equal to 746 watt-hours.
coincident with the opening of the horn. The feed horseshoe coil See HAIRPIN COIL and HAIRPIN
line consists of a waveguide that joins the an- COUPLING COIL.
tenna at the narrowest point (throat) of the horn. horseshoe magnet A (usually permanent) magnet
This type of device is used alone in microwave having the shape of a horseshoe or a U and a
transmitters known as Gunnplexers. The device rectangular cross section.
works well in the feed systems of large dish an- host A programmable computer that gathers and
tennas; the horn is pointed toward the center of stores the information from all of the data-entry
the dish, in the opposite direction from the fa- terminals in a system.
vored direction of the dish. See also DISH AN- HOT 1. Abbreviation of HORIZONTAL OUTPUT
horn cutoff frequency The lowest frequency at TAL OUTPUT TUBE.
which an exponential horn will function properly. hot 1. Pertaining to an object from which heat en-
ergy is transferred to the environment by radia-
tion, convection, and/or conduction. 2. Charged
Coupling to an electrical potential, either positive or nega-
to tive, with respect to common ground. 3. Per-
waveguide taining to a conductor that carries a high
radio-frequency (RF) current or voltage.
hot carrier In a semiconductor, a charge carrier
(electron or hole) whose energy is higher than
that of majority carriers normally encountered in
the same material.
hot-carrier diode A semiconductor diode having a
metal base that receives HOT CARRIERS from a
semiconductor layer. The unit has a fast switch-
ing speed because there are virtually no minority
carriers”either injected or stored.
Hotel Phonetic alphabet code word for the letter H.
hot-filament gas detector A gas detector in which
the sensor is a heated filament acting as one arm
of a Wheatstone bridge circuit. The bridge, previ-
ously balanced, becomes unbalanced when gas
impinges upon the filament and changes its re-
hot junction The heated junction in a two-junction
thermocouple circuit. Compare COLD JUNCTION.
Maximum hot line 1. An energized wire, transmission line, or
signal busbar. 2. A private communications channel
(wire or radio) kept in constant readiness for in-
stant use between persons of high authority.
horn antenna
346 hot-pen recorder • H scope

hot-wire relay A time-delay relay in which actuat-
ing current heats a wire, causing it to expand,
eventually opening or closing the contacts. Also
hot-wire sensor See HEATED-WIRE SENSOR.
hot-wire transducer See HOT-WIRE MICRO-
hour Abbreviation, h; (sometimes, hr). A unit of
time measure equal to 60 minutes or 3600 sec-
onds. Compare MINUTE, 1 and SECOND, 1. Also
see TIME.
housekeeping In digital-computer operations, the
part of a program that attends to chores (e.g., set-
ting variables to zero), rather than being involved
in making computations for a solution.
howl A discordant sound produced in headphones
or a loudspeaker, usually as a result of acoustic
or electrical feedback.

howler 1. An audio-frequency alarm device. 2. A
hot-pen recorder See THERMAL RECORDER.
sound-emitting test device (see GROWLER, 1,
hot plate A metal device, usually heated by means

of electricity, used for the purpose of conducting
howl repeater A form of electric feedback in
certain experiments.
which a hum or howl occurs because of oscilla-
hot resistance The resistance of a component dur-
tion. The term is used to describe an oscillating
ing its operation (i.e., after it has been heated by
conduction in a wire-communications-system
ambient temperature or internal power dissipa-
tion). Compare COLD RESISTANCE.
hp Abbreviation of HORSEPOWER.
hot spark A brilliant flash seen when a capacitor
h-p Abbreviation of HIGH PRESSURE.
discharges through a spark gap in a vacuum.
H pad See H NETWORK.
hot spot 1. In a circuit or component, an area

h parameters Parameters of the four-terminal net-
whose temperature is ordinarily higher than
work equivalent of a transistor. They are hybrid
that of the surrounding area. 2. A local current
parameters (thus, h) because of their appearance
or voltage maximum on an antenna or transmis-
in mesh and nodal equations. The basic h param-
sion line. 3. In communications operations, a
eters are h11, input resistance with output short-
geographic location in which reception is
circuited; h12, reverse voltage ratio with input
markedly better than in other nearby places or
open-circuited; h21, forward current gain with
from which the transmitted signal appears to be
output short-circuited; and h22, output conduc-
tance with input open-circuited.
hot-strip ammeter A current meter similar to the
h particle A positive hydrogen ion or proton ob-
hot-wire meter, except that it has a heated metal-
tained by bombarding a hydrogen atom with al-
lic strip instead of a heated wire.
pha particles or high-velocity positive ions.
hot-stylus recorder See THERMAL RECORDER.
HPF Abbreviation of highest probable frequency.
hot-tip writing The use of a heated-tip stylus in
hp-hr Abbreviation of HORSEPOWER-HOUR.
graphic recording. Also see THERMAL RE-
hot-wire ammeter See HOT-WIRE METER.
H plane The plane of the magnetic field of an an-
hot-wire anemometer An electrical anemometer
tenna, or the magnetic component of an electro-
whose indication is based on the cooling effect of
magnetic field. Compare E PLANE.
the wind on a heated filament.
H-plane bend In a waveguide, a smooth change in
hot-wire flowmeter An instrument for determin-
the direction of the axis perpendicular to the di-
ing the rate of flow of a gas in a pipe or other
rection of polarization.
channel. The circuit is similar to that of the gas
H-plane tee junction A waveguide tee junction,
detector and hot-wire anemometer.
whose structure changes in the magnetic-field
hot-wire gasmeter See GAS DETECTOR.
plane. Also see WAVEGUIDE JUNCTION and
hot-wire instrument See HOT-WIRE METER.
hot-wire meter A meter in which current heats a
hr Abbreviation of HOUR. (Also, h.)
wire, stretching it so that it moves a pointer
H scan A radar display in which the target is rep-
across a scale over a distance proportional to the
resented by two close blips, approximating a line,
magnitude of the current.
whose shape is proportional to the sine of the tar-
hot-wire microphone A microphone in which
get™s angle of elevation.
sound waves vary the temperature of a heated
H scope See H SCAN.
wire and, accordingly, its electrical resistance.

HSM • Huygens™ principle

HSM Abbreviation of high-speed memory. hum field The magnetic field surrounding a con-
HTL Abbreviation of HIGH-THRESHOLD LOGIC. ductor carrying hum-frequency alternating cur-
hub The hole in the center of a magnetic tape reel. rent.
hue The quality of having a particular visible humidity The amount of moisture in the air. Also
color; an attribute that depends on the wave- see ABSOLUTE HUMIDITY and RELATIVE HU-
length(s) of light emitted or reflected. Thus, elec- MIDITY.
tromagnetic energy at a wavelength of 700 humidity meter See ELECTRIC HYGROMETER
nanometers (nm) has a red hue; energy at a and ELECTRONIC HYGROMETER.
wavelength of 400 nm has a violet hue. Compare humidity sensor A pickup whose resistance or ca-
SATURATION, 2. pacitance varies proportionally with ambient hu-
hue control Also called tint control. In a color tele- midity.
vision receiver, a control that allows adjustment hum interference Electrical interference resulting
of the color wavelength, but does not affect the from HUM in any of its various electrical forms
saturation (intensity). (see HUM, 1“4).
hum 1. Alternating current having a frequency of 60 hum loop A ground loop that results in undesired
Hz. 2. Residual ripple in the output of a power sup- hum in the output of an amplifier.
ply, having a frequency of 60 Hz or 120 Hz, de- hummer A nonelectronic audio oscillator similar to
pending on the type of rectifier circuit used. 3. An the fork oscillator, but using a thick, metal reed,
electromagnetic field of long wavelength, usually instead of a tuning fork. A carbon microphone
originating from utility lines and having a primary button attached to the reed provides the feedback
frequency of 60 Hz. 4. The effects of low-frequency path necessary for sustained oscillation.
electromagnetic fields or currents, such as moving
horizontal bars on a television screen. 5. An acous-
tic disturbance of long wavelength (low pitch).
human engineering 1. Also called user-friendli-
ness. The extent to which an electronic or elec- Carbon
tromechanical device or system is easy to microphone
operate. 2. The branch of engineering devoted to button
AF output
interfacing human beings with the machines and
instruments they operate. Both a science and an
art, the discipline is concerned with the safest
and most efficient design, arrangement, and op-
eration of equipment.
human interface The interface between a sophisti-
cated electronic device and a human operator.
human-made interference Also called artificial in-
terference. Electromagnetic interference to radio
and television receiving systems or to data termi-
nals, originating from artificial sources (such as
radio transmitters, certain electrical appliances,
and internal-combustion engines). Of the numer- hum modulation Undesirable modulation of a ra-
ous different forms, some affect only a narrow dio signal or audio amplifier output signal by
band of frequencies or set of frequencies, and HUM interference.
others affect a wide band of frequencies. hump 1. Either the positive or the negative half-
humanoid robot A robot that bears structural re- cycle of a sine wave; that is, either the portion
semblance to a human being (e.g., has arms, a from 0 degrees to 180 degrees, or the portion from
head, and perhaps legs). In its most advanced 180 degrees to 360 degrees. 2. A curve whose
form, such a robot is an ANDROID. graph is a multiple of the sine function, and
hum-balance potentiometer A potentiometer whose domain is restricted to a half-cycle (0 to
connected across an alternating-current power 180 degrees or 180 to 360 degrees). See, for ex-
supply, with its slider grounded. At a certain set- ample, DOUBLE-HUMP RESONANCE CURVE
ting, hum interference is nulled. and DOUBLE-HUMP WAVE.
hum bars See HORIZONTAL HUM BARS. hunting An undesirable condition in which an
hum bucking The reduction of hum interference electrical or electromechanical system oscillates
by introducing an alternating-current voltage of back and forth, relative to some mean mode of
the same frequency and amplitude as the hum, operation (“hunts” for the mode), sometimes
but opposite in phase. eventually settling down at the mode. It can occur
hum-bucking coil An auxiliary coil used in con- in a servo system because of overcompensation,
junction with the field and voice coils of an elec- lack of hysteresis, or both.
trodynamic speaker. Reduces hum interference Huygens™ principle The observation that an ad-
via HUM BUCKING. vancing wave is the resultant of secondary waves
348 Huygens™ principle • hygrometer

hydroacoustic transducer A transducer that con-
that arise from points in the medium that have
verts energy from the high-pressure flow of a fluid
already been passed.
into acoustic energy.
HV Abbreviation of HIGH VOLTAGE.
hydrodynamic pressure The pressure of a fluid in
H vector A vector representing the magnetic field
of an electromagnetic wave. Compare E VECTOR.
hydroelectric Pertaining to the production of elec-
hW Abbreviation of HECTOWATT.
tricity by water power, as by a generator turned
H-wave mode In a waveguide, a mode of transmis-
by water turbines.
sion in which the electric lines of flux are at right
hydroelectric machine A device for generating
angles to the direction of the waveguide. Also
electricity from high-pressure steam escaping
called transverse-electric (TE) mode.
from a series of jets.
hy Occasional abbreviation of HENRY. The SI ab-
hydroelectric power See WATER POWER.
breviation and symbol, H, is preferred.
hydrogen Symbol, H. A gaseous element. Atomic
hybrid Descriptive of a device that is an offspring
number, 1. Atomic weight, 1.00794. Used in
of other devices or a product of dissimilar tech-
making semiconductor materials, it is the lightest
nologies (but using elements of each). See,
and most abundant element in the universe.
hydrogen atmosphere The nonoxidizing atmo-
hybrid active circuit An active circuit (such as an
sphere in which semiconductor materials are
amplifier, oscillator, or switch) using a combina-
melted and processed, and in which semiconduc-
tion of two dissimilar active devices (e.g., transis-
tor crystals are grown. Occasionally, helium is
tors and vacuum tubes).
used instead of hydrogen.
hybrid coil A special type of bridging transformer
hydrogen atom A single atom of the element hy-
used in wire telephony to prevent self-oscillation
drogen, consisting of one electron and one pro-
in a repeater amplifier that operates in both di-
hydrogen-ion concentration See pH.
hybrid computer A computer system incorporat-
hydrogen lamp A glow-discharge lamp that pro-
ing more than one major computer technology.
duces light by means of the ionization of rarefied
Examples: analog/digital and digital/neural-
hydrogen gas. Visible light is emitted at discrete
hybrid electromagnetic wave Abbreviation, HEM
hydrokinetic Pertaining to fluids in motion or the
wave. An electromagnetic wave whose electric-
forces behind such motion.
field and magnetic-field vectors are both in the di-
hydrolysis The process whereby chemical sub-
rection of propagation.
stances become ionized in water solution, pro-
ducing electrolytes.
hybrid integrated circuit Abbreviation, HIC. An
hydromagnetics See MAGNETOHYDRODYNAM-
integrated circuit embodying both integrated and
microminiature discrete components (i.e., one
hydromagnetic wave In a fluid, a wave in which
combining both monolithic and thin-film con-
the energy is propagated via magnetic and dy-
namic modes.
hybrid junction 1. See MAGIC TEE. 2. A four-
hydrometer An instrument for measuring the spe-
terminal device, such as a resistor circuit, special
cific gravity of liquids.
transformer, or waveguide assembly, in which a
hydrophone An underwater sound-to-electricity
signal applied to one pair of terminals divides and
transducer (microphone).
appears at only the two adjacent terminals.
hydropower See WATER POWER.
hybrid microcircuit A microcircuit containing dif-
hydrostatic pressure The pressure of a fluid at
fused or thin-film elements interconnected with
separate chip elements.
hygristor A resistor, the resistance of which de-
hybrid parameters See H PARAMETERS.
pends on humidity. A common application is in
hybrid ring A hybrid waveguide junction (see HY-
the measurement of relative atmospheric humid-
BRID JUNCTION, 2) consisting essentially of a
reentrant line with four side arms. Used as an
hygrogram A graphic rendition of atmospheric hu-
equal power divider.
midity versus time, made by a HYGROGRAPH.
hybrid-tee See HYBRID JUNCTION, 1.
hygrograph A device that produces a graphic
hybrid thin-film circuit A microcircuit in which
recording of atmospheric humidity as a function
semiconductor devices and discrete components
of time. Consists essentially of a HYGROMETER
are attached to passive components and conduc-
connected to a permanent data-storage device,
tors that have been electrodeposited on a sub-
such as a computer or pen recorder.
hygrometer An instrument for measuring humidity.
hybrid transformer See HYBRID COIL.
hydroacoustic Pertaining to the sound of fluids,
especially water, under pressure.
hygroscopic material • hyperpolarization

sumed to be in phase with the signal from an-
hygroscopic material A material that absorbs
other antenna, when actually the two compo-
moisture from the air, but not enough to get wet
nents differ by an integral number of whole
(e.g., lime and silk). Compare DELIQUESCENT
wavelengths. 2. The angular error, in degrees,
minutes, or seconds of arc, resulting from a mis-
hygrostat A humidity-sensitive relay or switching
calculation of phase in an interferometer.
hyperbolic face contour See HYPERBOLIC GRIND.
hygrothermograph A graphic recorder indicating
hyperbolic functions The nonperiodic functions of
humidity and temperature on the same chart,
a hyperbolic angle. Hyperbolic functions are re-
both as functions of time.
lated to the hyperbola in the same manner that
hyperacoustical zone In the upper atmosphere, a
common trigonometric functions are related to
region in which the distance between air
the circle. Hyperbolic functions are useful in cal-
molecules is comparable to the wavelengths of
culations involving traveling waves on transmis-
audible sound. As the altitude increases within
sion lines, attenuator design, and wave-filter
this zone, the upper-frequency limit of effective
sound propagation decreases. At altitudes above
hyperbolic grind The shape (approximately hyper-
this zone, no audible sound can be propagated.
bolic) to which the face of a magnetic recording
hyperbola A conic-section curve satisfying the
head is ground. It provides optimum contact with
the tape and ensures good high-frequency re-
(x “ x0)2/a2 “ (y “ y0)2/b 2 = 1
where x and y are the independent and depen- hyperbolic horn A horn antenna whose cross-
dent variables, x0 and y0 are the coordinates of sectional area is a hyperbolic function of the
the center, a is half the length of the major axis, distance along the axis.
and b is half the length of the minor axis. hyperbolic logarithm See NAPIERIAN LOGA-
hyperbolic navigation A radionavigation system
in which the operator of an aircraft or boat deter-
mines position by comparison of two received sig-
nals. The two transmitters radiate signals from
Cone known positions and with known timing charac-
axis teristics. The time delay from each transmitter is
determined, resulting in two hyperbolic curves on
a map. The point of intersection of the curves is
the location of the aircraft or ship.
hyperbolic radian A unit of measure derived from
a hyperbolic angle. A hyperbolic radian is the hy-
perbolic angle that encloses an area of 0.5 when
the distance along the x-axis to the hyperbola is
unity. Also see HYPERBOLIC ANGLE. Compare
(x0, y0) hyperbolic trigonometry The branch of mathe-
matics dealing with the theory and application of
hyperbolic angles and their functions.
hypercardioid microphone A unidirectional mi-
x crophone with exceptional sensitivity in front,
and minimal responsiveness from the sides and
hypercardioid pattern A directional CARDIOID
PATTERN with accentuated responsiveness or
emission in the favored direction (front), and
greatly suppressed responsiveness or emission in
hyperbola other directions (sides and rear).
hyperfocal distance The shortest distance to
which a lens can be focused without degrading
hyperbolic angle An angle subtended by a sector
definition at infinity.
of a hyperbola in a manner analogous to that in
hyperfrequency waves See MICROWAVES.
which a circular angle is subtended by an arc of a
hypernik See HIPERNICK.
hyperon Any one of various particles having a
hyperbolic-cosine horn See CATENOIDAL HORN.
mass greater than that of a neutron or proton.
hyperbolic error 1. In an interferometer, a miscal-
hyperpolarization The production of an increased
culation in the direction of arrival of a signal. The
voltage across a biological membrane.
signal from one antenna in the system can be as-
350 hypersonic • hysteresis error

causing magnetization to lag behind the magne-
hypersonic Pertaining to speeds of at least five
tizing force. 2. A similar electrostatic action in a
times that of sound. In air at normal atmospheric
ferroelectric dielectric material. 3. In a servo
pressure, such speeds are more than approxi-
system, the condition in which a variable quan-
mately 1700 meters, or 5600 feet, per second.
tity lags the effect or stimulus that causes it to
hypersonic speed Any speed greater than five
change. The plot for this is a double-line HYS-
times the speed of sound in a given medium.
hypersyn motor A high-efficiency, high-power-
hysteresis brake A brake whose retarding action
factor synchronous motor combining the advan-
comes from hysteresis in a permanent-magnet
tages of the direct-current-excited synchronous
motor (stiffness), the hysteresis motor (synchro-
hysteresis clutch A magnetic clutch whose output
nizing torque), and the induction motor (high
torque (for synchronous drive or continuous slip)
starting torque).
comes from hysteresis in a permanent-magnet
hypervelocity Velocity in excess of 3 kilometers
per second.
hysteresis coefficient In a sample of iron whose
hypotenuse The side of a right triangle opposite to
volume is one cubic centimeter, the energy in
the right angle.
ergs dissipated during one cycle of magnetization.
Also called coefficient of hysteresis.
hysteresiscope An oscilloscope that is specially
designed to display the hysteresis curve of a ma-
terial. Compare HYSTERESIGRAPH.
hysteresis curve A response curve depicting hys-
teresis in a magnetic material, a dielectric, or a
servo system. A graph of the extent to which a
variable quantity lags the effect or stimulus that
causes it to change (e.g., a curve showing the ef-
fect of response delay in a thermostatically con-
trolled heating/cooling system).





hypothesis An idea, concept, or system that seems
true or workable, but must be subjected to logical
analysis and/or practical testing to prove its va-
Off On
hypsometer An altimeter in which a thermistor
(connected to a battery and current meter) is im-
| |
mersed in a boiling liquid. Because the liquid™s
65 70 75
boiling point is proportional to altitude, it affects
the resistance of the thermistor and, hence, the
Temperature, Fahrenheit
deflection of the meter.
hysteresigram The hysteresis-curve record pro-
hysteresis curve
hysteresigraph A graphic recorder that displays or
records the hysteresis curve for a material. Also hysteresis cycle A complete hysteresis curve.
see HYSTERESISCOPE. hysteresis distortion Signal distortion in iron-
hysteresimeter See HYSTERESIS METER. core components, such as coupling transformers,
hysteresis 1. The tendency of a magnetic mate- resulting from hysteresis in the iron.
rial to saturate and retain some of its mag- hysteresis error In a meter, a difference in indica-
netism after the alternating magnetic field to tions for increasing and decreasing current, an
which it is subjected reverses polarity, thus effect caused by hysteresis in iron meter parts.
hysteresis heater • Hz

hysteresis motor A synchronous motor that does
hysteresis heater An induction heater in which
not require direct-current excitation, and does
heating results from hysteresis loss in the load.
not have salient poles. It is started by means of
hysteresis loop See HYSTERESIS CURVE.
hysteresis losses that the rotating magnetic field
hysteresis loss Power loss caused by hysteresis in
causes in the secondary.
a magnetic material exposed to an alternating
hysteretic constant For a ferromagnetic material,
magnetic field, or in a dielectric material exposed
hysteresis loss in ergs per cubic centimeter of
to an alternating electric field. It is characterized
material per cycle of magnetization.
by the generation of heat.
hysteretic loss See HYSTERESIS LOSS.
hysteresis meter An instrument that determines
hystoroscope A device used to determine the mag-
the hysteresis loss in a ferromagnetic material in
netic characteristics of a material.
terms of the torque produced when the material
Hz Abbreviation of HERTZ.
is rotated in a magnetic field, or vice versa.
I 1. Symbol for CURRENT. 2. Symbol for INTRIN- ICEO Symbol for the static reverse collector (leakage)
current in a common-emitter-connected transis-
tor with an open-circuited base.
ice loading 1. In an antenna, power-line system,
i 1. Symbol for the unit imaginary number, the
or other structure, the additional stress caused
square root of -1. (Also, j.) 2. Subscript for IN-
by accumulation of ice. 2. The weight or thick-
ness of ice a structure can safely withstand.
ice-removal circuit A high-voltage, low-frequency
power supply used to heat certain antennas to
RENT. (Also, Ii.) 6. Symbol for a unit vector parallel
melt ice that accumulates on them.
to the x-axis. 7. Symbol for INCIDENT RAY.
ICET Abbreviation of Institute for the Certification of
Iac Symbol for the ac component of a COMPOSITE
Engineering Technicians (National Society of Pro-
fessional Engineers).
ICME Abbreviation of International Conference on
Medical Electronics.
Ico Symbol for the collector cutoff current (static
leakage current) of a bipolar transistor (see CUT-
IB 1. Symbol for plate power-supply current. 2. Oc-
icon In a graphical computer interface, a symbol
casional symbol for plate current (usually, IP).
that aids the user in recognizing a selection that
IBM Abbreviation for International Business Ma-
can be made.
chines Corporation.
iconoscope A camera tube in which an electron
IC 1. Abbreviation of INTEGRATED CIRCUIT. 2.
beam scans a photomosaic on which the image is
focused. The light-sensitive droplets of the mo-
IC 1. Symbol for transistor COLLECTOR CUR-
saic form tiny capacitors with the insulated,
RENT. 2. Occasional symbol for grid current (usu-
metallic backplate of the mosaic, each capacitor
ally, IG).
becoming charged by the light of the picture. As
ICAD Abbreviation of integrated control and dis-
the electron beam scans the mosaic, each capac-
itor discharges as the beam strikes it, delivering
an output pulse proportional to the light intensity
at that spot in the picture.
ICBO Symbol for the static reverse collector (leakage)
IC tester An instrument for checking the operation
current in a common-base connected transistor
of an integrated circuit.
with an open-circuited emitter.
ICBS Abbreviation of interconnected business sys-

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identification division The division (one of four)
Optical image Photocathode
in a COBOL program that describes and identi-
fies the program being compiled.
Collector plate
identification, friend or foe Abbreviation, IFF. A
technique in which a radar station transmits an
interrogating signal and the station questioned
replies automatically with a suitable pulse or
other signal if it is aboard a friendly aircraft or
vessel. If it is aboard an enemy vehicle, the sta-
Output tion gives no reply or sends an unsatisfactory
identifier A data file identification label in an in-
put/output device, or a label that identifies a spe-
cific storage location.
Electron gun
identity element A logic element that, upon re-
Deflecting coils
ceipt of two input signals, provides an output
that is logic 1 (high) only if the input signals are
both logic 1 (high) or logic 0 (low).
idiochromatic Possessing the photoelectric pro-
perties of a true crystal.
I display See I SCAN.
ID Abbreviation of INSIDE DIAMETER.
idle channel noise A measurement of wideband
IDA Abbreviation of integrodifferential analyzer.
noise. The total energy at an output of an inte-
Idc Symbol for the dc component of a COMPOSITE
grated circuit or other communications stage
with that output grounded (idle).
ideal Pertaining to a circuit, device, material, or
idle character A digital character that conveys no
manner of operation that is assumed to conform
information, but helps maintain synchronization
to the theoretical best-case example; it is not
between the transmitter and receiver. Sometimes
usually realized in real life. Thus, an ideal reac-
called a blank.
tance has no inherent resistance.
idler wheel In a phonograph or magnetic tape
ideal capacitor A capacitor having zero dielectric
recorder, an auxiliary, rubber-coated wheel that
loss and a constant value of capacitance at all
transfers rotary motion from the motor pulley to
alternating-current frequencies.
the platter or the rim of the capstan flywheel.
ideal component A theoretical component that is
idle time The period during which data processing
assumed to be 100-percent efficient and to have
equipment, although operable, is not in use.
no extraneous properties. Compare PRACTICAL
idling Standby equipment operation, as when vac-
uum-tube filaments in a radio-frequency power
ideal crystal A piezoelectric crystal that acts as a
amplifier are kept hot”even when the amplifier is
theoretically perfect tuned circuit, that is, an
not actually being used to transmit a signal.
ideal capacitor and inductor.
idling current The current flowing in a device dur-
ideal inductor An inductor having zero loss and a
ing a standby period, as opposed to operating
constant value of inductance at all alternating-
current. Also called STANDBY CURRENT.
current frequencies.
idling frequency In a parametric amplifier, the dif-
I demodulator In a color-television receiver cir-
ference between the signal frequency and pump
cuit, a demodulator that receives the chromi-
nance and 3.58-MHz oscillator signals and
idling power See STANDBY POWER.
delivers a video output corresponding to color in
idling voltage The voltage required by or mea-
the picture.
sured in a device that is in standby mode.
identical vectors Equal vectors that have the
ID(off) Symbol for drain cutoff current in a field-effect
same initial point or point of application.
identification 1. In radar operations, the (often
IDOT Abbreviation of instrumentation online tran-
automatic) determination of the target™s identity.
IDP 1. Abbreviation of INDUSTRIAL DATA PRO-
FOE. 2. In digital computer operations, a symbol
or set of symbols within a label identifying a unit
PROCESSING. 3. Abbreviation of INTERMODU-
of data or its location.
identification beacon 1. A beacon used for the de-
termination of a particular geographic location.
VOLTAGE in a field-effect transistor.
2. An automatically transmitted station-identifi-
cation signal or code, usually superimposed on
IEC Abbreviation of integrated electronic compo-
the regular transmission in the form of a subcar-
rier or subaudible signal.
354 IEE • illuminated pushbutton

IEE Abbreviation of Institution of Electrical Engi- engine. See, for example, CAPACITOR-
IEEE Abbreviation of Institute of Electrical and Elec- ignition voltage See IGNITION POTENTIAL.
tronics Engineers. ignitron A form of rectifier tube that contains ion-
IES Abbreviation of Illuminating Engineering Soci- ized mercury. It is used with some extremely
ety. high-voltage power supplies.
ac supply
IFB In an integrated circuit, current limit feedback

or feedback current.
IF converter The converter (first detector-oscilla-
tor) section of a superheterodyne radio receiver. Iron anodes
IF gain 1. The amplification provided by the inter- dc load
mediate-frequency (IF) channel of a superhetero-
dyne receiver, usually specified in decibels. 2. A
control that allows adjustment of the amplifica- Steel tank
tion in the IF channel of a superheterodyne radio
Water jacket
IFIPS Abbreviation of International Federation of Mercury cathode
Information Processing Societies.
IF strip A (sometimes removable) circuit section
containing a complete intermediate-frequency ignore character 1. A character used as a signal to
channel. inhibit an action. 2. A digital character that is ig-
IF/THEN/ELSE In computer systems and artificial nored by the system.
intelligence, a two-way choice that is made dur- IGSS Symbol for GATE REVERSE CURRENT in a
ing the execution of a program. For example, in field-effect transistor.
finding the absolute value of a number, the logic IGY Abbreviation for INTERNATIONAL GEOPHYSI-
proceeds as follows: “IF x < 0, THEN multiply x by CAL YEAR.
-1; otherwise (ELSE) leave it alone.” IH 1. Symbol for HOLD CURRENT. 2. Symbol for
IG Symbol for GATE CURRENT. IHFM Abbreviation for Institute of High Fidelity
IG Symbol for GRID CURRENT. Manufacturers.
ignition coil A small open-core transformer having POWER-HOURS.
a high step-up turns ratio for converting Ii 1. Symbol for INPUT CURRENT. 2. Symbol for IN-
6- or 12-volt battery potential to the high voltage STANTANEOUS CURRENT (also, i).
needed in an automotive ignition system. IK Symbol for CATHODE CURRENT.
ignition interference Electrical noise generated IL Symbol for current in an inductor.
by the ignition system of an internal combustion
engine. LOGIC. (Also IIL.)
ignition potential 1. The minimum voltage illegal character 1. A character or bit group that is,
needed to cause electrical discharge in an inter- according to some standard, invalid. 2. A bit group
nal combustion engine. 2. See BREAKDOWN that represents a symbol in a character set.
VOLTAGE, 1, 2. illuminance The amount of luminous flux received
ignition reserve The extra voltage provided by the per unit surface area, measured in lux (lumens
starter, as compared with the voltage actually per square meter).
needed for ignition of an internal-combustion en- illuminant-C In color television, the reference
gine. white that closely resembles average daylight.
ignition system An electrical or electronic system illuminated pushbutton See LIGHTED PUSH-
that supplies the high voltage in an automotive BUTTON.
illuminated switch • image transfer constant

illuminated switch See LIGHTED SWITCH. compression can provide a compression factor of
illumination 1. Visible light. 2. The condition of as much as 100:1 without significant degradation
being irradiated by visible light. 3. The intensity of image quality.
of visible light irradiating an object or region. image converter 1. A device that changes an in-
illumination control A photoelectric circuit that visible image into a visible image. Examples in-
automatically regulates electric lights, according clude the snooperscope, an infrared-to-visible
to the amount of daylight. converter, and photographic apparatus for in-
illuminometer A device for measuring the inten- frared, ultraviolet, and X-ray wavelengths. 2. A
sity of visible light, or, less often, infrared or tube that operates as an image converter.
ultraviolet. In its simplest form, the meter image dissector See DISSECTOR TUBE.
consists of a photovoltaic cell, a potentiometer for image effect The effect of reflection of electromag-
adjusting the sensitivity, and a microammeter. netic waves from the ground. An IMAGE AN-
More sophisticated devices include direct-current TENNA appears to radiate from a point beneath
amplification. the effective RF ground plane. The depth of the
image antenna below the effective RF ground
plane is equal to the height of the actual antenna
above the effective RF ground plane.
image frequency The frequency of the image re-
sponse in a superheterodyne radio receiver. See
image impedance The property of a network in
which the load impedance is “seen,” looking into
the output terminals with the generator con-
nected to the opposite end, and the generator
impedance is “seen,” looking into the input ter-
minals with a load connected to the opposite
image intensification An increase of the bright-
ness of the display on a cathode-ray tube.
image intensifier A device that increases the
brightness of the spot produced when a beam of
electrons or X rays hits a fluorescent screen.
Im 1. Abbreviation of maximum current. (Also, Imax).
image interference A type of interference that can
2. Abbreviation of meter current.
occur in superheterodyne circuits. It occurs when
image 1. In a superheterodyne circuit, a spurious
there is a sufficiently strong signal on the IMAGE
response whose frequency differs from that of the
desired signal by twice the intermediate fre-
image orthicon See ORTHICON.
quency. 2. A picture on the screen of a television
image phase constant The imaginary-number
receiver or computer display. 3. A pattern on the
screen of an oscilloscope tube. 4. A picture on the
mosaic of a television camera tube. 5. A duplicate
image potential The potential energy of a charged
of a computer storage area that is in another part
particle at a given distance from a metal surface.
of storage or on another medium.
The metal surface acts in a way similar to a mir-
image admittance The reciprocal of IMAGE IM-
ror; a reflected image of the object, having equal
charge but opposite polarity, is formed on the
image antenna An imaginary “mirror” antenna
other side of the surface.
below the effective radio-frequency (RF) ground
image ratio See SIGNAL-TO-IMAGE RATIO.
surface, at a depth equal to the height of the
image rejection In a superheterodyne radio re-
true radiating antenna above effective RF
ceiver, the suppression or elimination of IMAGE
INTERFERENCE by means of a selective circuit,
image attenuation constant The real-number
such as a radio-frequency preamplifier.
image response In a superheterodyne receiver, an
undesired response to signals removed from the
image compression Any of various methods by
desired frequency by twice the intermediate fre-
which the number of bytes in a digital image can
be reduced, without significant degradation of
image transfer constant A number depicting the
image quality. The two most common methods
transfer of power by an impedance network. It
are JPEG (Joint Photographic Experts Group) im-
has the same value, regardless of the direction of
age compression and fractal image compression.
transmission through the network. Also see IM-
Other schemes include MPEG (Moving Picture Ex-
perts Group) image compression and Indeo, devel-
oped by Intel Corporation. Fractal image
356 imaginary axis • impedance-matching network

imaginary axis In a vector diagram of complex impedance arm The network branch that contains
impedance, the axis of the imaginary-number one or more impedances, as opposed to an arm
component (jX). that contains only resistance or (predominantly,
imaginary number A real-number multiple of the reactance). Also called impedance leg.
positive square root of -1. Engineers depict the impedance branch See IMPEDANCE ARM.
positive square root of -1 by the lowercase letter j; impedance bridge 1. An alternating-current (ac)
mathematicians use the lowercase letter i. Engi- bridge (commonly operated at 1 kHz) used to
neers write imaginary numbers in the form jX, measure resistance, inductance, capacitance,
and mathematicians write Xi, where X is a real and resistive components associated with induc-
number. tors and capacitors, from which impedance can
imaginary-number component The imaginary- be calculated. 2. Sometimes, an ac half-bridge
number part of a COMPLEX NUMBER. circuit in which an unknown impedance is com-
Imax Abbreviation of maximum current. pared with a known resistance. 3. A radio-
IM distortion meter INTERMODULATION ME- frequency bridge circuit whose balancing element
TER. reads impedance directly in ohms.
IM distortion percentage See INTERMODULA- impedance bump A discontinuity in the character-
TION-DISTORTION PERCENTAGE. istic impedance of a radio-frequency transmis-
Imin Abbreviation of minimum current. sion line. It is often caused by the use of improper

imitation The transmission of false signals for splicing techniques.
purposes of deception. For example, during impedance coil See CHOKE COIL.

wartime, the signals from an enemy station might impedance converter See IMPEDANCE TRANS-
be recorded and retransmitted. FORMER.
immediate access 1. The ability of a computer to impedance-coupled amplifier An amplifier using
store and retrieve data in a minimal amount of capacitor/coil combinations for interstage and
time. 2. Computer storage that can be accessed output load coupling.
in a minimal amount of time. impedance drop In an alternating-current circuit,
immediate address An instruction address that is the complex sum of the resistance drop and reac-
used as data by that instruction. tance drop.
IM meter See INTERMODULATION METER. impedance ground A ground connection in which

immitance Impedance or admittance; a contrac- the impedance at the operating frequency is de-
tion of IMPEDANCE and ADMITTANCE. Example: termined by a network of resistors, capacitors,
a negative-immitance circuit. and/or inductors.
immortal knowledge Knowledge that can be kept impedance leg See IMPEDANCE ARM.
indefinitely in the form of detailed computer data impedance magnetometer A device that is used
files. Some scientists and sociologists believe that for measuring small local variations in the inten-
this will eventually have a profound effect on the sity of the earth™s magnetic field. A small change
way that future generations view history. in the intensity of the magnetic field will cause a
impact excitation See SHOCK EXCITATION. change in impedance of a nickel-iron wire having
impact strength 1. The ability of a component or high permeability.
material to withstand mechanical shock loading. impedance match The condition (for maximum
2. The work required to fracture the material un- power transfer) when the transmitting impe-
der shock loading. dance equals the receiving impedance, or when a
IMPATT diode Acronym for impact avalanche tran- suitable transformer is inserted between different
sit time diode. A microwave semiconductor (sili- impedances for matching purposes. Also see
con or gallium arsenide) diode exhibiting negative IMPEDANCE MATCHING.
resistance resulting from the combined effects of impedance matching 1. The adjustment or modi-
charge-carrier transit time and impact avalanche fication of two impedances so that they are iden-
breakdown. It is used as an oscillator or ampli- tical, that is, the two resistive components are
fier. equal, and the two reactive components are
IMPATT oscillator A microwave oscillator that equal. 2. The insertion of a suitable transformer
uses an IMPATT DIODE. or network between circuits having different
impedance Symbol, Z. Unit, ohm. The total opposi- impedances, for the purpose of optimizing power
tion offered by a circuit or device to the flow of al- transfer.
ternating current. It is the vector sum of impedance-matching network A network of dis-
RESISTANCE and REACTANCE. This is a COM- crete components, often adjustable, that is used
PLEX NUMBER whose real-number component is to match a circuit having a certain impedance to
resistance R, and whose imaginary-number com- a circuit having a different impedance. An
ponent is reactance jX; mathematically, Z = R + jX. example is the inductive-capacitive (LC) cou-
impedance angle The angle between the resis- pler, also called a transmatch, commonly used
tance and impedance vectors in an IMPEDANCE to match a radio transmitter to an antenna
TRIANGLE. system.

impedance-matching transformer • impulse ratio

impedance-matching transformer See IMPED- imperfection A fault in the lattice of a crystal. Also
impedance meter See Z METER. implementation 1. Putting a system into opera-
impedance plethysmograph An electronic device tion and evaluating its performance. 2. Doing
used to measure changes in the chemical content all that is necessary to install a device or sys-
of body cells. tem.
impedance poles See POLES OF IMPEDANCE. implosion The inward collapse of an evacuated
impedance ratio The quotient of two impedances chamber, such as the envelope of a cathode-ray
that are related in some situation, such as tube. It is the opposite of explosion, an outward
impedance match or impedance mismatch. The bursting.
impedance ratio of a transformer is equal to the impregnant A substance for the IMPREGNATION
square of the turns ratio. of electronic components. Examples: waxes, oils,
impedance transformer 1. A transformer for con- liquid plastics, and varnish.
verting an impedance to a different value. The impregnation The process of filling the spaces
turns ratio is equal to the square root of the within a material or structure with an insulating
impedance ratio. 2. An emitter follower or source compound. Various electronic components, such
follower circuit, used primarily to match a high as capacitors, inductors, transformers, transis-
impedance to a lower impedance. 3. A short- tors, and diodes, are impregnated for protection
circuited transmission-line section used to match and stability.
or convert impedances at radio frequencies. impressed voltage The voltage applied or pre-
sented to a circuit or device.
impulse 1. A signal of extremely short duration
(e.g., a noise burst). 2. A brief, unidirectional
surge in voltage (usually) or current.
Zp Primary Secondary Zs impulse excitation Driving a tank circuit with a
single pulse, then allowing it to oscillate at its
own frequency until another driving pulse ar-
T = Npri /Nsec rives.
impulse frequency In a digital telephone, the
number of pulse periods per second, correspond-
impedance transformer
ing to a dialed digit, generated by the pulse
impulse generator See MARX GENERATOR.
impedance triangle A triangular vector diagram in
impulse noise Electrical noise from short-duration
which the impedance vector is the hypotenuse,
pulses, such as those produced by an automotive
and the reactance and resistance vectors are the
ignition system.
perpendicular sides.
impulse ratio The ratio Vp/Vs, where Vp is the
breakdown (or flashover or sparkover) voltage
+XL caused by an impulse, and Vs is the correspond-
ing voltage at the crest of the power-frequency
’R +R


impedance triangle

impedance vector In a vector diagram, the resul-
tant (vector) representing the combined reactance
and resistance vectors. Also see IMPEDANCE
impedance zeros See ZEROS OF IMPEDANCE.
imperative macroinstruction A MACROIN-
STRUCTION used to create object (machine lan-
guage) program instructions.
imperative statement A source language program
instruction that is converted into object program
(machine language) instructions.
358 impulse relay • inclusive-OR

impulse relay A relay that is able to close or open inch-pound Abbreviation, in-lb. A unit of work
completely when driven by a short pulse. equal to a force of 1 pound exerted over a dis-
impulse speed The switching rate of a telephone tance of 1 inch. Compare FOOT-POUND.
dialing device as it transmits pulses. incident 1. A failure in a computer system requir-
impulse timer A synchronous-motor-driven ing the intervention of an operator in removing or
timer whose cams can control many circuits; it revising the job involved. 2. Pertaining to a ray or
can advance by a number of specified incre- rays of energy striking a surface or boundary, or
ments, as controlled by an integral stepping encountering a device (such as an antenna or
mechanism. photovoltaic cell).
impulse transmission A method of transmission incidental AM Undesired amplitude modulation in
in which defined impulses are used to denote a frequency-modulated signal. Compare INCI-
changes in signal content or format. DENTAL FM.
impurity A substance added to an intrinsic semi- incident field intensity The field strength of an
conductor to alter its electrical properties. electromagnetic field as it arrives at a receiving
impurity atom In a processed semiconductor ma- antenna.
terial, an atom of an IMPURITY material that pro- incidental FM Undesired frequency modulation in
duces either n- or p-type properties to the an amplitude-modulated signal. Compare INCI-
intrinsic semiconductor. DENTAL AM.
impurity density In the manufacturing process of incidental time Computer time devoted to other
a semiconductor material, the amount of impu- than program runs or program development.
rity added to the original semiconductor. incident light The light that strikes or enters an
impurity ion In a crystal, an ion in a space be- altering device or medium. See INCIDENT RAY.
tween atoms, or one taking the place of an atom. incident power In a transmission line, the power
impurity level 1. The energy existing in a semi- that reaches the end of the line. Compare RE-
conductor material as a result of doping (the ad- FLECTED POWER.
dition of an impurity). 2. See IMPURITY incident ray The ray that strikes the surface of a
DENSITY. reflecting, refracting, or absorbing body. Com-
impurity material See IMPURITY. pare REFLECTED RAY and REFRACTED RAY.
IN Abbreviation for INTELLIGENT NETWORK. incident wave 1. A wave propagated to the iono-
In Symbol for INDIUM. sphere. Compare REFLECTED WAVE and RE-
In Symbol for the nth value of current in a series of FRACTED WAVE. Also see IONOSPHERE and
values. IONOSPHERIC PROPAGATION. 2. A wave that
in 1. Abbreviation of INPUT. 2. Abbreviation of encounters a change (in density, for example) in a
INCH. propagation medium or the transition point be-
inaccuracy 1. The state or condition of instru- tween media.
ment error. 2. The difference between the actual in-circuit tester An instrument that permits the
value of a parameter and the value indicated by checking of components (especially transistors)
an instrument. 3. The percentage of instrument without removing them from the circuit in which
error. they are wired.
inactive leg Within a transducer, an electrical inclination 1. At a given geographic location, the
component whose characteristic remains un- angle between the earth™s magnetic lines of flux
changed when the stimulus (quantity being and the horizon. This angle ranges from 0 degrees
transduced) is applied; specifically, a Wheatstone at the geomagnetic equator to 90 degrees at the
bridge element in a transducer. geomagnetic poles. Compare DECLINATION, 1. 2.
inactive lines In a conventional television picture, The angle between the plane of a satellite orbit
blanked lines that do not contribute to the visible and the plane containing the equator of the earth,
part of the image. Approximately half of these planet, or star around which the satellite re-
lines are at the top of the screen; the other half volves. Generally measured as the angle at which
are at the bottom. the satellite crosses the equator while passing
inactive time The period during which a radioac- from the southern hemisphere to the northern
tivity counter is insensitive to ionizing agents. hemisphere. This angle is between 0 and 90 de-
incandescence The state of glowing from intense grees for satellites in non-retrograde orbits, and
heat, as when a metal becomes white hot from an between 90 and 180 degrees for satellites in ret-
electric current flowing through it. rograde orbits.
incandescent lamp A filament-type lamp. The fila- inclinometer An instrument for measuring INCLI-
ment becomes so hot when an electric current NATION. One form consists of a magnetic needle
passes through it that it glows brilliantly. mounted so that it can swing inside a vertically
inch Abbreviation, in. A unit of linear measure in mounted circular scale.
the English system; 1 in. = 2.54 centimeters = inclusive-OR Also called OR operation. A logical
0.0254 meter. operation between two operands, the result of
inching See JOGGING. which depends on rules for combining bits in
inclusive-OR • indexing

each position within the operands: an output of 1 incremental display A device that converts digital
results if one or both of the bits have a value of 1; data into a form for display (characters; graphs).
zero only if both are zero. Compare EXCLUSIVE- incremental inductance The inductance exhib-
OR. ited by an inductor, such as an iron-core choke,
incoherent light Electromagnetic radiation in the carrying a direct current.
visible spectrum in which the waves are not incremental permeability The permeability ex-
aligned (not in phase) and can be of more than hibited by a material when an alternating-current
one wavelength. magnetizing force is superimposed upon a direct
incoherent radiation Electromagnetic radiation in current.
which the waves are not aligned (not in phase) incremental plotter A device that, by direction of
and can be of more than one frequency or wave- a computer program, provides the results of a
length. program run in the form of curves or points on a
incoming inspection The examination of equip- curve, along with annotational characters.
ment and materials as they enter a factory or lab- incremental representation For incremental
oratory, for the purpose of identifying damaged or computers, a method of representing variables in
faulty units. terms of changes in the variables.
incoming line A line that enters a device, facility, incremental sensitivity The smallest change in a
or stage. Compare OUTGOING LINE. quantity under measurement that can be de-
Incompleteness Theorem A mathematical theo- tected by the instrument used.
rem of significance in artificial intelligence. For ind 1. Abbreviation of indicator. 2. Abbreviation of
any consistent set of axioms (postulates), there INDUCTANCE (more commonly, L). 3. Abbrevia-
are always more true statements than provable tion of INDUCTOR (More commonly, L).
statements. indefinite integral See INTEGRAL, 1.
incomplete program Also called incomplete rou- Indeo Also called Digital Video Interactive (DVI). A
tine. A computer program of generalized steps method of IMAGE COMPRESSION developed by
that must be augmented with specific require- Intel Corporation.
ments to be implemented for a given operation. independent equations A set of equations having
inconsistency Contradictory computer state- one common solution.
ments, as detected by the program. independent events In probability and statistics,
inconsistent equations A set of equations that the case where the occurrence of one event has
have no common solution. no effect on the occurrence of another.
Increductor A specialized radio-frequency mag- independent failure A circuit failure whose direct
netic amplifier or saturable reactor. cause is not related to malfunctions elsewhere in
increment 1. The difference between two succes- the system.
sive values of a variable. 2. A small change in a independent mode In tracking supplies, an op-
quantity, such as mass, distance, or time. 3. A tional method of operation in which the separate
quantity to be added to another quantity. 4. The units are adjustable independently of each other.
difference in value between adjacent hash marks Compare TRACKING MODE.
on a meter scale. independent variable A changing quantity whose
value at any instant is not governed by the value
of any other quantity. Compare DEPENDENT
4 6
3 7 index 1. A reference line, hair, or point (e.g., a file
2 8 index). 2. In mathematics, an exponent. 3. A ratio
1 of one quantity to another, as index of refraction.
dc Volts 10 4. In a computer memory, a table of references in
a key sequence; it can be addressed to find the
addresses of other data items. 5. A number that
is used to select a specific item within an array of
items in memory.
index counter Also called tape counter. In a mag-
Increment = 0.5 V netic tape recorder, a (usually electromechanical)
counting device that the operator can refer to in
increment, 4 order to find material on the tape.
indexed address During or preceding the execution
of a computer program instruction, an address
incremental computer A computer that operates
that is modified by the content of an index register.
on changes in variables. Example: differential an-
indexing 1. An information retrieval technique
used with files on a direct-access storage medium
incremental digital recorder A magnetic tape
or on tables in memory. 2. To modify an instruc-
recorder that moves the tape across the record
tion using an index word.
head in increments.
360 index of modulation • indium

index of modulation In frequency modulation, the indirectly controlled Influenced by a directly con-
ratio of carrier frequency deviation to modulating trolled parameter, but not itself directly con-
frequency. trolled.
index of refraction Symbol, n. The ratio v1/v2, indirectly grounded Connected to earth or to the
where v1 is the speed of energy propagation in lowest-potential point in a system inadvertently
the first medium through which the energy or through a roundabout path (e.g., by means
passes, and v2 is the speed in the second of an indirect ground). Compare DIRECTLY
medium. GROUNDED.
index register Abbreviation, XR. In digital com- indirectly heated cathode An electron-tube cath-
puter operations, a register holding a modifier ode consisting of a cylindrical or rectangular
that allows data to be directly addressed (each sleeve coated with a substance that is a rich emit-
program refers to an index register when ad- ter of electrons; it is heated by a filament inside
dressing storage locations). Also called MODI- the cylinder.
FIER REGISTER. indirectly heated thermistor A thermistor whose
index word A word (bit group) containing a modi- temperature is changed by a built-in heater (fila-
fier that will be added to a basic instruction when ment) operated by the control current.
it is executed during a program run. indirectly heated thermocouple A meter thermo-
India mica High-grade mica mined in India. Its ex- couple heated by a small heater (filament)
cellent dielectric properties make it useful for ca- through which the signal current passes.
pacitor stacks, high-Q radio-frequency circuits, indirect material A semiconductor substance in
and other critical applications. which electrons move from the conduction
indicated horsepower Abbreviation, ihp. Horse- band to the valence band in discrete jumps or
power calculated from data or ratings, as opposed steps.
to measured horsepower. indirect measurement The measurement of a
indicated horsepower-hours Abbreviation, ihp- quantity by comparing it with a similar quantity,
hr. Horsepower-hours based on calculation of in- using an instrument that requires adjustment or
dicated horsepower. manipulation (rather than a simple meter). For
indicating fuse A fuse that provides some signal example, resistance can be measured with a
(such as a protruding pin) to show that it has bridge, instead of an ohmmeter. Compare DI-
indicating instrument An instrument, such as a indirect piezoelectricity In a piezoelectric crystal,
meter, that provides direct readings of a mea- the application of a voltage for the purpose of pro-
sured quantity, as opposed to an instrument, ducing a strain on the crystal. A piezoelectric
such as a bridge, that must be manipulated and buzzer operates on this principle.
whose operation must often be followed by calcu- indirect scanning A method of video scanning, in
lations. which a fast-moving spot of light scans the film or
indicating lamp A lamp that is marked or coded so an object and is passed through the film (or re-
that when it is on or off it conveys information. flected by the object) to a photocell.
indicator 1. Meter (see METER, 1). 2. See MONI- indirect wave 1. In communications, a wave that
TOR. 3. See ANNUNCIATOR. 4. In a computer, a arrives at a receiver after having traveled via re-
device that can be set by a specific condition (e.g., fraction, reflection, or both. 2. A radio wave prop-
by a negative result or error indicator). agated via the ionosphere. 3. A wave reflected
indicator probe A test probe having a built-in me- from some object, such as the moon or a meteor
ter. trail. 4. A wave received from a satellite, originat-
indicial response Symbol, I(T). The sum of the ing from a distant earth station.
transient and steady-state responses to a unit indium Symbol, In. A metallic element. Atomic
function. number, 49. Atomic weight, 114.82. Used as a
indirect addressing In computer programming, dopant in semiconductor processing.
a technique in which the address in an instruc-
tion refers to a different location containing an-
Ionized layer
other address, that can specify yet another
address or an operand. Also called multilevel ad-
indirect coupling Collectively, capacitive and in-
ductive coupling, as opposed to direct coupling. TX
indirect ground An unintentional ground connec-
tion (e.g., accidental grounding of part of a cir-
cuit) or one obtained through a roundabout path.
indirect light Light that has been reflected from
one or more surfaces. Compare DIRECT LIGHT. indirect wave
indoor antenna • induction modulator

indoor antenna An antenna erected and operated inductance filter A filter using only an inductor,
in a building, but kept away from other objects as usually a coil of wire.
much as possible. inductance-resistance time constant The time
indoor radiation Electromagnetic radiation from constant t (see ELECTRICAL TIME CONSTANT) of
the part of an antenna feeder or lead-in that is in- a circuit containing, ideally, only inductance and
side the transmitter building. resistance. Mathematically, t = LR, where t is in
indoor transformer A power service transformer seconds, L is the inductance in henrys, and R is
that, for protection against the elements, is in- the resistance in ohms. Also called LR time con-
stalled inside the building it serves. stant.
induced Brought about by the influence of a mag- inductance standard A highly accurate, stable in-
netic or electric field. ductor used in precision measurements. Also see
induced charge An electric charge produced in a PRIMARY STANDARD and SECONDARY STAN-
body by the electric field surrounding another DARD.
charge. induction 1. The ability of an alternating, pulsat-
induced current An alternating current estab- ing, or otherwise changing current flowing in one
lished in one circuit by the alternating magnetic circuit to set up a current in a nearby circuit. The
field of another circuit. Also see INDUCTION. circuits need not be physically connected, but
induced EMF See INDUCED VOLTAGE. need only be linked by magnetic lines of flux. Also
induced failure A form of component failure that see SELF-INDUCTION. 2. The phenomenon
occurs because of operation beyond the normal whereby a body becomes electrically charged by
specifications. the field surrounding a nearby charged body.
induced voltage An alternating voltage set up Also see ELECTRIC CHARGE.
across one circuit (especially a coil) by the alter- induction coil A special high-voltage step-up
nating magnetic field of another circuit. Also see transformer having an open core and a vibrator-
INDUCTION. interrupter in series with the primary winding,
inductance Symbol, L. Unit, henry. In a conduc- which carries direct current from a battery. The
tor, device, or circuit, the inertial property current is broken up into short pulses by the in-
(caused by an induced reverse voltage) that op- terrupter, and a high alternating-current voltage
poses the flow of current when a voltage is ap- is generated in the secondary winding.
plied; it opposes a change in current that has induction compass A compass whose indications
been established. Also see HENRY, INDUCTION, depend on current induced in a coil revolving in
and MUTUAL INDUCTANCE. the earth™s magnetic field. Compare GYROCOM-
inductance bridge An alternating-current bridge PASS and MAGNETIC COMPASS.
for measuring inductance in terms of a standard induction factor The ratio of total current to non-
inductance or a standard capacitance. See, for productive current in an alternating-current cir-
example, HAY BRIDGE, MAXWELL BRIDGE, and cuit.
OWEN BRIDGE. induction field The portion of an electromagnetic
inductance-capacitance Abbreviation, LC. 1. A field that returns to a radiator, such as a coil, as
combination of inductance and capacitance in a opposed to the RADIATION FIELD.
circuit, such as a filter, a parallel-resonant cir- induction frequency converter A mechanical de-
cuit, or a series-resonant circuit. 2. Pertaining to vice used for converting a signal at a fixed fre-
a device for measuring inductance and capaci- quency to a signal at another fixed frequency.
tance (e.g., LC bridge and LC meter). induction furnace A furnace in which high-
inductance-capacitance bridge An alternating- frequency magnetic fields induce currents in
current bridge for measuring inductance and ca- metal ores, causing the ore to become hot enough
pacitance only. to melt.
inductance-capacitance filter A filter composed induction heater A high-power, radio-frequency
of inductors and capacitors. Also called LC filter. generator designed especially for induction heat-
inductance-capacitance meter A direct-reading ing.
meter for measuring inductance and capacitance. induction heating The heating of metallic work
inductance-capacitance-resistance Abbrevia- samples by placing them in (but insulated from) a
tion, LCR. 1. A combination of inductance, capac- WORK COIL carrying current from a high-power
itance, and resistance in a circuit, such as a basic radio-frequency generator. The workpiece is heated
tuned circuit. The resistive component represents by radio-frequency currents induced in it as a re-
loss in the inductor and capacitor. 2. Pertaining sult of the intense alternating magnetic field within
to a device for measuring inductance, capaci- the coil. Compare DIELECTRIC HEATING.
tance, and resistance (e.g., LCR bridge and LCR induction loss Loss of energy from a current-
meter). carrying conductor because of inductive coupling
inductance-capacitance-resistance bridge See to a nearby conductor.
inductance coil See INDUCTOR. CAL MODULATOR.
362 induction motor • inductive transducer

induction motor An electric motor in which the
stator™s rotating magnetic field makes the rotor
induction speaker An acoustic loudspeaker in
which an audio-frequency current is passed
through a diaphragm or coil located in a constant
magnetic field. This results in movement of the
diaphragm or coil.
induction transducer See INDUCTIVE TRANS-
induction-type landing system See DINGLEY
induction welding Welding in which the heating
current flowing in the workpieces is induced by
an electromagnetic field.
inductive capacitor A wound capacitor in which
the inductance of the roll is controlled and speci-
fied. Such a capacitor is useful in compact filters
and in single-frequency bypassing, where the re-
active components are supplied by the capacitor.
Compare NONINDUCTIVE CAPACITOR. having a specified resonant frequency. Compare
inductive logic A form of reasoning that demon-
strates that a certain conclusion is highly proba-
Metal case
ble, given a certain set of circumstances. This is


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