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