18WuD2x

382 iridescence • I s
Enclosure
iridescence A sparkling, colorful appearance in a
material, resulting from refraction, internal reflection,
and interference in light waves passing
through the substance. It is especially noticeable
in quartz and certain gems.
iridium Symbol, Ir. A metallic element of the platinum
group. Atomic number, 77. Atomic weight,
192.22.
iron Symbol, Fe. A ferromagnetic, metallic element.
Atomic number, 26. Atomic weight,
55.847. Iron (and its special form, steel) is widely
used in magnetic circuits.
iron/constantan thermocouple A thermocouple
consisting of a junction between wires or strips of
IRON and CONSTANTAN.
iron core A transformer or choke core made from
iron or steel. The core is usually laminated to reduce
eddy-current loss.
iron-core coil An inductor having an iron or steel
core, usually laminated to reduce eddy-current
loss.
iron-core IF transformer An intermediate-frequency
transformer having a core of powdered
iron, a form of iron that has the advantage of high
permeability while greatly minimizing eddy currents.
iron-core transformer A transformer whose coils
are wound on a core of laminated iron or steel.
iron loss Power lost in the iron cores of transformers,
inductors, and electrical machinery as a result
of eddy currents and hysteresis.
iron magnet A permanent magnet consisting of
magnetized iron or a mixture of iron and nickel.
iron oxide A compound of iron and oxygen, whose
most familiar form is common rust. The several
variants have characteristics that depend on the
number of iron and oxygen atoms in the ironoxide
molecule. See, for example, MAGNETITE
and RED OXIDE OF IRON.
iron pyrites Formula, FeS 2 . Natural iron sulfide
that occurs as bright yellow crystals in its natural
state.
iron-vane meter An alternating-current meter
whose movable element, a soft iron vane, carries
the pointer and pivots near a similar, stationary
vane. The vanes are mounted in a multiturn coil
of wire. The current flows through the coil, the resulting
magnetic field magnetizing the vanes.
Because the magnetic poles of the vanes are
identical, they repel each other; the movable vane
is deflected (against the torque of returning
springs) over an arc proportional to the current,
carrying the pointer over the scale.
irradiance The amount of radiant flux impinging
on a unit surface area; it is generally specified in
watts per square meter (W/m 2 ).
irradiation 1. Exposure of a device to radioactivity
or X rays. 2. The total radiant power density that
is incident upon a receiving surface.
irrational number A number that cannot be expressed
as the quotient of two integers. Its deci-
Needle
Bearing
with
spring
Movable vane
iron-vane meter
Input
with coil
Fixed
vane
mal expansion is nonterminating and nonrepeating.
irregularity 1. The condition of being nonuniform,
or rapidly fluctuating, rather than constant. 2. A
departure from normal operating conditions. 3.
Nonuniformity in a surface. 4. Nonuniform distribution
of matter. 5. Nonuniform distribution of
data.
irregular wave A wave disturbance, or the plot of
such a disturbance versus time, that has a complex,
periodic, repeating nature.
IR viewer A device that allows observation of images
at infrared wavelengths. See SNIPERSCOPE
and SNOOPERSCOPE.
I s 1. Symbol for source current in a field-effect
transistor. 2. Symbol for screen current in a vacuum
tube.