18WuD2x

polarizing filter • polygraph 543
through it to be polarized in any particular plane
between horizontal and vertical, depending on
the degree of rotation. Also see POLARIZED
LIGHT.
polarography In chemistry, a form of qualitative or
quantitative analysis utilizing IE curves obtained
when the voltage is gradually increased across a
solution in ELECTROLYSIS.
polar orbit
An orbit that carries a satellite over the
geographic polar regions of the earth. This type of
orbit is oriented at, or nearly at, 90 degrees with
respect to the equator, and can have a period
ranging from about 90 minutes to several weeks
or even months. Low-earth-orbit (LEO) satellites
generally have such orbits.
Equator
Satellite
orbit
North
pole
polar orbit
Earth
polar-orbiting satellite Any satellite in a POLAR
ORBIT.
polar planimeter See PLANIMETER.
polar relay See POLARIZED RELAY.
polar response The horizontal-plane directional
response of an antenna or other transducer.
pole 1. An extremity or terminus that possesses
POLARITY. Examples: magnetic pole and electric
pole. 2. The movable member of a switch. 3. One
of the frequencies at which a transfer function
becomes infinite.
pole face The smooth end surface of a pole piece.
pole piece 1. A section of specially shaped iron or
steel that is attached to a magnetic core. 2. Half
of a two-piece magnetic core that terminates in a
pole.
pole shoe In an electric motor, the section of the
field pole nearest the armature.
poles of impedance For a reactive network, the
frequencies at which the impedance is infinite.
Compare ZEROS OF IMPEDANCE.
poles of network function The values at which a
network function is infinite. Compare ZEROS OF
NETWORK FUNCTION.
poles of transfer function The frequencies at
which a transfer function becomes infinite. Compare
ZEROS OF TRANSFER FUNCTION.
police robot A proposed robotic machine, either
autonomous or remotely controlled (teleoperated),
that would be used to assist in law enforcement,
particularly in dangerous operations.
poling The deliberate adjustment of electromagnetic-field
polarity.
Polish notation In Boolean algebra, a form of notation
wherein the variables in a statement are
preceded by the operators.
polling In data transmission, a technique in which
channels being shared by more than one terminal
are tested to find one over which data is
coming in, or to ascertain which is free for
transmission.
polonium Symbol, Po. A radioactive metallic element.
Atomic number, 84. Atomic weight, approximately
209.
polychromatic radiation 1. Visible-light radiation
having more than one wavelength; in particular,
covering a broad range of wavelengths. 2. Electromagnetic
radiation over a broad band of wavelengths.
polycrystalline material A substance, such as a
semiconductor, of which even a very small
sample consists of a number of separate crystals
bound tightly together. Compare SINGLE-
CRYSTAL MATERIAL.
polydirectional microphone See OMNIDIREC-
TIONAL MICROPHONE.
polyelectrolyte An ELECTROLYTE having high
molecular weight.
polyester A resin made by reacting a dihydroxy alcohol
with a dibasic acid.
polyester backing A polyester tape on the surface
of which iron oxide is deposited to yield a magnetic
recording tape.
polyethylene A plastic insulating material. Dielectric
constant, 2.2. Dielectric strength, 585 V/mil.
polyethylene disc A phonograph disc made of
polyethylene.
polygonal coil A coil wound on a form having a
polygonal, rather than circular cross section.
Some polygonal forms have as many as 12 sides
in cross section.
polygraph An instrument for measuring and
recording electrical signals proportional to blood
pressure, skin resistance, breathing rate, and
other reactions that vary under emotional stress.
Also called LIE DETECTOR. Compare PATHOME-
TER.