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positive temperature coefficient • potential energy 547
positive temperature coefficient Abbreviation,
PTC. A number expressing the amount by which a
quantity (such as the value of a component) increases
when temperature is increased. The coefficient
is stated as a percentage of the rated value
per degree, or in parts per million per degree.
Compare NEGATIVE TEMPERATURE COEFFI-
CIENT and ZERO TEMPERATURE COEFFICIENT.
positive transmission In facsimile or television, a
form of amplitude modulation in which the picture
brightness is directly proportional to the signal
strength at any given instant of time.
positive valence The valence of a positive ion.
positron A positively charged particle having the
same mass as that of the electron, and the same
magnitude of electric charge, but positive (instead
of negative). Sometimes called positive electron.
post See BINDING POST.
post- Prefix meaning “following,” “subsequent to,”
or “behind.”
post-accelerating electrode In a cathode-ray
tube, the high-voltage electrode that produces
POST-DEFLECTION ACCELERATION of the electron
beam. Also called INTENSIFIER ELEC-
TRODE.
postacceleration See POST-DEFLECTION ACCEL-
ERATION.
post-alloy-diffused transistor Abbreviation,
PADT. A transistor in which electrodes are diffused
into the semiconductor wafer after other
electrodes have been alloyed.
post-conversion bandwidth The bandwidth of a
signal after it has been converted from one frequency
to another.
post-deflection accelerating electrode See
POST-ACCELERATING ELECTRODE.
post-deflection acceleration In a cathode-ray
tube, the intensification of the electron beam
following beam deflection. Also see POST-
DEFLECTION CRT.
post-deflection CRT An oscilloscope tube provided
with a high-voltage intensifier electrode in
the form of a ring encircling the inside flare of the
tube, between the deflecting plates and the
screen. The deflected electron beam is accelerated
by this electrode. This arrangement allows
the beam to be deflected at low velocity and high
sensitivity, then to be accelerated for a brighter
image.
post edit The editing of data in a computer output.
postemphasis See DEEMPHASIS.
post-equalization 1. In sound recording and reproduction,
equalization during playback. Compare
PREEQUALIZATION. 2. See DEEMPHASIS.
postmortem An investigation into the cause of
failure of a circuit, device, or system.
postmortem dump At the end of a computer program
run, a dump to supply information for debugging
purposes.
post office box A type of wheatstone bridge that
contains resistance coils in a special box. The
coils are connected so that they can be replaced
by shorting connectors.
pot 1. See POTENTIOMETER. 2. See DASHPOT.
3. Abbreviation of POTENTIAL. 4. To encapsulate a
circuit in a potting compound, such as epoxy resin.
potassium Symbol, K. A metallic element of the alkali-metal
group. Atomic number, 19. Atomic
weight, 39.098.
potassium chloride Formula, KCl. A compound
used as a phosphor coating on the screen of a
nearly permanent-persistence cathode-ray tube.
The fluorescence is magenta or white, as is the
phosphorescence.
potassium cyanide Formula, KCN. A highly toxic
salt that is an electrolyte in some forms of electroplating.
potassium dihydrogen phosphate Abbreviation,
KDP. An inorganic ferroelectric material.
pot core A magnetic core for a coil, made of ferrite
or of powdered iron, consisting of a central rod, a
surrounding potlike enclosure, and a lid. The rod
passes through the center of the coil, and the pot
and lid completely enclose the coil. This arrangement
provides a completely closed magnetic circuit
and coil shield.
Slot for coil
pot core
Slot for
coil
Clamping
bolt
potential See ELECTROMOTIVE FORCE.
potential barrier The electric field produced on
each side of a semiconductor junction by minority
carriers (i.e., by holes in the n-layer and electrons
in the p-layer) that face each other across
the junction, but cannot diffuse across the junction
and recombine.
potential coil The shunt coil in a conventional
wattmeter.
potential difference See ELECTROMOTIVE
FORCE and VOLTAGE.
potential divider See VOLTAGE DIVIDER.
potential drop 1. A voltage difference between two
points in a circuit. 2. The voltage across a resistor
in a direct-current circuit.
potential energy Energy resulting from the position
of a body or particle (e.g., the energy stored