PERMANENT MAGNET SPEAKERA speaker with a permanent magnet mounted on soft iron pole
PERMEABILITYThe measure of the ability of a material to act as a path for magnetic lines of force 
PERSISTENCEThe length of time a phosphor dot glows on a CRT before disappearing  .
PHANTASTRONA variable-length sawtooth generator often used to produce a sweep on an A-scope
PHASEThe angular relationship between two alternating currents or voltages when the voltage or current
is plotted as a function of time. When the two are in phase, the angle is zero; both reach their peak
simultaneously. When out of phase, one will lead or lag the other; that is, at the instant when one is at
its peak, the other will not be at peak value and (depending on the phase angle) may differ in polarity as
well as magnitude .
PHASE ANGLEThe number of electrical degrees of lead or lag between the voltage and current
waveforms in an ac circuit  .
PHASE MODULATION (pm)Angle modulation in which the phase of the carrier is controlled by the
modulating waveform. The amplitude of the modulating wave determines the amount of phase shift,
and the frequency of the modulation determines how often the phase shifts .
PHASE-SHIFT DISCRIMINATORSee FOSTER-SEELEY DISCRIMINATOR .
PHASE SHIFTERA device used to change the phase relationship between two ac signals .
PHASE-SHIFT KEYINGSimilar to ON-OFF cw keying in AM systems and frequency-shift keying in
FM systems. Each time a mark is received, the phase is reversed. No phase reversal takes place when a
space is received .
PHASE SPLITTERA device that provides two output signals from a single input signal. The two output
signals differ from each other in phase (usually by 180 degrees) .
PHOSPHORThe material used to convert the energy of electrons into visible light .
PHOTOCELLA light-controlled variable resistor which has a light-to-dark resistance ratio of 1:1000.
Used in various types of control and timing circuits .
PHOTODIODEA light-controlled PN junction. Current flow increases when the PN junction is exposed
to an external light source .
PHOTOELECTRIC VOLTAGEA voltage produced by light .
PHOTOETCHINGChemical process of removing unwanted material in producing printed circuit boards
PHOTOTRANSISTORAn optoelectronic device that conducts current when exposed to light. Produces
more current and is much more sensitive to light than the photodiode .
PHOTOVOLTAIC CELL (SOLAR CELL)A device that acts much like a battery when exposed to
light and converts light energy into electrical energy .