photoconductive
cell Material whose resistance decreases or conductance
increases when exposed to light.
photoconduction A process by
which the conductance of a material is change by incident
electromagnetic radiation in the visible light spectrum.
photodetector Component used to
detect or sense light.
photodiode
A semiconductor diode that changes its electrical characteristics in
response to illumination.
photometer Meter used to measure
light intensity.
photon Discrete portion of
electromagnetic energy. A small packet of light.
photoresistor Also known as a
photoconductive cell or light dependent resistor. (LDR) A device whose
resistance decreases with exposure to light.
photovoltaic
cell Component commonly called a solar cell used to
convert light energy into electrical energy.
pi Value representing
the ratio between the circumference and diameter of a circle and equal
to approximately 3.142.
pierce
oscillator A variation of the colpitts oscillator.
This oscillator uses a quartz crystal in place of the inductor found
in the colpitts oscillator feedback network. The crystal maintains a
highly stable output frequency.
piezoelectric
crystal Crystal material that will generate a voltage
when mechanical pressure is applied and conversely will undergo
mechanical stress when subjected to a voltage.
piezoelectric
effect The production of a voltage between opposite
sides of a piezoelectric crystal as a result of pressure or twisting.
Also the reverse effect which the application of a voltage to opposite
sides causes a deformation to occur at the frequency of the applied
voltage. (Converts mechanical energy into electrical energy and
electrical energy into mechanical energy.)
pinch-off
region A region on the characteristic curve of a FET in
which the gate bias causes the depletion region to extend completely
across the channel.
plastic film
capacitor Capacitor in which alternate layers of
aluminum foil are separated by thin films of plastic dialectric.
plate Conductive electrode in
either a capacitor or battery. In vacuum tube technology, it is the
name given to the anode.
plug Movable connector that is
normally connected into a socket or jack.
pnp transistor A bipolar
junction transistor with an n-type base and p-type emitter and
collector.
pole In an active filter, a
single RC circuit. A one pole filter has one capacitor and one
resistor. A two pole filter has two RC circuits and so
on.
polar
coordinates Either of two numbers that locate a point
in a plane by its distance from a fixed point and the angle this line
makes with a fixed line.
polarity Term used to describe
positive and negative charges.
polarized A component which must
be connected in correct polarity to function and/or d/or prevent
destruction. Example: Electrolytic capacitor.
positive Polarity of point that
attracts electrons as opposed to negative which supplies
electrons.
positive
charge A charge that exists in a body that has fewer
electrons than protons.
positive
feedback A feedback signal that is in phase with an
amplifier input signal. Positive feedback is necessary for
oscillation to occur.
positive
ground A system whereby the positive terminal of the
source is connected to the system's conducting chassis.
positive
ion Atom that has lost one or more valence electrons
resulting in a net positive charge.
potential
difference Voltage difference between two points which
will cause current to flow in a closed circuit.
potential
energy Energy that has potential to do work because of
its position relative to others.
potentiometer A variable
resistor with three terhree terminals. Mechanical turning of a shaft
can be used to produce variable resistance and potential. Example: A
volume control is usually a potentiometer.
power Amount of energy converted
by a circuit or component in a unit of time, normally seconds.
Measured in units of watts. (joules/second).
power
amplifier An amplifier designed to deliver maximum
power output to a load. Example: In an audio system, it is the power
amplifier that drives the loudspeaker.
power derating
factor A transistor rating that tells how much the
maximum allowable value of PD decreased for
each 1°C rise in ambient temperature.
power
dissipation Amount of heat energy generated by a device
in one second when current flows through it.
power
factor Ratio of actual power to apparent power.
power
loss Ratio of power absorbed to power delivered.
power
supply Electrical equipment used to deliver either AC
or DC voltage.
power supply
rejection ratio A measure of an op-amps ability to
maintain a constant output when the supply voltage varies.
primary First winding of a
transformer. Winding that is connected to the source as opposed to
secondary which is a winding connected to a load.
primary
cell Cell that produces electrical energy through an
internal electrochemical action. Once discharged a primary cell
cannot be reused.
printed circuit
board Insulating board containing conductive tracks for
circuit connections.
programmable
UJT Unijunction transistor with a variable intrinsic
stand-off ratio.
propagation Travelling of
electromagnetic, electrical or sound waves through a medium.
propagation
delay Time required for a signal to pass through a
device or circuit.
propagation
time Time required for a wave to travel between two
points.
protoboard Board with provision
for attatching components without solder. Also called a breadboard.
Primarily used for constructing experimental circuits.
proton Sub atomic particle
within the nucleus of an atom. Has a positive charge.
pulse Rise and fall of some
quantity (usually voltage) for a period of time.
pulse fall
time Time for a pulse to decrease from 90% of its peak
value to 10% of its peak value.
pulse repetition
frequency The number of times per second that a pulse
is transmitted. Pulse rate.
pulse repetition
time Time interval between the start of two consecutive
pulses.
pulse rise
time Time required for a pulse to increase from 10% of
its peak value to 90% of its peak value.
pulse
width Time interval between the leading edge and
trailing edge of a pulse at a point where the amplitude is 50% of the
peak value.
push>push-pull
amplifier Amplifier using two active devices operating
180° apart.
Pythagorean
theorem A theorem in geometry: The square of the
hypotenuse of a right triangle equals the sum of the squares of the
other two sides. In electronics used for vector analysis of AC
circuits.