[align=left]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
Traveling 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 attaching 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
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Q
Q
Quality factor of an inductor or capacitor. It is the ratio of a component’s reactance (energy stored) to its effective series resistance (energy dissipated). For a tuned circuit, a figure of merrit used in bandwidth calculations. Q is the ratio of reactive power to resistive power in a tuned circuit. Also the symbol for charge in coulombs (Q for quantity).
quiescent
At rest. For an amplifier the term is used to describe condition with no active input signal.
quiescent point
( A point on the DC load line of a given amplifier that represents the quiescent (no signal) value of output voltage and current for the circuit.
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R
radar
Acronym for "radio detection and ranging" A system that measures the distance and direction of objects.
radioastronomy
Branch of astronomy that studies the radio waves generated by celestial bodies and uses these emissions to obtain information about them.
radio broadcast
Transmission of music, voice and other information on radio carrier waves that can be received by the general public.
radio communication
Term used to describe the transfer of information between two or more points by use of radio or electromagnetic waves.
radio-frequency amplifier
Amplifier having one or more active devices to amplify radio signals.
radio-frequency generator
Generator capable of supplying RF energy at any desired frequency in the radio-frequency spectrum.
radio-frequency probe
Probe used in conjunction with an AC meter to measure radio-frequency signals.
RC
Abbreviation for "resistance capacitance" also abbreviation for "radio controled" as in "RC model airplanes."
RC time constant
Product of resistance and capacitance in seconds.
reactance
Symbol "X". Opposition to current flow without the dissipation of energy. Example: The opposition provided by inductance or capacitance to AC current.
reactive power
Also called imaginary power or wattless power. It is the power value in "volt amps" obtained from the product of source voltage and source current in a reactive circuit.
real number
Number having no imaginary part.
receiver
Unit or piece of equipment used to receive information.
recombination
Process by which a conduction band electron gives up energy (in the form of heat or light) and falls into a valence band hole.
rectangular coordinates
A Cartesian coordinate of a Cartesian coordinate system whose straight-line axes or coordinate planes are perpendicular.
rectification
Process that converts alternating current to direct current.
rectifier
Diode circuit that converts alternating current into pulsating direct current.
regulated power supply
Power supply that maintains a constant output voltage under changing load conditions.
regulator
Device or circuit that maintains a desired output under changing conditions.
relay
Electromechanical device that opens or closes contacts when a current is passed through a coil.
relative
Not independent. Compared with or with respect to some other measured quantity.
relaxation oscillator
Free running circuit that outputs pulses with a period dependent or one or more RC time constants.
reluctance
Resistance to the flow of magnetic lines of force.
remanence
Amount a material remains magnetized after the magnetizing force has been removed.
residual magnetism
Magnetism remaining in the core of an electromagnet after the coil current is removed.
resistance
Symbolized "R" and measured in ohms. Opposition to current flow and dissipation of energy in the form of heat.
resistive power
Amount of power dissipated as heat in a circuit containing resistive and reactive components. True power as opposed to reactive power.
resistive temperature detector
(RTD) Temperature detector consisting of a fine coil of conducting wire (such as platinum) that will produce a relatively linear increase in resistance as temperature increases.
receptivity
Measure of a material’s resistance to current flow.
resistor
Component made of material that opposes flow of current and therefore has some value of resistance.
resistor color code
Coding system of colored stripes on a resistor to indicate the resistor’s value and tolerance.
resonance
Circuit condition that occurs at the frequency where inductive reactance (XL) equals capacitive reactance (XC).
reverse bias
Bias on a PN junction that allows only leakage current (minority carriers) to flow. Positive polarity on the n-type material and negative polarity to the p-type material.
reverse breakdown voltage
Amount of reverse bias that will cause a PN junction to break down and conduct in the reverse direction.
reverse current
Current through a diode when reverse biased. An extremely small current also referred to as leakage.
reverse saturation current
Reverse current through a diode caused by thermal activity. This current is not affected by the amount of reverse bias on the component, but does vary with temperature.
RF
Abbreviation for "radio frequency."
rheostat
Two terminal variable resistor used to control current.
right angle triangle
Triangle having a 90° or square corner.
ripple frequency
Frequency of the ripple present in the output of a DC source.
ripple voltage
The small variations in Dc voltage that remain after filtering in a power supply.
rise time
Time for the leading edge of a pulse to rise from 10% of its peak value to 90% of its peak value.
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