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Dictionary of Electronics
"Q" to "r-2r ladder" |
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- 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 a condition with no active input signal.
- quiescent point
- (Q 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.
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.
- radiocommunication
- 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 Cartesion coordinate system whose straight-line axes or coordinate planes are perpendicular.
- rectangular wave
- Also known as a pulse wave. A repeating wave that only operates between two levels or values and remains at one of these values for a small amount of time relative to the other value.
- rectification
- Process that converts alternating current to direct current.
- rectifier
- Diode circuit that converts alternating current into pulsating direct current.
- reed relay
- Relay consisting of two thin magnetic strips within a glass envelope. When a coil around the envelope is energised, the relay,s contacts snap together making a connection between leads attached to the reed strips.
- regenerative feedback
- Positive feedback. Feedback from the output of an amplifier to the input such that the feedback signal is in phase with the input signal. Used to produce oscillation.
- 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.
- resistivity
- 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.
- RL differentiator
- An RL circuit whose output voltage is proportional to the rate of change of the input voltage.
- RL filter
- Selective circuit of resistors and inductors that offers little or no opposition to certain frequencies while blocking or attenuating other frequencies.
- RL integrator
- RL circuit with an output proportionate to the integral of the input signal.
- rms
- Abbreviation for "root mean square"
- rms value
- Rms value of an AC sine wave is 0.707 times the peak value. This is the effective value of an AC sine wave. The rms value of a sine wave is the value of a DC voltage that would produce the same amount of heat in a heating element.
- roll-off rate
- Rate of change in gain when an amplifier is operated outside of its bandwidth.
- rotary switch
- Electromechanical device that has a rotating shaft connected to one terminal capable of making or breaking a connection to one or more other terminals.
- R-2R ladder
- Network or circuit composed of a sequence of L networks connected in tandem. Circuit used in digital to analog converters.
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