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Glossary / Dictionary of Electronics Terms - R

radar - Acronym for "radio detection and ranging" A system that measures the distance and direction of objects.

radio astronomy - 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 controlled" 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 wattles 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.

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 energized, 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.

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.

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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