Electronics glossary part1

Electronics glossary

Absorption coefficient The ratio of the sound energy absorbed by a surface, to the total sound energy incident on it.

Access time Time interval between a received instruction to read data stored in memory and the output of the data from memory.

Accumulator 1 A secondary cell, which produces a potential difference. 2 A register within the central processing unit of a computer.

AC Abbreviation for alternating current.

Acoustic feedback Unwanted feedback of sound waves from the output of an acoustic system to its input, causing unpleasant audible oscillations commonly known as howling.

Acoustic wave Synonym for sound wave.

Adder Circuit in a digital computer which performs addition. Address Number that identifies a particular item of data in memory or input/output channel of a digital computer.

Admittance Reciprocal of impedance, symbol: Y. The unit of admittance is the Siemen.

Aerial Construction, usually of metal, which radiates or receives radio waves. Synonym for antenna.

AFC Abbreviation for automatic frequency control. Alphanumeric Alphabetical or numerical ordering. Alternating current An electric current which periodically changes direction.

AM Abbreviation for amplitude modulation. Ammeter Indicating meter used to measure current. Ampere Unit used to measure current.

Amplify Make larger, electronically.

Amplifier Electronic circuit which increases some aspect of an applied signal.

Amplifier stage A single stage of a complete piece of electronic equipment to amplify an electronic signal.

Amplitude The peak value of an alternating current.

Amplitude modulation Type of modulation in which the amplitude of a carrier signal is varied above and below its nominal amplitude, by an amount proportional to the varying amplitude of a message signal.

Analog Term used for a non-digital signal. Some part of the analog signal varies as the analog of a reference.

Analog-to-digital converter A circuit which converts an analog signal to a digital one.

AND gate Logic circuit whose output is high if all of its inputs are high.

Angular frequency Frequency of a periodic wave in radians s·1• Symbol: w.

Anode Positive electrode of a system. Antenna Aerial.

Antiphase Waveforms completely out of phase i.e. differing by 180°.

Aspect ratio Ratio of the width of a television picture to its height. Typically 4:3.

Assembler Computer program which converts a program written in assembly code to a machine code program.

Astable multivibrator A multivibrator circuit which produces an output of two continuously alternating states i.e. a square wave oscillator.

Asynchronous Untimed data transfer.

Attenuation Reduction in some aspects of a signal. Opposite of amplification.

Attenuator A circuit which attenuates an applied input signal. Audio frequency Sound waves within the frequency range of the human ear i.e. having a frequency between about 20 to 20,000 Hz.

Automatic frequency control Circuit to control the frequency of an applied signal.

Automatic gain control Circuit to control the amplitude of an applied signal.

Automatic volume control Synonym for automatic gain control.

Avalanche breakdown Phenomenon which occurs in a reverse­ biased semiconductor junction, in which free charge carriers within the junction multiply.

Background noise See noise.

Balanced A transmission line with two conducting wires, each of which has the same resistance to ground, is said to be balanced.

Band I A coloured ring on an electronic component. 2 A specific range of communications frequencies.

Band-pass filter A filter which allows a specific range of frequencies to pass, while attenuating all other frequencies.

Band-stop filter A filter which attenuates a specific range of frequencies, while passing all other frequencies.

Bandwidth The band of frequencies a circuit passes without the circuit's output amplitude falling by a specified fraction (usually one half) of the maximum amplitude.

Base One of the three terminals of a bipolar transistor.

BASIC A high-level computer programming language.

Bass An audio amplifier tone control which attenuates or amplifies bass (i.e. low) frequencies.

Batch processing A computing method used in large computing systems, in which a number of previously prepared programs are run in a single batch.

Battery A source of electricity, consisting of two or more cells connected together.

Baud Unit of data modulation rate, corresponding to one transmitted signalling element per second. Often incorrectly confused with data signalling rate, measured in bits per second.

Beat A periodic signal produced when two signals of similar frequency are combined. The beat is caused by interference: the frequency of the beat is defined by the difference in frequency between the two interfering signals. Synonym for heterodyne.

Bel Unit used to express power ratios in electronics. See decibel.

Beta The common emitter forward current transfer ratio of a transistor. Symbol: or hre

Bias For a transistor to operate correctly the proper potentials have to be present at its emitter, base and collector. Normally the term bias refers to the voltage applied to the base to bring the operating point to a linear part of the amplification curve. For germanium transistors this is usually 0.3 V with respect to the emitter and for silicon transistors at least 0.6 V.

Bias voltage A standing voltage applied to an electronic component.

Binary code Numerical representation which has a base of two and, therefore, only two digits: 0 and I.

Bipolar transistor A transistor in which both types of charge carriers (i.e. electrons and holes) are used in operation.

Bistable Abbreviation of bistable multi vibrator: a circuit which has two stable states. Commonly known as aflip-flop.

Bit Abbreviation of binary digit. One of the two digits (0 or I) of binary code.

Black box Any self-contained circuit, or part of a system, which may be considered a separate entity. Because of this, a user or circuit designer does not need to understand the black box's internal operation -just its effect on external circuits.

Blocking capacitor A capacitor used in a circuit to prevent direct current flow between two parts of the circuit.

Bode diagram A graph in which gain and/or phase shift caused by a circuit, is plotted against frequency of applied signal.

Breadboard A plug-in method of temporarily assembling circuits, for design of test purposes.

Breakdown The sudden change from a high resistance to a low resistance which occurs when the breakdown voltage of a reverse biased semiconductor junction is exceeded.

Bridge A network of components, generally arranged in a square formation.

Bridge rectifier A full-wave rectifier circuit, composed of four diodes in a bridge.

Brightness A surface's brightness is the property by which the surface appears to emit light in the direction of view. This is a subjective quantity.

Broadcast Radio or television transmission.

Bubble memory A type of computer memory device which, although solid-state, is not of semiconductor origin. Data is stored as tiny domains of magnetic polarisation.

Bucket-brigade See charge coupled device.

Buffer Circuit interfacing two other circuits, used to prevent interference from one to the other.

Bug A computer program fault.

Bus l A conductor between two or more parts of a circuit, generally of high current carrying capacity. 2 A set of conductors between parts of a computer system.

Byte A group of bits, treated as a single unit of data in a computer system. Generally, though not necessarily, a byte is taken to be a group of eight bits.

Cable A set of conductors, insulated from each other but enclosed in a common outer sheath.

Capacitance The property of two isolated conductors whereby they hold an electrical charge. Symbol: C. Unit: F.

Capacitor An electronic component, which has two isolated conductive plates. A capacitor may therefore hold an electrical charge.

Carrier I A signal which is modulated by a message signal to allow communications e.g. amplitude modulation. 2 A hole, or electron in a semiconductor device, which carries charge.

Cathode Negative electrode of a system.

Cathode ray A beam of electrons, generated in a cathode ray tube.

Cathode ray oscilloscope An electronic test instrument which allows a signal to be displayed on its screen, as a graph of voltage against time. Abbreviated: CRO.

Cathode ray tube Glass evacuated tube allowing a beam of electrons to be generated, focused and positioned onto its face (screen). Cathode ray tubes form the display device in common televisions and cathode ray oscilloscopes. Abbreviated: CRT.

CCITT Abbreviation for International Telegraph and Telephone Consultative Committee. A body which recommends standards concerning voice and data communications systems.

Ceefax See teletext.

Cell Device which produces a potential difference by chemical means. Two or more cells in combination form a battery.

Central processing unit The part of a digital computer that controls the computer operation. Abbreviation: CPU.

Channel I A communications path between a transmission source and receiver. 2 The region between the source and drain of a field effect transistor.

Charge carrier A hole or electron in a semiconductor.

Charge coupled device A semiconductor memory device comprising a number of memory cells, each of which may hold a charge. Each charge is passed along from cell to cell, earning the device the nickname bucket-brigade device. Abbreviation: CCD.

Chip I A small piece of semiconductor material containing a single electronic component, or an electronic circuit. A chip is found within every transistor or integrated circuit. 2 Nickname for an integrated circuit.

Clock A circuit or device which generates a periodic signal (generally a square wave) to synchronise operations of a digital system.

CMOS Abbreviation for complementary metal oxide semiconduc­ tor.

Coax Abbreviation for coaxial cable.

Coaxial cable A cable with an inner conductor comprising one or more strands of wire, and an outer conduction sheath. The conductors are insulated from each other and the whole arrangement is covered in an outer layer of insulating material.

Coil Conductor(s) wound in a number of turns.

Collector One of the three terminals of a bipolar transistor. Colour code Method of marking an electronic component with information regarding its value, tolerance and any other aspects which may be of interest to its user.

Complementary pair Most modem transistor audio amplifiers make use of a pair of transistors, one npn and the other pnp, with similar characteristics and closely matched gains in the driver or output stage: they are referred to as a complementary pair.

Computer An automatic system, which processes information according to instructions contained in a stored program.

Conductor A material with low resistance to the flow of electric current.

CPU Abbreviation for central processing unit.

CRO Abbreviation for cathode ray oscilloscope.

Crosstalk Interference between signals of two adjacent communi­ cations channels.

CRT Abbreviation for cathode ray tube.

Current Rate of flow of electricity. Symbol: /. Unit: ampere (abbreviated: amp: A).

Cut-off frequency Frequency at which a circuit output falls to a specified fraction (usually one half) of the maximum.

Cycle Complete set of changes in a regularly repeating wave. Darlington pair A combination of two transistors which operate as if they are a single transistor, with a gain given by the product of the individual transistors' gains.

dB See decibel.

DC Abbreviation for direct current.

DC voltage Common term to mean direct voltage.

Debug The action of finding and correcting computer program faults.

Decibel Dimensionless unit expressing the ratio of two powers. Under certain conditions it may also be used to express the ratio of two voltages or currents.

Demodulation See modulation.

Demodulator A circuit which demodulates a received, modulated signal in a communications system. Synonymous with detector.

Demultiplexer See multiplexer.

Detector See demodulator.

Device An electronic component or system which contains at least one active element.

Diac Bi-directional voltage breakdown diode; passes current above a certain breakdown voltage. Normally employed with a triac in an AC control circuit.

Dielectric A material which is an insulator and can sustain an electric field. The layer of insulating material between the conduct­ ing plates of a capacitor is a dielectric.

Dielectric constant The ratio of the capacitance of a capacitor with a dielectric, to the capacitance of the capacitor with the dielectric replaced by a vacuum. Synonymous with relative permittivity. Symbol: Jl,.

Differential amplifier An amplifier which produces an output signal which is a function of the difference between its two inputs. Principle of the operational amplifier.

Differentiator A circuit which produces an output signal which is a function of the differential of its input signal.

Digital A circuit or system responding to, operating on, and producing fixed, discrete voltages. Where only two levels are used, the circuit or system is said to be binary digital.

Digital computer See computer.

Digital multimeter A multimeter which is capable of measuring and displaying a number of electrical quantities as a decimal value.

Digital voltmeter A voltmeter which displays a measured voltage as a decimal value.

DIL Abbreviation of dual-in-line.

Diode An active electronic component with two electrodes, which allows current flow in one direction but not in the other. Many derivative types of diode exist.

Diode transistor logic Family of logic integrated circuits built using diodes and transistors. Abbreviation: DTL.

Dioptre The unit of measure of lens power; the reciprocal of the focal length expressed in metre.

Dipole aerial Simplest type of aerial, in which a standing wave of current is symmetrical about its mid-point.

Direct current A unidirectional, constant current. Abbreviation: DC.

Direct voltage A unidirectional, more or less constant voltage.

Distortion Extra unwanted components in the output of a system which have been added by the system itself. There are many types of distortion.

Doping The addition of impurities to a pure semiconductor material in order to affect the numbers and types of charge carriers present. Donor impurities are added to form an n-type semiconduc­ tor. Acceptor impurities are added to form a p-type semiconductor.

Double-pole switch A switch with two electrically independent switching mechanisms. _

Drain One of the three connections of a field effect transistor.

Drift A variation of an electrical property with time.

Dry battery A battery of two or more dry cells.

Dry cell A cell whose contents are in non-liquid form.

Dry joint A faulty soldered joint.

DTL Abbreviation for diode transistor logic.

Dual-in-line Standard package for integrated circuits, in which the connection pins are in two parallel rows, either side of the body.

Duplex Simultaneous operation of both channels of a communica­ tions link.

DMM Abbreviation for digital multimeter.

DVM Abbreviation for digital voltmeter.

EAR OM Abbreviation for electrically alterable read only memory.

Earphone Small loudspeaker which fits into the ear. Earth The arbitrary zero point in electrical potential. Earth current Current which flows to earth.

Earth fault Fault occurring in a circuit or system, when a conductor is connected to earth or a low resistance occurs between the conductor and earth. Causes an unacceptable earth current.

ECL Abbreviation for emitter coupled logic.

Edge connector A connector which is pushed onto the edge of a printed circuit board. Tracks on the printed circuit board are taken to the edge forming connections.

EEROM, E2ROM Abbreviation for electrically erasable read only memory.

EHT Abbreviation for extra high tension.

Electrically alterable read only memory See read only memory.

Abbreviation: EAROM.

Electrically erasable read only memory See read only memory.

Abbreviation: EEROM; E2ROM.

Electrode Part of a component or system which gives out or takes in charge carriers.

Electrolysis Chemical change caused by an applied current through an electrolyte.

Electrolyte Material which allows conduction due to its dissocia­ tion into ions.

Electrolytic capacitor A capacitor in which the dielectric is formed by electrolytic action.

Electromagnet A component which becomes a magnet only when a current flows through it.

Electromagnetic spectrum Complete frequency range of electromagnetic energy.

Electromotive force Potential difference produced by an electrical energy source. Abbreviation: EMF. Symbol: E. Unit: Volt.

Electron Atomic particle which possesses a negative charge of magnitude 1.602 x 10·9 coulomb and a mass of 9.109 x 10·3 kg. Movement of electrons in one direction is equal to current flow in the opposite direction.

Electron beam Beam of electrons given off from an electron gun, typically in a cathode ray tube. Synonymous:cathode ray.

Electron gun Arrangement which is used to generate an electron beam in a cathode ray tube or similar.

Electronvolt The energy gained by one electron when passing across a potential difference of one volt. Symbol: eV.

Element Substance consisting of atoms of only one type.

EMF Abbreviation for electromotive force.

Emitter One of the three terminals of a bipolar transistor.

Emitter follower A single transistor amplifier whose output is between emitter and earth.

Enable Activate a circuit or device.

Encoder Circuit, system or device producing an output which is a coded version of the input.

Energy bands Theoretical levels of energy which electrons of an atom possess.

Equalisation Process whereby the distortion produced by a system may be compensated for.

Equaliser Circuit or device which causes equalisation.

Equivalent circuit A circuit comprising simple (generally passive) elements, used to model the action of a complex circuit under specified conditions.

Erase Remove stored information.

Error Difference between the correct value of something and its actual value.

Exclusive OR gate Logic circuit with two or more inputs, whose output is high if and only if one input is high. Abbreviation: XOR.

Facsimile A picture transmission system by which pictorial images can be transmitted using an ordinary communications link. Abbreviation: fax.

Failure Ceasing of a component or system's ability to function correctly.

Failure rate The number of failures which may be assumed by a component or system, in a given time. The failure rate is given by:

f MTBF

where MTBF is the mean time between failures.

Fall-time The time taken by a logic device or circuit to change output state from high to low.

Fan-out The maximum number of circuits which may be driven by the output of a similar circuit.

Farad Unit of capacitance. Symbol: F.

Feedback The return of some part of a circuit or system's output, to its input in such a way as to control the function of the circuit or system.

FET Field effect transistor. The FET makes use of the electric field established in a p- or n-type channel of semiconductor material to control the flow of current through the channel. The field is

established by the bias applied to the gate connections and the FET is thus a voltage-controlled device. This means it has a much higher input impedance than ordinary transistors. The main connections are

the source, drain and gate but some FETs have additional connec­ tions.

Fibre optics See optical fibre.

Field I Region affected by some phenomena. 2 Set of bits forming a unit of data with a specific purpose. 3 Set of lines of a displayed television picture.

Field effect transistor A unipolar transistor (i.e. with only one p-n junction). Abbreviation: FET.

Filter Circuit which passes some applied frequencies of signals while restricting others.

Fleming's left-hand rule When the thumb, first finger and middle finger of the left hand are held naturally at right angles, the thumb represents the direction of motion, the first finger represents the magnetic field, and the middle finger represents the current in an electric motor.

Fleming's right-hand rule Similar to Fleming's left-hand rule, but representing a dynamo, with the right-hand.

Flicker The eye's perception of fluctuations of brightness when the fluctuations occur more rapidly than the persistence of vision.

Flicker noise See noise.

Flip-flop Nickname for a bistable multivibrator.

Floating Term describing a part of a circuit which is not connected.

Floating-point representation Means of expressing a number with the use of a mantissa and an exponent.

Floppy disk Magnetic memory medium used by computers as auxiliary memory.

FM Abbreviation forfrequency modulation.

Forward bias When a voltage is applied across a semiconductor junction, the junction is said to be forward-biased when the current through the junction is the greater of the two ways. Thus, a diode is forward-biased when it conducts and reverse-biased when it does not conduct.

Frame One complete television picture.

Frequency Number of complete oscillations or cycles of a periodic signal in one second. Unit: hertz (Hz). Frequency (j) is related to the wavelength(;\,) of the signal by the signal velocity (v), where:

Frequency division multiplex A system in which a number of message signals are combined into one. Each message signal is modulated onto a different carrier wave frequency so that a number of frequency band channels exist. Abbreviation: FDM.

Frequency modulation Type of modulation in which the carrier frequency is varied up and down by the message signal. The carrier amplitude remains constant. Abbreviation: FM.

Frequency range Range of frequencies a circuit will operate on. Frequency response Variation with frequency of the gain of a circuit. Drawn as a graph, usually of gain in decibels against a logarithmic scale of frequency Frequency spectrum A graph, chart, or table showing the frequencies of all electromagnetic waves, related to types e.g. X­ rays, radio waves, audio waves and so on.

FSD Abbreviation forfull scale deflection.

Full scale deflection Maximum value displayed by measuring equipment. Abbreviation: FSD.

Full wave rectifier A circuit which rectifies both positive and negative half cycles of an applied AC wave.

Function generator A circuit or piece of test equipment which generates a variety of waves e.g. sine, sawtooth, square, for use in testing other circuits.

Fundamental frequency Generally the lowest sine wave frequency present in a complex periodic waveform.

Fuse Device which is intended to cause an open circuit when the current taken by a circuit goes above a specified level. Generally, a fuse is formed using a short length of fuse wire which, at a specified frequency and voltage, will melt i.e., 'blow' at the fuse's current rating, thus breaking the power supply connection.

Fusible link memory Type of read only memory device consisting of a matrix of fusible links. Data may be programmed into the device by 'blowing' selected links.

Gain Measure of a circuit's effect on the amplitude of an applied signal. Can be stated in terms of the ratio between output and input signals as a decimal number, or in decibels.

Gain control A control which may be used to vary the gain of a circuit.

Ganged Term used to describe variable components which are mechanically coupled so that they all vary simultaneously when a single control is varied.

Gate I A circuit having two or more inputs and one or more outputs. The output(s) varies as a direct result of the states of the inputs. 2 One of the terminals of a field effect transistor.

Gating signal A signal which, when applied to a gate is used to control the gate's output such as the output may be on (and produce an output signal which is some function of another input) or off (producing no output).

Geostationary orbit A satellite orbit in which the satellite lies about 36,000 km above the earth's equatorial plane, such that the satellite appears stationary to an observer on earth.

Germanium Semiconductor element used in the majority of early transistors and diodes.

Giga Unit prefix which means a multiplication factor of 1012. Abbreviation: G.

Graphics Display of graphical symbols and scenes, generated by a computer.

Ground Synonym:earth. Abbreviation: Gnd.

Guard band Range of frequencies between two ranges of transmission frequencies, left unoccupied to minimise interference.

Half-adder Elementary digital circuit composed of logic gates. See adder.

Half-duplex A pair of transmission channels over which two-way communications may take place, although only one channel is operational at any one time, is said to allow half-duplex communica­tions.

Half wave rectifier A circuit which rectifies only one half of each cycle of an applied AC wave.

Hall effect An electromagnetic phenomenon which occurs when a current carrying conductor is placed in a magnetic field, the direction of which is perpendicular to the directions of both the current and its own magnetic field.

Ham Colloquial term denoting an amateur radio transmitting/ receiving enthusiast.

Hardware Physical parts of a computer system, e.g. printer, keyboard, VDU and so on.

Harmonic A signal present in a complex periodic waveform, which is a multiple of the fundamental frequency. The second harmonic is three times and so on.

Head Transducer of a magnetic recording system which allows electrical signals to be changed into a magnetic field to write data onto the medium, or converts magnetic data into electrical signals.

Headset Pair of earphones.

Heatsink Metal attachment mechanically connected to a heat producing element in a circuit (e.g. a power transistor) to ensure heat is dissipated away from the element, preventing damage by excessive heat.

Henry Unit of magnetic inductance. Symbol: H.

Hertz Unit of frequency. Equivalent to one cycle of a periodic wave which occurs in one second. Symbol: Hz.

Heterodyne Production of beats by combination of two signals which interfere. Used in a superheterodyne radio receiver to produce an intermediate frequency.

HF Abbreviation for high frequency. hce and hFE See beta.

Hifi Acronym for high fidelity.

High fidelity Commonly used term denoting audio reproduction equipment of good quality.

High frequency Bands of radio transmissions around I 0 MHz. Abbreviation: HF.

High level programming language A computer programming language which is more like human language or mathematical notation than the machine code used by the central processing unit of the computer.

High logic level Term denoting a logic I level (in positive logic).

High pass filter A filter which allows signal frequencies above a specific comer frequency to pass without attenuation. Signal frequencies below the comer frequencies are attenuated.

High tension Voltages in the range between about 50 V to 250 V. Abbreviation: HT.

Holding current The value of current which must be maintained to hold a thyristor in its on state. If the current through the thyristor falls below the holding current, the thyristor turns off and ceases conduction.

Hole An empty space in a semiconductor material due to a 'missing' electron. As electrons are negatively charged, holes are positive. Holes, like electrons, may be thought of as charge carriers, moving through the semiconductor material thus forming a current.

Hole current The current through a semiconductor due to the movement of holes under an applied voltage.

Howl Colloquial term for the sound caused by acoustic feedback.

HT Abbreviation for high tension.

Hum Capacitive or magnetic interference between a mains powered device such as a power supply, and local equipment such as an amplifier. Often heard in audio frequency systems as a low drone of mains supply frequency, or a harmonic of that frequency.

Hunting A system's oscillation about its desired point, caused by over-correction.

Hybrid integrated circuit An integrated circuit comprising a number of discrete components attached to a substrate and interconnected to form a circuit. See integrated circuit.

Hybrid-1t A type of equivalent circuit used to show transistor operation.

Hysteresis Phenomenon occurring in some circuits or systems, in which the output lags behind a changing input. A hysteresis loop is formed -a graph of output against input -which shows that the value of output depends on whether the input is increasing or decreasing in value.

Hz Abbreviation for hertz.

IC Abbreviation for integrated circuit.

IEC Abbreviation for International Electrotechnical Commission.

lEE Abbreviation for Institute of Electrical Engineers.

IEEE Abbreviation for Institute of Electrical and Electronic Engineers.

IF Abbreviation for intermediate frequency.

IGFET Abbreviation for insulated gate field effect transistor.

I2L Abbreviation for integrated injection logic.

Illuminance Luminous flux perpendicularly reaching a surface per unit area. The unit of illuminance is the lumen m·2 or lux.

Image frequency Unwanted input frequency to a radio, causing a spurious output. Synonym:second channel frequency.

Image interference Interference caused by an image frequency. Impedance The opposition of a circuit to alternating current flow. Impedance matching The matching of impedances between two

circuits, to ensure maximum transfer of power from one circuit to the other.

Impulse noise Noise in an electronic system caused by a single disturbance. See noise.

Impulse voltage A single, rapidly occurring, pulse of voltage. Impulses are generally unwanted, as they tend to cause impulse noise throughout the system.

Impurities Atoms in a semiconductor material, not of the semiconductor element itself. Impurities may occur naturally or may be deliberately introduced. See doping.

Incandescence When a material gives off visible light due to its high temperature.

Incandescent lamp Lamp which emits light when its filament is heated by an electric current. The filament often reaches tempera­ tures of 2,500°C and over.

Index error An error occurring in a measuring instrument such that when no measurand is present (i.e. with zero input) a non-zero reading is obtained. Synonymous: zero error.

Indirect wave Radio wave which is reflected by the ionosphere

i.e. it does not travel directly from transmitter to receiver.

Induce To cause a change in electrical or magnetic conditions in a system, by changing the electrical or magnetic conditions of another local, system.

Inductance A constant occurring when a circuit is magnetically linked with the current flowing through it. Unit: henry.

Induction Abbreviation of electromagnetic induction or electrostatic induction.

Inductor A component which has inductance. Generally, inductors are constructed of some form of coil.

Information technology The study of the combined effects of electronics, computing and communications. Abbreviation: IT.

Infrared radiation Invisible electromagnetic radiation with wavelengths of about 730 nm to about I mm.

Inject To introduce charge carriers into a semiconductor junction area.

Input I The signal applied to a system. 2 The terminal at which the input signal is applied.

Input impedance The impedance which a circuit presents to an input signal.

Input/output Term applying to operations performed by, or devices connected to a computer, which allow the computer to receive and send out data. Abbreviation: 1/0.

Instantaneous value The value of any measurand which varied with time e.g., instantaneous voltage, instantaneous current.

Institute of Electrical and Electronics Engineers A standardisa­ tion body in the USA. Abbreviation: IEEE.

Institute of Electrical Engineers A UK standardisation body. Abbreviation: lEE.

Instruction set The complete list of operations which may be performed by the central processing unit of a computer.

Insulate To prevent unwanted current flow by sheathing a conductor with non-conductive material.

Insulated gate field effect transistor Type of construction of field effect transistor, used in MOSFETs. Abbreviation: IGFET.

Insulator A non-conductor. A material with a very high resistance to flow of electric current. Current flow is assumed to be negligible.

Integrated circuit A device which contains a complete circuit. One of two main methods are used in manufacture. A (hybrid integrated circuit) is manufactured from discrete components, attached to a substrate and interconnected by layers of metallisation. A monolithic integrated circuit is made by building up all compo­ nents within the circuit onto a single chip of silicon. In recent usage, integrated circuit, chip, microchip, have all become synonymous. Abbreviation: IC.

Integrated injection logic A type of monolithic integrated circuit construction. Abbreviation: I2L.

Integrator Circuit which performs the equivalent of a mathemati­ cal integration on an applied input signal.

Intelligent Any system with processing and storage capabilities, whose actions may be controlled by stored instructions, is said to be intelligent.

Intelsat Acronym of International Telecommunications Satellite Consortium.

Intensity Denoting magnetic or electric field strength.

Interactive Tenn used to denote computer operation where user and computer communicate in a continuous manner. Generally refers to an on-line situation.

Interference A disturbance to any signal in a system, causing additional, unwanted signals. Interference may be natural or manmade. See hum, crosstalk, image frequency.

Interlaced scanning Scanning method used in a television system in which lines are scanned in two separate scans, even lines and odd lines.

Intermediate frequency Signal generated in a heterodyne-based radio receiver, where the received radio signal is combined with a local oscillation signal. Abbreviation: IF. See heterodyne, beats.

Internal resistance The small resistance inherent in any source of electricity. Internal resistance limits the voltage which may be produced by the electricity source under load conditions.

International Electrotechnical Commission An international standardisation body. Abbreviation: IEC.

International Radio Consultative Committee An international standardisation committee: part of the International Telecommunica­ tions Union. Abbreviation: CCIR.

International Telecommunications Union An international standardisation body. Abbreviation: ITU.

International Telegraph and Telephone Consultative

Committee An international standardisation committee: part of the International Telecommunications Union. Abbreviation: CCITT.

Inversion The production of an opposite polarity in a semiconduc­ tor device, due to an applied electric field.

Inverter I A circuit which produces an output the inverse of an applied input signal. A digital inverter produces an output which is the opposite logic state to that of the input. 2 A circuit which converts a direct current to an alternating current.

1/0 Abbreviation for input/output.

Ion A particle of material (an atom, molecule, group of atoms, or group of molecules) with an electric charge. Negative ions are called anions: positive ions are called cations.

ISO Abbreviation for International Standards Organisation.

Isolate To disconnect two parts of a system, ensuring that no electrical connection exists.

ITU Abbreviation for International Telecommunications Union.

Jack A connector pair (plug and socket) allowing quick and easy input or output connections, to or from a circuit or system. Many sizes and types are available.

Jam To cause interference in radio-type transmissions, rendering correct reception impossible.

JEDEC Abbreviation for Joint Electron Device Engineering Council.

JFET Abbreviation for junction field effect transistor.

JK flip-flop A type of flip-flop circuit.

Johnson noise A type of noise generated by the random movement of electrons in resistive components, due to thermal activity. Synonymous: thermal noise.

Josephson junction The junction between a thin layer of insulated material and a superconducting material. A superconducting current can flow across the junction even without an applied voltage.

JUGFET Abbreviation for junction field effect transistor.

Junction I The boundary between two layers of material in an electronic device. 2 An electrical connection.

Junction box An enclosed container, in which wires or leads from circuits may be joined, by screw terminals or other means.

Junction capacitance Capacitance between pn junctions in a semiconductor device. Also called barrier depletion layer or transition capacitance. See neutralisation.

Junction field effect transistor A type of field effect transistor. Abbreviation: JFET; JUGFET.

Junction transistor Abbreviation for bipolar junction transistor.

Keyboard Part of a computer, with a typewriter-style appearance, allowing input of instructions and data to the computer.

Kilo- I A prefix denoting a multiple of 103• Abbreviation: k. 2 A prefix to a computing term, denoting a multiple of 210 i.e. I 024. Abbreviation: K.

Kirchhotrs laws Two basic laws of electricity. The first states that: the algebraic sum of all currents into and out of a point in a circuit is zero. The second states that: the algebraic sum of the products of current and resistance in each part of circuit is equal to the algebraic sum of the voltages.

Klystron An electron gun device, used as an amplifier or oscillator at high radio frequencies.

Lag The delay between one waveform and another, measured in time or as an angle. See lead.

Lamination Thin sheet material, used to make the laminated core of a wound component e.g. a transformer, a relay.

Land A contact on a printed circuit board. Language Short for programming language.

Large scale integration A level of integration used in the manufacture of integrated circuits. Abbreviated: LSI.

Laser An acronym for light amplification by stimulated emission of radiation. A laser device is a source of coherent, monochromatic light. The light may not be visible but may be of ultra-violet or infra­ red origin.

Latch Common name for a bistable multivibrator or flip-flop. LCD Abbreviation for liquid crystal display.

LC network A tuned circuit containing inductance and capaci­ tance.

Lead I The amount by which one waveform is in front of another measured as a time interval or as an angle. See lag. 2 An electrical conductor, used to make an electrical connection between two parts of a circuit or system.

Lead-acid cell A secondary cell or accumulator comprising lead metal cathodes and lead dioxide anodes, with a dilute sulphuric acid electrolyte. Lead-acid batteries, formed by a number of series connected cells are commonly used in cars.

Leading edge The portion of a pulse which signals the commence­ ment of the pulse.

Leakage Current flow through a circuit or component due to faulty insulation.

Leakage current That current which flows due to leakage.

Leclanche cell A primary cell comprising a carbon-rod anode and a zinc cathode, with an ammonium chloride solution electrolyte. Leclanche cells with a paste-based ammonium chloride electrolyte are said to be dry and form the basis of many available cells used in common battery-powered appliances.

LED Abbreviation for light emitting diode.

Left-hand rule See Fleming's rules.

LF Abbreviation for lowfrequency.

Light emitting diode A semiconductor diode which emits light as the result of an electroluminescent effect. As electron and hole combine near the junction of the diode, sufficient energy is released to form light. The emitted light is of a particular frequency and so of a particular colour. Light emitting diodes of red, yellow, orange, green and blue are available, as well as infra-red varieties. Abbreviation: LED.

Light sensitive devices Light and heat both affect the conductivity of a pn junction. Devices are available in which a pn junction is exposed to light so as to make use of this property. Light falling on the junction liberates current carriers and allows the device to conduct.

Linear Any circuit or system which produces an output directly proportional to the input at any time, is said to be a linear circuit or system.

Lines The physical paths followed by the electron beam of a television receiver's cathode ray tube across the screen. Standard UK television pictures are composed of 625 lines.

Line of flux Imaginary line in a magnetic field. The direction at any point along a line of flux is that of the magnetic flux density.

Line of force Imaginary line in an electric field, the direction of which at any point represents the field's direction at the point.

Liquid crystal display A display comprising a thin layer of liquid crystal material between two electrodes. Application of a potential difference across the electrodes causes the liquid crystal material to change in respect of light transmission. Abbreviation: LCD.

Load I A circuit or system which absorbs power from any other circuit or system. 2 The output power provided by a circuit or system.

Load characteristic A characteristic curve, typically for a transistor, in which the relationship between variables is plotted.

Load impedance The impedance presented to a circuit or system by its load.

Load line A line drawn on the load characteristics of a component which shows the relationship between voltage and current in the circuit.

Local oscillator An oscillator within a radio receiver operating on the superheterodyne principle.

Logic circuit A circuit which performs a logical operation such as AND, OR, NOT, NAND, NOR, EXOR.

Logic diagram A diagram showing the logic elements of a logic circuit.

Logic symbol Graphical symbol representing a logic element. Long-tailed pair A circuit containing two transistors coupled

together so that their emitters are joined with a common emitter bias resistor which provides a constant current. The long-tailed pair forms the basis of a differential amplifier.

Long wave A radio frequency wave with a wavelength between about Ito 10 km.

Loss A dissipation of power due to the resistance of current flow. Lossless A circuit or system which theoretically loses no power

due to resistance.

Lossy A circuit or system which loses a great deal of power due to resistance.

Loudness Subjective measure of sound intensity. Although dependent on intensity it also varies with frequency and timbre of the sound.

Loudness level A comparison of a sound's loudness with a standard sound loudness. The standard sound is a sinusoidal note which has a frequency of 1,000 Hz. The unit ofloudness level is the phon.

Loudspeaker A transducer which converts electrical energy into sound energy. Typically, loudspeakers are electromagnetic devices which rely on the applied electrical signal to move a coil of wire in a magnetic field. Attached to the coil is a cone of material which thus also moves with the electrical signal. The cone causes a movement

of air, which the ear detects as sound.

Low frequency Radio signals in the frequency band of 30kHz to 300 kHz, having wavelengths between Iand I0 km.

Abbreviation: LF.

Low level programming language A computer programming language which comprises instructions to the computer in machine code i.e. binary codes which the computer can directly understand.

Low logic level Term denoting a logic 0 level (in positive logic). Low-pass filter A filter which allows signal frequencies below a

specific comer frequency to pass without attenuation. Signal frequencies above this comer frequency are attenuated.

LSI Abbreviation for large scale integration. See integrated

circuit.

Luminance A surface's luminance is the objective measure of the light emitted per unit projected area of surface, the plane of projection being perpendicular to the direction of view. The unit of luminance is the candela m·2•

Luminous intensity The unit of luminous intensity is the candela (cd).

Machine code The binary codes understood by the central processing unit of a computer.

Magnet Term applied to a substance which generates a magnetic field. A magnet can be temporary or permanent.

Magnetic bubble memory See bubble memory.

Magnetic circuit A closed path of lines of magnetic flux. Magnetic field Space surrounding a magnet which contains a

magnetic flux. A magnetic field may be represented by lines of

force.

Magnetic field strength Magnetising force. Symbol: H.

Unit: ampere per metre (A m·1).

Magnetic flux The flux through an area in the space surrounding a magnet. Symbol: <ll. Unit: weber.

Magnetic flux density Magnetic induction. The magnetic analogue of the electric field. Symbol: B. Unit: tesla (T), or weber per square metre (w m·2).

Magnetism The collection of properties exhibited by a magnet or magnets.

Mains Domestic electricity supply distributed through the National Grid system. A voltage of 240 VAC, at a frequency of 50 Hz is obtained from all domestic outlets.

Mains hum See hum.

Make To close a circuit by means of a switch or similar compo­ nent.

Make and break Type of switch which is automatically opened and closed, thus making and breaking the circuit, by the circuit which it forms part of.

Man-made noise See noise.

Mark-space ratio The ratio between a pulse's duration and the time between successive pulses.

Maser An acronym for microwave amplification by stimulated emission of radiation. Similar to laser except radiations are part of the microwave frequency band, not light.

Mask Photographic reproduction of the circuit to be integrated into an integrated circuit chip by photographic or other means.

Matched termination A load attached to a circuit or system such that it absorbs all the power available from the circuit or system.

Mean life The mean time to failure of a component, circuit or system.

Measurand The quantity to be measured by measuring equipment. Medium frequency Radio signals in the frequency band of

300kHz to 3 MHz, having wavelengths between 100m to I km.

Abbreviation: MF.

Medium wave A radio frequency wave with a wavelength placing it in the medium frequency band.