Page 85 - The Illustrated Dictionary of Electronics

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70 berkelium • biased off

berkelium Symbol, Bk. A radioactive elemental few feet above ground and run in a straight line
metal produced artificially. Atomic number, 97. for one to several wavelengths. It is generally
Atomic weight, 247. used for reception at low and medium frequen-
beryllia Formula, Be0. Beryllium oxide, used in cies, the best response is to vertically polarized
various forms as an insulator and structural ele- signals arriving from one or both directions in
ment (as in resistor cores). line with the wire. It can be left unterminated for
beryllium Symbol, Be. An elemental metal. Atomic bidirectional response, or it can be terminated at
number, 4. Atomic weight, 9.01218. Beryllium is its far end by a noninductive resistor of about 600
present in various dielectrics and alloys used in ohms for a unidirectional response.
electronic components. beyond-the-horizon propagation See FORWARD
Bessel functions Sophisticated mathematical SCATTER.
functions for dealing with periodic electronic phe- bezel A faceplate for an electronic instrument,
nomena in which the waveform often displays usually having a fitted rim and cutouts for knobs,
decrement. Also called cylindrical functions. switches, jacks, etc.
beta Symbol, β. The current gain of a common- BFO Abbreviation of BEAT-FREQUENCY OSCIL-
emitter bipolar transistor stage. It is the ratio of LATOR.
the induced change of collector current to the ap- BG Abbreviation of BIRMINGHAM WIRE GAUGE.
plied change of base current: β = dIC/dIB. Also abbreviated BWG.
beta circuit The output-input feedback circuit in B-H curve A plot showing the B and H properties of
an amplifier. a magnetic material. Magnetizing force H is plot-
beta cutoff frequency The frequency at which the ted along the horizontal axis, and flux density B
current amplification of a bipolar transistor falls is plotted along the vertical axis.
to 70.7% of its low-frequency value. B-H loop See BOX-SHAPED LOOP.
beta particles Minute radioactive subatomic bits B-H meter Any instrument for displaying or evalu-
identical to the electron or positron, and emitted ating the hysteresis loop of a magnetic material.
by some radioactive materials. Also see BETA bhp Abbreviation of brake horsepower.
RAYS. Bi Symbol for BISMUTH.
beta rays Rays emitted by the nuclei of radioactive bias 1. Any parameter of which the value is set to a
substances, consisting of a stream of beta parti- predetermined level to establish a threshold or
cles (i.e., electrons or positrons) that move at ve- operating point. Although it is common to think
locities up to 299.8 million meters per second. of bias currents and bias voltages, other parame-
Compare ALPHA PARTICLE and GAMMA RAYS. ters (e.g., capacitance, resistance, illumination,
beta-to-alpha conversion For a bipolar transistor, magnetic intensity, etc.) can serve as biases. 2. In
the conversion of current amplification expressed a high-fidelity audio system, a circuit in a tape
as beta (β) to current amplification expressed as recorder/player that optimizes performance for a
alpha (α): α = β/(β + 1). particular type of recording tape.
betatron A particle accelerator in which injected bias current A steady, constant current that pre-
electrons are given extreme velocity by being pro- sets the operating threshold or operating point
pelled in circular paths in a doughnut-shaped of a circuit or device, such as a transistor,
glass container. The term comes from the fact diode, or magnetic amplifier. Compare BIAS
that high-speed electrons constitute BETA PAR- VOLTAGE.
TICLES. bias current drift The ratio of a change in input
beta videocassette recorder The earliest scheme bias current to a change in ambient temperature,
for videocassette recording, developed by Sony generally expressed in nanoamperes per degree
corporation in the 1970s. Compare VHS video- Celsius.
cassette recorder. bias distortion Distortion caused by operation of a
beta zinc silicate phosphor Formula, (Zn0 + tube or transistor with incorrect bias so that the
Si0 2):Mn. A phosphorescent substance used to response of the device is nonlinear.
coat the screen of a cathode-ray tube. The fluo- biased diode A diode having a dc voltage applied in
rescence is green-yellow. either forward or reverse polarity. Current flows
BeV Abbreviation of billion electronvolts. Also see readily through the forward-biased diode; the re-
ELECTRONVOLT, GEV, MEV, and MILLION verse-biased diode appears as an open circuit.
ELECTRONVOLTS. This abbreviation has been The biased diode is the basis of clippers, limiters,
supplanted by the SI (International System of slicers, and similar circuits.
Units) abbreviation GeV, for GIGAELECTRON- biased off In a circuit or device, the state of cutoff
VOLTS. caused by application of a control-electrode bias.
bevatron An accelerator (see ACCELERATOR, 1) Examples include collector-current cutoff (when
similar to the synchrotron, which accelerates the dc base bias of a bipolar transistor reaches a
particles to levels greater than 10 GeV. critical value), and drain-current cutoff (when the
Beverage antenna (Harold H. Beverage.) A nonres- dc gate bias reaches a critical value in a field-
onant, directional long-wire antenna, erected a effect transistor).