18WuD2x

570 quantizer • quarter wavelength
quantizer A circuit or device that selects the digital
subdivision into which an analog quantity is
placed (e.g., an analog-to-digital converter).
quantizing See QUANTIZATION.
quantometer An instrument for measuring magnetic
flux.
quantum 1. Abbreviation, Q. Plural, quanta. In
physics, the elemental unit or particle of electromagnetic
energy. The energy contained in one
such particle is directly proportional to the frequency,
and inversely proportional to the wavelength.
2. See PHOTON. 3. Any discrete unit
derived by QUANTIZATION.
quantum chromodynamics A term coined by Professor
Murray Gell-Mann for the theory of quarks
and gluons.
quantum counter A radiation-counter tube with a
window for the admission of light to the cathode.
quantum efficiency See QUANTUM YIELD.
quantum electrodynamics A branch of quantum
mechanics that involves the motions of electrons,
photons, and muons caused by electromagnetic
action. Quantum electrodynamics takes relativistic
effects into account.
quantum electronics The branch of electronics
concerned with energy states in matter.
quantum equivalence The principle that one electron
is emitted for each photon absorbed by a material
(when the photon has the necessary energy).
quantum jump The abrupt movement of a particle
from one discrete energy state to another.
quantum level The orbit or ring occupied by an
electron in an atom.
quantum mechanics A branch of physics concerned
with the behavior of matter and energy, on
the basis of observable data.
quantum noise A noise signal arising from random
variations in the average rate at which
quanta impinge upon a detector.
quantum number A number that describes the energy
level, or change in energy level, for a particle.
quantum statistics A branch of QUANTUM ME-
CHANICS concerned with the distribution of elementary
particles through various quantized
energy levels.
quantum theory The theory that the emission or
absorption of energy by atoms or molecules occurs
in discrete packages or units, rather than
continuously. Each unit is the emission or absorption
of an energy packet called a QUANTUM.
Thus, radiant energy is thought to be divided into
quanta.
quantum transition The movement of an electron
from one energy level to another within an atom.
quantum yield The photoelectric efficiency of a
light-sensitive surface in terms of the number of
electrons emitted for each absorbed quantum of
light.
quark A hypothetical particle having a fractional
electrical charge; quarks are thought to be constituents
of other subatomic particles.
quarter-deflection method A method of measuring
high-frequency resistance, involving the use
of a sine-wave signal source, a standard noninductive
variable resistor, and a square-law radiofrequency
ammeter.
quarter-phase See TWO-PHASE.
quarter wave 1. The length of time corresponding
to 90 electrical degrees in a wave disturbance.
2. The distance in space, or along a wire or feed
line that corresponds to 90 electrical degrees in a
wave disturbance.
quarter-wave antenna An antenna in which the
radiator is an electrical quarter-wavelength long
at the operating frequency.
Ground
radials
1/4-wave
radiator
quarter-wave antenna
Coaxial
line
Earth
quarter-wave attenuator In a transmission line or
waveguide, two energy-absorbing structures separated
by an odd number of quarter wavelengths
so that the reflection from one structure is canceled
by that from the other.
quarter-wave balun A balun using quarter-wave
elements. One form of this device consists of
a grounded quarter-wavelength-long cylinder
closed at one end and open at the other, for
matching an unbalanced low-impedance line to a
balanced high-impedance line.
quarter wavelength Symbol, λ/4. The distance that
corresponds to 90 degrees of phase as an electromagnetic
(EM) field is propagated. In free space, it
is related to the frequency by a simple equation
L ft = 246/f
where L ft represents λ/4 in feet, and f represents
the frequency in megahertz. If λ/4 is expressed in
meters, then the formula is
L m = 75/f