18WuD2x

4 absolute units • A-B test
absolute units Fundamental physical units (see
ABSOLUTE SYSTEM OF UNITS) from which all
others are derived. See, for example, AMPERE,
OHM, VOLT, and WATT.
absolute value The magnitude of a quantity without
regard to sign or direction. The absolute value
of a is written |a|. The absolute value of a positive
number is the number itself; thus, |10|
equals 10. The absolute value of a negative number
is the number with its sign changed: |-10|
equals 10.
absolute-value circuit A circuit that produces a
unipolar signal in response to a bipolar input and
in proportion to the absolute value of the magnitude
of the input.
absolute-value computer A computer in which
data is processed in its absolute form; i.e., every
variable maintains its full value. (Compare to
INCREMENTAL COMPUTER.)
absolute-value device In computer practice, a device
that delivers a constant-polarity output
signal equal in amplitude to that of the input
signal. Thus, the output signal always has the
same sign.
absolute zero The temperature –273.16°C
(459.7°F and 0 Kelvin). The coldest possible
temperature, representing the complete absence
of heat energy.
absorbed wave A radio wave that dissipates in the
ionosphere as a result of molecular agitation.
This effect is most pronounced at low and
medium frequencies.
absorptance The amount of radiant energy absorbed
in a material; equal to 1 minus the transmittance.
absorption The taking up of one material or medium
by another into itself, as by sucking or
soaking up. Also, the retention of one medium (or
a part of it) by another medium, through which
the first one attempts to pass. See, for example,
ABSORBED WAVE, ABSORPTION COEFFI-
CIENT, DIELECTRIC ABSORPTION. Compare
ADSORPTION.
absorption band See ABSORPTION SPECTRUM.
absorption circuit A circuit that absorbs energy
from another circuit or from a signal source—especially
a resonant circuit, such as a wavemeter
or wavetrap.
absorption current In a capacitor, the current resulting
from absorption of energy by the dielectric
material.
absorption dynamometer A power-measuring instrument
in which a brake absorbs energy from a
revolving shaft or wheel.
absorption fading Fading of a radio wave, resulting
from (usually) slow changes in the absorption
of the wave in the line of propagation.
absorption frequency meter See WAVEMETER.
absorption line See ABSORPTION SPECTRUM.
absorption loss 1. Transmission loss caused by
dissipation of electrical energy, or conversion of it
into heat or other forms of energy. 2. Loss of all or
part of a skywave because of absorption by the
ionosphere. Also called ionospheric absorption or
atmospheric absorption.
absorption marker A small blip introduced onto
an oscilloscope trace to indicate a frequency
point. It is so called because it is produced by the
action of a frequency-calibrated tuned trap, similar
to an absorption wavemeter.
absorption modulation Amplitude modulation of a
transmitter or oscillator by means of an audiofrequency-actuated
absorber circuit. In its simplest
form, the modulator consists of a few turns of wire
coupled to the transmitter tank coil and connected
to a carbon microphone. The arrangement
absorbs energy from the transmitter at a varying
rate as the microphone changes its resistance in
accordance with the sound waves it receives.
absorption spectrum For electromagnetic waves, a
plot of absorption coefficient (of the medium of
propagation) versus frequency. Also called EMIS-
SION SPECTRUM.
absorption trap See WAVETRAP.
absorption wavemeter A resonant-frequency indicating
instrument that is inductively coupled to
the device under test.
absorptivity In audio and microwave technologies,
a measure of the energy absorbed by a given volume
of material.
A-B test Comparison of two sounds by reproducing
them in alternating succession.