18WuD2x

exponential horn • external damping device 271
(approximately 2.71828), and m is the horn flaring
constant.
exponential increase The continuous increase of
a quantity, according to the equation y = e x ,
which depicts the natural growth curve.
exponential line A transmission line whose characteristic
impedance varies exponentially with its
electrical length.
exponential quantity A quantity involving an exponential
(e.g., 3e x ).
exponential series A mathematical series based
on exponential expressions. Example: e x = 1 + x +
(x 2 /2!) + (x 3 /3!) + (x 4 /4!) + . . .
exponential sweep In cathode-ray-tube (CRT) devices,
such as oscilloscopes, a beam sweep that
starts fast and slows exponentially.
exponential transmission line See EXPONEN-
TIAL LINE.
exponential waveform Any waveform in which the
rate of change in the amplitude is directly or inversely
proportional to the instantaneous amplitude.
The absolute value of the derivative of such
a waveform is equal to the absolute value of the
instantaneous amplitude, multiplied by a constant
that depends on the amplitude units.
exposure 1. The total amount of radiation received
in a given area, or by a given sample, or by a person,
over a specified length of time. 2. The extent
to which a photographic film has been darkened
or otherwise modified by visible light, infrared, ultraviolet,
or X rays.
exposure meter 1. A usually simple instrument
for measuring light intensity—especially for photographic
purposes. A common form consists of a
self-generating photocell connected to a directcurrent
microammeter. 2. A device that indicates
the amount of ionizing radiation that has been received
over a given period of time.
Photovoltaic
cell
Sensitivity
exposure meter
Meter
expression control A volume control in an electronic
organ.
extended double Zepp antenna See DOUBLE-
EXTENDED ZEPP ANTENNA.
extended memory In personal computer systems,
memory beyond the first megabyte (1 MB). There
is no limit in theory to the extent of this memory,
although it is limited by current technology. Used
in high-level programs—especially those involving
graphical applications, artificial intelligence,
or intensive calculations. Resides in integrated
circuits (ICs) in the computer, and is normally
volatile (i.e., it is not retained when power is removed).
Compare EXPANDED MEMORY.
extended octaves Audio-frequency tones above or
below the normal range of an electronic musical
instrument. Special circuits must be added to
make the extended octaves available.
extended play Pertaining to a recorded phonograph
disc that provides a longer playing time
than conventional discs of the same size and
recording speed.
extender A substance added to an encapsulant to
make it go further.
extensimeter See EXTENSOMETER.
extension cable A flexible, low-capacitance (usually
concentric) cable for connecting part of one
circuit to part of another. Extension cables are
available with a variety of end connectors.
extension cord A flexible power cord having a
male plug on one end and female receptacle on
the other.
extension loudspeaker An auxiliary loudspeaker
serving areas in which the main speakers can’t be
adequately heard.
extensometer An instrument used to measure
small amounts of expansion, contraction, or deformation.
exterior label On a diskette or tape cartridge used
for computer data storage, a written identification
on the housing or cartridge, as opposed to the label,
which is recorded on the diskette or tape itself.
external armature In a dynamo-type machine, an
armature that rotates around the outside of the
field magnets, as opposed to the usual (inside) arrangement.
external capacitor A high-value capacitor connected
externally to an oscillator or sweep generator
to lower its frequency.
external circuit A circuit or subcircuit connected
and external to a main equipment.
external controls 1. Control devices that are connected
to, but operated away from, a main circuit.
2. Manual or screwdriver-adjusted controls
that are mounted on the panel of an equipment,
as opposed to those mounted in the case or behind
the panel.
external critical damping resistance The value of
external resistance that must be connected to a
galvanometer or other meter to produce critical
damping.
external damping device A resistor or shortcircuiting
bar connected temporarily between the
terminals of a meter to keep its movement immobile
during transportation.