18WuD2x

268 even-line field • excited state
the even-numbered lines. Compare ODD-LINE
FIELD.
even parity check A check to verify the presence of
an even number of ones or zeros in a group of bits.
event An occurrence that affects the state of a
computer file.
event counter Any device that measures the number
of specified events taking place within a certain
interval of time.
evolution Extracting a root of a number (e.g.,
square root, cube root, etc.).
E wave In microwave operations, the transverse
magnetic (TM) wave. Also see WAVEGUIDE
MODES.
EWR Abbreviation of EARLY-WARNING RADAR.
EWS Abbreviation of early-warning system.
E X 1. Symbol for voltage drop across a reactance.
2. Symbol for EXCITATION ENERGY.
exa- Symbol, E. A prefix meaning 10 18 (International
System of Units).
exalted-carrier reception In radio reception, overcoming
the effects of selective fading by maintaining
the carrier at a high amplitude. This is
accomplished before demodulation by removing
the carrier from an amplitude-modulated or phasemodulated
signal, amplifying it, and reinserting it
at a higher amplitude with the sidebands.
exc 1. Abbreviation of EXCITER. 2. Abbreviation of
EXCITATION.
except gate A logic gate that delivers an output
pulse when an input pulse is present at one or
more of a set of input terminals, and absent from
one or more of another set of input terminals.
Also called exclusive-OR element.
excess charge The amount of overcharge for a
storage battery.
excess conduction In a semiconductor, current
conduction by excess electrons.
excess electron 1. An electron that, when introduced
into an atom, results in a negative ion. 2.
An electron resulting from the addition of a donor
impurity to a semiconductor substance.
excess meter A meter that integrates the amount
of power in excess of some predetermined level.
excess minority carriers The number of minority
carriers in excess of the normal equilibrium number
in a semiconductor material.
excess modified index of refraction Symbol, M.
For waves transmitted through a refracting
medium, a modified index of refraction greater
than unity.
excess noise Electrical noise caused by current in
a semiconductor material.
excess sound pressure Unit, dyne/cm 2 . In a
medium conducting sound waves, the quantity
P i – P s , where P i is total instantaneous pressure at
a given point in the medium, and P s is static pressure
in the absence of the sound waves.
excess-three code A computer code derived from
binary notation by adding binary three (i.e.,
0011) to each four-bit group. Thus, decimal seven
is 1010 in the code (it is 0111 in binary). Unlike
the binary representation for zero, the excessthree
representation (0011) contains two ones, a
feature that distinguishes actual zero from a machine
fault.
exchange 1. To reverse the contents of two memory
banks. For example, if the memory banks are
called A and B, an exchange is the placing of the
contents of memory A into memory B, and the
placing of the contents of memory B into memory
A. The original contents are removed. 2. A twoway
sequence of data transmissions. 3. A designated
location in a telephone circuit.
exchange line A telephone line.
exciplex In a laser, a method of adjusting the color
by means of chemical reactions in organic dyes.
excitant The electrolyte in a voltaic cell.
excitation 1. Supplying input-signal driving current,
driving power, or driving voltage. 2. Inputsignal
driving current, driving power, or driving
voltage.
excitation anode In a mercury-pool tube, an auxiliary
anode whose operation maintains the cathode
spot when no output current is being drawn
from the tube.
excitation current 1. Input-electrode current in
an excited transistor amplifier. 2. Grid current in
an excited vacuum-tube amplifier. 3. Current
flowing in the circuit of the excitation anode of a
mercury-pool tube. 4. Current flowing in the exciter
circuit of an alternator. 5. Shunt-field current
in a motor.
excitation energy 1. Symbol, E X . In artificial
transmutation, the energy of a nucleus when protons
of less than maximum energy have been
emitted from the atom. 2. Electrical energy required
by a transducer.
excitation purity In color television, complete saturation
of a hue (i.e., there is no contamination
by other colors, and the saturated hue is distributed
uniformly).
excitation voltage 1. The signal voltage that
achieves, or is required for, excitation (see EXCI-
TATION, 1). 2. The value of driving voltage.
excitator An electrical discharger.
excited atom An atom in which one or more
electrons have been pushed out of their normal
orbits into higher ones by energy applied from the
outside.
excited-field speaker A dynamic speaker in which
the magnetic field is provided, not by a permanent
magnet, but by direct current flowing
through a large coil of wire wound around the
speaker core. The coil usually acts as a filter
choke in the power supply of the attendant amplifier
or receiver.
excited state In artificial transmutation, the state
of the nucleus when protons of less-than-maximum
energy have been emitted from the atom.
The energy of the protons, in this instance, is
greater than the ground state.