18WuD2x

648 speed of transmission • spiral distortion
bits per second (bps), characters per second (cps),
characters per minute (cpm), or words per minute
(wpm). It is used primarily for digital codes.
speedup capacitor See COMMUTATING CAPACI-
TOR.
SPFW Abbreviation of SINGLE-PHASE FULL-WAVE.
sp gr Abbreviation of SPECIFIC GRAVITY.
sphere 1. A closed surface in three-dimensional
space, represented by the set of all points
equidistant from a specified center point. 2. A
solid in three-dimensional space, represented by
the set of all points on or within a closed surface,
as defined in 1.
sphere gap A spark gap in which the spark passes
between two polished metal spheres. When the
air gap is adjustable, unknown high voltages can
be measured in terms of the largest gap width at
which sparking occurs. Compare NEEDLE GAP.
sphere-gap voltmeter See SPHERE VOLTMETER.
sphere voltmeter A gap voltmeter using a SPHERE
GAP.
spherical aberration In a spherical lens, mirror, or
reflecting dish, distortion as a result of the spherical
(as opposed to paraboloidal) shape of the surface.
This causes the focus to be elongated into a
short line segment along the principal axis.
spherical angle An angle formed by the intersection
of two arcs on the surface of a sphere.
spherical coordinate geometry A scheme for
guiding a robot arm in three dimensions via
SPHERICAL COORDINATES. The length (radius)
of the arm can be varied, as can the elevation (latitude)
and azimuth (longitude).
spherical coordinates A method of defining a
point (P) in three-space using two angles (latitude
and longitude) and a radial distance (r) from the
origin.
spherical degree A unit equal to 1 ⁄720 of the surface
area of a sphere.
spherical distance The length of the shortest arc
(lying on a great circle) connecting two specified
points on a sphere.
spherical divergence The manner in which energy
normally propagates from a fixed point source in
three dimensions. Wavefronts expand from the
source in the form of spheres, whose centers are
at the point source.
spherical reflector A microwave reflector (dish)
whose contour is that of a sphere, rather than
that of a paraboloid.
spherical wave A wave characterized by wavefronts
that are concentric spheres.
spheroidal antenna A sheetmetal or wire-mesh
antenna having the cross section of a sphere that
is flattened at the ends of one axis.
SPHW Abbreviation of SINGLE-PHASE HALF-WAVE.
spider 1. The flat, round, springy part that holds the
apex of the vibrating cone of a dynamic speaker.
2. A quickly assembled, chassisless hookup in
which the pigtails of components form the wiring
and the mechanical support for a circuit.
spiderweb antenna A set of dipole antennas for
different frequencies, arranged in a common
(usually horizontal) plane. The result is a broadband
antenna.
Radiators
spiderweb antenna
Radiators
Feed line
spiderweb coil A flat, single-layer coil in which a
strand of wire is woven over and under the
spokes of a wheel-like form, and having the general
appearance of a spiderweb. The criss-cross
winding reduces distributed capacitance by
breaking up the parallelism of adjacent turns.
spike 1. A current or voltage pulse of extremely
short duration. 2. A sharp transient, such as an
overshoot on a pulse or square wave.
spike suppressor A clipper or similar device for removing
a spike from a signal voltage.
spin A quantity of angular momentum possessed
by a subatomic particle. It can be positive, negative,
or zero, but it always exists in integral multiples
of 1 ⁄2.
spindle
1. The pivoted shaft that carries the movable
element and rotates between the pivots in a
meter movement. 2. The rotor of an alternator—
especially when the rotor is a permanent magnet.
3. The rotating shaft in a motor, generator, or
similar electric machine.
spinning electron An electron having nonzero angular
momentum.
spinthariscope An optical device for observing the
effect of alpha particles emitted by a radioactive
substance, from the scintillations they produce
upon striking a small, fluorescent screen.
spiral coil See DISK WINDING.
spiral distortion A form of television camera-tube
distortion caused by spiraling of the electrons as
they are emitted from the photocathode. The result
is a twisted image.