A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Seebeck
Effect
If two junctions of dissimilar conductors
in a circuit are held at different temperatures, an emf develops causing a
current to flow in the circuit. The thermoelectric emf VAB for two materials
A and B is VA-VB , where VA and VB
are characteristic of materials A and B respectively. This implies VAB -
VCB.
Seismic
Waves
From the focus, shock waves spread out through
the earth known as seismic waves.
Seismogram
A record by a
seismograph on a display screen or paper print out.
Seismograph
An instrument
that makes a record of seismic waves caused by earthquakes. Seismographs are
equipped with electromagnetic sensors that translate ground motions into
electrical charges, which are processed and recorded by instruments; analog or
digital circuits.
Seismology
Seismology is
the branch of science that deals with earthquakes, their effects, the movement
of the Earth's tectonic plates, and prediction of earthquakes.
Selection
Rules
The rules connecting
the characteristics of the transition in terms of change in angular momentum
and parity, with the transition order, are called as “selection rules”.
Self
Diffusion
Atomic migration in pure metals.
Self
Induction
The property of
the circuit by virtue of which any change in current in it hence change in
magnetic flux in it, induces an emf in it is called as self induction.
Self
Powered Neutron Detector (SPND)
In
very large reactor plants, the need exists to monitor neutron flux in various
portions of the core on a continuous basis. This allows for quick detection of
instability in any section of the core. This need brought about the development
of the self-powered neutron detector that is small, inexpensive, and rugged
enough to withstand the in-core environment. The self-powered neutron detector
requires no voltage supply for operation.
The central wire of a
self-powered neutron detector is made from a material that absorbs a neutron
and undergoes radioactive decay by emitting an electron (beta decay). Typical
materials used for the central wire are cobalt, cadmium, rhodium, and vanadium.
A good insulating material is placed between the central wire and the detector
casing. Each time a neutron interacts with the central wire it transforms one
of the wire’s atoms into a radioactive nucleus. The nucleus eventually decays
by the emission of an electron. Because of the emission of these electrons, the
wire becomes more and more positively charged. The positive potential of the
wire causes a current to flow in resistor, R. A milli voltmeter measures the
voltage drop across the resistor. The electron current from beta decay can also
be measured directly with an electrometer.
Semiconductor
Solids which have conductivity less than
metals but more than that of insulators are classified as semiconductors. In
terms of energy band structure, at 0K, completely filled valence band separated
from empty conduction band by a relatively narrow forbidden gap generally less
than 2eV.
Sextant
A navigational
instrument containing a graduated 60-degree arc, used for measuring the
altitudes of celestial bodies to determine latitude and longitude is called as
sextant.
Shadow
A shadow is
a dark shape on a surface that is made when something stands between a light
and the surface.
or
An
area that is not or is only partially irradiated or illuminated because of the
interception of radiation by an opaque object between the area and the source
of radiation is called as shadow.
Shake
It is smallest unit of time; 1shake = 10-8
sec.
Shear
A force applied
so as to cause or tend to cause two adjacent parts of same body to slide
relative to each other in a direction parallel to their plane of contact.
Shearing
Strain
It is the ratio
of relative displacement between two layers of the body to the normal distance
between those two layers. It can be expressed as the angle through which line
originally normal to the fixed surface is turned.
Shell
Model
A shell model is
one in which the system is thought to consist of individual particles moving in
bound orbitals in response to the remainder of the system. Each orbital
has a well designated energy, angular momentum, and parity associated with
it. In an atom, the electrons are bound to the highly charged nucleus,
which contains most of the mass of the atom, by the electric force. Since
most of the mass is contained in the nucleus, the electrons can move in orbits
relatively free of any obstacles and hence would suffer very few collisions in
their eternal orbiting about the nucleus. In such a model, treated
quantum-mechanically, no two electrons, two protons, or two neutrons can occupy
the same quantum state, i.e. have identical sets of quantum numbers. This
principle attributed to Pauli results in a finite number of such particles
occupying a given energy level, and thus, leads to the concept of closed (or
filled) levels (or shells). When a shell is filled, any additional
particles of that type must be put in a different level (shell).
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