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
Standard
Model
All the particles and their
interactions observed to date can be described by a quantum field theory called
the Standard Model. The Standard Model has 40 species of elementary particles (24
Fermions, 12 vector Bosons, and 4 scalars), which can combine to form composite
particles, accounting for the hundreds of other species of particles discovered
since the 1960s.
Star
A star is
a massive,
luminous sphere of plasma held
together by its own gravity. A
star is so massive that its core is extremely dense and hot. At the high core
temperatures of a star, atoms move so fast that they sometimes stick to other
atoms when they collide with them, forming more massive atoms and releasing a
great amount of energy. This process is known as nuclear fusion. A star usually
consists of Hydrogen and Helium.
Stark
Effect
The splitting of atomic spectral lines as a
result of an externally applied electric field was discovered by Stark, and is
called the Stark effect. It is analogue effect of Zeeman Effect. The Stark
effect has been of benefit in the analysis of atomic spectra, and a major tool
for molecular rotational spectra.
State
Function
If the change in
a property of a system depends only on initial and final states and not on path
of process carried out in going from initial to final state, then the property
is said to be state function of system.
States
of Matter
States of matter in
physics are the distinct forms that different phases of matter take on.
Static
Electricity
It is electric
charge that has accumulated on an object. Static electricity is often created
when two objects that are not good electrical conductors are rubbed together,
and electrons from one of the objects rub off onto the other.
Static
Friction
The friction that
acts due to tendency of relative motion between two surfaces in contact is
called static friction.
Stationary
Waves
When two simple
harmonic waves of same amplitude, frequency and time period travel in opposite
directions in a straight line, the resultant wave obtained is called stationary
or a standing wave. In a stationary wave, nodes and antinodes are formed
alternatively. All particles except at nodes vibrate simple harmonically with
the time period equal to that of each component wave.
Statistical
Equilibrium
An ensemble is said to be in statistical
equilibrium if the probabilities of finding the phase points in the various regions
of phase space and the average values of properties of its systems are
“independent of time”.
Statistical
Mechanics
It is the branch
of science which establishes the interpretation of macroscopic behavior of
system in terms of its microscopic properties. It doesn’t deal with motion of
each particle but it takes into account the average or most probable properties
of system without going into interior details of characteristics of its
constituents. The larger is the number of particles in physical system
considered, the more nearly correct are statistical predictions.
Steady
State Diffusion
The diffusion condition for which there is
no net accumulation or depletion of diffusing species. The diffusion flux is
independent of time.
Stefan
– Boltzmann’s Law
Loss of heat per second from unit surface
area of a black body at an absolute temperature ‘T’ surrounded by atmosphere at
an absolute temperature ‘To’, is directly proportional to difference
in fourth power of absolute temperature of that body and surrounding
atmosphere.
(or)
Total
amount of radiant energy emitted by a black body per second per unit area is
directly proportional to fourth power of its absolute temperature. E α T4; E = σ T4; σ is Stefan’s constant.
Stefan’s Law
The radiant
energy emitted per second per unit area by a perfectly black body is directly
proportional to the fourth power of the absolute temperature of the body.
Step-Down
Transformer
Transformer in
which secondary voltage is less than its primary voltage.
Step-Up
Transformer
Transformer in
which secondary voltage is greater than its primary voltage.
Stern
– Gerlach Experiment
In 1921, an
experiment conducted by Otto stern and Walter Gerlach has shown that each
electron, in addition to its orbital angular momentum L, possess an intrinsic
angular momentum referred to as spin ‘S’. The Stern-Gerlach experiment has proved
spatial quantization by showing that electron spin in quantized into two states
and provided a major impetus for development of quantum theory of atom.
Stethoscope
A medical instrument for listening to the sounds made with in body, typically consisting of a disc that transmits the sound through hollow tubes to ear pieces.
