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
Polarization
Index
It is the ratio of the Insulation
Resistance measured pertaining to an insulator for 10 minutes to the insulation
resistance value measured after 1 minute. The Polarization Index should be
above 2.0 to be permissible.
Polarization
(Dielectric)
The total electric dipole moment per unit
volume of dielectric material is called as polarization. It is also a measure
of contribution to total electric displacement by a dielectric material.
or
For
an atom, the displacement of center of negatively charged electron cloud
relative to the positive nucleus is called as polarization. This is induced by
an electric field. A phenomenon observed in dielectrics.
Polarization
The property of
acquiring one sidedness by a wave is known as “Polarization”. The wave
unsymmetrical about a direction is called polarized wave while that symmetrical
is called unpolarized wave. The “Polarization” is phenomenon which shows that
electromagnetic waves are transverse in nature.
Polaroid
It is a simple
and cheap device to obtain the plane polarized light. It consists of tiny
crystals of quinine idosulphate in a film of nitro cellulose with their optic
axis parallel to each other. When an un polarized light is incident on it, each
ray splits into two polarized refracted rays, out of which one of the refracted
ray, having the vibrations perpendicular to principal section is completely
absorbed, while other refracted ray having vibrations parallel to principal
section, is transmitted. Each polarized film has a characteristic direction
which is called as direction of polarization.
Polyatomic
Molecule
It is a molecule
containing more than two atoms.
Polycrystal
It is a substance in which crystal
structure is a collection of many small crystals or grains.
Polygon
A closed plane geometrical figure (2 D)
having 3 or more straight sides that meet in pairs in same number of vertices,
and do not intersect other than at these vertices. The sum of interior angles
is (n-2)×180o
for n-sides; sum of exterior angles is 360o.
Polymer
A solid, non-metallic, normally organic
compound of high molecular weight; the structure of which is composed of small
repeating units is called as polymer.
Polymorphism
The property
exhibited by some crystals according to which they exist at different crystal
structures at different temperatures.
Polytropic
Process
Any thermodynamic process represented by PVn
=const is known as polytropic process.
Population
Inversion
Process by which
number of atoms in excited state (meta-stable) is made higher compared to atoms
in ground state which increases stimulation probability high in LASER, is
called population inversion.
Positive
Feedback
When the feedback
energy is in phase with input signal and thus aids it is called “positive
feedback”. This mechanism increases gain of amplifier.
Positron
The positron is
anti particle of an electron with same mass and spin as electron and charge
equal in magnitude but opposite in sign to that of electron. In 1928, Paul
Dirac was first to postulate Positrons existence and in 1932 Carl D. Anderson
discovered it as the first evidence of anti-matter in his experimental study of
cosmic rays.
Positronium
Positronium is a
semistable, Hydrogen like atomic configuration consisting of a positron and
electron revolving about their common center of mass before the process of
annihilation occurs. Because it consists of two particles of equal mass. Positronium
is sometimes considered to be the lightest atom. Its life time is of order of
10-7 sec and its reduced mass equals 0.5Me. Croation physicist
Stjepan Mohorovicic predicted the existence of Positronium in 1934 and the
Austrian American physicist Martin Deutsch discovered it in 1951.
Potential
Energy
Energy possessed
by a body by virtue of its state or position is called as potential energy. In fact
it is referred as stored energy of body.
Powder
Metallurgy
The fabrication of metal pieces having
intricate and precise shapes by the compaction of metal powders, followed by
densification heat treatment is called as powder metallurgy.
Powder
Method of X-rays
Physical technique used for the
identification of substances, and for other types of analyses, principally for
crystalline materials in the solid state. In these techniques, a monochromatic beam
of x-rays is directed onto a polycrystalline (powder) specimen, producing
a diffraction
pattern that
is recorded on film or with a diffractometer. This x-ray pattern is a
fundamental and unique property resulting from the atomic arrangement of the
diffracting substance. Different substances have different atomic arrangements
or crystal structures, and hence no two chemically distinct substances give
identical diffraction patterns. Identification may be made
by comparing the pattern of the unknown substance with patterns of known
substances in a manner analogous to the identification of people by their fingerprints.
The x-ray powder method is widely used in fundamental and applied research; for instance, it is used in the analysis of raw materials and finished products, in phase-diagram investigations, in following the course of solid-state chemical reactions, and in the study of minerals, ores, rocks, metals, chemicals, and many other types of material. The use of x-ray powder diffraction methods to determine the actual atomic arrangement, which has been important in the study of chemical bonds, crystal physics, and crystal chemistry.
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