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
Planet
The term "Planet"
is derived from the Greek word "Planetes" - meaning wanderer. Astronomers
of the International Astronomical Union (IAU) voted on and passed the first
scientific definition of a planet in August 2006. According to this new
definition, an object must meet three criteria in order to be classified as a
planet. First, it must orbit the Sun. Second, it must be big enough for gravity
to squash it into a round ball. And third, it must have cleared other objects
out of the way in its orbital neighborhood. To clear an orbit, a planet must be
big enough to pull neighboring objects into the planet itself or sling-shot
them around the planet and shoot them off into outer space.
Planck’s
Law
Planck in 1900
propounded quantum theory to explain black body radiation successfully. According
to Planck, the emission and absorption of radiation is not continuous, but is
in form of bundles or packets of definite energy. Each bundle or packet is
called quanta. Each photon has definite energy and definite momentum whose
value is proportional to the frequency of radiation.
Plancks
Constant
It is universal
constant, named after its Planck who proposed quantum theory. As per the theory,
energy of photon is proportional to frequency of radiation. The proportionality
constant is named as planks constant. The value is 6.67x10-34
joule second.
Plasma
Phase of matter
that has enough energy for electrons to get separated from nucleus. It consists
of independently moving electrons and nuclei. It is conductive and reacts
strongly to electric and magnetic fields.
Plastic
Deformation
It is deformed
state of a substance where the stress is no longer proportional to strain and
permanently non recoverable. From atomic perspective, plastic deformation
corresponds to breaking of bonds with original atom neighbors and then
reforming bonds with new neighbors as large number of atoms more relative to
each other.
Plasticity
The property of a
solid body whereby it undergoes a permanent change in shape or size even after
removal of deforming forces when subjected to a stress exceeding particular
value, called yield value.
Plutonium
It is second Transuranic
element of the actinide series to be discovered. Pu239, isotope of Plutonium
has a half life of 24,100 years. It is formed in reactor pile by bombardment of
U238 with neutrons. It is fissionable upon incidence of neutrons.
Pneumatics
It is concept in applied physics which
deals with study of application of pressurized air or gases to do mechanical
work.
Point
Defect
The departure
from periodic arrangement around the vicinity of a lattice point is termed as
point defect. Two types of point defects normally found in crystalline ionic
substances are i) Schottky defect ii) Frenkel defect
Point
Group
Collection of symmetry operations which
when applied about a lattice point leaves the lattice invariant. The group of
such a set of symmetry operations is called a point group.
Poise
A unit of
coefficient of viscosity, defined as the tangential force per unit area
required to maintain unit difference in velocity between two parallel planes
separated by 1cm of fluid.
Polar
coordinates
Two coordinates
used for locating a point in a plane by the length of its radius vector and the
angle this vector makes with polar axis.
Polar dielectric
Dielectrics which
have non symmetrical structure having permanent dipole moment.
Polar
molecule
A molecule in which
there exists a permanent electric dipole moment by virtue of the asymmetrical
distribution of positively and negatively charged regions.
Polariscope
An
optical device used to measure rotation of plane vibration of polarized light.
or
A
instrument used for detecting polarized light or examining objects under
polarized light especially for detecting stress or strain in transparent
materials.
Polarimeter
The device which
measures the angle by which plane of polarization of the incident plane polarized
light is rotated by a given optically active substance is called as
polarimeter.
Polarization
(Electromagnetic Wave)
The property of
acquiring one sidedness by a wave is known as polarization. The wave
unsymmetrical about a direction is called polarized wave while symmetrical is
called as unpolarized wave. The polarization is the phenomenon which shows that
electromagnetic waves are transverse in nature.
Polarization (Ionic)
Displacement of anions & cations in opposite direction.
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