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
Physics
Physics
is the science of matter and its motion—the science that deals with concepts
such as force, energy, mass, and charge.
As an
experimental science, its goal is to understand the natural world. In one form
or another, physics is one of the oldest academic disciplines; through its
modern subfield of astronomy, it may be the oldest of all.
Sometimes synonymous with philosophy,
chemistry and even certain branches of mathematics and biology during the last
two millennia, physics emerged as a modern science in the 17th century and
these disciplines are now generally distinct, although the boundaries remain
difficult to define. Advances in physics often translate to the technological
sector, and sometimes influence the other sciences, as well as mathematics and
philosophy.
Physiorption
It is an exothermic, reversible surface
phenomenon, which occurs at low temperatures as per which adsorbate molecules
are attracted by weak Vanderwaal’s forces towards adsorbent molecules.
Pickling
Process of
chemical removal of oxides and other surface layers, leaving the cleaned part
with a metallic appearance is called as pickling.
Piezoelectric
Crystal
Crystal subjected
to mechanical stress, results in polarization and there occurs emission of
electrons. It acts as a mechanical tranducer.
Piezoelectric
Effect
Phenomenon
exhibited by certain symmetric crystals. In this effect, if one pair of
opposite faces of a crystal is subjected to pressure, the other pair of
opposite faces develops opposite electric charges. The sign of the charges
changes when the faces are subjected to tension instead of pressure.
Piezoelectric
Oscillator
When two opposite faces of a crystal like
quartz, tourmaline etc, are being cut perpendicular to optic axis, are
subjected to alternating voltage, the other pair of opposite faces experiences
stresses and strains. The quartz crystal will continuously contract and expand.
Elastic vibrations are setup in crystal. When frequency of alternating voltage
is equal to natural frequency of vibration of crystal or its simple higher
multiples, the crystal is thrown into resonant vibrations and the amplitude
will be large. These vibrations are longitudinal in nature.
PIN
Diode
Diode which
consists of PN junction with a wide intrinsic region sandwiched between N and P
region. The intrinsic region is very lightly doped either ‘P’ type or ‘N’ type.
They are used in switches etc.
PIN
photo diode
It is a junction photo diode operated in
reverse bias in which an undoped intrinsic region is inserted between P+ &
N+ regions. Upon photons incidence on a PIN diode, photons are absorbed mainly
in depletion region. The absorbed photons create electron-hole pairs. The photo
generated carriers in the depletion region are accelerated in opposite
directions by reverse bias and give rise to a photo current.
Pirani
Gauge
It is named after
its constructor Pirani. It consists of glass or metal envelope containing a
heated filament of a metal with a high temperature coefficient of resistance,
such as Platinum or Tungsten. As the pressure in gauge tube increases, the
temperature of the filament and therefore its electrical resistance tend to
decrease. The usual control circuit for a Pirani gauge is Wheatstone bridge, in
which one leg of the bridge is the filament of the gauge tube and the other
three legs have resistances nearly equal to that of the gauge tube.
Pitch
It is defined as
sensation of ear that depends upon frequency. A shrill sound is produced by a
source of high frequency. The pitch of sound changes due to Doppler principle.
Pitch
of Sound
Sensation which depends upon the frequency.
Planck’s
Constant
Constant introduced by Max Planck for
explaining quantum nature of light. Energy of light radiation is defined to
have value of product of Planck’s constant and its frequency. The value of
Planck’s constant is 6.674 x 10-34 joule seconds.
Planck’s
Law
To explain black
body radiation successfully, Planck in 1900, propounded quantum theory,
according to which emission and absorption of radiation is not continuous but
is in form of bundles or packets of definite energy. Each photon has definite
energy and momentum whose value is proportional to frequency of radiation.
Plane
of Polarization
Plane which is perpendicular
to plane of vibration and pass through the direction of propagation of light is
called plane of polarization.
Plane
of Vibration
The plane which
contains the direction of vibrations of electric vector in the polarized light
and the direction of travel of light is called plane of vibration.
Plane
Polarized Light
In plane polarized light, there are vibrations only along a line in particular plane perpendicular to the direction of propagation of light.
