Physics Dictionary (Contd....)
Aurora
It
is a luminous atmospheric phenomenon appearing as streamers or bands of light
sometimes visible in the night sky in northern or southern regions of the
earth. It is thought to be caused by charged particles from the sun entering
the earth’s magnetic field and stimulating molecules in atmosphere.
Avalanche Multiplication
Phenomenon
observed in gas filled detectors as per which when high electric field is
applied to anode wire, there occurs rapid multiplication of charges created in
primary ionization event near the wire where electric field intensity is high.
This process is called avalanche multiplication.
Average Binding Energy
It
is obtained by dividing total binding energy of a nucleus by the number of
nucleons in nucleus. This energy is a measure of strength of nuclear bonding.
The more tightly bound the nucleons; the more stable the nucleus becomes and
larger is its binding energy.
Avogadro Number
The
number of atoms or molecules in a mole of a substance is called Avogadro’s
number.
Avogadro’s Law
Equal
volumes of ideal gases existing under same conditions of temperature and
pressure contain equal number of molecules.
Avogadro’s Principle
Whenever
a body is fully or partially submerged in a fluid, a buoyant force acts on the
body from the surrounding fluid. The force is directed upward and has a
magnitude equal to weight of fluid that has been displaced by body.
Axial Chromatic Aberration
For
an object at infinity, the difference in focal length of a lens for the red and
violet light is called the axial chromatic aberration.
Axis of Precession
The
axis about which the direction of rotation of body precesses is called as axis
of precession.
Axis of Rotation
When
a rigid body undergoes a combined translation and rotational motion, there is
at least a point inside or outside the body whose velocity is zero. The body is
said to have pure rotation about that point. Then axis passing through that
point and perpendicular to plane of rotation is known as axis of rotation.
Axis
Vertical
and horizontal lines that make up quadrants of coordinate plane are referred to
as axis.
Babinet’s Compensator
It
is a device used for producing circular & elliptically polarized light and
for their detection.
Back EMF
It
is the electromagnetic force in an inductive circuit which acts in such a
direction so as to oppose any change of current in the circuit.
Background
Term
generally used in nuclear physics. The background radiation refers to the energetic
particles reaching earth surface mainly due to cosmic rays comprising neutrons,
muons, neutrinos, gamma etc.
Baking
Process
in which materials meant for vacuum application are subjected to heat condition
to reduce outgassing rate.
Ballistic Galvanometer
A
moving coil galvanometer, in which coil has high inertia that indicates
presence of an electric charge by single impulse imparted to coil by small
instantaneous current, the quantity of electricity that passes being
proportional to deflection of coil.
Ballistic Pendulum
A
physical pendulum consisting of a large mass suspended from a rod; when it is
stuck by a projectile, its displacement is used to measure the projection’s
velocity.
Ballistics
Science
of mechanics that deals with behavior and effects of projectiles, especially
bullets, rockets etc.
Balmer Series
The
spectrum of wavelength falling in visible region due to transition of electrons
from higher orbits to second orbit is called Balmer series.
Band Spectrum
This
spectrum is due to transition of electrons combined with rotatory, translatory
and vibration effects of molecules. Hot gases in molecular state produce band
spectrum. It is also called molecular
spectra. It consists of bright bands of different colors over dark background. Each
band consists of closely spaced lines. The spacing between two bands and also width
of the band depends on nature of compound. At very high temperature, the band
spectrum changes to line spectrum as the molecules split in to atoms.
Band Theory
Theory
which aims at classifying materials as conductors, insulators, semiconductors
based on the distribution of electron energy states. In solids, due to
proximity of atoms, each distinct atomic state splits into series of closely
packed electron states called as electron energy band. There are three types of
electron band structures possible at 0 K as per this theory.Physics Dictionary (Contd...)
Atmospheric Electricity
The
conductivity of atmosphere arises from ions created by cosmic rays. The
conductivity is variable; as we go to higher altitudes, conductivity gradually
increases and at about 50km, atmosphere is pretty good conductor. This
electrical phenomenon takes place between two conducting spherical surfaces,
earth and top of stratosphere. Each of these surfaces is equipotential.
Atmospheric Pressure
The
atmospheric air exerts normal pressure upon all surfaces with which it is in
contact, and is known as atmospheric pressure.
Atom Bomb
Nuclear
weapon which harnesses the forces that hold the nucleus of an atom together, by
using the energy released when the nucleus splits into nucleons. The atom bomb
works on principle of nuclear fission. Nuclear reactions occur when neutrons
are fired at closely packed atoms with heavy fissile nuclei like uranium-235 / Plutonium
isotopes. This leads to nuclear fission which further converts to chain
reaction.
Atom Percent (at %)
It
is defined as concentration specification on basis of number of moles (or
atoms) of a particular element relative to the total number of moles (or atoms)
of all elements within an alloy.
Atom
It
is tiny basic unit of matter which is neutral and from which any substance gets
constructed. It has positively charged nucleus constituting nucleons (Protons
& Neutrons) surrounded by electrons revolving round the nucleus.
Atomic Clock
It is
accurate type of time device in the world, which is controlled by vibrations of
an atomic or molecular system such as Cesium or Ammonia. The precision of an
atomic clock depends on fact that an atom, caused to oscillate, will always
vibrate at same frequency. NIST-F1, the United States standard atomic clock, is
said to be so accurate that it would neither gain nor lose a second in over 30
yrs. They are used as primary standard in global navigation satellite system
such as GPS.
Atomic Mass Unit (amu)
It is
defined as 1/12 of mass of Carbon-12 atom. It is average of Proton & Neutron
rest mass i.e. 1.67377 x 10-24 gm. The unit is used to express
relative masses of various isotopes of element.
Atomic Number
The
number of protons found inside the nucleus of a particular atom. The modern
periodic table is structured based on this number.
Atomic Orbital
A
quantum state attributed to electron around atom in quantum mechanics to
describe wave characteristic of electron.
It is expressed by mathematical function which is used to calculate
probability of finding any electron in any specific region around atom’s
nucleus.
Atomic Packing Fraction
It
is the ratio of volume of atoms per unit cell to volume of unit cell in a
crystal structure.
Atomic Physics
It
is study of structure of atom, arrangement of electrons around nucleus i.e.
energy states, interaction of atoms with other particles and with electric and
magnetic fields.
Atomic Radius
It
is defined as half the distance between neighboring atoms in a crystal of a pure
element.
Atomic Structure
It
is study of configuration of atom which is essential for knowing many
phenomenon involving electrons. Bohr’s atomic model is early model which has
explained structure of atom to a great extent. Later the limitations of that model
overcome by attributing dual nature to particle. The atomic structure
represents the manner in which electron states are occupied.
Atomic Weight
It
is the weighted average of the atomic masses of an atom’s naturally occurring
isotopes. It is usually expressed in amu.
Atomicity
Total
no. of atoms present in one molecule of an element of a substance is called as
atomicity.
Atto
Prefix
in metric system denoting a factor of 10-18.
Audio Frequency
It
is the frequency range of periodic vibrations audible to human ear. The range
is 20Hz to 20 KHz.
Audio Meter
It
is an instrument for measuring hearing activity for pure tones of normally
audible frequencies.
Aufbau’s Principle
Principle
which states that sub-shell of lower energy in an atom is filled up first while
that of higher energy is filled up later.
Auger Effect
See
Auger electron.
Auger Electron
In
photoelectric effect, following expulsion of photoelectron, another electron
from high energy state may occupy its location emitting X-ray photon. This
photon may in turn eject electron from loosely bound outer electron shell, called
auger electron and such photoelectric effect is called “Auger Effect”.
Physics Dictionary (Contd...)
Atmospheric Electricity
The
conductivity of atmosphere arises from ions created by cosmic rays. The
conductivity is variable; as we go to higher altitudes, conductivity gradually
increases and at about 50km, atmosphere is pretty good conductor. This
electrical phenomenon takes place between two conducting spherical surfaces,
earth and top of stratosphere. Each of these surfaces is equipotential.
Atmospheric Pressure
The
atmospheric air exerts normal pressure upon all surfaces with which it is in
contact, and is known as atmospheric pressure.
Atom Bomb
Nuclear
weapon which harnesses the forces that hold the nucleus of an atom together, by
using the energy released when the nucleus splits into nucleons. The atom bomb
works on principle of nuclear fission. Nuclear reactions occur when neutrons
are fired at closely packed atoms with heavy fissile nuclei like uranium-235 / Plutonium
isotopes. This leads to nuclear fission which further converts to chain
reaction.
Atom Percent (at %)
It
is defined as concentration specification on basis of number of moles (or
atoms) of a particular element relative to the total number of moles (or atoms)
of all elements within an alloy.
Atom
It
is tiny basic unit of matter which is neutral and from which any substance gets
constructed. It has positively charged nucleus constituting nucleons (Protons
& Neutrons) surrounded by electrons revolving round the nucleus.
Atomic Clock
It
is accurate type of time device in the world, which is controlled by vibrations
of an atomic or molecular system such as Cesium or Ammonia. The precision of an
atomic clock depends on fact that an atom, caused to oscillate, will always
vibrate at same frequency. NIST-F1, the United States standard atomic clock, is
said to be so accurate that it would neither gain nor lose a second in over 30
yrs. They are used as primary standard in global navigation satellite system
such as GPS.
Atomic Mass Unit (amu)
It
is defined as 1/12 of mass of Carbon-12 atom. It is average of Proton & Neutron
rest mass i.e. 1.67377 x 10-24 gm. The unit is used to express
relative masses of various isotopes of element.
Atomic Number
The
number of protons found inside the nucleus of a particular atom. The modern
periodic table is structured based on this number.
Atomic Orbital
A
quantum state attributed to electron around atom in quantum mechanics to
describe wave characteristic of electron.
It is expressed by mathematical function which is used to calculate
probability of finding any electron in any specific region around atom’s
nucleus.
Atomic Packing Fraction
It
is the ratio of volume of atoms per unit cell to volume of unit cell in a
crystal structure.
Atomic Physics
It
is study of structure of atom, arrangement of electrons around nucleus i.e.
energy states, interaction of atoms with other particles and with electric and
magnetic fields.
Atomic Radius
It
is defined as half the distance between neighboring atoms in a crystal of a
pure element.
Atomic Structure
It
is study of configuration of atom which is essential for knowing many
phenomenon involving electrons. Bohr’s atomic model is early model which has
explained structure of atom to a great extent. Later the limitations of that
model overcome by attributing dual nature to particle. The atomic structure
represents the manner in which electron states are occupied.
Atomic Weight
It
is the weighted average of the atomic masses of an atom’s naturally occurring
isotopes. It is usually expressed in amu.
Atomicity
Total
no. of atoms present in one molecule of an element of a substance is called as
atomicity.
Atto
Prefix
in metric system denoting a factor of 10-18.
Audio Frequency
It
is the frequency range of periodic vibrations audible to human ear. The range
is 20Hz to 20 KHz.
Audio Meter
It
is an instrument for measuring hearing activity for pure tones of normally
audible frequencies.
Aufbau’s Principle
Principle
which states that sub-shell of lower energy in an atom is filled up first while
that of higher energy is filled up later.
Auger Effect
See
Auger electron.
Auger Electron
Physics Dictionary (Contd...)
Anti Logarithm
If ‘y’ is result of logarithm of a given
number ‘x’ then ‘x’ is antilog of ‘y’.
Anti Matter
Matter
which comprises of antiparticles.
Anti Particle
Every
fundamental particle is presumed to have an antiparticle which has same mass
but opposite charge.
Anti-Node
Position
of particles on a wave which vibrate simple harmonically with maximum amplitude
is called anti node.
Antistokes Lines
The
smaller frequency lines in Raman spectra are called Anti-Stokes lines.
Aphelion
The
point in the orbit of planet, at which it is farthest from sun, is termed as
Aphelion.
Aperture
Word
attributed to small opening in an optical system or arrangement or instrument,
through which light is made to pass for focusing it on to any plane.
Aplanatic Points
See
Aplanatism
Aplanatism
The
property of the surface by virtue of which all rays starting from a particular
point object on its axis, after reflection or refraction at the surface,
converge or appear to diverge from a single point image, is called aplanatism
and the particular object and image points are called aplanatic points while
the surface is said to be aplanatic surface with respect to those two
points.
Apochromat
A
term applied to photographic & microscope objectives indicating highest
degree of color correction.
Apogee
Point
at which a satellite or any object orbiting earth is farthest from center of
earth. At its apogee, object travels slower than at any other point in orbit.
Arc
The arc refers to the set of points on a circle that
lie in the interior of circle. The arc can be any part of circumference.
or
The arc is a closed segment of a differentiable curve
in the 2D plane.
Archimedes Principle
As per this principle when a body is fully or
partially submerged in a fluid, a buoyant force from the surrounding fluid acts
on the body. The force is directed upward and has a magnitude equal to weight
on fluid that has been displaced by body.
Area
It
is mathematical quantity that describes the amount of space extended by two
dimensional surface area in the plane.
Artificial Transmutation
An
artificially induced nuclear reaction caused by the bombardment of a nucleus
with subatomic particles or small nuclei. The phenomenon was first observed and
proposed by Ernest Rutherford.
Asteroids
They
are small, rocky objects revolving around the sun that are too small to be
called planets. They are also called Planetoids.
Astigmatism
Defect
in optical system where rays that propagate in two perpendicular planes have
different foci. It is a vision condition that causes blurred vision either due
to the irregular shape of cornea, the clear front cover of the eye, or
sometimes the curvature of the lens inside the eye. An irregular shaped cornea
or lens prevents light from focusing properly on the retina, the light sensitive
surface at the back of the eye. As a result, vision becomes blurred at any distance.
Astronaut
A
person who is trained to pilot, navigate, or otherwise participate as a crew
member of a space craft is known as Astronaut.
Astronomical Unit (au)
An astronomical unit is approximately mean distance
between Earth and Sun. It is a derived constant and used to indicate distances
with in solar system. Symbol au is recommended by international astronomical
union.
1a.u. = 149,597,870.691 KM
Astronomy
It
is the Branch of science which deals with study of universe comprising
celestial objects such as planets, stars etc. outside earth atmosphere. The
study covers evolution, composition, motion, etc of universe.
Astrophysics
The
branch of astronomy that deals with the physical and chemical processes that
occur in stars, galaxies and interstellar space is called Astrophysics.
Astrophysics deals with structure & evolution of stars, properties of
interstellar space and its interaction with system of stars, and with structure
and dynamics of cluster of stars such as galaxies.
Athermanous
Substances
opaque to the thermal radiation are called athermanous.
Atmosphere
The
mixture of gases surrounding the earth or other celestial body, held in place
by gravity is referred to as atmosphere. It forms five distinct layers at
different heights. The earth’s atmosphere consists in ascending order, the
Troposphere (containing 90% of the atmosphere mass), the Stratosphere, the Mesosphere,
the Thermosphere and Exosphere. Atmosphere is composed primarily of Nitrogen
(78%), Oxygen (21%) and plays major role in water cycle, Nitrogen cycle &
Carbon cycle.
Physics Dictionary (Contd...)
Anelasticity
In
some engineering materials, there also exists time dependent elastic strain
component. That is elastic deformation will continue even after stress
application and upon load release, some finite time is required for complete
recovery. This time dependant elastic behavior is known as anelasticity. ther particles and with electric and magnetic
fi
Anemometer
The
term is derived from Greek word “anemos”, meaning wind. It is device used for
measuring speed of air flow in wind tunnels, and in other gas flow
applications.
Angle
The
amount of space between two straight lines having a common end point usually
measured in degrees.
Angle of
Incidence
Angle
between incidence ray and normal to the surface is called angle of incidence.
Angle of Minimum
Deviation
When
the angle of incidence in a prism is increased, the value of angle of deviation
first decreases and then increases. The minimum value of deviation is called
the angle of deviation.
Angle of
Reflection
It
is the angle between reflected ray and normal to the surface, from which light
is reflected.
Angle of
Refraction
It
is the angle between refracted ray and the surface from which light is
refracted.
Angstrom
It
is the unit of length usually used to express sizes at atomic scale. It is
equal to 10-10 meter.
Angular Acceleration
It
is defined as the rate of change of angular velocity.
Angular Aperture
Angular
aperture of an objective is largest angular extent of wave surface which it can
transmit.
Angular Displacement
When
a particle describes circular path, the angle described by the radius vector in
a given time interval is called angular displacement. Its direction is
perpendicular to plane of rotation along the axis.
Angular Momentum
It
is the ability of a body by virtue of which it imparts rotatory motion to other
bodies. Angular momentum is product of linear momentum and perpendicular
distance of direction of linear momentum from center of rotation.
Angular
velocity
It is defined as rate of change of angular
displacement.
Anisotropy
It
is the phenomenon of exhibiting different values of a physical property in
different crystallographic directions.
Annealing
It
is the process of heat treatment of metal by which microstructure and
consequently properties of a material are altered. Annealing is generally
heating of metal to specific temperature, for certain duration and then allowed
to cool slowly thus softening by re-crystallizing. Cold worked metals usually
undergo this for relieving strain.
Anode Rays
Rays
of positively charged particles formed inside gas discharge tubes. These rays
were discovered by Goldstein in 1886.
Anode
It
is the electrode in an electrochemical cell that experiences oxidation, or
gives up electron.
Anodizing
It
is an electrochemical metal finishing process used for increasing thickness and
toughness of the naturally occurring protective oxides on surface of metals.
The process is called anodizing, as the part to be chemically treated forms the
anode electrode of electric circuit. The process increases non-corrosiveness
& non-conductivity.
Anomalous Dielectric
Dispersion
The
fall in permittivity of a dielectric material with increasing frequency of
external electric field is a phenomenon called anomalous dielectric
dispersion.
Anomalous Expansion
of Water
When
temperature of water is raised from 0 oC, its volume decreases up to
4 oC and above 4 oC its volume increases. This is called
anomalous expansion. It is due to formation of more number of Hydrogen bonds.
Anomalous
Zeeman Effect
When
spectral lines of an atom split into three or more unequally spaced lines in
the presence of magnetic field then the phenomenon is called as anomalous
Zeeman effect. This usually happens for the systems where net spin i.e. spin
quantum number is not zero.
Antenna
A
type of transducer that converts RF fields into alternating current or vice
versa. A receiving antenna intercepts RF energy and delivers oscillating
electric current to electronic equipment, and the transmitting antenna is fed
with electric current to generate RF field. They consist of metallic
conductors, electrically connected to transistor or receiver.
Anti Ferromagnetism
Phenomenon
of magnetic moment (spin moments) of neighboring atoms or ions aligned in
exactly opposite directions.
Subscribe to:
Posts (Atom)