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.