Galaxy
A collection of
stars, gas and dust bound together by gravity. The Milky Way galaxy contains
our solar system.
Galilean
Telescope
Galileo in 1906,
constructed a telescope which provides an erect image of an object only with
help of two lenses. It consists of converging lens serving as objective and
diverging lens as eyepiece. The eye piece is situated in front of focal point
of objective, at a distance from focal point equal to focal length of eyepiece.
It has disadvantage of narrow field of view.
Galilean
Transformation
The consequences
of research work of Galileo on the motion of projectile led him to formulate
Galilean transformations. These are used to relate the motions which are
observed by two observers in two different observers in two different inertial
frames. As per Galilean transformation, the motion of a particle projected at
any angle may be derived from the motion of particle thrown vertically upward.
Galvanic
Cell
Device used to
convert chemical energy into electrical energy. Galvanic cell can be used as a
source of electric current due to spontaneous reaction occurring within the
cell.
Galvanometer
Instrument used
to indicate presence, direction or strength of small electrical current.
Current flowing through the galvanometer passes through a coil near a
magnetized needle on a pivot; the strength of current in coil regulates the
strength of magnetic field that displaces the needle. Galvanometers can be used
directly as ammeters and are core elements of many ohmmeters.
Gamma
Ray Spectrometer
Instrument used
for quantitative study of energy spectra of gamma ray sources. It reads out
distribution of intensity of gamma rays with energy thus revealing nature of
radioactive nuclides, amount of activity etc.
Gamma
Rays
Electromagnetic
radiation emitted from nucleus as a result of transition of nucleons between
energy states inside nucleus.
or
Electromagnetic
radiation emitted in annihilation reaction between matter and antimatter.
Gamma
Spectroscopy
It is a radio
chemistry measurement method which determines the energy and count rate of
gamma rays emitted by radioactive substances.
Gas
Amplification
Multiplication of
charge carriers in gas filled detectors produced by primary ionization in high
E/P value, by secondary ionization. The gas amplification is characterized by
first Townsend coefficient. It represents the average number of electron – ion
pairs formed per unit length due to motion of an electron along the electric
field direction.
Gas
Constant
See universal gas
constant.
Gas
Degeneracy
The deviations
from perfect gas behavior exhibited by Bose Einstein gas is termed as gas
degeneracy.
Gas
Multiplication
Term related to
gas filled radiation detectors. Phenomenon of multiplying charge carriers
created due to primary ionization of gas by incident radiation in the gas. The
charge carriers i.e. electrons drift towards the anode at positive potential.
The electrons gain momentum and get accelerated to high energies which can
transfer to other atoms resulting in emission of further electrons called
secondary electrons. The phenomenon of multiplication of charge in gas under influence
of external high voltage is called gas multiplication.
Gas
The gaseous state
above critical temperature of substance is called as gas.
Gauge
Pressure
When pressure is
measured either above or below atmospheric pressure as an arbitrary datum then
it is called as gauge pressure.
Gauss
Eye Piece
It is similar to
Ramsden’s eyepiece with the only difference that there is a thin glass plate
inclined at 45o in between the two lenses. Hence cardinal points of
gauss eye piece are located at some positions as that of Ramsden’s eye piece.
Gauss’s
Theorem of Electrostatics
The net outward
electric flux through any closed surface of any shape in an electric field is
equal to 1/εo times the total charge contained within
that surface.
Gauss’s
Theorem of Magnetism
The total
magnetic flux through any closed surface is always zero.
Gaussian
Distribution
If
the number of events is very large, then the Gaussian distribution function may
be used to describe physical events. The Gaussian distribution is a continuous
function which approximates the exact binomial distribution of events. The Gaussian distribution is also commonly called the
"normal distribution" and is often described as a "bell-shaped
curve".
It is a distribution of the values of a variable that when plotted, produces a symmetrical, bell-shaped curve that rises smoothly from a small number of cases at each extreme to a large number of cases in the middle.
