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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.


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.


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.    


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.