PHYSICS DICTIONARY

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LED

It is a forward biased PN junction which emits light when energized. The electrons that are injected into P-region makes a downward transition from conduction band to the valence band, and recombine with holes emitting photons with energy equal to band gap energy.


Lens

It is an optical device which transmits & refracts light, converging or diverging the beams.


Lenz’s Law

When an electromotive force is induced in a conductor by any change in relation between the conductor and the magnetic field, the direction of electromotive force is such as to produce a current whose magnetic field will oppose the change.


Lepton

Any Fermion lighter than Proton is called Lepton.


Lienard Wiechart Potential

Lienard Wiechart potentials are magnetic vectors which are used to find radiation from accelerated charges moving on a specified trajectory path. Relativistic retarded potentials are called Lienard Wiechart potentials.


Light

The term light is generally applied to visible light having wavelength in the range of 380nm to 740nm.


Light Year

Unit of distance used in astronomy. As defined by International Astronomical Union (IAU), it is the distance that light travels in vacuum in one Julian year. It equals about 5.88 Trillion miles or 9.46 Trillion kilometers.


Lightening Conductor

It is originally proposed by Benjamin Franklin. It is a metallic rod generally attached to roof of building. A good conducting wire is connected from lightening conductor to the conductive grid buried in the earth. When lightning strikes, the enormous current would be driven to ground through conducting wire which offers low resistance path to ground.


Limiting Friction

Least force necessary to set a body in motion.


Linde’s Process

It is a process of liquefication of gas which depends on Joule Thomson effect. The Linde’s process is known as adiabatic expansion of compressed gas.

 

Line Spectrum

Hot gases or vapors in atomic state produce line spectrum. Line spectrum is due to electronic transition from higher orbits to lower orbits. Line spectrum is characteristic property of the atom producing light and it differs from one element to other. Line spectrum is also called ionic spectrum or atomic spectrum. It consists of bright lines of different colors against dark background. The intensity of one line is different from other. Line spectrum is “discontinuous “one.


LINEAC (Linear Accelerator)

Device/ arrangement to accelerate charged particles like electrons/protons to high energies of order of MeV. It is an arrangement of lengthy volume containing multiple tubes called drift tubes whose potential is varied by predetermined RF oscillator such that the charged particle leaving each tube will leave with high energy.


Linear Attenuation Coefficient

If a collimated beam of mono energetic gamma rays of intensity ‘IO’ passes through a thickness ‘x’ of absorber, the intensity ‘Ix’ of emerging photons which have not suffered any interaction is given by Ix = Io e-µx. ‘µ’ is called linear absorption coefficient.


Linear Energy Transfer

A measure of the ability of biological material to absorb energy from ionizing radiation, specifically for charged particles traversing a medium, the energy lost per unit length of path.


Linear Momentum

Linear momentum of a body is ability of body to impart motion to other bodies. It is product of mass and velocity of a body.


Linear Regression

Linear regression is a method of estimating or predicting a value of some dependent variable given the values of one or more independent variables. Like correlations, statistical regression examines the association or relationship between variables.

or

Linear regression refers to fitting a straight line to the data. The fitting is mostly done using a technique called least square fitting.


Linear System

A system where all the interrelationships among the quantities involved are expressed by linear equations which may be algebraic, differential or integral is called as linear system.


Liquification of Gases

Process of liquefying gas by applying pressure on it at a temperature below its critical temperature.

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