PHYSICS DICTIONARY

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Climate

The climate where you live is called regional climate. It is the average weather in a place over more than thirty years. To describe the regional climate of a place, people often tell what the temperatures are like over the seasons, how windy it is, and how much rain or snow falls. The climate of a region depends on many factors including the amount of sunlight it receives, its height above sea level, the shape of the land, and how close it is to oceans. Since the equator receives more sunlight than the poles, climate varies depending on distance from the equator.


Clipping Circuit

Circuit with which the waveform is shaped by removing a portion of applied wave is known as clipping circuit.


Clock

Mechanical / electrical device used for measuring and recording time.


Closed System

System which cannot exchange matter with surroundings but only exchanges energy with surroundings.


Closely Packed Structure

Crystal structures which have high atomic packing fraction. There are two types of closely packed structures i) Hexagonal closely packed   ii) Face centered closely packed.


Cloud Chamber

The first instrument which made possible visual observation of tracks of charged particles in their passage through matter was Wilson’s cloud chamber. The principle of the chamber is that super cooled vapor condenses only on charged particles and if charged particles are not present, they remain in vapor phase. If saturated vapor in a chamber is suddenly subjected to an adiabatic expansion, there will be an increase in volume which produces cooling rendering saturated vapor to a super saturated unstable state. If some ions are present in the chamber then condensation takes place on them. Ions are produced by passage of high energy particles through chamber leading to tracks. 


Cloud

Visible mass of fine water droplets, ice particles suspended in atmosphere at high altitudes above sea level.


Cluster

 Group of galaxies is called as cluster.


Co- axial System of Lenses

A combination of lenses having a common principal axis is called a co- axial system of lenses.


Coaxial Cable

Cables having construction of coaxial geometry in which central conductor is separated from braid by insulator  


Cobalt-60

This is a radioactive element formed by bombarding stable isotope of Cobalt i.e. Co59 with neutrons. Cobalt-60 has half life of 5.3 years which decays by emitting beta followed by gamma rays. In 99.87% decays, the gamma rays are emitted with 1.17 MeV and in other cases with 1.33 MeV.


Coefficient of Areal Expansion

The ratio of increase in area per degree rise of temperature to the original area of solid.


Coefficient of Contraction

It is defined as the ratio of the minimum cross-sectional area of a jet of liquid discharging from an orifice to the area of the orifice.


Coefficient of Linear Expansion

The ratio of increase in length per degree rise of temperature to the original length of solid.


Coefficient of Mutual Inductance

When two inductors are coupled, the mutual inductance is proportional to square root of product of two inductances. The coupling coefficient has value between 0 and 1.


Coefficient of Restitution

The coefficient of restitution is a measure of the elasticity in a one-dimensional collision. It could be defined as the ratio of the relative velocity after impact to the relative velocity before the impact of two colliding bodies.


Coefficient of Self Inductance

It is a quantity that relates magnitude of self induced voltage in coil to the rate of change of current in the coil. Its SI unit is Henry.


Coefficient of Static Friction

It is proportionality constant between friction and normal force acting on the object over the surface.


Coefficient of Linear Expansion

The ratio of increase in length per degree rise of temperature to the original length of the solid.


Coefficient of Superficial Expansion

The ratio of increase in area per degree rise of temperature to the original area of the solid.


Coefficient of Volume Expansion

The ratio of increase in volume per degree rise of temperature to the original volume of the solid.

 

Coercive Field or Coercivity

In case of ferromagnetic or ferrimagnetic materials, a critical magnetic field must be applied in direction opposite to original field to reduce the magnetic flux density inside the specimen to zero, which is called coercive field and the phenomenon is called coercivity.


Coherence length

It is defined as the maximum distance up to which the pair of electrons (cooper pair) is correlated to produce superconductivity.


Coherence Source

The source which emits coherent waves with respect to both time & space is called coherent source.


Coherent Scattering

Type of scattering in which photon when interacts with matter excites atom and gets scattered.


Coherent Waves

Two light waves of same frequency having constant phase difference are known as coherent waves.


Cohesion

The force of attraction between molecules of same substance is called as cohesion.


Cohesive Energy of Crystal

Energy of crystal is lower than that of free atoms by an amount equal to the energy required to pull the crystal apart into a set of free atoms. This is called binding energy or cohesive energy.


Cold Neutrons

Neutrons having energy less than thermal neutrons are called as cold neutrons. 


Cold Welding

Welding in which fusion of metal is achieved only by applying pressure and no heat. 


Collimator

Device used for constraining the size and angle of spread of a beam of radiation or particles parallel to the tube axis to traverse required length.


Collision

It is the interaction between the bodies for a small time interval due to which the redistribution of momentum takes place.


Colloid

Particles substantially larger than atoms or ordinary molecules but too small to be visible to naked eye. In other words, any particle having dimension in range 10-7  To 10-3  cm. 

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Chi square Test

It is also called goodness of fit test. The test allows testing hypothesis using nominal or ordinal data. It does this by testing whether one set of proportions is higher or lower than you would expect by chance. Chi square summarizes the discrepancy between the observed and expected frequencies.


Choke Coil

An inductance coil used in alternating current circuits to limit the current without dissipation of power is called as choke coil. Choke consists of a pure copper wire wounded on a rectangular soft iron to minimize eddy currents and hysteresis losses. 


Chord

A line segment connecting two points in a circle.


Chromatic Aberration

The type of aberration found in images formed by lenses when the source of light is not monochromatic. Formation of a colored and blurred image of white object by a lens due to dispersion is called chromatic aberration. 


Chromosphere

It is narrow layer above Photosphere. It constitutes gaseous layer. It can’t be seen by naked eye and usually appears as narrow, red ring around sun.


Circle

It is a geometrical plane figure which is locus of all points equidistant from central point.


Circular Motion

It is motion of an object in a circle at a constant speed.


Circular Polarization

Light is said to be circular polarized if two electromagnetic waves are perpendicular to each other having same amplitude and phase difference of 90o.


Circularly Polarized Light

When two plane polarized light waves superpose with a definite phase difference, the resultant light vector revolves with fixed amplitude in a plane perpendicular to direction of propagation of light. In some special cases, the tip of light vector describes a circle. This light is called circularly polarized light.   


Circumference

Perimeter of circle is called as circumference.


Cladding

Process of covering fuel bundles in nuclear reactors to avoid direct physical contact to the moderator or coolant is called as cladding. The cladding material is transparent to the thermal neutrons and withstands very high temperatures. 


Classical Physics

Classical physics is the branch of physics which depends on Newton’s laws of motion. Classical physics is usually divided into several branches, each of which deals with a group of related phenomena. Mechanics is the study of forces and their effect on matter. Dynamics is the study of change in motion because of force. Hydromechanics is the mechanics of fluids; that is, of liquids and gases. Hydromechanics is also known as fluid mechanics. Statics deals with how force affects bodies in constant motion and moving in a constant direction. Optics is the study of the behavior of light. Thermodynamics is the study of heat, and how heat energy is stored, transmitted, and converted to other forms of energy. Acoustics is the study of sound. The study of electricity and magnetism also forms a branch of classical physics.  


Clausius Clapeyrons Equation

Thermodynamics equation which tells us that the change in melting or boiling point with the change in pressure in terms of latent heat of fusion or latent heat of vaporization. It is expressed as

T(dP/dt)=L /T(V2-V1)    

‘T’ is Constant Temperature;    ‘P’ is Pressure

      ‘L’ is Latent heat at const temperature. V2 and V1 are specific volumes of substance before and after change in state without change in temp.

     If V2 > V1; Melting point increases with increase in pressure and boiling point increases with increase in pressure.

     If V2<V1; Melting point decreases with increase in pressure.


Clausius Mossotti Relation

It is the relation between macroscopic dielectric constant and microscopic polarization.


Clausius Statement of Second Law of Thermodynamics

It is impossible for a self acting machine, to transfer heat continuously from one body to another at high temperature.


Clausius Theorem

The sum of quantities of heat transfer during the isothermal change divided by absolute temperature of isothermal in a reversible cycle is zero.


Cleavage

For most brittle crystalline materials, crack propagation corresponds to the successive and repeated breaking of atomic bonds along specific crystallographic planes. This phenomenon is called as cleavage. 


Clebsch-Gordon Coefficient

The Clebsch-Gordan coefficients are sets of numbers that arise in angular momentum coupling under the laws of quantum mechanics. 

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Cerenkov Radiation

Electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than phase velocity of light in that medium. The charged particles polarize the molecules of that medium, which then turn back rapidly to their ground state emitting radiation in the process.  For instance, speed of light in water is 0.75C. Matter can be accelerated beyond this speed during nuclear reactions and in particle accelerators.


Cermet

A composite material, consisting of a combination of ceramic and metallic materials is called as ceramic. The most common cermets are the cemented carbides, compound of an extremely hard ceramic, bonded together by a ductile metal such as Cobalt or Nickel. 


CGS Units

Acronym for Centimeter – Gram – Second system is a metric system of physical units based on centimeter as unit of length, gram as a unit of mass, and second as a unit of time.


Chain Reaction

Process of multiplicity of neutrons in nuclear reactor to sustain nuclear fission is called as chain reaction. It was proposed by Leo Szilard in 1933.


Chandrasekhar Limit

It was proposed by Chandrasekhar that no white dwarf star can have mass larger than 1.4 times mass of sun.


Characteristic X-ray Radiation

The production of "characteristic" X-rays by electron bombardment of pure elements was first observed in 1909 by Charles G. Barkla and C.A. Sadler. When heavy metals are bombarded with energetic particles, electrons may get knocked out. If the electrons are knocked out from the inner shells of atom, the vacancy is filled by the transition of electrons from outer shells. This will result in emission of quantized photons, "characteristic" of the element.


Charge Conjugation

It is defined as interchange of particles and antiparticles. It doesn’t simply mean a change over the opposite electric charge or magnetic moment, but the sign of certain charge quantum numbers also change. 


Charge Coupled Device

It is a light sensitive integrated circuit that stores and displays the data for an image in such a way that each pixel in the image is converted into an electrical charge, the intensity of which is related to color in the color spectrum.


Charge Transfer Device

A charge-transfer device has a metal oxide semiconductor (MOS) structure that is composed of many independent pixels where charge is stored in such a way that the charge pattern corresponds to the irradiation pattern. These devices can be linear or two-dimensional. According to the method used to detect the charge pattern, two types of charge-transfer devices can be distinguished: charge-coupled devices (CCDs) and charge-injection devices (CIDs).


Charge

It is characteristic of an object that expresses the extent to which it has excess or deficiency of electrons. If the object has deficiency of electrons, then it is said to be having negative charge. In fact it is technical term used to indicate that an object has been prepared to participate in electrical forces.


Charles law

At constant pressure, the volume of a given mass of gas is directly proportional to its absolute temperature.

(or)

At constant pressure, volume of a given mass of a gas increases (or decreases) by (1/273)th part of its volume at 0 oC, on increasing (or decreasing) the temperature by 1oC.


Chemiluminescence

Phenomenon of emission of electromagnetic radiation as light by the release of energy from a chemical reaction is called as chemiluminescence.


Chemisorption

If the adsorbate molecules are bound to the surface of adsorbent by chemical bonds, the adsorption is known as chemical adsorption or chemisorption.


Cherenkov Radiation

When a high energy charged particle with non – zero rest mass, such as an electron, travels faster than speed of light in a medium, then it emits a special kind of radiation called Cherenkov radiation. The wavelength of Cherenkov photons falls in and around visible region of EM spectrum. In fact, first Cherenkov radiation was observed by Pavel Cherenkov in 1934 as blue light coming from a bottle of water undergoing bombardment by particles from a radioactive source.


Chi-square Distribution

It is one of the most widely used probability distribution  in  inferential statistics, e.g., in hypothesis testing or in construction of confidence intervals. The Chi-Square distribution is merely the distribution of the sum of the squares of a set of normally distributed random variables. Its value stems from the fact that the sum of random variables from any distribution can be closely approximated by a normal distribution as the sum includes a greater number of samples. Thus the test is widely applicable for all distributions.