PHYSICS DICTIONARY

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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 1^oC.

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. 

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Cathodic Sputtering

The deposition of metal film by sputtering from a cathode through glow discharge method was first observed by Groove. The ejection of atoms from cathode surface by impinging  energetic particle ions of noble gases such as Helium, Argon, Neon, Krypton at a reduced pressure under high DC voltage give rise to phenomenon called as sputtering.    

Cation

A positively charged metallic ion.

Cauchy’s Dispersion Formula

An empirical expression giving an approximate relation between the refractive index ‘n’ of a medium and the wavelength  ‘λ’ of light. The empirical formula is n = A + B/ λ² where A & B are constants; ‘n’ is refractive index; ‘λ’ is wave length.

Causality Law

Effect cannot precede Cause. The law states that “The interval between two events is same in all inertial frames of reference”.

Causality

The relation between Cause and Effect; later is consequence of first.

Cavendish Experiment

The experiment performed by British scientist Henry Cavendish in 1797-98 using torsion balance to measure the force of gravity between masses in the laboratory, and is the first experiment to yield accurate values for the gravitational constant.  

Celestial Body

It is natural body outside Earth’s atmosphere. Celestial body refers to a single, cohesive structure that is bound together by gravity or electromagnetism and is associated with position in space. 

Celsius Scale

It was named after Swedish astronomer Anders Celsius, who established it. It is the scale designed by considering temperature difference between reference temperatures of freezing & boiling points of water divided into 100 degrees. The freezing point is taken as 0^oC & boiling point as 100^oC. The Celsius scale is widely known as centigrade scale because it is divided into 100 degrees.

Celsius

It is unit of temperature. On Celsius scale of temperature, the lower fixed point is melting point of pure ice at normal atmospheric pressure. This is called 0 ^oC. The upper fixed point is the boiling point of pure water which is designated as 100 ^oC. The gap between the two fixed points is divided into 100 equal parts or degrees.

Cema

One limitation of Kerma is that it is defined only for uncharged particles, such as photons. For charged particles, another quantity called Cema has been introduced. It is analogous to Kerma in definition and is mathematically written as C= dE_con/dM; where dE_con; ‘V’ is the energy lost by charged particles in a material of mass dM. The SI units of Cema are J/kg or Gray.

Center of Mass Frame

It is any inertial frame in which center of mass remains at rest.

Center of Mass

It is the point at which whole mass of body is supposed to be confined. It may lie inside or outside the body. 

Centi

It is a prefix in the metric system denoting a factor of one hundredth. It is used with meter to express lengths in centimeters, a common unit of length in CGS system.

Central Tendency

The central tendency of a distribution is a number that represents the typical or most representative value in the distribution. Measures of central tendency provide researchers with a way of characterizing a data set with a single value. The most widely used measures of central tendency are the mean, median, and mode.

Central Force

A force whose line of action is always directed toward a fixed point is called central force. The point, toward or from which force acts is called central force.

Centre of Gravity

 It is the point of a body through which its weight acts.

Centrifugal Force

It is the radial force acting outwards on the agency which makes body to move in a circular path.

                                              or

The pseudo force which acts radially outwards on body moving along a circle.

Centripetal Acceleration

The acceleration of object in uniform circular motion, which points towards center, is called as centripetal acceleration.

Centripetal Force

It is the force which acts perpendicular to direction of linear velocity to keep body in a circular motion. This force changes direction of linear velocity but not its magnitude.

Centroid

The name attributed to geometrical center of objects shape.

Ceramic

The term “Ceramic” comes from Greek word “keramikos”, which means “burnt stuff” indicating that desirable properties of these materials are normally achieved through high temperature heat treatment process called firing.

or

A compound of metallic and non-metallic elements, for which the inter-atomic bonding is predominantly ionic. 

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Capacitance

It is the ability of dielectric material between conductors to store charge, when a difference of potential exists between the conductors.

Capacitor

Passive device designed to store electrical charge. It is an arrangement of two conductors separated by dielectric.

Capillarity

The phenomenon of rise or fall of liquid in a capillary tube is known as capillarity.

Capillary Tube

It is a very thin tube made of rigid material such as plastic or glass. The tube is used to collect samples of liquids which flow into tubes against effects of gravity in a physical process called capillary action. The process uses two physical forces; “Surface Tension” and “adhesion”.

Carat

It is a unit used for measure of proportion of gold in an alloy, expressed as number of parts of gold in 24 parts of alloy. At present, 1 carat =200 mgm.

Carbon-Nitrogen Cycle:

A chain of thermonuclear reactions in which Nitrogen isotopes are formed in intermediate stages and Carbon acts essentially as a catalyst to convert four Hydrogen atoms into one Helium atom with the emission of two positrons is called as Carbon-Nitrogen cycle. The entire sequence is thought to generate significant amount of energy in the sun and certain other stars.

Carburizing

It is a process by which surface Carbon concentration of a ferrous alloy is increased by diffusion from surrounding environment.

Cardinal points

Points of an optical system, if known, the image would be determined easily without knowing the details of structure of system. Cardinal points constitute two principal points, two focal points and two nodal points.

Carnot’s Engine

Theoretical ideal engine, the concept of which is proposed by Sadi Carnot in 1824. As per this concept, there is no loss of heat due to friction etc and working substance is perfect gas. The engine is reversible and its efficiency depends only on temperature of source and sink, between which it works. No engine in practice can have efficiency more than it.

Carnot’s Cycle

Heat engine cycle concept proposed by Nicolas Sadi Carnot in 1823. It is the most efficient heat engine cycle consisting of two isothermal and two adiabatic processes. It is a reversible cycle involving no change in entropy i.e. it is an ideal concept in which total heat supplied is converted to work.

Carnot’s Theorem

Carnot’s theorem states that “working between the two given temperatures, no engine can be more efficient than a reversible Carnot engine. In other words, efficiency of a reversible engine is greater for two given temperatures than any other engine. 

Carrier Wave

Wave which carries information from transmission station and receiving station.

Cartesian Coordinates

Cartesian coordinates are rectilinear two dimensional or three dimensional, which are also called rectangular coordinates. The 3 axes of 3 dimensional Cartesian coordinates conventionally denoted by X, Y & Z axes are chosen to be linear and mutually perpendicular. In 3 dimensions, the coordinates X, Y & Z may lie anywhere in interval (-∞ & +∞ ).

Cathetometer

It is an instrument for the accurate measurement of small difference of height; especially of the differences in the height of upper surfaces of two columns of mercury or other fluid, or of the same column at different times. It consists of a telescope leveling apparatus which sides up or down a perpendicular metallic stand very finely graduated. The telescope is raised or depressed in order to sight the objects or surfaces, and the differences in vertical height are known.   

Cathode Ray Oscilloscope

It is an electronic display unit, first developed by German Physicist Ferdinand Braun in 1897. It contains a cathode ray tube that generates an electron beam that is used to produce visible patterns, or graphs, on a phosphorescent screen. The graphs plot the relationships between two or more variables, with horizontal axis normally being a function of time and vertical axis usually function of voltage generated by input signal to the oscilloscope. It is widely used test instrument for commercial engineering & scientific applications comprising acoustic research, television production engineering and electronics design.   

Cathode Ray Tube

An arrangement of vacuum tube equipped with electron gun which emits electrons. The electrons are accelerated and made to pass through electromagnetic field which gets deflected and falls on to fluorescent screen to form images.

Cathode Rays

Electron beam in vacuum tubes is referred to as cathode rays. They were first observed by German physicist Johann Hittorf and were named in 1876 by Goldstein.

Cathode

It is the electrode in an electrochemical or galvanic couple at which a reduction reaction occurs; thus the electrode that receives electrons from an external circuit is called as cathode.