PHYSICS DICTIONARY

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Calcination

Process of heating a substance in air or oxygen to bring about changes in physical or chemical constitution like thermal decomposition, phase transition etc is called as Calcination.

(or)

In Solgel method, the term applies to the heating of a polymer network containing metal compounds, to convert it into oxide network.  

Calcite

Calcite is also called Iceland spar. Its chemical name is hydrated calcium carbonate. It is a colorless crystal which is transparent to Visible & UV light. It exhibits property of double refraction of light and is uniaxial type.

Calculus

It is the branch of mathematics which focuses on limits, functions, derivations, integrals and infinite series to study the change in function pertaining to physical quantity.

Calorie

Quantity of energy required to heat 1 gram of water through 1^oC 

Calorimeter

Apparatus used to measure amount of heat absorbed or evolved during chemical reaction that is  change of phase or formation of solution.

CAMAC Layout

CAMAC modules are housed in a CAMAC crate, which can accommodate up to 24 normal CAMAC modules. Each module slot is called as station. Besides these 24 stations there is another one reserved for the crate controller module. The controller module is an integral part of the system and cannot be replaced by some other module. Also, some controller modules have double widths and therefore take up two slot positions. In such a case, the crate can accommodate up to 23 normal modules. The back plane of a CAMAC crate is called DATA WAY. DATA WAY consists of not only control, data, and bus lines but also module power lines. These lines are connected to the modules through sockets. There are standard guidelines for the current consumption at these sockets. The current should not exceed more than 3A at any of the sockets. Furthermore the power dissipation per station should not exceed 8W. However this rating can be relaxed in certain situations up to a maximum of 25W. The power rating for the whole crate is 200W.

 

CAMAC Logic

The CAMAC logic conforms to the standard TTL and DTL series logic with one exception that the signal convention is inverted such that the high state corresponds to logic 0 and low state to logic 1.

CAMAC Standard

CAMAC is an acronym of Computer Automated Measurement and Control. This standard was originally defined in 1969 by the ESONE Committee and was later on jointly standardized by the NIM and ESONE committees. With its built-in controllers and interface capabilities, CAMAC provides a more versatile architecture than NIM, though at the expense of much more complicated and difficult customization. The standard CAMAC backplane is called DATAWAY, which can be directly interfaced to a computer. This feature of CAMAC system makes it far more advantageous over its NIM counterpart where backplane does not have this functionality. In this way one can talk to any module in the crate through simple CAMAC commands without the need to connect it directly to a computer.

Camera

Device equipped with lens for capturing light from objects and forms images on a film or stores in the form of an image digitally. The lenses are made in a wide range of focal lengths. The term camera comes from word obscura (Latin for “dark chamber”) on early mechanism for project images.

Canal Rays

Beams of positive ions created in certain types of gas discharge tubes containing rarefied gas. They were first observed in Crooke’s tube during experiments by German scientist Eugen Goldstein in 1886.

Candela

A unit of luminous intensity equal to 1/60 of luminous intensity per square centimeter of a black body radiating at the temperature of solidification of Platinum (2046 K)

(or)

The candela is luminous intensity in a given direction, of a source that emits monochromatic radiation of frequency 540 x 10¹² Hz and that has a radiant intensity in that direction of 1/683 Watt per Steradian.     

Canonical Ensemble

It is a collection of large number of essentially independent systems having same temperature, volume and number of particles.  

PHYSICS DICTIONARY

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Babinet’s Compensator

It is a device used for producing circular & elliptically polarized light and for their detection.

Back EMF

It is the electromagnetic force in an inductive circuit which acts in such a direction so as to oppose any change of current in the circuit.

Background

Term generally used in nuclear physics. The background radiation refers to the energetic particles reaching earth surface mainly due to cosmic rays comprising neutrons, muons, neutrinos, gamma etc.

Baking

Process in which materials meant for vacuum application are subjected to heat condition to reduce outgassing rate.

Ballistic Galvanometer

A moving coil galvanometer, in which coil has high inertia that indicates presence of an electric charge by single impulse imparted to coil by small instantaneous current, the quantity of electricity that passes being proportional to deflection of coil.

Ballistic Pendulum

A physical pendulum consisting of a large mass suspended from a rod; when it is stuck by a projectile, its displacement is used to measure the projection’s velocity.

Ballistics

Science of mechanics that deals with behavior and effects of projectiles, especially bullets, rockets etc.

Balmer Series

The spectrum of wavelength falling in visible region due to transition of electrons from higher orbits to second orbit is called Balmer series.

Band Spectrum

This spectrum is due to transition of electrons combined with rotatory, translatory and vibration effects of molecules. Hot gases in molecular state produce band spectrum.  It is also called molecular spectra. It consists of bright bands of different colors over dark background. Each band consists of closely spaced lines. The spacing between two bands and also width of the band depends on nature of compound. At very high temperature, the band spectrum changes to line spectrum as the molecules split in to atoms.     

 

Band Theory

Theory which aims at classifying materials as conductors, insulators, semiconductors based on the distribution of electron energy states. In solids, due to proximity of atoms, each distinct atomic state splits into series of closely packed electron states called as electron energy band. There are three types of electron band structures possible at 0 K as per this theory.

Band Width

Term used in amplifier. It is the band of frequencies over which the amplification gain remains constant.

Bar

It is a unit of pressure.

Barns

Unit used for nuclear scattering interactions. It is used to represent the measure of probability of interaction between small particles. The value of one barn is 10^-28 m² and is approximate crossection area of Uranium nucleus.   

Barometer

Instrument invented by Evangelista Torricelli to measure atmospheric pressure and hence for assisting in forecasting weather. 

Bartlett Force

It is type of nuclear force in which there is exchange of spin coordinates but not position coordinates between nucleons.

Baryons

They are a type of Fermions which are heavier than mesons.  They constitute the two nucleons with anti particles & Hyperons. 

or

Fermions whose mass is at least as great as mass of Proton and which can interact strongly are called Baryons.

Battery

A battery is an electrochemical cell which consists of an anode, a cathode and an electrolyte. It is used to provide a static potential for power or release electrical charge when needed.

BCC

It is a crystal structure equivalent to two interpenetrating simple cubic cells. The total number of atoms in unit cell is two. The coordination number is eight.

Beat Frequency

Phenomenon which can be heard when two sound waves of different frequency approach human ear; constructive and destructive interference leads to alternation of soft and loud sound. "The beat frequency equals absolute value of the difference in frequency of the two waves."

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Aberration
Defect in images formed by optical system arrangement.

Aberration of Starlight
The phenomenon of apparent displacement of star in the sky due to finite speed of light and motion of earth in its orbit about the sun is known as aberration of starlight.

Abrasive
A hard and wear resistant material that is used to wear, grind or cut away other material.


Abscissa
The horizontal coordinate of a point in a plane Cartesian coordinate system obtained by measuring parallel to the X-axis is called as abscissa.


Absolute Error
The difference between true value and measured value is called as absolute error.


Absolute Humidity
Absolute humidity denotes the amount of humidity in air regardless of the saturation level, expressed as the total mass of water molecules per air volume.


Absolute Permeability
Constant of proportionality between magnetic density and magnetic field strength of a material put in uniform magnetic field.


Absolute permittivity
Permittivity of vacuum is called absolute permittivity and its value is 8.85 x 10-12 F/m.


Absolute pressure
When pressure is measured above absolute zero (or complete vacuum), it is called as absolute pressure.


Absolute Temperature
Temperature measured using Kelvin scale when zero is absolute zero.


Absolute Zero
The temperature at which entropy of a system reaches minimum is referred as absolute zero.


Absorbed Fraction
A term used in internal dosimetry. It is the fraction of photon energy (emitted within a specified volume of material) that is absorbed by volume. The absorbed fraction depends on source distribution, photon energy, size, shape and composition of volume.


Absorbing Power
The ratio of amount of radiations absorbed by the body in a certain time to the amount of radiations incident on it in the same time is called absorbing power of body.


Absorptance
Ratio of amount of radiation absorbed by a surface to the amount of radiation incident upon it is called as absorptance. It is measure of ability of an object to absorb radiation.


Absorption Spectrum

Absorption spectrum is the characteristic property of absorbing material. Using this spectrum, one can identify what are the elements present in absorbing material. It is due to absorption of radiation by matter. Absorption is based on Kirchhoff’s law, which states that a substance which emits particular wavelength of radiation when excited also possess the property of absorbing the same wavelength from incident radiation when unexcited. Absorption spectra consist of dark lines over a bright background. When the white light is passed through the gas in atomic state (say sodium vapor), line absorption spectrum is formed. When white light is passed through molecular gas (say iodine vapor), band absorption spectrum is formed.

Absorption
The optical phenomenon where by the energy of a photon of light is assimilated with in a substance, normally by electronic polarization or by an electron excitation event.


Absorptivity
It is fraction of radiant energy falling upon the body which is absorbed or transformed into heat. This ratio varies with character of the surface and the wave length of incident energy.


Abundance
The ratio of the number of atoms of a specific isotope in a mixture of isotopes of an element to the total number of atoms present is called abundance. It is expressed in percentage.


Acceleration
It is a physical quantity which is defined as rate at which velocity of an object change with time.


Acceleration due to Gravity
The acceleration acquired by body due to gravitational pull is known as acceleration due to gravity.


Accelerator
Device used to accelerate charged particles to gain high energies. They are used in medical applications, making of radio isotopes etc.

Stefan's -Boltzmann Law

This law states that the total amount of radiant energy emitted by a black body per second per unit area is directly proportional to the fourth power of its absolute temperature i.e. E∝T⁴ or E=𝜎T⁴ where 𝜎 is called Stefan's constant. It has a value of 5.67 x 10⁻⁸ Wm⁻²K⁻⁴. This law is strictly true only when the medium surrounding the black body is vacuum.

The same law was established later by Boltzmann theoretically from thermodynamical considerations. Hence, this law is known as Stefan-Boltzmann law.

Consider the case of black body 'A' at absolute temperature 'T1' which is surrounded by another black body at absolute temperature 'T2'.

Now, 

Heat lost by black body 'A' is 𝜎T1⁴ 
Amount of heat absorbed by black body 'A' from black body 'B' is  𝜎T2⁴.

Therefore, Net amount of heat emitted by body 'A' per second per unit area is 𝜎(T1⁴ - T2⁴).

This is the form of "Stefans Boltzman Law". 

Note: This law is true only when medium surrounding the body is vacuum.

What is Statistical Mechanics?

When we consider bodies at macroscopic level they consist of uncountable atoms or molecules i.e. about 10²³ atoms/gm.mole. In such cases we cannot predict the result of interactions between atoms with the help of ordinary classical laws of motion.

Statistical Mechanics is the branch of Science which establishes the interpretation of macroscopic behaviour of system in terms of its microscopic properties.

The main theme is that it doesn't deal with motion of each particle but it takes into account the average or most probable properties of system without going into interior details of characteristics of its constituents.

The larger is the number of particles in the physical system considered, the more nearly correct are the statistical predictions. The smaller is the no. of particles (no. of degrees of freedom) in a mechanical system, the methods of mechanical system cease to have meaning.

Before the advent of quantum theory Maxwell, Boltzmann, Gibbs etc applied statistical methods making the use of classical physics. These statistical methods are known as Maxwell Boltzmann Statistics.

These statics explained successfully many observed physical phenomenon like temperature, pressure, energy etc; but couldn't explain adequately several other experimentally observed phenomenon like black body radiation, specific heat at low temperature etc.

In order to explain such phenomenon "quantum statistics" was introduced and developed by Fermi, Dirac, Bose, Einstein with new approach by using new quantum idea of discrete exchange of energy between system.

i) Bose-Einstein Statistics
ii) Fermi-Dirac Statistics

Atomic Structure - Important Points for competetive exams

1. Distance of closest approach: It is the distance from which the nucleus of an atom, the alpha particle comes to rest and its kinetic energy is totally converted  into electrostatic potential energy. It is denoted by ro.

ro = (1/4πεₒ)*[(2ze²)/(1/2)*(V²m)]

2. Diameter of atom: 10⁻¹⁰ meter

3. Diameter of Nucleus: 10⁻¹⁴ meter 

4. Impact Parameter(b):  (1/4πεₒ)*[(ze²tan𝜃)/(1/2)*(U²m)]; U is velocity of alpha particle

5. Impact Parameter(b) is inversely proportional to the angle of scattering(𝜃).

6. The equation mvr =n*(h/2π) is called "Bohrs quantisation condition".

7. The equation h𝝂=Ei-Ef is called "Bohr's Frequency condition".

8. Bohr's Radius r = (n²h²εₒ)/πme²

9. Velocity of electron (V) = e²/2nhεₒ 

10. If 'C' is velocity of light; V = [(1/4πεₒ)*(2πe²/Ch)]*(C/n)

11. The factor [(1/4πεₒ)*(2πe²/Ch)] is called fine structure constant. It is denoted by '𝛼'

12. The value of 𝛼=1/137; V = (1/137)*(C/n)

13. Energy of electron En = -(1/4πεₒ)²*(2π²me⁴/n²h²)

14. An electron can have only some definite values of energy while revolving in the orbits n=1,2,3,..... It is called energy quantization.

15. Energy Quantization: 

      E1 = -(1/4πεₒ)²*(2π²me⁴/n²h²) ;
      E2 = (1/4)*E1
      E3 = (1/9)*E1   ............................E∞ = 0

      E = -13.6/n²

 16. Rydberg's constant for Hydrogen (RH) is (1/4πεₒ)²*(2π²me⁴/ch³). Its value is 1.09678 x 10⁷m⁻¹

 17. Value of (1/4πεₒ) is 9x10⁹ C²N⁻¹m⁻².

 18. The charge 'e' of the electron is measured by Millikan's Oil drop method.

 19. The ratio of charge to mass(e/m) for an electron is measured by "Thomson".  

 20. Mass of electron(m) = 9.1 x 10⁻³¹ Kg

 21. Mass of Proton is 1835 times that of mass of electron.

 22. Canal Rays or Positive Rays are discovered by "E. Goldstein". Wien observed that these rays can be deflected in magnetic field and hence they are called Positive Rays.   

23. Rest mass energy of electron is 931 MeV

24. Orbital frequency of electron is (1/T) = (V/2πr)

25. Ionization energy of a Hydrogen atom is 13.6 eV

26. The excitation energy required by the electron to excite from state n1 to state n2 is En₂-En₁

Spectral series of Hydrogen atom

27. Lyman series lie in Ultravoilet region.

28. Balmer series lie in near UV region and visible region.

29. Paschen series lie in infrared region.

30. Brackett series also lie in infrared region. 

31. Pfund series also lie in far infrared region.

                                                          (1/) = R[(1/nf²)-(1/ni²)]

In addition to the above, nf=6, Humprey series results.

32. Velocity of an electron is independent of its mass.

33. Velocity of an electron is inversely proportional to the orbit.

34. The electron in the inner most orbit has highest velocity.

35. Velocity of a electron is independent of its mass.   

36. Orbital frequency is inversely proportional to the cube of 'n' i.e. 𝜈∝(1/n³).

37. If Ep & Ek represents Potential & Kinetic energies of the orbital electron, then Ek = -Ep/2.

38. When a Hydrogen atom is raised from the ground state to an excited state both kinetic energy and potential energy decrease.E∝(1/n²).

39. The energy difference between two consecutive energy levels decreases as the quantum number 'n' increases.

40. Bohr used conservation of angular momentum to explain his theory.

41. The velocity of an electron in the ground state is e²/2hεₒ = 2 x 10⁶ m/sec 

42. The ground state energy of Hydrogen atom is -13.6 eV. The energy needed to ionise the Hydrogen atom from its second excited state is 1.51 eV.

43. According to Bohr's principle, the relation between principle quantum number(n) and radius of orbit is  r ∝ n²