PHYSICS DICTIONARY

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

<Prev>                   <Next> 

Fabry Perot Interferometer

An interferometer made of a transparent plate with two reflecting surfaces or two parallel highly reflecting mirrors. It is named after Charles Fabry & Alfred Perot. It makes use of multiple reflections between two closely spaced partially silvered surfaces. Part of light is transmitted each time the light reaches second surface, resulting in multiple offset beams which can interfere with each other. The large number of interfering rays produces an interferometer with extremely high resolution, somewhat like multiple slits of all diffraction grating increase its resolution.

Face Centered Cubic structure(FCC)

The crystal structure found for many metals has a unit cell of cubic geometry, with atoms located at each of the corners and the centers of all cubic faces.

Fahrenheit Scale

Temperature scale introduced by German physicist Daniel Gabriel Fahrenheit in 1724. On this scale, the freezing point of water is 32 degree Fahrenheit and boiling point 212 degree Fahrenheit at standard atmospheric pressure. This puts boiling and freezing points of water exactly 180^o apart. Therefore a degree on Fahrenheit scale is 1/180 of interval between freezing and boiling point. A temperature interval of 1^oF is equal to an interval of 5/9 ^oC.  

Farad

It is SI unit for capacitance. It is named after English Physicist Michael Faraday. A capacitor is said to have one Farad value when one coulomb of stored charge causes a potential difference of 1 Volt across its terminals.

1Farad = 1 Coulomb / Volt.

Faraday Effect

The rotation of plane of polarization of a light beam when plane polarized light is passed through a substance in a magnetic field; the direction of travelling of light is parallel to magnetic lines of force. For a given substance, the rotation is proportional to thickness traversed by light and to the magnetic field strength.

Faraday’s Constant

The total charge carried by 1 mole of electrons is given by   96487 Cmol^-1. The quantity is known as Faraday constant.

Faraday’s Law of Electrolysis

The quantitative relationships between electricity and chemical change where first described by Michael faraday in 1830. These are

i) The mass of a chemical substance involved at an electrode is directly proportional to quantity of electricity passed through the cell.

ii)The mass of different substances produced by a given quantity of electricity are proportional to equivalent mass of substances.    

Mathematical representation

a) m α Q     b)  m α M/v_e

where ‘m’ represents mass of substance deposited at cathode; ‘M’ represents molar mass of substance; v_e denotes stoichometric number of electrons in reaction involving reduction/oxidation of chemical species at respective electrode of electrolytic cell.

Faraday’s law of Electromagnetic Induction

 It states that induced emf in a closed circuit is equal to negative rate at which magnetic flux through it changes.

Fast Neutrons

Neutrons possessing high kinetic energies in the million electron volt range are called fast neutrons.

Fathom(ftm)

It is a unit of length used especially for measuring depth of water. 1 ftm = 1.8288 meters. 

Fault

Places where rock structures have broken apart and can slide past each other are called faults.

Feedback

The process of injecting a portion of output energy of some device to the input is known as feedback.

Femto

It is a prefix in the metric system denoting a factor of 10^-15.

Fermat’s Principle of Extremum Path

Fermat, in 1658, postulated that “a ray of light in passing from one point to another by any number of reflections or refractions chooses a path along which the time taken is least or extremum.                                                                                                      

Fermi Dirac Statistics

Statistics proposed by Fermi & Dirac. The postulates are as follows:   

i) Applicable to identical & indistinguishable particles with spin odd multiple of half, such as electrons, protons, neutrons etc, which are called the Fermions;

ii) The minimum volume of a phase cell is h³, so the number of phase cells cannot be increased.

iii) No new microstate is obtained by the interchange of position of particles in a cell.

iv)There cannot be more than one particle in a cell i.e. Pauli’s exclusion principle is obeyed.  

PHYSICS DICTIONARY

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

<Prev>                   <Next> 

Earth

One of the nine planets revolving around sun and is third planet orbiting from sun. The distance of orbit from sun is 149,600,000Km and has diameter of 12,756.3Kms. It is the fifth largest of the planets. The Mass is about 5.97x10²⁴ Kg

Echo

Repetition of sound produced due to reflection by a distant extended surface like cliff, hill, well, building etc., is called an echo. The effect of sound on human ear remains 1/10^th of second. If sound reflects back in a time less than 1/10^th of second, no echo is heard.

Eddy Current

When a metal body is moved in a magnetic field in such a way that the magnetic flux through it changes or is placed in a changing magnetic field, induced current circulates throughout the body.  They are called eddy currents.

Edge Dislocation

A linear crystalline defect associated with the lattice distortion produced in the vicinity of the end of an extra half plane of atoms within a crystal. The burgers vector is perpendicular to the dislocation.

Effective Mass of Electron

The mass of an electron inside crystal appears, in general, different from free electron mass and is referred to as effective mass. The effective mass can be greater or lesser than electron mass.

Efficiency of Engine

The ratio of useful work obtained by the engine in one cycle to the heat absorbed from the source is called efficiency of engine.

Effusion

Effusion is the process in which individual molecules flow through a hole without collisions between molecules. This occurs if diameter of the hole is considerably smaller than the mean path of molecules. According to Graham’s law, rate at which gas effuse is dependent on their molecular weight; gases with lower molecular weight effuse more quickly.

Eigen Function

It is wave function for a given physical system which contains measurable information about system. 

Eigen Value

The word is derived from German word “Eigenwert” which means characteristic value. A scalar associated with a given linear transformation of vector space and having the property that there is some non zero vector which when multiplied by scalar is equal to vector obtained by letting the transformation operate on the vector.

 

Einstein Shift

In astrophysics, gravitational red shift or Einstein shift is the process by which electromagnetic radiation originating from a source that is in gravitational field is reduced in frequency, or red shifted, when observed in a region of a weaker gravitational field. This is a direct result of Gravitational time dilation - as one moves away from a source of gravitational field, the rate at which time passes is increased relative to the case when one is near the source. As frequency is inverse of time (specifically, time required for completing one wave oscillation), frequency of the electromagnetic radiation is reduced in an area of a higher gravitational potential (i.e., equivalently, of lower gravitational field). There is a corresponding reduction in energy when electromagnetic radiation is red-shifted, as given by Planck's relation, due to the electromagnetic radiation propagating in opposition to the gravitational gradient.

Einstein Theory of Specific Heats

A theory of the specific heat capacity of solids put forward by Albert Einstein in 1906, in which it was assumed that the specific heat capacity is a consequence of the vibrations of the atoms of the lattice of the solid. Einstein assumed that each atom has the same frequency. The theory leads to the correct conclusion that the specific heat of solids tends to zero as the temperature goes to absolute zero, but does not give a correct quantitative description of the low temperature behavior of the specific heat capacity.

PHYSICS DICTIONARY

 A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

<Prev>                   <Next>

D’Alembert Principle

It is alternative form of Newton’s second law of motion which has been named after its introducer, French physicist Polymath Jean Le Rond D’Alembert. It states that difference between forces acting on a system of mass of particles & time derivatives of momentum of system itself along any virtual displacement consistent with constraints of system is zero.        

Daltons Law of Partial Pressure

Law proposed by John Dalton in 1801 which states that “the total pressure exerted by the mixture of non-reactive gases is equal to the sum of partial pressures of individual gases.

Damped Vibration

When pendulum vibrates in air medium, there are frictional forces and consequently energy is dissipated in each vibration. Thus amplitude decreases continuously with time, and finally oscillations die out. Such vibrations are called damped vibrations. 

 

Damping

It is phenomenon of dying out of mechanical or electrical oscillations due to external forces.

Daniel Cell

It was invented in 1836 by john Fredric Daniel, a British chemist. It is a type of cell having a zinc anode in dilute Sulphuric acid separated by a porous barrier from a copper cathode in copper Sulphate solution. The principle behind the cell is that a liquid solute called electrolyte between metal plates begins to dissolve zinc and copper into positively charged ions as ions leave the metal, free electrons remain behind. The zinc dissolves more rapidly than the copper, which means that the zinc soon contains more electrons. If one connects two pieces of metal with a wire the electrons will migrate through the wire from zinc to copper, creating electric current.

Dark Matter

Hypothetical predicted matter by astrophysicists, which is not seen directly by telescopes. The unaccounted missing mass is termed as dark matter. It neither emits nor absorbs light. It was first postulated by John Oort in 1932.   

Davisson Germer Experiment

In 1927, Clinton J. Davisson and Lester H. Germer confirmed experimentally the wave nature of electrons by bombarding a nickel target with electrons and measuring the intensity of electrons scattered from target. Davisson and Germer determined wavelength of electrons from known atomic separation and the measured Bragg angle at which the electron intensity exhibited a maximum. They found that the wavelength calculated is well in agreement with electron wavelength calculated from debroglie relationship. Davisson and Germer experiment demonstrated diffraction of electrons and gave evidence of wave nature of electron.

Day

Unit of time defined as interval equal to 24 hours.

                                        (or)

 The interval of light between two successive nights; The time between sunrise and sunset.

Debroglie Wave

 Wave nature attributed to particle.

Debroglie Wave length

Ratio of Planck’s constant to momentum of particle. 

Debroglie’s Hypothesis

Hypothesis put forward by French scientist Debroglie, as per which materialistic particle possess both wave and particle characteristics. The wave and particle nature for matter are complimentary in nature.

Debye Theory of Specific Heats

A theory of the specific heat capacity of solids put forward by Peter Debye in 1912; in which it was assumed that the specific heat is a consequence of the vibrations of the atoms of the lattice of the solid. In contrast to the Einstein theory of specific heat, which assumes that each atom has the same vibration frequency, Debye postulated that there is a continuous range of frequencies that cuts off at a maximum frequency, which is characteristic of a particular solid. The theory leads to the conclusion that the specific heat capacity of solids is proportional to T³, where T is the thermodynamic temperature. This result is in very good agreement with experiment at low temperatures. The Debye temperature is characteristic of a particular solid.

Debye

It is unit of electric dipole moment.

1 Debye = 3.33 x 10^-30 Coulomb-meter  

PHYSICS DICTIONARY

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

<Prev>                   <Next>

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.