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> 

Gay-Lussac’s Law

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

Geiger Muller Counter

In 1928, Geiger & Muller in Germany developed this counter. The counter is used for detection of level of radiation. The device is a gas filled type radiation detector working in Geiger Muller region, in which the pulse height output is same for any event occurring inside the counter. Essentially they all have a metallic cylindrical cathode with a Tungsten wire of about 0.1mm diameter stretched along its axis. The wire which is insulated from cathode serves as anode. The evacuated counter is filled with suitable gas along with quenching gas at vacuum pressure. The counters are usually used to detect radiation of low energy level.

Geiger-Nuttal Law

This law implies an empirical relation between range of an alpha particle ‘R’ and decay constant ‘λ’  of alpha emitter as Log R = A Log λ + B Where ‘A’ is a constant having same value for all three radioactive series and ‘B’ is constant, different for each series. This law has acquired prominence in nuclear physics because it enabled physicists to estimate half lives of alpha emitters which couldn’t be easily determined by experimental results. 

Generalized Coordinates

A set of variables used to specify the position and orientation of a system, in principle defined in terms of Cartesian coordinates of systems particles. The number of such coordinates equals the number of degrees of freedom set of the system also known as Lagrangian coordinates.

Geocentric Theory

Theory proposed by Ptolemy, as per which all the planets and the sun revolve round the earth.

Geocentric

Relating to a model of the solar system or universe, having the earth as the centre.

Geomagnetism

The branch of geophysics which deals with study of magnetic field associated with earth.

Geophysics

It is study of the earth by quantitative physical methods, especially by seismic reflection and refraction, gravity, magnetic, electrical, and electromagnetic and radioactivity methods. It includes branches of seismology (earth quakes & elastic wave), gravity & geodesy (earth’s gravitational field, size and form of earth) and the atmospheric pressure.

 

Geo-stationary Satellite

A satellite which appears to be stationary relative to the earth is called as geo-stationary satellite. The direction of motion and magnitude of orbital velocity of satellite are same as that of earth. The time period of revolution of a parking satellite is 24 hours. Height of the geo-stationary orbit above the surface of earth is about 36000 KM.

Giant Stars

Stars, which have relatively larger radius for its mass and temperature that burns Hydrogen at much faster value than a dwarf star. They are much more luminous and have shorter life spans. They usually end their lives as supernovae.

Gibbs Energy Function

Thermodynamic Function at isothermal (const temp) & isobaric conditions (constant pressure).

Mathematical expression is G = G _{(T, P, N)} ; G= H - TS

Gibbs Paradox

An unaccountable increase of entropy by 2NKlog2 even when allowing the mixing of two same gases which is against the result in agreement with thermodynamic reversible process i.e., change in entropy should be zero.  ‘N’ is total no. of gas molecules in ensemble and  ‘K’ is Boltzman constant.

Gilbert

It is unit of magnetic potential. It is the magnetic potential against which one erg of work is done when unit magnetic pole is transferred.

Gluon

 A quantum of color field that binds quarks into nucleons and also nucleons into nuclei is called as Gluon.

GM Region

One of the six regions of operation, in which gas filled radiation detector, may be operated. In this region of operation, the gas multiplication is so high that the final total charge formed is independent of initial ion pairs formed by impinging radiation which is because of mechanism called ‘Geiger Discharge’. 

Gold Leaf Electroscope

Device used to detect electric charge. It was one of the most popular instruments used by scientists to study electricity. An electroscope has a thin layer of gold leaf attached to a metal stem. When the electroscope is charged the leaf is repelled by the stem and rises.

Gradient

Gradient is a vector operation which operates on a scalar function to produce a vector whose magnitude is the maximum rate of change of function at the point of gradient and which pointed in direction of maximum rate of change. If ‘S’ is a surface of a constant value for function f(x,y,z) then gradient on surface defines a vector which is normal to the surface. 

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> 

Fraunhofer Lines

When sun’s light is allowed to fall on slit of a spectrometer, its spectrum is found to consist of many dark lines. The lines are called Fraunhofer lines. The number of lines is approximately 700. These lines are due to absorption of certain wavelengths in sunlight by gases in sun’s outer sphere.   

Fraunhofer’s Diffraction

Type of diffraction in which light rays from a source of light kept at a finite distance are made incident on obstacle or aperture in form of a parallel beam by using a convex lens. The source is placed in focal plane and convex lens. The light rays diffracted by obstacle or aperture are focused on a screen kept at a finite distance by means of another convex lens with which screen is placed in its focal plane. The diffraction pattern in this is the image of source.

Free Electron

Electron which is not bounded to any atom or molecule or ion and moves freely in crystal structure under influence of constant electric potential is termed as free electron.

Free Fall

It is motion of a body due to only gravitational force acting on it. Freely falling bodies doesn’t get influenced by air resistance and they accelerate downwards with 9.8m/sec.

Free Oscillation

The oscillation of a physical system with its natural frequency and under no external influence other than impulse that initiated the motion is called as free oscillation.

Free Vibration

When a particle vibrates continuously under no external force such as friction etc, then such vibration is called free vibration.

Freezing Point

The temperature, at which vapor pressure of solid phase of a substance becomes equal to vapor phase of its liquid phase, is known as freezing point of a substance.

Frenckel Defect

The type of defect in crystalline ionic substance, in which, the ion, instead of being in its expected location, is found in one of the interstices. Frenckel defects are more common in ionic crystals where size of cation is such that it can be accommodated in interstitial sites.

Frequency Modulation

Type of modulation in which frequency of carrier wave is changed in accordance with intensity of the signal without changing amplitude.  

 

Frequency

The rate at which an event occurs over a particular period of time or in given sample is called frequency. It can also be defined as number of cycles per unit time.

Fresnel Biprism

Optical device consisting of two prisms of very small refracting power, set base to base and which forms two images of a single source. It is often used to produce interference fringes.

Fresnel’s Diffraction

The type of diffraction formed when source of light or the screen on which diffraction pattern formed or both are at a finite distance from the obstacle or aperture. The incident wave front may be plane, spherical or cylindrical. The diffraction pattern is the image of obstacle or aperture.     

Friction

Friction is tangential force between the contact surfaces of two bodies.

Full Moon

Full moon is when the sun and the moon are facing opposite, being in opposite direction from an earth perspective. A full moon is the lunar phase that occurs when the Moon is completely illuminated as seen from the Earth.

Full Wave Rectifier

Device in which current flows through the load in some direction for both half cycles of input ac voltage is called full wave rectifier.

Fundamental Frequency

Lowest frequency of periodic wave function is termed as fundamental frequency. 

Fundamental Particles

The word fundamental implies that the particles are basic building blocks of matter. They are nothing but quanta of corresponding field. Study of fundamental particles is basis to understand radiation phenomena. We may regard any radiation as a flux of elementary particles.

Fundamental Quantity

The physical quantity which does not depend on other quantities is known as fundamental quantity.

Fundamental Unit

The unit used to measure fundamental quantity is called fundamental unit.

Fusion Bomb

See hydrogen bomb. 

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> 

Fluidity

It is physical property of a substance which makes it to flow. The molecules of such substance move one past other. The substance assumes the shape of its container.

Fluorescence

Phenomenon of luminescence in which emission of light occurs during excitation or within 10^-8 Sec after the excitation source is removed.

Fluorescent Lamp

Lamp contains a tube filled with inert gas & a small amount of mercury vapor (low pressure). It doesn’t have filament running through it instead they are equipped with coiled Tungsten filaments coated with an electron emitting substance. The fluorescent light occurs in two stages. First, electrons emitted from cathodes create an electrical arc through Mercury vapor. Then the resultant UV radiation strikes Phosphor coating which then gives off visible light.     

Flux (Energy)

The energy flux is a measure of the total energy incident on a surface per unit area per unit time. Another term used for this quantity especially in dosimetry, is the energy fluence rate.

Flux (particle)

Particle flux simply represents the number of particles incident on a surface per unit area per unit time. In the field of dosimetry, this quantity is also known as particle fluence rate.

Focal length

The distance from the lens to that point where light rays converges or diverges (depends on type of lens). Focal length decides the lens strength/power. Lens power is inversely proportional to focal length. 

Focal point

Focal points are a pair of points on principal axis of a system such that all rays starting from one focal point, after passing through the system, become parallel to the principal axis and parallel rays after refraction through the optical system converge at second focal point. First point is object point on principal axis for which the image point is at infinity and the second focal point is the image point on principal axis for which object point is at infinity.

Focaults Pendulum

It is a device used to demonstrate the rotation of earth and the fact that earth is not an inertial frame of reference.

Focus

The place in the earth crust, where the vibrations come from, is called focus of earth quake.

 

Force

Mass of an object times the acceleration it gained.

Forced Vibration

This is vibration of the body which exists because of exertion of external periodic force constantly on body. 

Forward Bias

Term used in solid state physics. It is state of biasing P-N junction where ‘P’ junction is at higher potential compared to ‘N’ junction. This type of biasing reduces width of depletion Layer in P-N junction and the diode conducts electrically.

Forward Biased Diode

The ‘P’ junction of P-N diode is kept at high potential and ‘N’ junction at low potential.

Fourier Theorem

Fourier theorem deals with the summation of a number of simple harmonic vibrations in which the vibrations are in the same straight line. The theorem also helps in the synthesis and analysis of complex forms of vibrations. This theorem was formulated by J.B.T Fourier in 1828. The theorem states that any finite, continuous and single valued periodic function can be expressed as summation of number of simple harmonic terms (sine and cosine functions) having the frequencies integer multiple of given function.   Fourier’s theorem deals primarily with the synthesis of a complex periodic vibration from simple harmonic terms and it gives a method to analyze a complex vibration into its component vibrations.

Frame of Reference

It is a coordinate system relative to which we describe the motion of body.

Franck & Hertz Experiment

It is the experiment which revealed the existence of discrete stationary states of electrons.

Franck-Condon Principle

According to this principle, an electronic transition takes place so rapidly that a vibrating molecule doesn’t change its inter nuclear distance appreciably during the transition. That is during an electronic transition, inter-nuclear distance remains the same, means straight line representing a transition between electronic states will be vertical. Transition between electronic states occurs vertically in a potential energy diagram.

Frank-Hertz Experiment

Experiment which was carried out by James Frank and Gustav Hertz in 1914 which revealed directly the existence of discrete quantized stationary energy states of electrons.