PHYSICS DICTIONARY

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Helion

Nucleus of a Helium- 3 atom consists of two protons and one neutron bound together with a total binding energy of 7.72 MeV. Helium-3 atom, a stable isotope of Helium with natural abundance of ~0.00014% consists of a nucleus (Helion) and two electrons.

Helmholtz Coil

Device introduced by German scientist Helmholtz. Device consist pair of conducting circular coils each having ‘N’ turns, and carrying a current, separated by a distance equivalent to the radius of circular loops produce a homogenous uniform magnetic field in the mid plane between two circular coils.

Helmoltz Function (or) Helmoltz’s Free Energy Function

It is thermodynamic energy function pertaining to thermodynamic process in which system exchanges heat with surrounding and there by maintains temperature constant.

Mathematically, A = A (T, V, N); A = U-TS

Henry

It is unit of inductance.

Hertz

 It is unit of frequency which is named after German physicist Heinrich Hertz.

Hertzian Wave

An electromagnetic wave produced by oscillations in electrical circuit with frequency in range 3x10¹⁰ to about 1.5x10⁵ Hertz. They are named after Heinrich Rudolph Hertz, a German physicist.

Hetero Junction

A PN junction that encompasses two different semi conductors is called as hetero junction. The most distinctive feature of such junctions is that the P and N region have different energy band gaps.

Hexagonal Closely Packed Crystal Structure

Crystal structure having unit cell which has top and bottom faces forming regular hexagon and surround a single atom in the center. Another plane provides three additional atoms.

Higgs Particle or Higgs Boson

It is first theorized in 1964 by British physicist Peter Higgs and others, which is presumed to be basic building blocks of matter to interact. They have been confirmed to exist on 14^th march 2013. The discovery of particle appears to confirm existence of Higgs field. The heavier particles interact strongly with Higgs field and light ones interact weakly with this field.

Hilbert Space

The mathematical concept named after David Hilbert generalizes notion of Euclidian space. It is an abstract vector space possessing structure of an inner product that allows length and angle to be measured.

Histogram

A histogram is graphical representation of distribution of data. It is an estimate of probability distribution of continuous variable.  It consists of tabular frequencies shown as adjacent rectangles, erected over discrete intervals, with an area equal to frequency of observations in the interval. The height of rectangle is also equal to frequency density of interval i.e. frequency divided by width of interval. The total area of histogram is equal to no. of data. 

Hole

For semiconductors and insulators, a vacant electron state in the valence bond that behaves as positive charge carrier in an electric field. A hole is not a particle and it doesn’t exist by itself.

Hologram

Consists of record of both amplitude and phase of light wave scattered from object so that it can give 3D view of the object but image cannot be observed directly from hologram because it requires reconstructing.

or

 It is counterpart of photographic negative. It consists of record of both amplitude and phase of light wave scattered from object so that it can give 3D view of the object, but image cannot be observed directly from hologram because it requires reconstructing. 

Holography

Holography dates from 1947, when British (native of Hungary) scientist Dennis Gabor developed the theory of holography while working to improve the resolution of an electron microscope. Gabor coined the term hologram from the Greek words ‘holos’ meaning "whole," and ‘gramma’, meaning "message".

Holography is "lens less photography" in which an image is captured not as an image focused on film, but as an interference pattern at the film. Typically, coherent light from a laser is reflected from an object and combined at the film with light from a reference beam. This recorded interference pattern actually contains much more information that a focused image, and enables the viewer to view a true three-dimensional image which exhibits parallax. That is, the image will change its appearance if you look at it from a different angle, just as if you were looking at a real 3D object.

Holonomic Constraints

Constraints which are expressible in the form of f(r₁,r₂, …..r_n, t) = 0.

Homo Junction

A junction containing only one semiconductor, such as silicon PN junction, is called Homo junction. 

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Hadrons

Kaons, Pions together with Baryons are placed in group of strongly interacting particles called Hadrons.

Half Life

Term used in nuclear physics. It represents the time it takes for a radioactive isotope for decaying its activity to half of its present value.

Half Wave Plate

Plate of uniaxial double refracting crystals such as quartz and calcite with optic axis parallel to their refracting surface, the thickness of which is such that it produces a path difference of λ/2 or a phase difference Π in between ordinary and extra ordinary waves.

Half-Wave Rectifier

Device which conducts current only during the positive half cycles of input ac supply. The negative half cycles of ac supply are suppressed i.e. during negative half cycles, no current is conducted and hence no voltage appears across load. Therefore, current always flows in one direction (DC) through load after every half cycle. 

Hall Effect

When a piece of semiconductor carrying a current is placed in a transverse magnetic field, an electric field is produced inside the conductor in a direction normal to both current and magnetic field.

Hall Mobility

Mobility of charge carriers under Hall Effect defined as product of hall coefficient and conductivity.

Hall Probe

Hall probe is a magnetic field sensor that passes electric current when the sensor is perpendicular to magnetic field. The stranger the magnetic field the more the current is converted to voltage. They are used for proximity switching, positioning etc.

Hamilton’s Principle

If a particle moves from one point to other in time interval t1 ≤ t ≤ t2, then the actual path it follows is the one for which action assume stationary value.

Hamiltonian Principle

The path actually traversed by a conservative, holonomic dynamical system from time t₁ to t₂ is one over which the integral of the lagrangian between limits t₁ and t₂ is stationary i.e., the time integral of lagrangian is extremum.

Hard Radiation

The term attributed to high energetic X-rays or gamma rays having high penetration power into almost all materials. 

Hardness

Mechanical property which is a measure of materials resistance to localized plastic deformation.

Harmonic Motion

 See simple harmonic motion.

Health Physics

It is branch of physics which deals with radiation protection of occupational workers in nuclear reactors and other radiation material handling centers.

 

Heat Capacity

The quantity of heat required to raise the temperature of the whole body there 1^oC or 1^oK is called heat capacity of body.

Heat Engine Law

Conversion of total heat energy into work is impossible.

Heat Engine

It is cyclic process in which heat is continuously converted into mechanical work. It has 3 main parts: source, sink and working substance. i) Source of heat at constant temperature to drive heat; ii) Sink at constant temperature, heat can be supplied without change in temperature. iii) Working substance: absorbs heat from source, converts part of the heat into mechanical work & rejects remaining heat to sink.

Heat

It is a form of energy (kinetic energy of molecules constituting the body) which produces sensation of warmth.

                                      (or)

It is energy that is transferred between a system and its environment because of a temperature difference that exists between them.

Heavy Water

Also referred as Deuterium oxide, is a type of water in which Deuterium (an isotope of Hydrogen) substitutes Hydrogen i.e. D₂O. It has importance for having properties like Neutron moderation, high boiling point etc.

Heisenberg Forces

Type of nuclear force in which there is exchange of both spin and position coordinates.

Heisenberg’s Uncertainty Principle

Based on wave nature of matter, Heisenberg proposed a principle according to which, macroscopically it is possible to exactly measure position of moving particle and momentum associated with it but microscopically it is not possible. According to this principle, product of uncertainties in the measurement of position and momentum is of order of h/2π; where ‘h’ is Planck’s constant.

Helicity

Lee and yang suggested that the violation of parity in beta decay was direct consequence of longitudinal polarization of emitted electrons and Neutrons. The state and degree of longitudinal polarization of particles is represented by the term Helicity.

Heliocentric Theory

The theory proposed by Nicolas Copernicus, a polish astronomer. Heliocentric system first appeared in his book “De revolutionibus orbium coelestium”, “on the revolutions of heavenly bodies” which appeared in 1543. “Helios” in Greek means “sun”. Heliocentric means that the sun is at the center. As per this theory, sun remains at center and all the planets revolve round it. The moon is only celestial sphere in the system that revolves round the earth and together around sun. 

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Graham’s Law

At constant pressure and temperature, the rate of diffusion of a given mass of gas is inversely proportional to the square root of its density.

Grain Boundary

It is defined as boundary separating two small grains or crystals having different crystallographic orientations in poly-crystalline materials.

Grain

Many crystalline solids are composed of collection of many small crystals called grains.

Gram Atomic Weight

Quantity of an element whose weight in grams is equal to atomic weight of element is called Gram Atomic Weight.

Gram Molecular Volume

The volume occupied by a mole of any gas is called gram molecular volume.

At 0^oC and 76 cm Hg pressure, the gram molecular volume of any gas is 22.4 liters.

Gram Molecular Weight

Relative molecular mass of a substance expressed in grams with reference to the atomic weight of Hydrogen.

Gramophone

 It is the first device for recording and replaying.

Grand Canonical Ensemble

It is collection of large number of essentially independent systems having same temperature, volume and chemical potential.  The individual systems of a grand canonical ensemble are separated by rigid permeable and conducting walls.

Grand Unified Theory

Physics theory that can combine 3 of 4 fundamental forces into one single equation. The four forces are strong nuclear force, the weak nuclear force, electromagnetic force and gravitational force. Combining of 3 interactions strong nuclear, weak nuclear and electromagnetic force is called unified theory.

Gravitational Constant

The gravitational force between two unit masses separated by unit distance is called universal gravitational constant. The value of “G” is 6.67*10^-11    Nm² Kg^-2.

Gravitational Force

It is a long range and central force, which is attractive in nature and acts between any two masses in the universe.

 

Gravitational Intensity

Gravitational force of attraction exerted by a body on unit mass is called gravitational intensity.

Gravitational Mass

The ratio of gravitational force acting on a body to the acceleration due to gravity is called as gravitational mass.

Gravitational Potential

Gravitational potential at a point in gravitational field is amount of work done in bringing a unit mass from infinity to that point.

Graviton

Hypothetical particle assumed to be responsible for gravitational field just as photons for electromagnetic field. They are categorized as mass less Boson having spin-2 and mass zero.

Gravity

Phenomenon of attraction between two bodies due to existence of gravitational force acting along the line joining their centers.

Gray

It is the SI unit for Radiation Absorbed Dose (RAD) which is equal to absorption of 1 Joule per Kg of material.

Great Circle

A great circle of sphere is intersection of sphere and plane which passes through center point of sphere. It is the largest possible circle that can be drawn around a sphere. All spheres have great circles. Great circle has same circumference and the center point same as its sphere. The geometry of spheres is useful for mapping the earth and other planets. All the meridians on earth are great circles.

Green House Effect

In green house, plants etc are enclosed in glass structure. The glass allows short wavelength radiation to enter. This radiation is absorbed by plants matter. It is subsequently radiated in the form of longer wavelength heat radiation, infrared rays. But they are not allowed to escape from glass. The heat radiation is trapped in green house keeping it warm. Similar effect takes place in atmosphere and is called green house effect.                                        

Green’s Theorem

This theorem is an applicable of fundamental theorem of calculus to integrating a certain combinations of derivatives over a plane. Suppose ‘R’ is a differentiable function. A double integral of certain type of function over a plane region ‘R’ can be expressed as line integral (of some function) along the boundary curve of R. This is called Green’s theorem.

Gregorian Telescope

Telescope designed by Scottish mathematician and astronomer James Gregory in 17^th century. It is a reflecting telescope that has a parabolic primary mirror and a hyperbolic secondary mirror, light is brought to focus through an aperture in center of primary mirror. 

Gross Error

The errors due to faulty adjustment or improper usage of an instrument are called gross errors.

Ground

Entity in electric or electronic circuits. 

Ground State

When all electrons occupy lowest possible energy state then atom is said to be in ground state.

Group Velocity

When a number of progressive waves of slightly different wavelengths in a group superpose each other, the velocity with which the wave packet or the point of reinforcement advances in medium is called group velocity. 

Guard Ring

Extra electrode used in gas filled radiation detectors to minimize surface electric leakage currents of insulators.

Gyration

Simultaneous precession, nutation & rotation of body is called gyration of the body.

Gyro Compass

A gyrocompass is a motorized gyroscope, used widely on ships employing an electrically powered fast spinning gyroscope wheel, whose angular momentum interacts with force produced by the earth’s rotation to maintain a north – south orientation of gyroscopic spin axis there by providing as stable directional reference.

Gyroscope

If the fixed point, about which a symmetrical body is spinning about its axis, coincides with center of gravity of body, then it is known as gyroscope. The device consists of rotation, precession and nutation.