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> 

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. 

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> 

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.