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Homogenous System

A physical system in which components do not differ from one another in composition or properties and are not separated from one another by surfaces of separation. All the physical characteristics of a homogenous system are either identical in all its components or change continuously from point to point.

Hooke’s Law

As per this law, for most metals that are stressed in tension and at relatively low levels, stress & strain are proportional to each other.


Within the elastic limit, stress is directly proportional to strain. The proportionality constant is known as modulus of elasticity or coefficient of elasticity of the body.


They are materials in which hopping conduction takes place. They are also called electron transfer materials.

Horse Power

It is unit of power. A horse transfers 750J of energy per second. This is a power output of 750W. One horse power is 750W.      

Hubble Constant

In 1929, Edwin Hubble announced that almost all galaxies appeared to be moving away from us. This phenomenon was observed as red shift of a galaxies spectrum. This red shift appeared to have a larger displacement for faint, presumably for such galaxies. Hence the farther a galaxy, the faster it is receding from earth. Hubble constant ‘H’ is given by H=v/d;  ‘v’ is galaxies radial outward velocity; ‘d‘ is galaxies distance from earth.

       Hubble constant is one of the most important numbers in cosmology because it may be used to estimate the size and age of the universe. It indicates the rate at which the universe is expanding.


The attribute of color by virtue of which it is discernible as red, green etc and which is dependent on its dominant wave length and independent of intensity or lightness.


To emit continuous low driving sound like that of speech sound when prolonged.


Amount of water vapor in air is called as humidity.

Humphrey Series

Spectrum of wavelength formed due to jumping of electrons from higher orbits to sixth orbit. The spectrum falls in far infra red region.

Hund’s Rule

Hund’s rule of maximum multiplicity describes the order in which electrons fill sub shells. Every orbital in a sub shell is singly occupied with one electron before any one orbital is occupied. All electrons in singly occupied orbital have same spin.

Huygens Eye Piece

Arrangement of lenses in which first Plano convex lens of focal length three times the focal length of second plano convex lens and the separation between the two lenses is two times the focal length of second lens.

Huygens Principle

Every point on a propagating wave front serves as source of spherical secondary wavelets, such that wave front at some later time is re-envelope of these wavelets. If the propagating wave has a frequency ‘ f ’ and is transmitted through the medium at a speed ‘ v ’, then secondary wavelets will have same frequency and speed.

Hybrid Orbitals

See hybridization


The Mixing of orbitals of valence shell of same atom to form new orbitals with same energy and shape. The resulting orbitals are called hybrid orbitals.

Hydraulic Press

Machine which uses Pascal’s theory for industrial purposes where a larger pressure is required for compressing metals in to thin sheets. They are also used to crush or punch the material into a thin sheet.


Electricity generated by using hydropower. It is the electricity produced through the use of gravitational force of falling water.


They are simplest organic compounds containing only Carbon and Hydrogen. They can be straight chain, branched chain or cyclic molecule.

Hydrogen Bomb

It is also called as thermo nuclear bomb whose enormous explosive power results from an uncontrolled, self sustaining chain reaction in which isotopes of Hydrogen combine under extremely highly temperatures to form Helium in a process known as ombine under extremely highly temperatures to form hecontrolled , self sustaining chain reaction in wnuclear fusion. The high temperatures are achieved by detonating atomic bomb. The presumable structure is as follows:

At its center is an atomic bomb; surrounding it is a layer of lithium deuterium  around it is a tamper, a thick outer layer , frequently of fissionable material, that holds the contents together in order to obtain a larger explosion. Neutrons from atomic explosions cause lithium to fission into Helium, Tritium and energy. The atomic explosion also supplies temperatures needed for subsequent fusion of Deuterium with Tritium, and of Tritium with Tritium (50,000,000 & 400,000,000 oC) respectively. Enough neutrons are produced in fusion reactions to produce further fission in the core and to initiate fissions in tamper.

Hydrogen Bond

The bond occurs between molecules in which one end is a Hydrogen atom. The Hydrogen atom is covalently bonded to a relatively large atom such as Nitrogen, Oxygen or Fluorine to form a permanent dipole.  


Branch of fluid dynamics which studies pressures exerted by fluids at rest.

Hygroscope or Hygrometer

Instrument which indicates the relative humidity or absolute humidity of air.


Property of absorbing water vapor in air and retaining it.

Hyper Charge

It is physical quantity which is twice the difference between actual charge and iso-spin component of a particle.


It is type of vision defect of eye in which image of nearby object is formed behind the retina. The objects at closer distance seem blurred and clear vision when looking objects in longer distance.


For two given points, the foci, a hyperbola is locus of points such that the diff between distances to each focus is constant. 

Hyperfine Structure

Interaction of spin orbit coupling splits the atomic levels & gives fine structure. These split levels further get split by J-I coupling and leads to hyperfine structure in spectral lines. The hyperfine levels are due to interaction of nuclear and magnetic moments. 


They come under Baryons which are extremely unstable and heavier particles.


It is a statement that explains or makes generalizations about a set of facts or principles, usually forming a basis for possible experiences to confirm its viability.


The irreversible magnetic flux density (B) versus applied magnetic strength (H) behavior found for ferromagnetic and ferrimagnetic materials. A closed B-H loop is formed upon field reversal. 

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