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
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.
(or)
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.
Hoppers
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.
Hue
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.
Hum
To emit
continuous low driving sound like that of speech sound when prolonged.
Humidity
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
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.
Hydro-Electricity
Electricity
generated by using hydropower. It is the electricity produced through the use
of gravitational force of falling water.
Hydro-Carbons
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 nuclear
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.
Hydrostatics
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.
Hygroscopic
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.
Hypermetropia
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.
Hyperbola
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.
Hyperons
They come under
Baryons which are extremely unstable and heavier particles.
Hypothesis
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.
Hysteresis
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.
