PHYSICS DICTIONARY

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Internal Conversion

In 1914, E. Rutherford suggested that nucleus in an excited state can perform a transition to a lower state not only by emitting gamma ray but also be transmitting energy directly to electrons surrounding nucleus. Energy involved in this nuclear transition gets transmitted directly to bound electron of atom and gets knocked out of atom. Electrons like this are called conversion electrons and process is called internal conversion.

Internal Dose

Internal dose means the dose received by internal organs of a living thing (actually we are almost always concerned with doses received by humans) by a source or sources inside the body. These sources may or may not be uniformly distributed throughout the organ under consideration.

Internal Energy Function

It is thermodynamics energy function at constant volume. Mathematical representation is U=U(S, V, N);             

Internal Energy

The energy possessed by a system due to its molecular constitution and the position of the molecules.        

Internal Radiation Sources

Our bodies contain some traces of radioactive elements that expose our tissues to continuous low level radiation. This internal radiation primarily comes from Potassium-40 and Carbon-40 isotopes. However the absorbed dose and the damage to tissues due to this radiation is minimal.

Internal Work

When work is done by one part of the system on another part of the system, them the work is termed as internal work.

Interpolation

Calculation of value of a function between the values already known.

Intrinsic Semi-conductor

Semiconductor in which concentration of electrons is equal to concentration of holes.

                                             or

When conductivity in crystalline semiconductor is due to solely the breaking of covalent bonds, the substance is said to be intrinsic semi conductor.

 

Invariant Tensor

The tensor which has the same component in all coordinate systems is said to be invariant tensors.

Inverse Square Law

 It states that the radiation flux is inversely proportional to square of the distance from point source. This law is consequence of the isotropic nature of a point source because such a source is expected to radiate equally in all directions. This law is applicable to point sources only.

Ion implantation

 Surface treatment technique used in semiconductor devices fabrication and material science engineering, in which, ions are accelerated and made to penetrate the surface of a component either to impart wear resistance or to alter elemental composition of target for changing physical, chemical or electrical properties of solid.

Ion

An ion is an atom or group of atoms that is not electrically neutral but instead carries a positive or negative electric charge.

Ionic Bonding

Type of bonding formed between metallic and non-metallic elements. Atoms of metallic element easily give up their valence electrons to non-metallic atoms.

Ionic Conduction

For ionic materials, a net motion of charged ions is possible that produces a current, termed as ionic conduction.

Ionization

It is process of converting an atom into an ion by addition or removal of electrons from its orbits.

Ionization Chamber

It is a radiation detector which works on principle of collection of charge because of primary ionization of gas by incident ionizing radiation. The charge is measured by electrometer and normally operates in current mode. The detector works in ionization region out of 6 regions of gas filled detector. Ionization chambers have two distinct disadvantages when compared to proportional counters: they are less sensitive, and they have a slower response time.

Ionization Potential

Amount of energy required to remove an electron from an isolated atom or molecule to an infinite distance, usually expressed in volts. It is also known as ionization potential.

Ionizing Radiation

Fast charged particles, which deliver their energy to matter directly through many small Coulomb-force interactions along their path, are referred to as “Directly ionizing radiation”.  X-rays or Gamma ray photons or Neutrons (i.e. uncharged particles) are called as “indirect ionizing radiation”, which first transfer their energy to the matter in which they pass, for generating charged particles in a relatively few large interactions. The resulting fast charged particles then in turn deliver the energy to the matter through Coulomb force interaction.    

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Induction Heating

It is process of heating metals without physical contact, which uses high frequency electricity to heat materials that are electrically conductive. A source of high frequency electricity is used to drive a large alternating current through a coil. The passage of current through this coil generates a very intense and rapidly changing magnetic field in the space within the work coil. The work piece to be heated is placed with inverse alternate magnetic field. The alternating magnetic field induces a current flow in the conductive work piece. Tremendous currents flow in work piece and are called as eddy currents.

Inelastic Collision

Collision in which only momentum is conserved but not kinetic energy; the colliding bodies undergo deformation.

Inertia

It is inherent property of a body which resists undergoing a change in velocity.

Inertial Frame

The frame with respect to which an un-accelerated body appears un-accelerated is called as inertial frame. In other words, frames which are at rest or in uniform translatory motion relative to one another are inertial frames.

                                               (or)

 Frame in which Newton’s first law is true.

Inertial Mass

The inertial mass of a body may be defined as the ratio of the inertial force acting on the body to the acceleration acquired.

Infrasonic Waves

Sound waves of frequency lower than audible limit are called infrasonic waves.

Inhomogeneous System

A linear system of equation AX=B is called inhomogeneous if B≠0.

Instrumental Error

The error is inherently present in the instrument. This error can be eliminated by replacing the instrument with a similar one or by using a different method for the measurement.

Insulation Resistance

Resistance offered by insulation between two electrodes. Unlike linear resistance, insulation resistance depends on many parameters like surface resistivity, purity of insulation, porosity etc.

Insulator

A non –metallic material that has a filled valence band at 0 K and a relatively wide energy band gap. Consequently, the room temperature electrical conductivity is very low, less than about 10^-10 Ohm.m^-1.

Intensity of Radiation

The intensity of radiation at a point is equal to the radiant energy incident per second on unit area of a surface when the surface is held normal to the incident radiation.

Intensity of Sound

It is the amount of energy passing through a square meter every second. It is measured in watts per square meter. The intensity of sound is related to its amplitude. If amplitude doubles, the intensity is four times greater. Increasing intensity of sound increases its loudness.

Intensity (Sound)

Average rate of transfer of energy per unit area, the area being perpendicular to the direction of propagation of sound.

                                                 or

Amount of sound energy crossing per second per unit area normal to the direction of sound wave.       

Inter Diffusion

Diffusion of atoms of one metal into another metal is called inter diffusion.

Interfacial Defect

Interfacial defects are boundaries that have two dimensions and normally separate regions of material that have different crystal structures and/or crystallographic orientations.

Interference of Light

The change in uniform distribution of light intensity in a medium due to superposition of two light waves of nearly equal amplitudes, but of same frequency travelling in same direction, is called interference of light.

(or)

Formation of maximum intensity at some points and minimum intensity at some other points by two identical light waves travelling in same direction is called interference of light.

Interferometer

An instrument that measures wavelength, minute distances, refracting of lenses, thickness etc by comparison of interference patterns generated by splitting and reuniting of a beam of light passed through a lens.  

Intermolecular Force

The term 'intermolecular forces' is used to describe all the forces, both attractive and repulsive, between groups of neutral molecules or atoms. Intermolecular forces are caused by the attractions and repulsions between the charged particles that make up the atoms in molecules. They are separated into two groups; short range and long range forces. Short range forces come into picture when the centers of the molecules are separated by three angstroms (10^-8 cm) or less. Short range forces tend to be repulsive, where the long range forces that act outside the three angstroms range are attractive. Long range forces are also known as Vander Waals forces. They are responsible for surface tension, friction, viscosity and differences between actual behavior of gases. Intermolecular forces are responsible for most properties of all the phases. 

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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.

(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 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.  

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.