PHYSICS DICTIONARY - I4

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Ionosphere

It is that part of atmosphere which is ionized by solar radiation.  The region exists at 85km to 600km altitude, and contains plasma.  It influences radiation propagation to distant places on earth.

Irradiation

Process of exposing a substance to radiation beam of selective dose/energy/type is called as irradiation.

Irrational Number

Real number which cannot be written as a simple fraction.

Irreversible Change

The change which cannot be reversed or the change which on reversing the process, magnitudes of ∆Q, ∆U & ∆W are not same as in direct process is called irreversible change.

Irreversible Process

An irreversible process does not involve restriction of adjusting the external conditions by infitesimal quantities. The system need not remain in equilibrium during the process. Irreversible processes are real processes and can be carried out experimentally. All spontaneous transformations which occur in nature are real processes and hence also irreversible.

Isobaric Process

A process taking place at constant pressure.

Isobars

Nuclides of different elements having same number of nucleons are called isobars.

Isochoric Process

A process taking place at constant volume.

Isolated System

The type of system which has no interaction with its surroundings. Neither energy nor matter can be transferred to or from it.

Isomers

Atoms having same atomic number and mass number but differ from one another in their nuclear energy states and exhibit differences in internal structure are called Isomers. These nuclei are distinguished by their different life times.

 

Isospin

Neutrons and Protons are similar in all respects except charge. On this basis, Heisenberg suggested that these particles are just different manifestations of same inherent particle, the nucleon. To describe their quantum state, quantum number used was termed as isotopic spin quantum number by wigner. It is generally named as isospin or T-spin. The isospin is a vector in a three dimensional space called isospin space which has no relation to physical space.    

Isothermal Process

It is a physical change in which temperature remains constant and there is exchange of heat between system and surroundings and Boyle’s law holds good for this process.

Isotones

Nuclides of elements having same number of Neutrons but different number of Protons are called as isotones.

Isotopes

The atoms of an element, which have same atomic number but different mass numbers are called as isotopes. Number of protons inside the nucleus and number of electrons outside the nucleus of such atoms is same but number of neutrons inside the nucleus is different.

Isotopic Abundance

Refers to the existence of fraction of given isotope for a given element in its normal state.

Isotropic Medium

The medium in which measured properties are independent of direction of measurement.

(or)

Substance in which a physical property have identical values in all crystallographic directions. 

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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.