PHYSICS DICTIONARY

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Kaon

Any of three unstable mesons, one having charge +1 and a mass of 966 electron masses, and two being electrically neutral, with a mass 974 electron masses. Their half-life is approximately 10^-8 seconds, and they decay through the weak force. 

Kellner’s Eye Piece

It consists of two plano-convex lenses of same focal lengths and separated by a distance equal to the focal length of either lens.

Kelvin Planck Statement

Conversion of total heat energy into work is impossible.

Kelvin

It is the unit of thermodynamic temperature; it is the fraction 1/273.16 of the thermodynamic temperature of triple point of water.

Kelvin’s Statement of Second Law of Thermodynamics

It is impossible to get a continuous supply of work by cooling a body to a temperature lower than that of coldest of its surroundings.

Kelvin’s Thermodynamic Scale

The ratio of two temperatures measured on absolute scale is equal to the ratio of heat absorbed to the heat rejected by a reversible engine working between these temperatures.

Kepler’s First Law

Every planet revolves round the sun in an elliptical orbit with the sun at one of its foci. This law is known as law of orbits.

Kepler’s Second Law

The radius vector joining a planet to the sun sweeps equal areas in equal intervals of time.

                                                  (or)

The areal velocity of a planet round the sun is constant. This law is known as “law of areas”.

Kepler’s Third Law

Square of the time period of revolution of a planet round the sun is directly proportional to the cube of mean distance of the planet from the sun.

Kerma

Kerma is an acronym of kinetic energy released in a medium per unit mass. It is defined as the total kinetic energy of all the charged particles liberated by uncharged particles per unit mass of the target material. Kerma is generally measured in the same units that are used for absorbed dose, that is, J/kg or Gray. Kerma is not independent of the type of the target material and therefore must always be defined with respect to the medium.

Mathematically, it is written as the quotient of the charged particle’s kinetic energy E_kin and the mass of the material dm, that is K= dE_kin/dm.

or

It is one of the quantities to describe the interaction of ionizing radiation with matter. It is defined as expectation value of energy transferred to charged particles per unit mass at a point of interest, including radiative loss of energy but excluding energy passed from one charged particle to another.

Kilo Calorie

The amount of energy required to increase the temperature of one kilogram of water by 1 ^oC.

Kilogram

The Kilogram is the usual scientific unit of mass. The standard Kilogram is the mass of a particular cylinder of Platinum Iridium alloy kept near Paris in France. All masses that are measured are compared with this.

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Josephson Junction

It is a device formed from sandwiching very thin insulator layer between two superconductors. There is continuous flow of electric current without influence of any external voltage in such devices, the effect which is named as Josephson Effect which was named after British scientist Brian Josephson who proposed it in 1962.

Joule Kelvin Effect

In physics, the Joule-Thomson effect or Joule-Kelvin effect describes the increase or decrease in the temperature of a real gas when it is allowed to expand freely at constant enthalpy (which means that no heat is transferred to or from the gas, and no external work is extracted). For each gas, there is a temperature of inversion above which the change is positive and below which it is negative.

Joule

It is SI unit of energy.

Joule’s Law of Heating

When a current of I amperes passes through a circuit of resistance R ohms for a time of t seconds then the heat produced is given by the relation H=I²Rt joules; The relation is known as the joule’s law of heating.

Joules Expansion

When a definite mass of a gas is expanded such that the external work done by the gas or on the gas is zero, neither the gas absorbs nor rejects any heat, then the expansion of gas is known as Joules expansion.

Joules Law (Gases)

Internal energy of an ideal gas only depends on its temperature ‘T’ and doesn’t depend on its volume ‘V’ and pressure ‘P’.

Joule-Thomson Effect

When a gas passes through an insulated porous plug from a constant high pressure to a constant low pressure, there is change in its temperature. This effect is called Joule-Thomson’s effect and the processes are called adiabatic throttling process.

Junction Diode

It is semiconductor device consisting of a single PN junction. It has a highly non linear current – voltage characteristic and is often used as a rectifying element.

Jupiter

Jupiter is the fifth planet from the Sun and by far the largest. Jupiter is more than twice as massive as all the other planets combined. The mass of Jupiter is 318 times that of Earth. It has orbit of 778,330,000 Km (5.20 AU) from Sun; Diameter of 142,984 km (equatorial); Mass of 1.900 x 10²⁷ Kg.

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Ice Point

The temperature, equal to 0 ^oC, at which pure water and ice are in equilibrium in a mixture at 1 atmosphere of pressure is called as ice point. Ice point is most important fixed point for defining temperature scales and for calibrating thermometers.

Ideal Fluid

Fluid is called as ideal fluid if it has zero viscosity, zero compressibility and its flow should be irrotational and steady.

Ideal Gas

It is the gas which perfectly obeys Boyle’s law and Charles law.

Identical Particles

If two particles are identical, no observable effects whatever can arise from interchanging them.  More precisely, all observable quantities must remain unaltered if the position, momentum and other dynamical variables such as spin of first particle are interchanged with those of second particle. 

Illumination

Process of focusing light on to something to make it visible or bright is called as illumination.

Image

It is an optically formed duplicate counterpart or other representative reproduction of an object, especially an optical reproduction formed by lens or mirror.

                                                 or

Optical appearance or counterpart produced by light from an object reflected in mirror refracted through lens.   

Imaginary Number

It is mathematical quantity of the form iX, where ‘X’ is real number. ‘I’ is unit imaginary number and   i² = -1.

Impedance

Characteristic of alternating current circuit made of two components: “resistance” and “reactance”,  which is a measure of total opposition to current flow. It is usually represented as Z= R+iX, where ‘R’ is ohmic resistance and ‘X’ is reactance.

Impulse

It is defined as change in momentum when large force acts for short time interval.

Impurity Diffusion

Process, where by atoms of one metal diffuse into another is termed as impurity diffusion.

 

Incandescence

Property of hot body which emits visible electromagnetic radiation by virtue of its temperature.

Independent Variable

Variable who values are independent of changes in the values of other variables. 

                                                          Or

Variable whose value determines the value of other variables.

Indirect Band Semiconductor

The semiconductor in which an electron in  conduction band (minimum) cannot fall to valence band maximum but must undergo change in momentum, which may be caused by traps in energy gap. Generally, the energy difference is given up as heat to lattice.

Indirectly Ionizing Radiation

It Comprises neutral particles (such as photons, X-rays, neutrons) that deposit energy in the absorber through a two-step process as follows: In the first step a charged particle is released in the absorber (photons release either electrons or electron/positron pairs; neutrons release protons or heavier ions). In the second step, the released charged particles deposit energy to the absorber through direct Coulomb interactions with orbital electrons of the atoms in the absorber.

Induced Charge

When a charged object is put close to a neutral object, charges are induced on the surface of the neutral object and are called induced charges.

Inductance

The energy density is proportional to the square of the magnetic field strength, which is in turn proportional to the current flowing through the coiled wire, so the energy stored in the inductor must be proportional to square of the current. The constant of proportionality is called as inductance. The unit is joules per ampere squared, abbreviated as Henry.

Induction

Concept discovered by Faraday in 1831. Any electric field that changes over time will produce magnetic field in space around it                                              

                                                               or

any magnetic field that changes over time will produce an electric field in the space around it.

Induction Coil

The induction coil was invented in the late nineteenth century as a source of high voltage for laboratory experiments. Induction coil is a device for converting low-voltage direct current (DC) into high-voltage alternating current (AC). It is a single coil of conductive material, often surrounding a metallic core, designed to establish a strong magnetic field around the coil. Changes in the current flow through the coil cause fluctuations in the magnetic field that induce a voltage across the coil. Induction coils are used for many purposes, especially as spark coils for firing spark plugs in automobile engines and starting oil burners.

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Galaxy

A collection of stars, gas and dust bound together by gravity. The Milky Way galaxy contains our solar system.

Galilean Telescope

Galileo in 1906, constructed a telescope which provides an erect image of an object only with help of two lenses. It consists of converging lens serving as objective and diverging lens as eyepiece. The eye piece is situated in front of focal point of objective, at a distance from focal point equal to focal length of eyepiece. It has disadvantage of narrow field of view.

Galilean Transformation

The consequences of research work of Galileo on the motion of projectile led him to formulate Galilean transformations. These are used to relate the motions which are observed by two observers in two different observers in two different inertial frames. As per Galilean transformation, the motion of a particle projected at any angle may be derived from the motion of particle thrown vertically upward.

Galvanic Cell

Device used to convert chemical energy into electrical energy. Galvanic cell can be used as a source of electric current due to spontaneous reaction occurring within the cell.

Galvanometer

Instrument used to indicate presence, direction or strength of small electrical current. Current flowing through the galvanometer passes through a coil near a magnetized needle on a pivot; the strength of current in coil regulates the strength of magnetic field that displaces the needle. Galvanometers can be used directly as ammeters and are core elements of many ohmmeters.

Gamma Ray Spectrometer

Instrument used for quantitative study of energy spectra of gamma ray sources. It reads out distribution of intensity of gamma rays with energy thus revealing nature of radioactive nuclides, amount of activity etc.  

Gamma Rays

Electromagnetic radiation emitted from nucleus as a result of transition of nucleons between energy states inside nucleus.

                                                      or

Electromagnetic radiation emitted in annihilation reaction between matter and antimatter.

Gamma Spectroscopy

It is a radio chemistry measurement method which determines the energy and count rate of gamma rays emitted by radioactive substances.

Gas Amplification

Multiplication of charge carriers in gas filled detectors produced by primary ionization in high E/P value, by secondary ionization. The gas amplification is characterized by first Townsend coefficient. It represents the average number of electron – ion pairs formed per unit length due to motion of an electron along the electric field direction.

Gas Constant

See universal gas constant.

Gas Degeneracy

The deviations from perfect gas behavior exhibited by Bose Einstein gas is termed as gas degeneracy.

Gas Multiplication

Term related to gas filled radiation detectors. Phenomenon of multiplying charge carriers created due to primary ionization of gas by incident radiation in the gas. The charge carriers i.e. electrons drift towards the anode at positive potential. The electrons gain momentum and get accelerated to high energies which can transfer to other atoms resulting in emission of further electrons called secondary electrons. The phenomenon of multiplication of charge in gas under influence of external high voltage is called gas multiplication.    

Gas

The gaseous state above critical temperature of substance is called as gas.

Gauge Pressure

When pressure is measured either above or below atmospheric pressure as an arbitrary datum then it is called as gauge pressure.

Gauss Eye Piece

It is similar to Ramsden’s eyepiece with the only difference that there is a thin glass plate inclined at 45^o in between the two lenses. Hence cardinal points of gauss eye piece are located at some positions as that of Ramsden’s eye piece.

Gauss’s Theorem of Electrostatics

The net outward electric flux through any closed surface of any shape in an electric field is equal to 1/ε_o times the total charge contained within that surface. 

Gauss’s Theorem of Magnetism

The total magnetic flux through any closed surface is always zero.

Gaussian Distribution

If the number of events is very large, then the Gaussian distribution function may be used to describe physical events. The Gaussian distribution is a continuous function which approximates the exact binomial distribution of events. The Gaussian distribution is also commonly called the "normal distribution" and is often described as a "bell-shaped curve".

It is a distribution of the values of a variable that when plotted, produces a symmetrical, bell-shaped curve that rises smoothly from a small number of cases at each extreme to a large number of cases in the middle.