PHYSICS DICTIONARY

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Latitude

A measure of relative position north or south on the Earth's surface, measured in degrees from the equator, which has latitude of 0°, with the poles having latitude of 90° north and south.


Lattice Vector

Unit cell in a crystal structure is defined by axial lengths called as lattice vectors.


Lattice Constant

The magnitude of lattice vector in a unit cell is called as lattice constant.


Lattice Energy

Energy required for separation of the ions of a crystal to an infinite distance from each other.


Lattice Parameters

The unit cell geometry is completely defined in terms of six parameters; the three edge lengths and three inter axial angles which were referred to as lattice parameters.


Lattice

Three dimensional array of points which coincide with atomic positions is called as Lattice.


Laue Method

In this method, a single crystal is held stationary in a beam of continuous wave length X-ray radiation. Various crystal planes select the appropriate wave length for constructive interference, and a geometric arrangement of bright spots is obtained on a film.


Law of Conservation of Angular Momentum

When no external torque acts, then angular momentum of rotating system remains conserved.


Law of Conservation of Energy

Energy can neither be created nor destroyed, but it can be transformed from one form to other.


Law of Conservation of Linear Momentum

When no external force acts upon a system, then the vector sum of momentum of all bodies of that system remains constant.


Law of Equipartition of Energy

The law has been deduced by James Clarke Maxwell. As per this law “total kinetic energy of a dynamical system is equally divided among all its degrees of freedom and it is equal or ½ KT per degree of freedom.


Law of Kinetic Friction

Kinetic friction is independent of area of contact; kinetic friction is independent of relative speed between two contact surfaces and is directly proportional to normal force.


Law of Radioactive Disintegration

In any radioactive substance, the number of atoms disintegrating per second is directly proportional to the number of atoms present.


Law of Static Friction

It states that static friction is independent of area of contact, depends on nature of surfaces in contact & maximum value is directly proportional to normal force.


Laws of Reflection

i)      Incident point, reflected point and normal drawn to plane of reflection are coplanar.

ii)    Angle of reflection is equal to angle of incidence.


Laws of Refraction

i)      Incident point, refracted point and normal drawn to plane of refraction are coplanar.

ii)    The relationship between angle of incidence (ØI) and angle of refraction (ØR) is expressed by    =   ;  n2 &n1 are refractive indices of two medium.


Least Count

It is the least amount of a quantity that can be measured accurately with an instrument.


Leak Rate

The real leak rate is quantity of gas flowing per unit time into the system. The leak rate of given system is expressed as pressure rise in a given time and for specific volume.

                                                 (or)

 The time required for a given quantity of gas to flow into the system.


Least Energy Principle

The principle that the potential energy of a system in stable equilibrium is minimum relative to that of nearby configurations. 


Least Squares Method

A method for determining the best value of an unknown quantity relating one or more sets of observations or measurements especially to find a curve that best fits a set of data. It states that sum of squares of deviations of the experimentally determined value from its optimum value should be minimum.  

                                                  or

A statistical technique to determine the line of best fit for a model. The least squares method is specified by an equation with certain parameters to observed data. This method is extensively used in regression analysis and estimation.


Leavo Rotatory

These are substances which rotate the plane of polarization of incident plane polarized light in the anti-clock wise direction when seen in direction of light are called Leavo rotatory. 

PHYSICS DICTIONARY

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Kilowatt

It is unit of electric power.


Kilowatt hour (KWH)

It is the unit of electrical energy


Kilowatt Hour

The kilowatt hour is a unit of energy equivalent to one kilowatt of power expended for one hour of time. An energy dissipation of 1 KWH represents 3,600,000 Joules.


Kinematics

Branch of mechanics that studies motion of a body or a system of bodies without considering its mass or forces acting on it.


Kinetic Energy

Energy associated with motion is called “kinetic” energy, from the Greek verb “kinein”, mean “to move”.


Kinetic Theory of Gases

They are set of postulates, by which physical properties of gases can be easily explained.


Kirchhoff’s First Law

It states that at any junction of several circuit elements, the sum of currents entering the junction must be equal to sum of currents leaving it.


Kirchhoff’s Second Law

The algebraic sum of charges in potential around any closed resistor loop must be zero.


Kirchoff’s Law (Thermal Radiation)

The ratio of emissive power to the absorption power is same for all bodies at a certain temperature for a certain wavelength and it is equal to emissive power of a perfectly black body at that temperature and wavelength.


Klystron

Device invented at Stanford University in 1937. It is a type of vacuum tube used as an amplifier / oscillator for UHF and microwave signals. A klystron tube makes use of speed controlled streams of electrons that pass through resonating cavity. Electrons in a klystron are accelerated to controlled speed by application of several hundred volts. As electrons leave the heated cathode of tube, they are directed through a narrow gap into resonating chamber, where they are acted upon by RF signal. The electrons bunch together and are directed into one or more additional chambers that are tuned at or near the tubes operating frequency.


Knot

Unit of speed equal to one nautical mile per hour.


Kronig Penny Model

 It is a simplified model for an electron in one dimensional periodic potential.


Kundt’s Law

Optical absorption bands of a solution are displaced toward the red when its refractive index increases because of changes in composition or other causes.


Kundt’s Tube

It is an acoustical apparatus, invented by German Physicist, August Kundt  (1866 ). It is used to find speed of sound in a solid rod or gas.


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.