PHYSICS DICTIONARY

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

<Prev>                   <Next>

Macroscopic

Large enough to be perceived or examined by naked eye.

(or)

Anything which is considered for bulk of matter as a whole.

Magnetic Dipole

An object such as current loop, an atom or a bar magnet, that experiences torques due to magnetic forces. 

Magnetic Field Intensity

It is measured by force acting on unit magnetic pole. The field intensity is also specified by number of lines of force intersecting unit area normal to the field, equal numerically to field strength in Oersted.

Magnetic Induction

When any substance is subjected to a magnetic field, the magnetic flux per unit area taken perpendicular to direction of the flux is called magnetic induction.

Magnetic Permeability

Property of materials modifying the action of magnetic poles placed there in and modifying the magnetic induction resulting when the material is subjected to a magnetic field or magnetizing force. The permeability may be defined as ratio of magnetic induction in the substance to magnetizing field to which it is subjected.

Magic Number

When the number of protons is 2,8,20,28,50,82 or the no. of neutrons is 2,8,20,28,50,82,126 the nucleus is observed particularly stable and these numbers are referred to as magic numbers. Nuclei in which the no. of protons as well as no. of neutrons is equal to magic number belong to most stable group of nuclei.

Magnetic Dipole

Small bar magnet composed of north and south poles.

Magnetic Flux Density

 Also called as magnetic induction represents magnitude of internal field strength with in a substance that is subjected to an external magnetic field.

Magnetic Moment

A vector quantity that is a measure of the torque exerted on a magnetic system when placed in magnetic field and that for a magnet is the product of distance between its poles and the strength of either pole. It is usually created by electric current flowing in wire or with orbital motion of spinning electron caused intrinsic magnetic moment.

Magnetic Potential

Magnetic potential at a point is measured by the work required to bring unit positive pole from an infinite distance (zero potential) to the point.

Magnetic Resonance Imaging (MRI)

The use of magnetic fields and radio waves (instead of the X-rays employed in the CT scan) to visualize body structures and how they function. The powerful magnet, large enough to enclose the body, forces the atomic nuclei in most material such as soft tissue to align themselves with the magnetic field. Radio waves are aimed at the selected area to excite the atoms which, when the waves are stopped, emit signals that are converted to computer-generated pictures.

Magnetic Susceptibility

 It is a dimension less quantity and is proportionality constant between magnetization & applied external magnetic field.   

Magnetism

Old study which deals with simplest sources of magnetic fields, the permanent (bar) magnets. Magnets and magnetic fields are dealt without considering electrical charges in motion.

 

Magnetization

The phenomenon of formation of magnetic dipoles inside material due to application of uniform magnetic field.

(or)

The total magnetic moment per unit volume of material is called as magnetization.   

Magnetoresistance

It is property of crystal to change its electrical resistance when a magnetic field is imposed on it.

Magnetometer

An instrument used for measuring the intensity or direction of a magnetic field, especially the earth’s magnetic field.

Magnetostriction

The phenomenon of change in shape and density of a substance, especially a ferromagnetic substance, when exposed to a magnetic field is called magnetostriction. 

Magnification

The apparent enlargement of an object by an optical instrument is called magnification.

PHYSICS DICTIONARY

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

<Prev>                   <Next> 

Laboratory Frame of Reference

Frame of reference, the centre of the coordinate system which lies on the laboratory in which experiment is done.

                                            or

The frame of reference in which laboratory measurement devices are at rest is usually referred as laboratory frame of reference.

Lambda Particle 

It is a elementary particle, which is neutral and discovered in cloud chamber experiments, having life time of order 10^-10 sec and has rest energy of about 1115 MeV. It doesn’t conserve parity and has spin- 1/2. It belongs to class of Hyperons.

Lambda Point

When Helium is cooled to a critical temperature of 2.17 K (called its lambda point), a remarkable discontinuity in heat capacity occurs, the liquid density drops, and a fraction of the liquid becomes a zero viscosity "superfluid". Super fluidity arises from the fraction of helium atoms which has condensed to the lowest possible energy. In simple terms, the Lambda point is the temperature below which normal fluid Helium (Helium-I) transitions to super fluid Helium-II 

Lambert

The unit of brightness or luminance in CGS system, equivalent to brightness of a perfectly diffusing surface that emits or reflects one Lumen per square centimeter. 1Lambert (L) = 1/π Candela/cm².

Lambert’s Law of Absorption

Each layer of equal thickness absorbs an equal fraction of light which traverses it.  

Lambert’s Law of Illumination

The illumination of a surface on which light falls normally from a point source is inversely proportional to square of distance of surface from source. If the normal to surface makes an angle with direction of rays, illumination is proportional to cosine of that angle.

Lambert’s law

Law which describes the attenuation of intensity of electromagnetic wave inside a medium is called as Lambert’s law.

 

Laminar Flow

It is type of fluid flow in which the fluid travels in regular paths. In laminar flow, sometimes called streamline flow, the velocity, pressure and other flow properties at each point in the fluid remain constant.

Laplace Equation

It is a mathematical equation which gives the divergence of the gradient of a function. Laplace’s equation is a  second-order partial differential equation widely useful in physics because its solutions (known as harmonic functions) occur in problems of electrical, magnetic, and gravitational potentials, of steady-state temperatures, and of Hydrodynamics. The equation was discovered by the French mathematician and astronomer Pierre-Simon Laplace (1749–1827).

Larmor’s Precession

When an atom is placed in an external magnetic field, the electron orbit precesses about the direction of external magnetic field. There will be change in angular velocity of electron without any change in form of orbit.

LASER

It is acronym for Light Amplification by Stimulated Emission of Radiation. It is that device which produces an intense, monochromatic, coherent and unidirectional light beam is obtained. It was discovered in 1950, by Town & Shallow. LASER produces a light beam in which all the waves are of same frequency.     

Latent Heat (Heat of Transformation)

The amount of energy per unit mass that must be transferred as heat when a sample completely undergoes phase transition.

(or)

The amount of heat needed to change the state of a given substance without any change in temperature.

Latent Heat of Fusion

The quantity of heat necessary to change one gram of solid to liquid without change of temperature, measured as calories per gram.

Latent Heat of Sublimation

The heat absorbed by one gram or unit mass of a substance in the process of changing from a solid to a gaseous state, at a constant temperature and pressure.

Latent Heat of Vaporization

The quantity of heat necessary to change one gram of liquid to vapor without change of temperature, measured as calories per gram.

Lateral Chromatic Aberration

The difference in length of red and violet images for an object at finite distance is called lateral chromatic vibration. 

PHYSICS DICTIONARY

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

<Prev>                   <Next> 

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.

PHYSICS DICTIONARY

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

<Prev>                   <Next> 

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.