physics Term - modern physic

MODERN PHYSIC
Absorptance:	The ratio of the total absorbed radiation to the total incident radiation.
Alpha particle:	The nucleus of a helium atom (two protons and two neutrons) emitted as radiation from a decaying heavy nucleus.
Antineutrino:	The antiparticle of neutrino, it has zero mass and spin ½.
Atomic mass unit:	It is equal to one-twelfth the mass of C -12 isotope of carbon, 1 amu = 1.66x 10-27 Kg.
Atomic number:	The number of protons in an atomic nucleus.
Avogadro number:	The number of molecules in a gram molecular weight of a substance, it is equal to 6.02 x 1023.
Avogadro's law:	Under the same conditions of temperature and pressure, equal volumes of all gases contain equal number of molecules.
Balmer lines:	Lines in the spectrum of hydrogen atom in visible range, produced by transition between n 2 and n = 2, n is the principal quantum no.
Baryon:	subatomic particle composed of three quarks.
Brownian motion:	The continuous random motion of solid microscopic particles when suspended in a fluid medium due to the consequence of ongoing bombardment by atoms and molecules.
Beta particle:	An electron emitted from a nucleus in radioactive decay.
Binding energy:	The net energy required to decompose a system into its constituent particles.
Ground state:	The lowest energy state of an atom.
Half-life:	The time during which half the number of atoms in the element disintegrate.
Heisenberg uncertainty principle:	It is impossible to have a particle that has an arbitrarily well-defined position and momentum at the same time.
Huygens'principle:	Each point on a light wavefront can be regarded as a source of secondary waves, the envelope of these secondary waves determining the position of the wavefront at a later time.
Isotope:	atoms of the same element with same atomic no (no of protons) but different mass no (no of neutrons).
Laser:	A device that produces coherent light by stimulated emission of radiation.
Luminosity:	The total amount of energy radiated each second from the surface of a source.
Lyman series:	A group of lines in the ultraviolet region in the spectrum of hydrogen.
Mass defect:	The difference between the sum of the masses of the individual nucleons forming a nucleus and the actual mass of that nucleus.
Mass number:	The sum of the number of protons and neutrons in a nucleus.
Mean life:	The average time during which a system, such as an atom, nucleus, exists in a specified form.
MeV:	Unit of energy, equal to 1.6 x 10-13 joules.
Mole:	The amount of a substance that contains Avogadro's number of atoms, ions, molecules, or any other chemical unit; a mole is 6.02 x 1023 atoms, ions, or other chemical units.
Nuclear fission:	The splitting a heavy nucleus into more stable, lighter nuclei with an accompanying release of energy.
Nuclear force:	The strong force that exists between the nucleons.
Nuclear fusion:	The combination of two lighter nuclei to form a heavier nucleus with an accompanying release of energy.
Nucleons:	A collective name for protons and neutrons.
Nucleus:	The central, positively charged, dense portion of an atom.
Paschen series:	A group of lines in the infrared region in the spectrum of hydrogen.
Pauli Exclusion Principle:	No two electrons in an atom can have the same four quantum numbers; thus, a maximum of two electrons can occupy a given orbital.
Photoelectric effect:	The emission of electrons in some materials when light of suitable frequency falls on them.
Photons:	A quanta of energy in light wave; the particle associated with light.
Planck's constant:	The ratio of energy to frequency, equal to 6.63 x 10-34 joule-sec.
Plasma:	A highly ionized gas composed entirely of equal number of positive ions and electrons.
Primary colors:	Three colors red, yellow and blue, which can be combined in various proportions to produce any other color.
Principle quantum number:	A quantum number that describes the main energy level of an electron in terms of its most probable distance from the nucleus.
Quanta:	Fixed amounts; usually referring to fixed amounts of energy absorbed or emitted by matter.
Quantum limit:	The shortest wavelength, present in a continuous x-ray spectrum.
Quantum mechanics:	Model of the atom based on the wave nature of subatomic particles, the mechanics of electron waves; also called wave mechanics.
Quantum numbers:	Numbers that describe energy states of an electron.
Radiant energy:	The form of energy that can travel through space; for example, visible light and other parts of the electromagnetic spectrum.
Radiation:	The emission and propagation of waves transmitting energy through space or through some medium.
Radioactive decay:	The natural spontaneous disintegration or decomposition of a nucleus.
Radioactive decay constant:	A specific constant for a particular isotope which is the ratio of the rate of nuclear disintegration per unit time to the total number of radioactive nuclei.
Radioactive decay law:	The rate of disintegration of a radioactive substance is directly proportional to the number of undecayed nuclei.
Radioactive decay series:	Series of decay reactions that begin with one radioactive nucleus that decays to a second nucleus that decays to a third nucleus and so on until a stable nucleus is reached.
Resonance:	When the frequency of an external force matches the natural frequency of the body then the body oscillates with large amplitude.
Scalar Quantity:	A physical quantity, which is described completely by its magnitude.
Spin quantum number:	From quantum mechanics model of the atom, one of four descriptions of the energy state of an electron wave; this quantum number describes the spin orientation of an electron relative to an external magnetic field.
Van der Wall's force:	General term for weak attractive intermolecular forces
Wien's displacement law:	For a black body, the product of the wavelength corresponding to maximum radiance and its absolute temperature is constant.
Zeeman Effect:	The splitting of the spectral lines in a spectrum when the source is exposed to a magnetic field.