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 Physics Definitions Critical Temperature : There are metals and compounds whose resistively goes to zero below a certain temperature Tc called critical temperature. Cross Field : If a uniform electric field and a uniform magnetic field are perpendicular to each other in such a way that they produce deflections of a charged particle in the opposite direction, they are known as cross fields. Conductors : Those materials whose electrical conductivity is very high are called conductors. e.g. copper, silver, aluminum etc. Conductivity : The reciprocal of resistively of a conductor is called its conductivity.It is denoted by the symbol σ. If a conductor has resistively ρ, then its conductivity is given by; σ = 1/ρ. Cylindrical Wavefront : When the source of light is linear, all the points equidistant from the linear source lie on the surface of a cylinder. Such a wavefront is called a cylindrical wavefront. Coherent Sources : Two sources of light which emit continuous light waves of the same frequency, same wavelength and have zero phase difference or constant phase difference at all times are called coherent sources. Continuous spectra : The spectra which consist of continuous range of wavelengths are called continuous spectra. Chain Reaction : The nuclear fission which once started continues till all the atoms of the fissionable material are disintegrated is known as chain reaction. Crystalline : Solid whose constituent particles (atoms or ions or molecules) are arranged in an orderly fashion throughout in a three-dimensional pattern are called crystalline solids e.g. NaCI, KCI, sugar, diamond etc. Crystallographic Axes : The lines drawn parallel to the lines of intersection of any three faces of the unit cell which do not lie in the same plane are called crystallographic axes. Crystal Lattice : A three-dimensional array of points showing how constituent particles are arranged in a crystal is known as crystal lattice. Crystal System : The different possible geometrical shape of crystal lattice are called crystal system. Conduction Band : The range of energies i.e. band possessed by conduction band electrons is known as conduction band. Page    1    2