Complex Body - A solid body which, above a critical stress, flows at a rate proportional to the excess of stress over the yield stress.

Compound Nucleus - In Bohr's theory of nuclear reactions a highly excited atomic nucleus, of short lifetime, formed as an intermediate stage in an induced nuclear reaction.

Compressibility - Of an isotropic material the reciprocal of the bulk modulus. It is the fractional change in volume produced by unit change of pressure.

Compressible Flow - Fluid flow in which changes in fluid velocity are accompanied by changes in fluid pressure and density.

Compressional Wave - In an elastic medium: a form of elastic wave motion in which the particles of the medium are displaced in a direction parallel to the direction of propagation.

Compression Efficiency - Of a compressor the ratio of the required to compress all the vapour delivered by the comp adiabatically and reversibly, to the actual work supplied vapour by the piston or blades of the compressor.

Compression Ignition - Ignition, as in an internal combustion which the charge in the cylinder is ignited by the  compression alone.

Compression Test - A test for the ductility and malleability of a pure metal bars in which a test .piece of given dimension compressed by a specified amount.

Compressor - A device for raising the pressure of a gas.

Compton Effect - The elastic scattering of a photon by an electron the electron can be considered to be free and stationary. It is important mode of scattering for X-and y-rays.

Compton Wavelength - The de Broglie wavelength, given by where h is Planck's constant m0 the rest energy of the electron and c the speed of light, which appears in the expression for the increase in wavelength arising from the Compton effect. This increase is (h/m0c) (l-cosΦ)  where Φ is the angle of deflection  the scattered photon.

Condensation - The process of forming a liquid (the condensate) from  its vapour.

Condensation Number - The ratio of the number of molecules condensing on a solid surface to the total number falling upon it. It is about ten times larger for dropwise than for filmwise condensation.

Condensed Phase - The solid or liquid state.

Condenser - (1) A former term for a capacitor. (2) an apparatus used condensing vapour obtained during distillation. (3) A chamber into which the exhaust steam from a steam engine or turbine delivered, to be condensed by the circulation or introduction cooling water. (4) Lens designed to control the intensity angular aperture of a beam of light in a optical or electron­-optical system; or a mirror designed to perform the same function in an optical system.

Conductance - (1) Of a conductor or an electrolyte: the real part of the admittance, i.e. the reciprocal of the resistance. (2) Of a dielectric: the quotient of the conduction current by the applied voltage. (3) Of a component of a vacuum system for a given gas the through put of the gas divided by its partial pressure difference       across the component, under steady conditions.

Conductance, Equivalent - The electrical conductance of a solution which contains 1 g-equiv weight of solute at a specified concentration, measured when placed between two electrodes separated by 1 cm.

Conductance, Mutual - A vacuum tube coefficient concerned with the effect of grid voltage on plate current. It is given by(   dip/deg)Ep constant where ip is the plate current, eg the grid voltage, and Ep the plate voltage. The mutual conductance is also known as the transconductance.

Conductance, Specific - An obsolescent term for electrical conductivity.

Conduction - The transmission of electrical, thermal or acoustic energy via a medium, without movement of the medium itself as such.

Conduction Band - A partially-filled energy band in a solid in which the electrons can move freely, thereby allowing the material to carry an electric current. Although, the term is often applied to metals, the distinction between the conduction and other bands is of greatest importance in connection with semiconductors and insulators.

Conduction Electron - An electron which is free to move under the influence of an external field, e.g. an electron in the conduction band of a solid. Sometimes referred to as a free electron.

Conductivity, Electrical - Of a material: the conductance, at a specified temperature, between the opposite faces of a cube of the material having sides of unit length. It is the reciprocal of volume resistivity. Formerly known as specific conductance.

Conductivity, Thermal - Of a material: the quantity of heat flowing per second per degree across unit area of the material (the plane of the area being perpendicular to the temperature gradient), for unit temperature-gradient.

Conductor - A substance through which electrical or thermal flows easily.

Cone Of Silence - A cone in which the radiation intensity of an omnidirectional aerial vanishes.

Conical Refraction - An effect observed in biaxial crystals whereby a ray incident in a particular direction is spread, on refraction, into a hollow cone of rays.

Conjugate Foci - Of an optical system: two points such that light rays emanating from one will be brought to a focus at the other.

Conjugate Planes - Of an optical system: planes perpendicular to the axis of the system such that any object point near the axis in one plane will be imaged in the other.

Conjugate Points - Of an optical system: the points of intersection of      the principal planes of the system with the optic axis.

Conservation Laws - For nuclear processes: "laws" expressing the constancy of certain quantitative features of a system of nuclear particles (including photons) when the system undergoes a change. They may be exact, i.e. believed to be exact and true for interactions in general, e.g. the total energy of a system (including the energy equivalent of the rest mass), or approximate, i.e. based on certain approximate features of the forces responsible for the interaction, e.g. based on the assumption that all the relevant forces are central.

Conservation of Angular Momentum - A principle stating that, in the absence of external forces, the angular momentum of a system is conserved if both orbital and spin angular momentum are taken in account.

Conservation of Charge - A principle stating that electric charge can neither be created nor destroyed. Its validity is essential for the whole of Maxwell's field theory, and in the context of relativistic.

Conservation of Energy - A principle stating that the total quantity of energy in a closed system is constant. Where the conversion of mass to energy, or vice versa, takes place, the energy of the system is understood to include the energy equivalent of all the mass in the system, according to the equation E = mc2 where E is the energy, m the mass and c the speed of light. Thus the principles of the conservation of energy and the conservation of mass are no longer to be considered as distinct.

Conservation of Linear Momentum - A principle stating that, in the absence of external forces, or if such forces cancel out, the vector of the linear momentum of a system remains constant in magnitude and direction and is not affected by processes occurring within the system.

Conservation of Mass - A principle stating that the total mass in a closed system is constant. The principle is valid in all conditions only when energy is also taken into account.

Conservative Field or Force - A field of force in which the total energy of a moving body is constant. In such a field the work done on the body in moving between any two points is independent of the path taken.

Conservative System - A system in which only conservative forces are operative.

Consonance - Of musical notes; the production of a sound that is pleasant to the ear when two or more notes are played together. Their frequencies generally bear a simple numerical relation to one another.

Constant-Potential Circuit - A high-voltage generating circuit in which the rectified output voltage is maintained constant, apart from a small ripple.

Constringence - For an optical glass: the ratio (n-l) ∂n, where n is the refractive index for a given wavelength (usually that of the helium d-line, 5875.6 Ả), and ∂n is the change of refractive index corresponding to two standard wavelengths (usually those of the hydrogen C-and F-lines, 6562.8Å and 4861.3 Å). It is measure of the dispersive power of the glass.