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Contact Angle - For a liquid drop resting on a solid surface: the angle (measured in the liquid) between the tangent to the surface the drop and the plane of the solid surface, at the point where the edge of the drop touches the solid, the tangent lying in a plane at right angles to the solid surface. Also called the wetting angle.
Contact Potential - More accurately contact potential difference: the potential difference, due to the difference in work function, arising when two solid surfaces are placed in contact.
Contact Resistance. - The electrical resistance at the point of contact between two conductors.
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Continuous Radiation - Radiation comprising a continuous range of X-ray wavelengths. It is also known as white radiation or heterogeneous radiation.
Continuous Spectrum - A spectrum in which radiation is distributed over an uninterrupted range of wavelengths in contrast to a line or band spectrum. I
Convection - The transport of heat by a moving fluid in contact with a heated body.
Convection Modulus: Grashof Number - A dimensionless number appearing in the expression for the heat transfer coefficient for natural convection due to the presence of a hot body. It is given by l3g α q2θ where l is a typical dimension of the hot body, is the η2
acceleration due to gravity, α is the temperature coefficient of the fluid density, q is the density and n the viscosity of the fluid, and is the temperature difference between the hot body and the fluid.
Convection, Natural - Convection in which the motion is caused by gravitational forces and which arises from density differences due to temperature gradients within a fluid. Natural convection which is not subjected to constraining boundaries is termed free convection.
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Cooling, Newton Law Of - States that the rate at which a body loses heat is proportional to the temperature difference between the body and the surrounding air. The law is true for quite large temperature differences, if the air is flowing past the body in a forced draught.
Co-operative Phenomenon - A process for which simultaneous interaction between the constituent systems of an assembly (a co-operative assembly) is required.
Coordinates, Laboratory System Of - Refers to the coordinate system, with the observer at rest, to which the experimental observation of such phenomena as collision processes is referred.
Coordinates, Polar - Two-dimensional co-ordinates, comprising the radial distance from the origin and the azimuthal angle.
Coordinates, Spherical - Coordinates referred to a sphere, and specified as the radial distance from the centre, the angle of longitude, and the angle of latitude.
Coriolis Effect - An effect typified by the deflection, relative to the surface of the rotating Earth, of any object moving with a constant velocity in space. It is usually described in terms of the Coriolis acceleration and Coriolis force.
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Cornea - The outermost part of the eye, just in front of the aqueous humour.
Corner Cube - A device, made with mirrors or reflecting wires, or cut from the solid, which has the property of reflecting light or radio waves back along the direction of incidence.
Corner Fracture - A term used in the field of explosive metal working to define a fracture surface produced by the interaction of two or more waves of tensile stress.
Cornu Prism - A prism of quartz, or similarly optically active material, which, used at minimum deviation, overcomes the doubling of an image occasioned by double refraction.
Coronagraph - A device which permits the observation of the sun's chromosphere, prominences and especially its corona, by the production of an artificial eclipse.
Corona, Solar - A bright white halo surrounding the Sun, seen during a total eclipse and also observable by a coronagraph. It emits a characteristic line spectrum.
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Cosmic Rays - Highly energetic extraterrestrial ionizing radiation. The primary cosmic rays, i.e. the cosmic rays incident on the top of the Earth's atmosphere, are predominantly composed of fully ionized (i.e. positively charged) atomic nuclei, having energies ranging from a few times 106 eV to 1018 or 1019 eV. The secondary cosmic rays, i.e. those produced in the Earth's atmosphere by the primary cosmic rays and other secondary cosmic rays, are complex in character and include nucleons, mesons, electrons, neutrinos, X-rays, y-rays, etc. (Note: 1 eV =1.6021 x 10-19 J.)
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Cosmic-Ray Shower - The practically simultaneous appearance of secondary particles derived from the more energetic primaries (of energy greater than 1013 eV) in groups which contain so many particles as to be recognizable experimentally as separate from the general cosmic-ray flux. In the atmosphere they extend over considerable areas, and are also referred to as extensive (air) showers or Auger showers.
Cosmology - The study of the structure of the universe as a whole, including cosmogony.
Cosmotron - The name given to the proton synchrotron at the Brookhaven National Laboratory. It delivers protons of 3000 MeV energy.
Convergence Limit (Spectroscopy) - (1) The long wavelength limit of an ionization continuum, e.g. the limit of a Rydberg series. (2) The limit corresponding to the point at which the separation between successive vibrational bands in an electronic band system decreases to zero.
Convergence Of Meridians - At a point on a plane representation of the Earth's surface: the angle between the tangent to the line representing the meridian at that point and tangent to the meridian at the origin of the projection.
Convergent Point - Of a moving star cluster: that point on the celestial sphere towards which all the stars appear to be moving.
Corpuscular Theory of Light - The view, formerly held, that a beam of light consists of a stream of fast-moving material particles. The modern counterpart of such a particle is the photon.
Correlation Energy - The energy associated with the Coulomb repulsion between electrons.
Correspondence Principle. The principle that, in the limit of high quantum numbers, the predictions of quantum theory agree with those of classical mechanics.
Corresponding States, Law of - Predicts that all substances obey the same reduced equation of state pVlRT = Z(pr, TR) where p is the pressure, V the volume, R the gas constant, and T the absolute temperature. Z(PR,TR) is a universal function of the reduced pressure PR and the reduced temperature TR i.e. the pressure and temperature expressed as fractions of their respective values at the critical point. See also: Thermodynamic similarity, principle of. Continental Drift - The breaking up and drifting apart of one or more land masses on the Earth to form the present continents.
Continentality - The extent to which the climate of a region is influenced by its distance from the sea, continental climate being one with large diurnal and annual ranges of temperature, which arise from the small effective reserve of heat or cold in a land surface.
Continuity of State - The transition between two states, as between the gaseous and liquid states (in either direction), without any discontinuity in physical properties. Cotton Balance - A balance for determining the intensity of a magnetic field. The field strength is obtained by measuring the force on a current-carrying conductor of special shape placed in the field.
Cotton-Mouton Effect - The double refraction of light in certain pure liquids (such as nitrobenzene) in a transverse magnetic field. The effect is also shown by some isotropic solids.
Cottrell Atmosphere - A cluster of impurity atoms which have migrated to a dislocation in a crystal.
Coulomb - The unit of electric charge in MKSA and SI units. It is the Coulomb Barrier 59
quantity of electricity transported in one second by a current of one ampere.
Coulomb Barrier. That part of the region of high potential energy through which a charged particle must pass on leaving or entering an atomic nucleus, which arises from the presence of electrostatic forces.
Coulomb Energy - (1) In a system of particles (e.g. a solid or an atomic nucleus): that part of the binding energy associated with electrostatic interaction between the constituent particles. (2) Of a covalent bond: the electrostatic interaction energy between two or more electron distributions in terms of which the actual electron distribution is described.
Coulomb Force: Coulomb Interaction - The attractive or repulsive force between two electric point charges. It acts along the line joining the two charges and is given, according to Coulomb's law of force, by Q1Q2/ε0r2 where Q1 and Q2 are the charges, r the distance between them, and ε0 is the permittivity of the medium. A negative value corresponds to an attraction and a positive value to a repulsion.
Coulomb Scattering: Rutherford Scattering - The scattering of a charged particle by the Coulomb field (electrostatic field) of a nucleus.
Coulometer: Voltameter - An electrolytic cell used for measuring the quantity of electricity passing through a circuit in a given time by the determination of the amount of metal deposited, or gas liberated, due to the passage of the current.
Coulometry - An analytical process in which a coulometer is used to determine the amount of a constituent present, by measuring the amount of current necessary to achieve a given reaction involving the constituent.
Counter - For ionizing radiation: a device which reacts to individual ionizing events,. this enabling them to be counted. The term is also loosely used to describe a complete counting system.
Counter, Geiger-Muller - A gas-filled ionization chamber, usually consisting of a hollow cylindrical cathode with a fine wire along its axis, which is operated in the Geiger region, and in which each ionizing event is followed by only one terminated discharge.
Counting-Rate Meter - An instrument which gives a continuous indication of the average rate of arrival of pulses from a counter.
Coupled Circuits - Usually describes circuits which are coupled, or interconnected, to each other by a common magnetic flux linking an inductor in each circuit (i.e. via a mutual inductance), or by a common capacitor.
Coupling - (1) In general, an interaction between different properties of a system, or between two or more systems. (2) For particles in an atom or nucleus: the Russell-Saunders coupling (L-S coupling), in which the resultant, L, of the oribital angular momentum of all particles interacts with the resultant, S, of the spins of all particles; or the j-j coupling, in which the total angular momenta (orbital plus spin) of the individual particles interact with one another; or a coupling intermediate between these two. (3) In molecular spectra: one of a number of five ideal ways (the Hund coupling cases) of coupling the electron spin angular momentum, S, the electron orbital angular momentum L, and the nuclear rotation angular momentum, N, to form a resultant, J.
Coupling Constant - A physical constant expressing the magnitude of the force exerted on a particle by a field.
CPS Tube: Emitron Tube - A television camera tube in which the optical image is focused on to it photo-emissive mosaic formed on a transparent dielectic and capacitatively associated with a conducing signal plate.
Creation Operator - In the quantum theory of fields: an operator which, when applied to a state vector фn that describes a system containing n particles, will yield a state vector фn+1, which describes a system having particles. See also: Destruction operator.>
Creep - Of a solid: the change of strain with time under the influence of a constant stress.
Crepuscular Rays - (1) Rays which are emitted by the Sun when below the horizon and rendered visible when scattered by clouds or mountains. (2) Rays from the Sun which pass through openings in the clouds and, on account of scattering, appear to be divergent.
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