# 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
C
capacitor: A device used in electric circuits that stores charge. It is made up of two leads connected to large plates that are separated by insulating material.
capillary action: The attraction of a liquid to the walls of a narrow tube, which cause it to rise up the tube.
catalyst: A chemical that changes the rate of a chemical reaction but is not itself changed.
cathode: The electrode at which reduction occurs. It is positively charged as electrons are used up here.
cation: A positively charged ion.
celestial equator: The intersection of the celestial sphere and the plane that passes through Earth’s equator.
celestial poles: The intersection of the celestial sphere and Earth’s axis.
celestial sphere: A hypothetical sphere, centred at the centre of Earth, in which the stars are fixed.
Celsius scale: A temperature scale whereby 0 degrees Celcius is the melting point of water and 100 degrees Celsius is its boiling point.
centrifugation: A technique for separating mixtures that involves spinning a mixture in a circle. The denser substance in the mixture traces out a larger circle and so separates from the other components.
Cepheid variables: Stars that vary their brightness in a regular way.
chemical: A substance either naturally present in the environment or synthetically made.
chemical bond: A link between two atoms or molecules based on the electrostatic forces of attraction between the atoms or molecules.
chemical change: A change that produces a new substance; often the change is irreversible.
chemical energy: A type of energy that represents the kinetic and potential energies of an atom, molecule or substance.
chemical equation: A symbolic representation showing the reactants and products involved in a chemical reaction. The chemical formulas of all substances are shown.
chemical equilibrium: A state where the rate of forward reaction equals the rate of reverse reaction in a chemical reaction.
chemical properties: The properties of a substance that involve the ability of the substance to undertake chemical reactions with other substances.
chemical reaction: A process whereby two or more substances interact and chemical bonds are broken and reformed to form new substances.
chemical sedimentary rock: A sedimentary rock formed through a chemical process after chemical weathering of rock.
chemical weathering: The process whereby rock materials are decomposed by chemical alteration of the parent material.
chemist: A scientist who deals with the science of chemistry.
chemistry: A branch of science that deals with the structure and interactions of materials.
chromatogram: A strip of paper that shows the spread of colours in chromatography.
chromatography: A technique that involves the separation of substances dissolved in a solvent.
chromosphere: Part of the Sun’s atmosphere.
circuit breaker: A device used in electric circuits that causes an open circuit if a large current passes through it.
closed universe: A type of ‘big bang’ universe in which the universe will eventually contract into the ‘big crunch’.
cog: A wheel with teeth that is part of a gear system.
colloids: Very small particles spread throughout a liquid, solid or gas. The particles are bigger than single molecules but so small that they do not settle on standing.
combustion: A chemical reaction that involves the chemical bonding of a substance to oxygen.
comet: A lump of icy material and dust that becomes visible if it approaches the Sun.
compound: A pure substance composed of two or more elements that have chemically combined in fixed proportions.
compression: A region within an object of higher than average pressure. In this region the particles of the material are closer together than other parts.
compression forces: Forces that compress, or squash, an object.
concave mirror or lens: A concave mirror converges the parallel light incident on it. A concave lens diverges parallel light that passes through it.
concentration: A measure of the amount of solute dissolved in a given quantity of solvent or solution.
condensation: A change of state from a gas to a liquid.
condensation nuclei: A small particle in the atmosphere around which water vapour condenses into a cloud droplet.
condensation point: The temperature at which a gas changes state to a liquid.
conduction: Heat transfer in which the material that is heated does not move with the heat transfer. The transfer of energy from one part of an object to another through collisions of the particles within the object.
conductivity: Ability of a substance to carry an electric current.
conductor: A substance that allows an electric current to pass. Metals are good conductors.
conjunction: An alignment where two objects in the solar system are lined up on the sky so that they have the same right ascension as seen from Earth.
conservation of atoms: In any chemical or physical change the number and type of atoms remains the same.
conservation of energy: In any chemical or physical change the total energy of all interacting substances remains constant.
conservation of mass: In any physical or chemical change the total mass of all the interacting substances (reactants, products and surrounding substances) remains the same.
constellation: A group of stars within a defined boundary on the celestial sphere. There are eighty-eight constellations.
contact forces: Forces that occur when objects are in contact. There are various types of contact forces: tension, compression and friction.
continental crust: The crust that holds landmasses.
continental drift: The theory that the continents were once joined into a single landmass that broke apart, with the various fragments (continents) moving with respect to one another.
convection: This occurs where energy is transferred from one place to another as the result of the bulk movement of particles from one place to another.
convection cell: The movement of magma in a vertical loop. Hot magma rises, cools and falls, and then heats up again.
conventional current direction: The direction positive charges flow around an electric circuit. The direction is from the positive terminal of the battery around the conducting path to the negative terminal.
convex lens or mirror: A convex mirror diverges the reflected light of parallel light incident upon it. A convex lens converges parallel light that passes through it.
corona: The outermost region of the Sun.
corrosion: The reaction of a metal with oxygen and other substances in the environment.
cosmic rays: Nuclear particles or nuclei arriving at Earth with great speed.
cosmogony: The study of the universe, usually applied in particular to the origin of the solar system.
cosmology: The study of the universe as a whole.
coulomb (C): The unit of electric charge.
covalent bond: The force of attraction formed when one or more pairs of electrons are shared between two nuclei.
crust: Earth’s outermost layer; the upper part of the lithosphere, which is separated from the mantle by the moho.
crystal lattice: A three-dimensional arrangement of atoms or ions in a regular pattern.
crystalline structure: A structure containing particles that are arranged in a regular way to form definite shapes.
current: The rate of motion of electric charges. Current is measured in amperes, so a current of 10 A means there is a flow of 10 C (coulombs) of charge moving passed a point every second.
current electricity: A phenomenon that involves the motion of electric charges.