C
Capacitor
A capacitor is a device which can store electrical charge. Capacitors are often used to introduce a time delay in electronic circuits. The SI unit of capacitance is the farad.
Carrier Wave
Carrier waves are used to carry information from transmitter to receiver. Thecarrier wave will be radio or microwave frequency. There are two methods of using the carrier wave to carry information - amplitude modulation and frequency modulation. In radio transmissions for example, the carrier is of a much higher frequency than the audio wave which is to be transmitted. The higher the frequency of the carrier, the higher the quality of the transmitted signal.
Cathode rays
Negatively charged particles (electrons) that are emitted from a negative terminal in an evacuated glass tube.
Cell
In electricity, a cell is a source of d.c. electricity. A cell can be made using two different metals inserted into a salt solution, for example. The metals react with the salt solution at different rates and in so doing, generate a small electrical current. Many cells can be combined to produce a battery of cells.
Celsius scale of temperature
In the celsius scale of temperature, the ice-point is taken as taken as the lower fixed point (0 deg C ) and the steam-point is taken as the upper fixed point (100 deg C). The interval between the ice point and steam point is divided into 100 equal divisions. Thus, the unit division on this scale is 1degC. This scale was earlier called the centigrade scale. 1 deg C = 9/5 deg F.
Center of mass
The balance point of an object.
Centigrade
Alternate name for the Celsius scale.
Centrifugal force
An apparent outward force on an object following a circular path that. This force is a consequence of the third law of motion.
Centripetal force
The force required to pull an object out of its natural straight-line path and into a circular path.
Chain reaction
A self-sustaining reaction where some of the products are able to produce more reactions of the same kind; in a nuclear chain reaction neutrons are the products that produce more nuclear reactions in a self-sustaining series
Charge
A numerical rating of how strongly an object participates in electrical forces.
Chemical Potential Energy
Chemical energy is a form of potential energy because it is stored energy. Energy stored in food, torch batteries and explosives like dynamite is all chemical energy. Chemical energy is released in a chemical reaction (like combustion of explosives or respiration in plant and animal cells).
Circuit
An electrical device in which charge can come back to its starting point and be recycled rather than getting stuck in a dead end.
Circular Motion
The motion of a body along a circular path is called circular motion.
Clock Pulse Generator
A simple circuit using a capacitor, resistor and transistor. The circuit generates 'clock pulses' - simply a regular sequence of logic LO and logic HI. The capacitor charges and discharges through the resistor. As the capacitor charges to a certain level, the inverter's input goes HI and its output goes LO. This this causes the capacitor to start discharging. When its voltage gets low enough, the inverter output goes back to HI and the cycle starts again.
By increasing the resistance or increasing the capacitance, the pulses can be generated more slowly.
Coefficient of cubical expansion
The increase in volume of a substance per unit original volume per degree rise in temperature is called its coefficient of cubical expansion. The SI unit of coefficient of cubical expansion is K-1.
Coefficient of linear expansion
The increase in length per unit original length per degree rise in temperature is called the coefficient of linear expansion. The SI unit of the coefficient of linear expansion is K-1.
Coherent
A light wave whose parts are all in phase with each other.
Collision
An interaction between moving objects that lasts for a certain time.
Comet
A comet is a small body orbiting our Sun, usually at great distance from Earth and with a highly elliptical orbit. They are composed of 'ices' and dust. As a comet approaches the inner solar system, the heat of the Sun vapourises volatile material from the surface and pushes the material directly away from the Sun. This gives rise to the 'ion tail', usually a ghostly blue colour and quite straight, it always points directly away from the Sun and has nothing to do with the direction of motion of the comet. A second tail exists, usually white and curved. This is dust which falls off the comet and is left in track of its orbit.
Component
The part of a velocity, acceleration, or force that is along one particular coordinate axis.
Compression
A part of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is called a compression.
Compressive stress
A force that tends to compress the surface as the earth's plates move into each other.
Concave
Describes a surface that is hollowed out like a cave.
Condensation (sound)
A compression of gas molecules; a pulse of increased density and pressure that moves through the air at the speed of sound.
Condensation (water vapor)
Where more vapor or gas molecules are returning to the liquid state than are evaporating.
Condensation nuclei
Tiny particles such as tiny dust, smoke, soot, and salt crystals that are suspended in the air on which water condenses condensation point the temperature at which a gas or vapor changes back to a liquid.
Condensation point
The temperature at which a gas or vapor changes back to a liquid.
Conductor
A material that allows electricity to flow easily through it. Copper, for example is a good conductor. Good conductors have a very low resistance. See also insulators and semi-conductors.
Conduction
The transfer of heat from a region of higher temperature to a region of lower temperature by increased kinetic energy moving from molecule to molecule.
Constructive interference
The condition in which two waves arriving at the same place, at the same time and in phase, add amplitudes to create a new wave.
Consumer Unit
Commonly known as the fusebox, the consumer unit is the part of the meter board which separates the incoming electrical supply into the various lighting and ring main circuits. Each of these circuits is protected by either a fuse or miniature circuit breaker (MCB).
Control rods
Rods inserted between fuel rods in a nuclear reactor to absorb neutrons and thus control the rate of the nuclear chain reaction.
Convection
The transfer of heat from one place to another by the motion of a gas or a liquid across the heated surface.
Convex
Describes a surface that bulges outward.
Conventional current
Opposite to electron current-that is, considers an electric current to consist of a drift of positive charges that flow from the positive terminal to the negative terminal of a battery.
Coulomb
Unit used to measure quantity of electric charge; equivalent to the charge resulting from the transfer of 6.24 billion particles such as the electron.
Coulomb's law
Relationship between charge, distance, and magnitude of the electrical force between two bodies.
Covalent bond
A chemical bond formed by the sharing of a pair of electrons.
Covalent compound
Chemical compound held together by a covalent bond or bonds.
Crest
The point of maximum positive displacement on a transverse wave is called a crest.
Critical angle
Limit to the angle of incidence when all light rays are reflected internally.
Critical mass
Mass of fissionable material needed to sustain a chain reaction.
Current
Electrical current is the rate of flow of electrical charge round a circuit. It is measured in amperes and should be measured in series with an ammeter.
Curvilinear Motion
The motion of a body along a curved path is called curvilinear motion.
Cycle
A complete vibration.