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AS&A Physics CD-ROM Glossary.Indd www.igcse.at.ua Glossary absoluteolute scale of temperaturetemperature seesee thermodynamic astronomical unitunit Th e averageaverage distance of the Earth scale from the Sun. absolute zero Th e temperature at which a attenuation Th e gradual loss in strength or intensity system has minimum internal energy; equivalent of a signal. to −273.15 °C. average speed Th e total distance travelled by an absorption line spectrum A dark line of a unique object divided by the total time taken. wavelength seen in a continuous spectrum. Avogadro constant Th e number of particles in one acceleration Th e rate of change of an object’s mole 23 −1 velocity: of any substance (6.02 × 10 mol ), denoted NA. bandwidth (communications) A measure of a = ∆v ∆t the width of a range of frequencies being transmitted. −2 Unit: m s . base station A receiver and transmitter used to accuracy An accurate value of a measured quantity is maintain contact with a number of mobile one which is close to the true value of the quantity. phones (cell phones) in a local area. acoustic impedance Acoustic impedance Z is best fi t line A line drawn through the points plotted the product of the density ρ of a substance and ρ on a graph so that it passes through as many points the speed c of sound in that substance (Z = c). as possible, taking into consideration a balance −2 −1 Unit: kg m s . between the number of points above and below activity Th e rate of decay or disintegration of the line. nuclei in a radioactive sample. binding energy Th e minimum external energy amorphous Describes a material whose particles are required to separate all the neutrons and protons arranged in a disordered way. of a nucleus. ampere Th e SI unit of electric current. bit A basic unit of information storage. Th e amount amplitude modulation A form of modulation where of information stored by a device that exists in the signal causes variations in the amplitude of a only two distinct states, usually given as the carrier wave. binary digits 0 and 1. amplitude Th e maximum displacement of a particle Boyle’s law Th e pressure exerted by a fi xed mass of from its equilibrium position. gas is inversely proportional to its volume, provided analogue signal A signal that is continuously the temperature of the gas remains constant. variable, having a continuum of possible values. braking radiation X-rays produced when electrons analogue-to-digital conversion (ADC) Conversion are decelerated (also called Bremsstrahlung of a continuous analogue signal to discrete radiation). digital numbers. brittle Describes a material that shows no plastic angular displacement Th e angle through which an deformation and breaks just beyond its elastic limit. object moves in a circle. Brownian motion Th e random movement of angular frequency Th e rate of change of angle small particles caused by bombardment of invisible expressed in radian per second: molecules. π angular frequency ω = 2 capacitance Th e ratio of charge stored by a capacitor T to the potential diff erence across it. angular velocity Th e rate of change of the angular carbon-dating A technique used to date relics using position of an object as it moves along a curved path. the carbon-14 isotope. antinode A point on a stationary wave with carrier wave a waveform (usually sinusoidal) that is maximum amplitude. modulated with an input signal to carry information. antiphase Describes two waves or oscillations that are cellular exchange A switching centre connecting all 180° out of phase. the base stations in an area. AS and A Level Physics © Cambridge University Press Glossary 1 www.igcse.at.ua www.igcse.at.ua centre of gravity Th e point where the entire weight control rods Rods of a neutron-absorbing material of an object appears to act. used to reduce the rate of a nuclear chain reaction. centripetal force Th e net force acting on an object coolant A substance used to transfer thermal energy moving in a circle; it is always directed towards the from the core of a nuclear reactor. centre of the circle. coulomb Th e SI unit of electrical charge. A charge of chain reaction An exponential growth of a fi ssion 1 C passes a point when a current of 1 A fl ows for reaction caused by the increasing fl ux of neutrons 1 s. 1 C = 1 A s causing fi ssion. Coulomb’s law Any two point charges exert an characteristic radiation Very intense X-rays electrical force on each other that is proportional produced in an X-ray tube having specifi c to the product of their charges and inversely wavelengths that depend on the target metal. proportional to the square of the distance between charge carrier Any charged particles, such as them. electrons, responsible for a current. count rate Th e number of particles (beta or alpha) Charles’s law Th e volume occupied by a gas at or gamma-ray photons detected per unit time by a constant pressure is directly proportional to its Geiger–Müller tube. Count rate is always a fraction thermodynamic (absolute) temperature. of the activity of a sample. closed system A system of interacting objects where cross-linking (cross-talk) A signal transmitted in there are no external forces. one circuit or channel picked up, undesirably, in coaxial cable An electrical cable with an inner another circuit or channel. conductor surrounded by a tubular insulating layer crystalline Describes a material whose particles are and an outside conducting layer. arranged in an ordered way. coherent Two sources are coherent when they emit damped Describes an oscillatory motion where the waves with a constant phase diff erence. amplitude decreases with time due to energy losses. collimated beam A parallel-sided beam of radiation. de Broglie wavelength Th e wavelength associated collimator A device for producing a parallel beam with a moving electron given by the equation: of radiation. λ h components (of a vector) Th e magnitudes of a = mv vector quantity in two perpendicular directions. decay constant Th e constant λ for an isotope that compression A region in a sound wave where the λ air pressure is greater than its mean value. appears in the equation A = N. It is equal to compressive Describes a force that squeezes an object. the probability of an isotope decaying per unit time computerised axial tomography A technique where interval. X-rays are used to image slices of the body in order decibel A logarithmic unit of measurement that to produce a computerised 3-D image. expresses the relative sizes of two powers using P conservation of momentum In a closed system, the formula 10 lg 1 . when bodies interact, the total momentum in any P2 specifi ed direction remains constant. density Th e mass per unit volume of a material: constructive interference When two waves reinforce ρ = m V to give increased amplitude. contact force Th e force an object exerts on another Unit: kg m−3. with which it is in contact. dependent variable Th e variable in an experiment contrast media Materials such as barium that easily which is controlled by the experimenter. absorb X-rays. A contrast medium is used to destructive interference When two waves cancel to reveal the outlines or edges of soft tissues in an give reduced amplitude. X-ray image. diff raction Th e spreading of a wave when it passes contrast In a high-contrast image, there is a big through a gap or past the edge of an object. diff erence in brightness between bright and digital signal A signal that has only a few possible dark areas. values, often only two. 2 AS and A Level Physics © Cambridge University Press Glossary www.igcse.at.ua www.igcse.at.ua digital-to-analogue conversion (DAC) Conversion electrolyte An electrically conducting solution. Th e of a series of digital numbers into a continuous conduction is due to positive and negative ions in analogue signal. the solution. dispersion Th e splitting of light into its diff erent electromagnetic spectrum A family of waves wavelengths. that travel through a vacuum at a speed of displacement Th e distance moved by an object 3.0 × 108 m s−1. in a particular direction (measured from a fi xed electronvolt Th e energy gained by an starting point). electron travelling through a p.d. of 1 volt. drag A force that resists movement of a body through 1 eV = 1.6 × 10−19 J. a fl uid. elementary charge Th e smallest unit of charge that ductile Describes a material that can easily be a particle or an object can have. It has a magnitude drawn into wires (e.g. copper). of 1.6 × 10−19 C. dynamics A study of motion involving force emission line spectrum A sharp and bright line of and mass. a unique wavelength seen in a spectrum. e.m.f. Th e total work done when unit charge energy level Th e quantised energy states of an moves round a complete circuit. Unit: J C−1 or electron in an atom. volt (V). equation of state Equation for an ideal gas: effi ciency Th e ratio of useful output energy to the total input energy for a device, expressed pV = nRT or pV = NkT as a percentage: (Also known as the ideal gas equation.) useful output energy effi ciency = × 100% equations of motion Four equations that can total input energy be used to determine quantities such as Einstein relation Th is refers to the equation for the displacement, initial velocity, fi nal velocity and energy of a photon – that is: acceleration.
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