Glossary<H1_EM> absorb take in or soak up, for example energy Afrom sound B absorption<txtGlss_wrd> process <TXT_GLSS> in which matter takes in background radiation nuclear radiation that energy, e.g. when an atom takes in energy from an is present in the environment as a result of the electromagnetic wave radioactive decay of certain elements; it is produced from natural sources (e.g., from radon gas in the acceleration rate at which an object speeds Earth’s crust) and from artificial sources (e.g., as a up, calculated from change in velocity divided result of testing nuclear weapons) by time; symbol a, unit metres per second squared, m/s2 becquerel unit of activity for a radioactive isotope, symbol Bq accuracy how close a measurement is to its true value beta particle fast-moving electron that is emitted by activity the rate at which unstable nuclei decay an atomic nucleus in some types of radioactive decay in a sample of a radioactive material; unit becquerel, Bq Big Bang theory generally accepted explanation for the origin of the universe, which states that the air resistance force produced by the collision of universe began from a very small region that was molecules in air with a moving object; the force acts extremely hot and dense to oppose the direction of movement black body object that absorbs all the radiation that alternating current (a.c.) electric current that falls on it continually changes direction black dwarf star at the end of its life, where no alpha particle a particle (two neutrons and two further nuclear fusion reactions take place and so no protons, same as a helium nucleus) emitted by an light is produced atomic nucleus during radioactive decay boundary line or surface between two different alternator device that produces an alternating media (e.g., the surface between air and glass), current using the generator effect, e.g., from the across which light may be refracted or reflected rotation of a coil in a magnetic field braking distance distance travelled by a vehicle after ammeter device that measures electric current the brakes have been applied before coming to a ampere SI unit of electric current, symbol A; an complete stop electric current of 1 A is equal to 1 C of charge passing through a point in a circuit in 1 s C amplitude maximum displacement of a wave or cancer disease in which uncontrolled division of cells oscillating object from its rest position takes place, forming a tumour; some types of cancer angle of incidence the angle between the incident are caused by the effects of ionising radiation on ray and the normal cells angle of reflection the angle between the reflected cell (electric circuits) circuit component that stores ray and the normal energy in the form of chemical energy a number of electric cells may be joined to form a battery atmospheric pressure force per unit area produced by the weight of air; it decreases as you go higher in cell (living things) smallest structural unit of a living the atmosphere organism; cells may be damaged by some types of ionising radiation atomic number number of protons in the nucleus of an atom of an element centre of mass a single point where the weight of an object can be considered to act attraction force that acts between two objects that tends to draw them closer together, e.g., the force chain reaction occurs when the neutrons released by a that arises between a positive electric charge and a nucleus undergoing fission go on to split more nuclei negative electric charge change of state process in which one state of matter average speed distance travelled by an object over a changes to another, e.g., solid melting to form liquid, measured time interval or gas condensing to form liquid Glossary 301 58774_P298_310.indd 301 11/3/16 12:43 PM Physics circuit diagram visual representation of electrical conservation of momentum a fundamental <H1_EM>components connected by wires, using standard principle of physics: the total momentum of a system symbols of objects after a collision is the same as the total momentum before the collision circuit symbol visual representation of an electrical component; a standard symbol exists for each type contact force force that acts at the point of contact absorbof electrical take componentin or soak up, for example energy between two objects (e.g., friction or the normal from sound reaction) closed system system that is not acted upon by any <txtGlss_wrd>external forces <TXT_GLSS>and does not exchange energy with contamination (radioactivity) the unwanted its surroundings presence of materials containing radioactive atoms commutator (split-ring) electrical connector control variable quantity in an experiment consisting of two semi-circular metal contacts, that is kept constant while the independent which is connected to a rotating coil in a dynamo variable is changed and the dependent variable is (to produce direct current) or a motor (to use direct measured current) convex lens lens that curves outwards with the compass (magnetic) device that shows the direction centre thicker than the edges – it causes light rays to of a magnetic field in which it is placed; typically come together (converge). The image produced by a a compass is made from a magnetised needle or convex lens can be either real or virtual pointer that is free to rotate coulomb SI unit of electric charge, symbol C components (forces) the result of breaking down count rate the number of decays recorded each or resolving a single force into two separate forces second by a detector (e.g. Geiger–Muller tube) acting in perpendicular directions, often horizontally and vertically CT (or CAT) scan scan that takes many X-ray images from different directions to build up a 3D image of compress squashing something into a smaller the body volume – liquids are incompressible: they cannot be squashed current (electric) flow of electric charge; the size of the electric current is the rate of flow of electric compression a region of a sound wave where the charge; symbol I, unit amps (A) particles are closer together concave lens lens that curves inwards with the D centre thinner than the edges – it causes light rays to spread out (diverge). The image produced by a dark energy unknown form of energy which is concave lens is always virtual thought to accelerate the expansion of the universe. conclusion section at the end of a report on an It is estimated to constitute around 68% of the total experiment that summarises how the results support energy in the universe or contradict the original hypothesis dark matter unidentified matter which doesn't reflect conductivity (thermal) quantity that measures the electromagnetic radiation and is thought to constitute rate at which thermal energy is conducted through around 27% of the total mass-energy of the universe a material; the higher the thermal conductivity, the data measurements of quantities in an experiment; higher the rate of thermal energy transfer data can be recorded in a table and used to produce conductor material or object that allows electric graphs charge to flow through it decay (radioactive) process in which the nucleus of conservation of electric charge a fundamental an atom breaks apart and emits radiation principle of physics: electric charge cannot be deceleration negative acceleration, when an object created or destroyed, only transferred from one slows down object to another; the total electric charge of a closed system is constant degrees Celsius unit of temperature, symbol °C; 1 1 °C is of the temperature difference between conservation of energy a fundamental principle of 100 physics: energy cannot be created or destroyed, only the melting point and boiling point of water transferred, stored or dissipated. This means that the density measure of the amount of substance per unit total energy of a closed system is constant. volume; symbol r, unit kilograms per metre cubed, conservation of mass a fundamental principle of kg/m3 physics: mass cannot be created or destroyed by dependent variable quantity in an experiment that physical changes or chemical reactions; the total is measured for each change in the independent mass of a system is constant variable 302 AQA GCSE Physics: Student Book 58774_P298_310.indd 302 11/3/16 12:43 PM diffuse reflection reflection from a rough surface, electric charge fundamental property of matter that so that an incident ray is scattered (reflected at many results in an electric field around an object; objects angles) can be electrically positive, negative or neutral (no overall charge); symbol Q, unit coulomb, C diode circuit component with a low resistance if it is connected one way around in a circuit, or a very high electric current flow of electric charge; the size of the resistance if it is connected the other way around; a electric current is the rate of flow of electric charge; diode allows current in one direction only symbol I, unit amps, A direct current (d.c.) flow of electric charge in one electric field region around an electrically charged direction only object in which a force acts on other electrically charged objects; the objects do not have to touch for directly proportional relationship a relationship the force to act of the form y proportional to (∝) x; plotting a graph of y against x will produce a straight line through electrical power amount of energy transferred each the origin second; symbol P, unit watts or joules per second, W or J/s displacement distance moved in a particular direction; it is a vector quantity and is equal to the