Key Concepts in Physics for Exams

Title: URL Source: blob://pdf/d0b1ad65-5178-4f52-a1e2-77ce27d001aa Markdown Content: Physics Past Paper Common Questions By Vasumitra Gajbhiye 1 # Physics Past Paper Common Questions By Vasumitra Gajbhiye # 1. Motion, Forces and Energy As the trolley moves across the rough surface, it slows down and stops. Explain, in terms of the work done, the energy change that takes place as the trolley slows down. work done against / due to / because of friction or kinetic energy (of trolley) used to do work kinetic energy decreases (to zero) thermal energy produced Why a bus begins to topple? line of action of centre of mass falls outside the base. State the principle of the conservation of momentum. no external forces OR isolated system sum of momenta / (total) momentum remains constant State the principle of conservation of energy. In a closed/ isolated system, total energy of the system is conserved/ constant. initial energy = final energy What is centre of mass? (the point) where (all) the mass can be considered to be concentrated State two properties of an object that may be changed by the action of forces. shape Physics Past Paper Common Questions By Vasumitra Gajbhiye 2size / volume / length / density / any linear dimension direction (of motion) / speed / velocity / momentum / kinetic energy / acceleration State the two conditions which must be true for an object to be in equilibrium. no resultant force OR forces are balanced OR all forces in opposite directions are equal OR forces cancel no resultant {moment / torque / turning effect} OR (sum of) clockwise moment(s) = (sum of) anticlockwise moment(s) Hookes Law State Hookes law extension is directly proportional to load (if elastic limit is not exceeded) Explain what is meant by the term limit of proportionality of the spring. up to the limit of proportionality, extension proportional to load What type of energy is stored in springs? Strain/ elastic potential energy. Terminal velocity Describe and explain the motion of an object released from top of an fluid, from when it is released until it reaches terminal velocity. (initial) acceleration caused by weight / force of gravity drag / resistance force increases (with speed) acceleration decreases as resistance force increase when weight(downward force) = resistance(upward force), (finally / at terminal velocity) no acceleration / constant speed (finally / at terminal velocity) no resultant force Explain why opening the parachute cannot reduce the speed of the skydiver to zero. Physics Past Paper Common Questions By Vasumitra Gajbhiye 3at zero speed there is no air resistance weight / downwards force is (still) acting or there is (now) a resultant force (downwards at zero speed) OR forces balance at a speed greater than zero speed cannot decrease / no deceleration once forces balance Why not 100% of GPE is converted to KE when an object falls? (work done against) friction / drag / resistance or thermal energy generated Particles arrangement and motion Describe the motion of molecules of the gas. Molecules move randomly/ in random directions Molecules have high speed Molecules collide with each other/ with walls. Molecules change direction in collision Molecules move in straight line between collision Molecules collide with the walls (of cylinder) Describe the motion of molecules of the solid. Molecules vibrate State two ways in which the molecular structure of liquid is different from the molecular structure of solid. Liquid molecules not in fixed position Liquid molecules have random/irregular arrangement Liquid molecules are (slightly) further apart State two ways in which the molecular structure of solids is different from the molecular structure of liquids. in solid, particles are arranged in regular lattice and just vibrate Physics Past Paper Common Questions By Vasumitra Gajbhiye 4in liquid, particles are arranged randomly, slide past each other, move. Describe, in terms of molecules and their motion, how a liquid differs from a gas. molecules close(r) molecules move only small distances (between collisions) or do not move freely molecules move in clusters or slide past each other State two ways in which the molecular structure of gas is different from the molecular structure of liquid. (gas) molecules further apart greater PE move singly/ in straight lines faster Why solids have fixed shapes? Explain in terms of forces between molecules and arrangement of molecules. Solids molecules in lattice arrangement solids strong forces between molecules Why liquids adapt to the shape of their container? Explain in terms of forces between molecules and arrangement of molecules. liquids molecules not fixed in place OR molecules have an irregular arrangement OR molecules (slightly) further apart (on average) than in solids OR spaces between the molecules liquids (average) forces too weak to keep molecules in a definite pattern OR forces just enough to hold molecules in the bulk of the liquid Why gas fills their container? Explain in terms of forces between molecules and arrangement of molecules. gases molecules far apart gases weak / no forces between molecules (except during collisions) Explain the melting of a solid in terms of molecules and energy. Physics Past Paper Common Questions By Vasumitra Gajbhiye 5molecules must be separated OR (intermolecular) bonds must be broken / overcome work done (against bonds) OR energy is required / needed NOT increase of KE / speed Explain, in terms of forces between molecules, why gases expand more than liquids when they have the same rise in temperature. Assume that the pressure remains constant. average distance between molecules greater (in gas) (attractive) forces between molecules lower or zero in gas Gas pressure Explain, in terms of the momentum of the molecules, how gas molecules exert pressure. molecules collide with walls momentum (of a molecule) changes / reverses force is exerted because force is rate of change of momentum or force is change in momentum per unit time (or per second) or F = mu - mv /t. force spread out over area / surface. p = F / A The gas bubble rises to the surface. The volume of the gas bubble increases as it rises higher in the water. Explain why the volume of the bubble increases. pressure in a liquid increases with depth OR pressure decreases (as bubble rises) pressure (of gas) is inversely proportional to volume OR internal pressure greater than external pressure (momentarily) OR (air) molecules do not have to hit surface of bubble as frequently (to stop the bubble collapsing) OR the bubble is not as strongly compressed Explain why the volume of the air in the balloon decreases as the temperature decreases. molecules move more slowly / have less kinetic energy Physics Past Paper Common Questions By Vasumitra Gajbhiye 6pressure (inside balloon) decreases or pressure is directly proportional to temperature or p Tvolume is directly proportional to temperature or V Tmolecular collisions less frequent molecular collisions less violent / hard / exert smaller impulse water / external pressure compresses balloon or water pressure greater (and balloon compressed) Explain what happens to the pressure of a constant volume of air when the temperature of the air increases. Use ideas of momentum of molecules in your explanation. (temperature of air increases) so molecules move faster / their KE increases molecules collide with walls of container and change momentum greater change of momentum when temperature is higher OR collisions more frequent OR harder collisions OR force = rate of change of momentum (higher force and hence) higher pressure If volume increase, what happens to the pressure. pressure decrease density decrease/ fewer atoms per unit volume rate of collisions decrease/ fewer collisions per unit volume Explain, in terms of the behaviour of the molecules, why the pressure has increase. (molecules) collide with walls more often OR more collisions with walls per second or per unit time OR greater force per unit area Moment What is meant by the moment of a force about a pivot. (moment of a force) is the turning effect (about a point / pivot) Physics Past Paper Common Questions By Vasumitra Gajbhiye 72. Thermal Physics Conduction Explain, in terms of the atomic lattice and electrons, how thermal energy is transferred through the aluminium. atoms (touching the hotplate) / lattice vibrate (faster) more atoms pass on energy / vibration to neighbouring atoms / to other atoms by collision atoms pass on energy to electrons electrons hit distant atoms or electrons move (through lattice) Describe, in terms of molecules, how thermal energy is transferred from the heated sand through the base of the plastic pot. (thermal energy is transferred by) conduction sand molecules gain KE OR vibrate more OR hit (other) molecules (when heated) OR Energy is transferred to molecules of plastic pot in contact with sand (through collisions) OR Energy OR (lattice) vibrations transferred to neighbouring molecules Explain how electrons transfer thermal energy through the metal of the can atoms / ions vibrate (vibrating) atoms / ions hit electrons electrons propelled / travelling through metal lattice/ moving through metal lattice electrons hit (distant) atoms and transfer energy to distant atoms free electrons / delocalised electrons mentioned Physics Past Paper Common Questions By Vasumitra Gajbhiye 8Liquid Explain, in terms of the water molecules, what happens to the thermal energy supplied to the water as it boils. energy used to breaks bonds. molecules escape from the liquid (as a vapour) (thermal energy) does work against intermolecular forces molecules separated/ moved apart and gain potential energy. Eventually, the water reaches boiling point. Thermal energy from the hotplate is still being transferred to the water. Explain, in terms of molecules, the effect of this thermal energy on the water. molecules escape from the liquid (as a vapour) bonds broken / (attractive) forces overcome molecules gain potential energy or work done (to separate molecules / break bonds / overcome forces) Describe what happens to molecules of the liquid as its temperature begins to increase. molecules (in liquid) move faster or gain energy molecules move apart (on average) Explain, in terms of molecules, why liquids are very difficult to compress molecules (already very) close / touching (repulsive) forces (very) large Explain, in terms of molecules, why a liquid expands when heated. molecules gain kinetic energy and move faster molecules push others away and move further apart As temperature increase, why does the ice starts to melt. k.e. of molecules / (thermal) energy absorbed (from water / surroundings) or energy absorbed from (cooling) water Physics Past Paper Common Questions By Vasumitra Gajbhiye 9supplies latent heat or energy used to overcome intermolecular forces / to break bonds Gas When the temperature of gases increased explain, in terms of molecules, what happens to the pressure of gas (Pressure of the gas) increases Molecules gain KE and move faster Molecules collide with/ hit walls more often/ frequently More collisions with wall per unit time (e.g. per second) Molecules collide with/ hit walls with greater force/ impulse/ harder. When the temperature of gases decreased explain, in terms of molecules, what happens to the pressure of gas molecules lose KE and move more slowly fewer collisions per unit time OR less hard collisions with walls/ balloon lower pressure OR BETTER: (Pressure of the gas) decrease Molecules lose KE and move slowly Molecules collide with/ hit walls less often/ frequently Fewer collisions with wall per unit time (e.g. per second) Molecules collide with/ hit walls with less force/ impulse/ harder. When volume is decreased explain, in terms of the behaviour of molecules, what happens to the pressure of gas. (Pressure of the gas) increases. Molecules close together Molecules collide with walls more often/ frequently OR more collisions with walls per second or per unit time. Physics Past Paper Common Questions By Vasumitra Gajbhiye 10 Greater force per unit area. When volume is increase explain, in terms of the behaviour of molecules, what happens to the pressure of gas. lower pressure fewer collision with wall/ balloon per second or per unit time. larger surface area of walls OR atoms further apart OR atoms travel further OR BETTER: (Pressure of the gas) decrease. Molecules further apart Molecules collide with walls less often/ frequently OR fewer collisions with walls per second or per unit time. Greater force per unit area. Explain, in terms of molecules, why gases are easiest to compress. More room for molecules OR molecules fit into gaps OR there are gaps between molecules. No/weak repulsive forces between molecules OR (repulsive) forces between molecules smaller OR pressure on walls, smaller OR only small pores/ pressure required. OR BETTER: Gas molecules are further apart so there is larger intermolecular space between molecules. No/ weak repulsive forces between molecules. Brownian motion Describe and explain the motion of smoke particles under microscope and account for this motion in terms of the air molecules. Smoke particles show random/ haphazard/ unpredictable/ movement Smoke particles show sudden change of direction/ zig-zag motion Smoke particles appear/ disappear from view OR go out of/ come into focus. Physics Past Paper Common Questions By Vasumitra Gajbhiye 11 IF THEY SAY TO ONLY EXPLAIN THE CAUSE OF THE MOTION OF SMOKE PARTICLE LEAVE THE FIRST THREE POINTS FROM ABOVE. Air molecules collide with smoke particles from all direction/ unevenly cause random motion of particles Air molecules move randomly. Air molecules faster Air molecules smaller lighter/ have smaller mass Difference State and explain how the size of attractive forces acting between the molecules of gas compares with the size of attractive forces between the molecules of a solid. (Attractive) forces (much) smaller between gas molecules Gas molecules (much) further apart. State and explain, in terms of the forces between the molecules, how the compressibility of a gas differs from that of a liquid. gases compressible OR liquids incompressible no/ weaker repulsive forces between molecules OR vice versa for liquid molecules. Explain in terms of molecules why it is possible to compress gas, but not liquid. Gas molecules (very) far apart from OR empty space between gas molecules. Molecules of liquid (very) close together compact OR are touching (each other). Explain, in terms of molecules, why a liquid expands more than a solid when heated. forces between liquid molecules weak(er than in solids) less energy / work done to separate molecules or greater separation for same work done / same increase in energy State ways in which evaporation differs from boiling. at surface/ not within liquid Physics Past Paper Common Questions By Vasumitra Gajbhiye 12 at any temperature/ not at boiling point (evaporation) causes cooling boiling requires a heat source bubbles rising State ways in which boiling differs from evaporation. boiling throughout liquid (evaporation at surface) boiling at one temperature (evaporation at any/ all temperature/ below boiling point). boiling produces bubbles (evaporation does not). boiling not affected by draught/ area (evaporation is) Evaporation Explain, in terms of the behaviour of molecules, the process of evaporation. some molecules at the surface gain more KE, so have more energy than others heat energy used to work done against/ overcome attractive forces between molecules. most energetic molecules escape from the surface of the liquid Explain, in terms of the behaviour of molecules, how evaporation process helps the body to cool down. evaporation OR heat/ (thermal) energy needed for evaporation leaves sweat cooler faster molecules/ higher energy molecules escape heat flows from body to warm the sweat (so body cools) Explain, in terms of molecules, how sweating helps to cool your body on a hot day (thermal) energy in the skin / body transferred to (molecules of) sweat These molecules (have enough KE to) escape from the skin / become water vapour Physics Past Paper Common Questions By Vasumitra Gajbhiye 13 Leaving behind molecules with lower energy Which leaves the skin / body at a lower temperature Explain, in terms of molecules, why temperature decreases during evaporation. Molecules do work against attractive forces as they evaporate. Faster/ more energetic water molecules (more likely to) escape from surface Slower/ less energetic molecules remain (so temperature is lower). Average energy of remaining molecules decrease. In terms of molecules, state and explain how the rate of evaporation of the puddles in is affected by a reduction of wind speed. Reduces (rate of evaporation) No/ fewer evaporated molecules blown away/ removed by wind, OR greater humidity/ vapour pressure. In terms of molecules, state and explain how the rate of evaporation of the puddles in is affected by an increase in water temperature. Increases (rate of evaporation) Molecules move faster/ have more energy OR molecules have energy to escape. Which container has faster rate of cooling wide and shallow OR narrow and deep. Water in wider container AND has water with larger surface (area). Rate of evaporation higher/ faster/ quicker OR higher chance of evaporation. Suggest ways in which the rate of evaporation can be reduced. Cover/ decrease surface area Reduce temperature Reduce draught(a current of cool air in a room or other confined space) Increase humidity of air. Suggest ways in which the rate of evaporation can be increased. Increase temperature/ supply more heat/ make hotter Physics Past Paper Common Questions By Vasumitra Gajbhiye 14 Blow air across surface. Reduce humidity Decrease pressure. Thermometer How to increase the range of a thermometer. capillary tube longer or liquid with lower expansivity or smaller bulb with less volume or increase diameter of tube. What happen to range if smaller bulb is used, with smaller volume of liquid? (range) increases and less expansion/increase in volume (of mercury per unit temperature rise) How to increase the sensitivity of a thermometer. capillary tube thinner/finer or liquid with higher expansivity or larger bulb with more volume of liquid or smaller bulb with same volume of liquid. State what is meant by a linear scale. same distance moved (by thread) for same temperature change State and explain the two features of a liquid-in-glass thermometer that are necessary for linearity statement 1: bore of constant (cross sectional) area explanation: idea of same movement / change in length of liquid / thread AND for same increase in volume / expansion (of liquid) statement: (liquid has) constant thermal expansion explanation: liquid moves same distance for each C temperature rise State what is meant by range. difference between the maximum temperature and minimum temperature it can measure State what is meant by sensitivity. Physics Past Paper Common Questions By Vasumitra Gajbhiye 15 distance moved by the thread per C OR per unit temperature change If a larger bulb is used, with more of the same liquid what happens to its sensitivity. greater sensitivity volume increase (of liquid in second thermometer) is greater or liquid moves a greater distance (for the same temperature increase) If a larger bulb is used, with more of the same liquid what happens to its range. smaller range and either of: smaller temperature increase for liquid / meniscus to reach end of tube expands more / greater sensitivity and tube of same length State physical properties that can be used to measure temperature expansion of liquid expansion of solid expansion of gas density (of liquid) (electrical) resistance State two benefits of using a thermocouple thermometer instead of a liquid-in-glass thermometer. large range (measure) high temperatures remote sensing small size OR small mass small thermal capacity suitable for data logging responds quickly OR measures rapidly varying temperatures OR temperature changing continuously State and explain the two features of a liquid-in-glass thermometer that are necessary for linearity. Physics Past Paper Common Questions By Vasumitra Gajbhiye 16 statement: bore of constant (cross sectional) area explanation: idea of same movement / change in length of liquid / thread AND for same increase in volume / expansion (of liquid) statement: (liquid has) constant thermal expansion explanation: liquid moves same distance for each C temperature rise Others Suggest how to reduce the loss of thermal energy from the surface of a block. lagging / insulation (around block) OR insulate (the block) raise temperature of block by a smaller amount OR heat for a shorter time OR use lower power heater for same time OR higher power for same temperature rise / shorter time polish the surface of the block OR wrap the block in shiny material OR paint (shiny) white reduce initial temperature of block (to below room temperature) OR raise temperature of room reduce draughts When temperature increase, explain in terms of molecules, why does the internal energy increase. kinetic energy (and potential energy) of molecules increase (hence internal energy increases) State, in terms of molecules, what is meant by an increase in internal energy. increase in kinetic energy of molecules or increase in potential energy of molecules What are the advantages of solar cells. no polluting gases / quiet / low maintenance / can be placed on roofs / clean / cheap to run What are the disadvantages of solar cells. Physics Past Paper Common Questions By Vasumitra Gajbhiye 17 intermittent supply / unattractive / takes up space / uses land / d.c. output What are the disadvantages of hydroelectric power schemes damage to habitats (for fish) / construction is expensive / droughts / flood risk if dam bursts State uses for infrared radiation. remote controls (infrared) sensors / alarms specific electrical appliances thermal imaging State two environmental benefits of the electrically powered bicycle. less noise OR no noise less OR no air / gaseous pollution (from the bicycle) OR does not produce acid rain (the bicycle) uses no / less fossil fuel does not contribute to greenhouse effect OR does not release CO2 What are the consequences of burning coal? air pollution / harmful gases / acid rain CO2 / greenhouse gases / contribution to global warming not renewable damage from mining / drilling or any valid environmental consequence of transport of coal # 3. Waves SOUND Sound waves from a television are diffracted through doorways. Light waves from a television are not diffracted through doorways. Suggest why light waves and sound waves behave differently in this situation. Physics Past Paper Common Questions By Vasumitra Gajbhiye 18 wavelength of light is (much) smaller than width of doorway or wavelength of sound wavelength of sound is similar to width of doorway OR width of gap for diffraction to occur OR larger wavelength results in greater diffraction ORA How compressions differ from rarefactions. compressions are regions of high pressure in compressions particles are close together than normal. What is rarefaction. region of low pressure where molecules/ particles are further apart. Why sound waves are described as longitudinal. particles vibrate/ oscillate OR compressions/ rarefactions move. in the direction of travel of the wave. What is meant by transverse wave. particles vibrate at right angle/ perpendicular to wave direction. State how longitudinal waves differ from transverse wave. (longitudinal wave) vibration direction parallel to propagation / energy travel direction transverse wave vibration direction perpendicular to propagation / energy travel direction consists of rarefactions AND compressions State how transverse waves differ from longitudinal wave. particles (in transverse waves) vibrate perpendicular to the direction of travel (of the wave) OR particles in longitudinal waves vibrate parallel to the direction of travel of the wave longitudinal waves have compressions and rarefactions transverse waves have troughs and crests Physics Past Paper Common Questions By Vasumitra Gajbhiye 19 Light State one use of optic fibres in medicine. Fibre passing to site to be examined / treated. Light travels down optic fibres by multiple total internal reflections at the inner surface in to the body. endoscopy use to view internal organs using cameras. State one use of optic fibres in communication. light encoded optic fibre transmits light. Light travels in fiber. total internal reflection at inner surface or within fibre. What is meant by total internal reflection? Reflection in a more optically dense material where there is no refracted ray OR all light in a more dense material is reflected./ incident ray in more dense material angle of incidence greater than critical angle no light refracted all the light is reflected reflected with i = r What is meant by critical angle? The greatest angle of incidence at which refraction can occur The angle of incidence at which the refracted ray travels along the boundary/ angle of refraction is 90. The angle of incidence/ above which total internal reflection occurs. What is principal focus? Point on the principal axis OR use of term paraxial OR centre line (point) where incident parallel rays meet after passing through lens OR origin of rays that emerge parallel after passing through lens Physics Past Paper Common Questions By Vasumitra Gajbhiye 20 Explain, in terms of the behaviour of light rays, what is meant by principal focus for a thin converging lens. (point) where (parallel) rays (of light) meet (after passing through lens) point) where parallel rays (of light) meet / are focussed (after passing through lens) or (point) through which rays (of light) that emerge parallel pass (before reaching lens) Explain, in terms of the wavefronts, why the light changes direction as it enters the solid. idea of one side of wavefront enters / hits solid first OR wavefront does not all hit the solid all at once; idea of this side slowed down first OR this side delayed relative to other side angle of wave(front) changes OR different parts of wavefront delayed by different amounts State what is meant by focal length distance between principal focus / focal point and optical centre / lens State why an image is virtual? rays do not meet at image / only appear to come from image / do not originate from image / cannot be seen on a screen / light does not pass through the image State why an image is real? light passes through it OR can be projected/seen on a screen OR refracted rays cross/meet State properties of the image formed by the mirror. virtual upright same size as object laterally inverted Describe one medical use of Xrays. Treating cancer absorbed by tumor tumor killed. X-ray shadowgraph absorbed by bones photograph is produced. Physics Past Paper Common Questions By Vasumitra Gajbhiye 21 State one reason why it is necessary to take safety precautions when Xrays are used. can cause burns / (cell) mutation / cell damage / tumours / cancer / damages DNA etc. State two conditions required for light to be totally internally reflected. light (must pass) from medium where it travels slower or to medium where it is faster or from medium with larger refractive index or to medium with smaller refractive index angle of incidence (must be) greater than the critical angle / sin1(1 n) Digital and Analogue signals What is meant by digital? consists of signal with two possible states - high and low state / voltage Describe the difference between digital and analogue signals? digital signal: consists of signal with 2 possible states - high and low states / voltages analogue signal: consist of signal with continuously varying voltage so can take any value What are the benefits of digital signals? Digital signals enable an increased rate of transmission of data compared to analogue Due to accurate signal regeneration, the range of digital signals is larger than the range of analogue signals (they can cover larger distances ). OR Longer range due to accurate signal regeneration. The signal can be regenerated so there is minimal noise Extra data can be added so that the signal can be checked for errors Physics Past Paper Common Questions By Vasumitra Gajbhiye 22 4. Electricity and Magnetism DC Motor Describe how the split-ring commutator on an electric motor works. brushes connect to other split ring every half turn reverses direction of current every half turn. Explain the purpose of the split-ring commutator. brushes connect to other split ring every half turn. keeps coil rotating (in the same direction) by changing direction of current (in the coil) every half cycle/180 degrees A split-ring commutator is an important feature of a DC motor. Suggest one reason why the DC motor cannot operate without a split-ring commutator coil does not continue to rotate in the same direction AC Generator How AC generators work? (as coil rotates) it cuts (magnetic) field between the magnets This induces an e.m.f. / voltage / p.d. (in the coil) This produces a current in the (coil transferred to the) galvanometer (via the slip rings and carbon brushes) Direction of current flow changes with each 180 degree rotation of coil What is the function of slip ring? (provide) continuous connection while coil rotating State the position of the rotating coil when the alternating output voltage is at a maximum value and explain why the maximum output occurs at this position. (plane of coil) horizontal Physics Past Paper Common Questions By Vasumitra Gajbhiye 23 maximum number of magnetic field lines are cut at fastest rate (coil cutting magnetic field the fastest) Transformer Explain how does a transformer works? alternating current in primary coil alternating magnetic field is produced in primary coil field channelled/transferred from primary to secondary by core induced EMF in secondary coil Why transformers do not work on DC current? There is no change in the magnetic field. With an unchanging field passing through the secondary coil, no voltage is induced in it. Why transformers dont work at DC? There is no change of flux. Explain why the power losses in transmission cables are lower when electrical energy is transmitted at higher voltages. smaller current (and same resistance when the power is transmitted and an equal rate) less thermal energy loss / produced (in cables) Safety Earthing question. Physics Past Paper Common Questions By Vasumitra Gajbhiye 24 An electrical device has a metal case. Explain the benefit of earthing the metal case. (if) live wire touches metal case prevents electrocution OR metal case cannot become live OR metal case always at earth potential / voltage Explain how a fuse protects a circuit. if current too high fuse melts What is the reason for choosing a particular fuse rating. fuse rating/value above but near (to) normal operating current/ 10 A OR fuse rating/value slightly higher (than) normal operating current /10 if too low it would break / blow / melt when the appliances are operating normally if fuse too high wouldnt break / blow until current was too high which would be dangerous (to people /wires /appliance) Physics Past Paper Common Questions By Vasumitra Gajbhiye 25 If there is high current why is it necessary to use thick wire? thick wires have a smaller resistance less thermal energy generated in wires more efficient OR less risk of fire / insulation melting Why circuit breakers are used? quick response protects against electric shock protects against overheating (easily) re-settable avoids damage to lawnmower State and explain why electrical sockets and plugs used outside in a garden need to be different from those that can be used safely in a room inside a house. conditions (outdoors) may be damp / wet water conducts (electricity) OR clear statement of need for waterproof / outdoor specification (components) State and explain why fuses and circuit breakers are installed in electrical circuits connected to the mains supply. protects components / appliances / circuit / wires / user / mains supply prevents electrical supply overheating / fires / electrocution / shocks excess current / power in circuit / wires OR fuse melts / blows OR circuit breaker opens Other Theory What is meant by electromagnetic induction? When magnetic fields cut by a conductor. induce current/emf What is electric field? A region in which an electric charge experiences a force. Physics Past Paper Common Questions By Vasumitra Gajbhiye 26 What is the direction of the electric field? direction of force on a positive charge. What is the direction of the magnetic field? the direction of the force on a N-pole Describe how to demagnetise a bar magnet using alternating current (AC) in a coil. place magnet in coil EITHER (gradually) withdraw magnet with ac (in coil) switched on OR reduce current to zero Describe how to demagnetise a bar magnet? heat magnet to high temperature / red hot hammer the magnet repeatedly / in EW direction (place) magnet in a coil / solenoid carrying AC. remove magnet from coil OR decrease current (slowly) to zero Describe how the cone of the loudspeaker produces this sound. it / cone vibrates any two from: alternating current (a.c.) (in coil / wire) or alternating magnetic field (neighbouring) air vibrates or vibrations passed on Physics Past Paper Common Questions By Vasumitra Gajbhiye 27 (producing) compressions and rarefactions / vibrations parallel to energy transfer vibrating at 15 000 Hz (this 15000 frequency will be given in question) What is the purpose of variable resistor? To vary the current across name component. Suggest a practical use for LDR. switch on street lights (at night) / turn on security light (at night) When describing the motion of ray of beam in magnetic field or electric field use the word deflect and curve , then state the direction. Earthing is only useful if live wire touches the appliance not when excess current flow into the circuit. Fuse are only useful when excess current flows into the circuit, not when live wire touch the appliance. # 5. Nuclear Physics State what is meant by nuclear fusion. joining together of (small / H) nuclei to produce a bigger nucleus of different element / He nucleus or with the release of energy State what is meant by nuclear fission. splitting of a nucleus into (2) parts forming light(er)nucleus State what is meant by background radiation? the radiation that is always present due the surrounding/environment in every day life. What are the sources of background radiation? soil / rocks / earth / cosmic rays / space / Sun / weapons testing / radon / nuclear waste Physics Past Paper Common Questions By Vasumitra Gajbhiye 28 Describe the composition and structure of a neutral atom of uranium235. (very small) nucleus and surrounded by electrons (in orbit / shells) 92 protons or 92 electrons or number of protons = number of electrons protons and neutrons in nucleus 143 neutrons Explain why radioactivity readings are not constant. (radioactive decay is a) random (process) Describe how the americium-241 ionises air alpha (particles emitted from americium) move close to / hit molecules in the air (between the metal plates) removing electrons (out of the molecules) Explain why an extremely high temperature is needed when forcing these two nuclei together. are positively charged / have like charges or need to come close together they repel each other (high temperature produces) high (kinetic) energy / momentum / speed / ability to do large quantity of work -particles ionise the air they pass through less strongly than the same number of -particles. Suggest why this is so. -particles have charge of smaller size -particles have smaller mass -particles have less energy -particles travel faster / less time near to air molecule effect / force on electrons in air molecules less Suggest reasons for using an particle emitter in a smoke detector. alpha particles highly ionizing / more ionising than beta particles or gamma rays AND ionise air more easily Physics Past Paper Common Questions By Vasumitra Gajbhiye 29 alpha particles short range (in air) AND stopped by smoke safer to use and cause less harm because they do not travel out of smoke detector as they have short range. How radioactive sources are stored and handled safely? detail of shielded storage (store in lead lined shield storage) detail of secure storage (store in safe and secure storage) protective clothing minimise exposure by time OR distance OR activity monitoring exposure detail of handling source appropriately for, e.g. use of tongs must be disposed of securely limitation of access to approved personnel procedure in place in case of accident / criminal act to protect people and / or environment Suggest and explain three precautions for the safe use of X-rays. shielding of operator behind screen / lead apron / out of room AND to limit absorb radiation shielding of other parts of patient with lead / shielding of other parts of patient AND to limit absorb radiation limit time of exposure / not too frequent / max number of X-rays per year AND to limit dose limit strength / intensity of X-ray beam AND to limit dose distance from source AND reduces intensity / amount of radiation / exposure State economic and environmental consequences of producing nuclear waste. must be stored with shielding must be stored securely / safely must be transported with shielding Physics Past Paper Common Questions By Vasumitra Gajbhiye 30 must be transported securely expensive to store expensive to transport in case of accident / terrorism could escape to environment / danger to people site of storage uninhabitable for thousands of years State two differences between nuclear fission and nuclear fusion. nuclear fission nucleus / atom splits (into two) AND nuclear fusion two nuclei / atoms join together One from: nuclear fission large(r) mass (number) OR heavy nuclei / atoms involved OR neutrons involved / emitted} AND nuclear fusion small(er) mass (number) OR light nuclei / atoms involved OR no neutrons fission in a nuclear reactor AND fusion in Sun / stars fission produces very radioactive / long lasting waste fission makes lighter new elements AND fusion makes heavier new elements fission at normal p / T AND fusion at high p / T fusion produces more energy (than fission) State use of radioactive nuclides in medicine. sterilisation of equipment, treatment of cancer, gamma for diagnosis, radiotherapy NOT any link to X-rays State and explain practical application of gamma rays? suitable application e.g. sterilisation of equipment, medical diagnosis / treatment, thickness control, detecting leaks / cracks, food preservation Physics Past Paper Common Questions By Vasumitra Gajbhiye 31 explanation e.g. destroys bacteria, destroys cancer cells, lower amount of radiation detected if thickness too large, radiation detected at site of leak, destroys microbes in food # 6. Space Physics How redshift supports big bang? the furthest galaxies show the biggest red shift (meaning that) the furthest galaxies are moving fastest suggesting that galaxies are moving away from earth (so the) Universe is expanding (extrapolating backwards this suggests that) the Universe started from an initial point Explain why it is summer in the northern hemisphere when it is winter in the southern hemisphere. It is summer in the northern hemisphere as it is tilted towards the Sun. The southern hemisphere is tilted away from the Sun and so it is winter there. How many days are there from one full Moon to the next? 27.5 days How much distance is a light year? 9.5*10^15 m Name the force which causes planets to orbit the Sun. gravity Name the force which keeps the Moon in orbit around the Earth. gravity What shape are planetary orbits? elliptical How is the orbit of a comet different to the orbit of a planet? Physics Past Paper Common Questions By Vasumitra Gajbhiye 32 more highly elliptical The Moon does not emit light. Explain how were able to see the Moon. The moon reflects light form sun. Describe the movement of the Moon. The Moon orbits the Earth, taking 27.5 days to do so From which two elements is the Sun mostly made? Hydrogen and helium What two properties do molecular clouds have that allow them to collapse? They are cold and dense enough to collapse. Explain how stars are formed. When a molecular cloud is cold and dense enough, clumps of it can collapse under the force of gravity. The clump collapse into a spinning sphere of superhot gas, which pulls in more matter from the molecular cloud. It becomes a star once nuclear fusion starts. Explain what is meant by nuclear fusion. Nuclear fusion is where light nuclei fuse (join) together to create a heavy nucleus of different element and some mass turns into energy Why can nuclear fusion only occur at high temperatures? The nuclei all have the same positive charge so need to be moving fast enough to overcome the electrostatic repulsion. Explain what is a protostar. A very young star that is still gathering mass from its parent molecular cloud. Explain what is a main sequence star. A stable part of a stars life cycle when it is burning hydrogen in its core before moving onto another stage of its life cycle once it has used up 12% of its hydrogen. Explain what is a red giant A star with a starting mass of less than eight solar masses that is burning helium in its core. Its shell of hydrogen has expanded and cooled. Physics Past Paper Common Questions By Vasumitra Gajbhiye 33 Explain what is a white dwarf. The final stage of a star that started with less than eight solar masses and has run out of fuel. Explain what is a supernova. An exploding star that began life with more than 8 solar masses and has run out of fuel. Explain what is a neutron star. A collapsed star composed almost entirely of neutrons when a star with more than 8 solar masses reaches the end of its life. Explain what is a black hole. This is the final stage in the life cycle of a star that started with more than 8 solar masses. It has enough mass left over after exploding as a supernova to collapse to a point where gravity is so strong that not even light can escape. Calculate the age of the universe from this graph. Step 1: find the Hubbles constant. using d/v d/v = 60000/3000 = 20 km/s per million light years. Step 2: convert this Hubbles constant to per seconds by dividing this Hubbles constant by speed of light in Km. 20 / 9.5*10^12 = 2.105263158*10^-12 per second. Step 3: find the reciprocal of this value to fin age of universe in seconds. Physics Past Paper Common Questions By Vasumitra Gajbhiye 34 1 / 2.105263158*10^-12 = 4.75*10^17s Step 4: convert it to years by dividing by (60*60*24*365) 4.75*10^17 / (60*60*24*365) = 15.1*10^9 years = 15.1 billion years. What do we call a large group of star? galaxy Why do these groups form? Gravity What causes the redshift in the light arriving from distant galaxies? The galaxies are moving away; the wavelength is redshifted/increased/ stretched; What two pieces of evidence suggest big bang? Red shift and Cosmic microwave background radiation. What does the big bang theory describe? Origin of the universe. What do scientists believe is the origin of CMBR? Radiation produced shortly after big bang. Why was the discovery of CMBR so important to the scientists believing the Big Bang theory to be correct? Provides evidence for big bang. Can only be explained using big bang. Explain what is meant by the Big Bang theory. Universe began at a (very) small (initial) point. explosion causing Universe to expand Why scientists cannot answer the question why the universe was created? no evidence. involve religious believes. What is redshift? Increase in observed wavelength of light. Why it is better to use the most recent value of Hubbles constant than older ones? Physics Past Paper Common Questions By Vasumitra Gajbhiye 35 data more reliable accept data is more accurate or improved equipment / techniques more technology is insufficient or data obtained from more (distant) galaxies accept a wider range of data accept data closer to the line of best fit or data less scattered accept no anomalous result(s) accept all data fits the pattern What is blueshift? decrease in observed wavelength of light and increase in frequency of light. Describe the life history of a star like sun. formed from dust/gases pulled together by gravity massive so very large gravitational forces (pulling inwards) hydrogen helium / fusion releases energy [not fission or just nuclear] high temperature creates high pressure (pushing outwards) long period when forces balance then expands red giant / red star then contracts to (dense) white dwarf / white star

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Physics Past Paper Common Questions By Vasumitra Gajbhiye 1

# Physics Past Paper Common Questions By Vasumitra Gajbhiye

# 1. Motion, Forces and Energy

As the trolley moves across the rough surface, it slows down and stops. Explain, in terms of the work done, the energy change that takes place as the trolley slows down. work done against / due to / because of friction or kinetic energy (of trolley) used to do work kinetic energy decreases (to zero) thermal energy produced Why a bus begins to topple? line of action of centre of mass falls outside the base. State the principle of the conservation of momentum. no external forces OR isolated system sum of momenta / (total) momentum remains constant State the principle of conservation of energy. In a closed/ isolated system, total energy of the system is conserved/ constant. initial energy = final energy What is centre of mass? (the point) where (all) the mass can be considered to be concentrated State two properties of an object that may be changed by the action of forces. shape Physics Past Paper Common Questions By Vasumitra Gajbhiye 2size / volume / length / density / any linear dimension direction (of motion) / speed / velocity / momentum / kinetic energy / acceleration State the two conditions which must be true for an object to be in equilibrium. no resultant force OR forces are balanced OR all forces in opposite directions are equal OR forces cancel no resultant {moment / torque / turning effect} OR (sum of) clockwise moment(s) = (sum of) anticlockwise moment(s)

Hookes Law

State Hookes law extension is directly proportional to load (if elastic limit is not exceeded) Explain what is meant by the term limit of proportionality of the spring. up to the limit of proportionality, extension proportional to load What type of energy is stored in springs? Strain/ elastic potential energy.

Terminal velocity

Describe and explain the motion of an object released from top of an fluid, from when it is released until it reaches terminal velocity. (initial) acceleration caused by weight / force of gravity drag / resistance force increases (with speed) acceleration decreases as resistance force increase when weight(downward force) = resistance(upward force), (finally / at terminal velocity) no acceleration / constant speed (finally / at terminal velocity) no resultant force Explain why opening the parachute cannot reduce the speed of the skydiver to zero. Physics Past Paper Common Questions By Vasumitra Gajbhiye 3at zero speed there is no air resistance weight / downwards force is (still) acting or there is (now) a resultant force (downwards at zero speed) OR forces balance at a speed greater than zero speed cannot decrease / no deceleration once forces balance Why not 100% of GPE is converted to KE when an object falls? (work done against) friction / drag / resistance or thermal energy generated

Particles arrangement and motion

Describe the motion of molecules of the gas. Molecules move randomly/ in random directions Molecules have high speed Molecules collide with each other/ with walls. Molecules change direction in collision Molecules move in straight line between collision Molecules collide with the walls (of cylinder) Describe the motion of molecules of the solid. Molecules vibrate State two ways in which the molecular structure of liquid is different from the molecular structure of solid. Liquid molecules not in fixed position Liquid molecules have random/irregular arrangement Liquid molecules are (slightly) further apart State two ways in which the molecular structure of solids is different from the molecular structure of liquids. in solid, particles are arranged in regular lattice and just vibrate Physics Past Paper Common Questions By Vasumitra Gajbhiye 4in liquid, particles are arranged randomly, slide past each other, move. Describe, in terms of molecules and their motion, how a liquid differs from a gas. molecules close(r) molecules move only small distances (between collisions) or do not move freely molecules move in clusters or slide past each other State two ways in which the molecular structure of gas is different from the molecular structure of liquid. (gas) molecules further apart greater PE move singly/ in straight lines faster Why solids have fixed shapes? Explain in terms of forces between molecules and arrangement of molecules. Solids  molecules in lattice arrangement solids  strong forces between molecules Why liquids adapt to the shape of their container? Explain in terms of forces between molecules and arrangement of molecules. liquids  molecules not fixed in place OR molecules have an irregular arrangement OR molecules (slightly) further apart (on average) than in solids OR spaces between the molecules liquids  (average) forces too weak to keep molecules in a definite pattern OR forces just enough to hold molecules in the bulk of the liquid Why gas fills their container? Explain in terms of forces between molecules and arrangement of molecules. gases  molecules far apart gases  weak / no forces between molecules (except during collisions) Explain the melting of a solid in terms of molecules and energy. Physics Past Paper Common Questions By Vasumitra Gajbhiye 5molecules must be separated OR (intermolecular) bonds must be broken / overcome work done (against bonds) OR energy is required / needed NOT increase of KE / speed Explain, in terms of forces between molecules, why gases expand more than liquids when they have the same rise in temperature. Assume that the pressure remains constant. average distance between molecules greater (in gas) (attractive) forces between molecules lower or zero in gas

Gas pressure

Explain, in terms of the momentum of the molecules, how gas molecules exert pressure. molecules collide with walls momentum (of a molecule) changes / reverses force is exerted because force is rate of change of momentum or force is change in momentum per unit time (or per second) or F = mu - mv /t. force spread out over area / surface. p = F / A The gas bubble rises to the surface. The volume of the gas bubble increases as it rises higher in the water. Explain why the volume of the bubble increases. pressure in a liquid increases with depth OR pressure decreases (as bubble rises) pressure (of gas) is inversely proportional to volume OR internal pressure greater than external pressure (momentarily) OR (air) molecules do not have to hit surface of bubble as frequently (to stop the bubble collapsing) OR the bubble is not as strongly compressed Explain why the volume of the air in the balloon decreases as the temperature decreases. molecules move more slowly / have less kinetic energy Physics Past Paper Common Questions By Vasumitra Gajbhiye 6pressure (inside balloon) decreases or pressure is directly proportional to temperature or p  Tvolume is directly proportional to temperature or V Tmolecular collisions less frequent molecular collisions less violent / hard / exert smaller impulse water / external pressure compresses balloon or water pressure greater (and balloon compressed) Explain what happens to the pressure of a constant volume of air when the temperature of the air increases. Use ideas of momentum of molecules in your explanation. (temperature of air increases) so molecules move faster / their KE increases molecules collide with walls of container and change momentum greater change of momentum when temperature is higher OR collisions more frequent OR harder collisions OR force = rate of change of momentum (higher force and hence) higher pressure If volume increase, what happens to the pressure. pressure decrease density decrease/ fewer atoms per unit volume rate of collisions decrease/ fewer collisions per unit volume Explain, in terms of the behaviour of the molecules, why the pressure has increase. (molecules) collide with walls more often OR more collisions with walls per second or per unit time OR greater force per unit area

Moment

What is meant by the moment of a force about a pivot. (moment of a force) is the turning effect (about a point / pivot) Physics Past Paper Common Questions By Vasumitra Gajbhiye 72. Thermal Physics

Conduction

Explain, in terms of the atomic lattice and electrons, how thermal energy is transferred through the aluminium. atoms (touching the hotplate) / lattice vibrate (faster) more atoms pass on energy / vibration to neighbouring atoms / to other atoms by collision atoms pass on energy to electrons electrons hit distant atoms or electrons move (through lattice) Describe, in terms of molecules, how thermal energy is transferred from the heated sand through the base of the plastic pot. (thermal energy is transferred by) conduction sand molecules gain KE OR vibrate more OR hit (other) molecules (when heated) OR Energy is transferred to molecules of plastic pot in contact with sand (through collisions) OR Energy OR (lattice) vibrations transferred to neighbouring molecules Explain how electrons transfer thermal energy through the metal of the can atoms / ions vibrate (vibrating) atoms / ions hit electrons electrons propelled / travelling through metal lattice/ moving through metal lattice electrons hit (distant) atoms and transfer energy to distant atoms free electrons / delocalised electrons mentioned Physics Past Paper Common Questions By Vasumitra Gajbhiye 8Liquid

Explain, in terms of the water molecules, what happens to the thermal energy supplied to the water as it boils. energy used to breaks bonds. molecules escape from the liquid (as a vapour) (thermal energy) does work against intermolecular forces molecules separated/ moved apart and gain potential energy. Eventually, the water reaches boiling point. Thermal energy from the hotplate is still being transferred to the water. Explain, in terms of molecules, the effect of this thermal energy on the water. molecules escape from the liquid (as a vapour) bonds broken / (attractive) forces overcome molecules gain potential energy or work done (to separate molecules / break bonds / overcome forces) Describe what happens to molecules of the liquid as its temperature begins to increase. molecules (in liquid) move faster or gain energy molecules move apart (on average) Explain, in terms of molecules, why liquids are very difficult to compress molecules (already very) close / touching (repulsive) forces (very) large Explain, in terms of molecules, why a liquid expands when heated. molecules gain kinetic energy and move faster molecules push others away and move further apart As temperature increase, why does the ice starts to melt. k.e. of molecules / (thermal) energy absorbed (from water / surroundings) or energy absorbed from (cooling) water Physics Past Paper Common Questions By Vasumitra Gajbhiye 9supplies latent heat or energy used to overcome intermolecular forces / to break bonds

Gas

When the temperature of gases increased explain, in terms of molecules, what happens to the pressure of gas (Pressure of the gas) increases Molecules gain KE and move faster Molecules collide with/ hit walls more often/ frequently More collisions with wall per unit time (e.g. per second) Molecules collide with/ hit walls with greater force/ impulse/ harder. When the temperature of gases decreased explain, in terms of molecules, what happens to the pressure of gas molecules lose KE and move more slowly fewer collisions per unit time OR less hard collisions with walls/ balloon lower pressure

OR BETTER:

(Pressure of the gas) decrease Molecules lose KE and move slowly Molecules collide with/ hit walls less often/ frequently Fewer collisions with wall per unit time (e.g. per second) Molecules collide with/ hit walls with less force/ impulse/ harder. When volume is decreased explain, in terms of the behaviour of molecules, what happens to the pressure of gas. (Pressure of the gas) increases. Molecules close together Molecules collide with walls more often/ frequently OR more collisions with walls per second or per unit time. Physics Past Paper Common Questions By Vasumitra Gajbhiye 10 Greater force per unit area. When volume is increase explain, in terms of the behaviour of molecules, what happens to the pressure of gas. lower pressure fewer collision with wall/ balloon per second or per unit time. larger surface area of walls OR atoms further apart OR atoms travel further

OR BETTER:

(Pressure of the gas) decrease. Molecules further apart Molecules collide with walls less often/ frequently OR fewer collisions with walls per second or per unit time. Greater force per unit area. Explain, in terms of molecules, why gases are easiest to compress. More room for molecules OR molecules fit into gaps OR there are gaps between molecules. No/weak repulsive forces between molecules OR (repulsive) forces between molecules smaller OR pressure on walls, smaller OR only small pores/ pressure required.

OR BETTER:

Gas molecules are further apart so there is larger intermolecular space between molecules. No/ weak repulsive forces between molecules.

Brownian motion

Describe and explain the motion of smoke particles under microscope and account for this motion in terms of the air molecules. Smoke particles show random/ haphazard/ unpredictable/ movement Smoke particles show sudden change of direction/ zig-zag motion Smoke particles appear/ disappear from view OR go out of/ come into focus. Physics Past Paper Common Questions By Vasumitra Gajbhiye 11 IF THEY SAY TO ONLY EXPLAIN THE CAUSE OF THE MOTION OF SMOKE PARTICLE LEAVE THE FIRST THREE POINTS FROM ABOVE.

Air molecules collide with smoke particles from all direction/ unevenly cause random motion of particles Air molecules move randomly. Air molecules faster Air molecules smaller lighter/ have smaller mass

Difference

State and explain how the size of attractive forces acting between the molecules of gas compares with the size of attractive forces between the molecules of a solid. (Attractive) forces (much) smaller between gas molecules Gas molecules (much) further apart. State and explain, in terms of the forces between the molecules, how the compressibility of a gas differs from that of a liquid. gases compressible OR liquids incompressible no/ weaker repulsive forces between molecules OR vice versa for liquid molecules. Explain in terms of molecules why it is possible to compress gas, but not liquid. Gas molecules (very) far apart from OR empty space between gas molecules. Molecules of liquid (very) close together compact OR are touching (each other). Explain, in terms of molecules, why a liquid expands more than a solid when heated. forces between liquid molecules weak(er than in solids) less energy / work done to separate molecules or greater separation for same work done / same increase in energy State ways in which evaporation differs from boiling.

at surface/ not within liquid Physics Past Paper Common Questions By Vasumitra Gajbhiye 12 at any temperature/ not at boiling point (evaporation) causes cooling boiling requires a heat source bubbles rising State ways in which boiling differs from evaporation.

boiling throughout liquid (evaporation at surface) boiling at one temperature (evaporation at any/ all temperature/ below boiling point). boiling produces bubbles (evaporation does not). boiling not affected by draught/ area (evaporation is)

Evaporation

Explain, in terms of the behaviour of molecules, the process of evaporation. some molecules at the surface gain more KE, so have more energy than others heat energy used to work done against/ overcome attractive forces between molecules. most energetic molecules escape from the surface of the liquid Explain, in terms of the behaviour of molecules, how evaporation process helps the body to cool down. evaporation OR heat/ (thermal) energy needed for evaporation leaves sweat cooler faster molecules/ higher energy molecules escape heat flows from body to warm the sweat (so body cools) Explain, in terms of molecules, how sweating helps to cool your body on a hot day (thermal) energy in the skin / body transferred to (molecules of) sweat These molecules (have enough KE to) escape from the skin / become water vapour Physics Past Paper Common Questions By Vasumitra Gajbhiye 13 Leaving behind molecules with lower energy Which leaves the skin / body at a lower temperature Explain, in terms of molecules, why temperature decreases during evaporation. Molecules do work against attractive forces as they evaporate. Faster/ more energetic water molecules (more likely to) escape from surface Slower/ less energetic molecules remain (so temperature is lower). Average energy of remaining molecules decrease. In terms of molecules, state and explain how the rate of evaporation of the puddles in is affected by a reduction of wind speed. Reduces (rate of evaporation) No/ fewer evaporated molecules blown away/ removed by wind, OR greater humidity/ vapour pressure. In terms of molecules, state and explain how the rate of evaporation of the puddles in is affected by an increase in water temperature. Increases (rate of evaporation) Molecules move faster/ have more energy OR molecules have energy to escape. Which container has faster rate of cooling wide and shallow OR narrow and deep. Water in wider container AND has water with larger surface (area). Rate of evaporation higher/ faster/ quicker OR higher chance of evaporation. Suggest ways in which the rate of evaporation can be reduced. Cover/ decrease surface area Reduce temperature Reduce draught(a current of cool air in a room or other confined space) Increase humidity of air. Suggest ways in which the rate of evaporation can be increased. Increase temperature/ supply more heat/ make hotter Physics Past Paper Common Questions By Vasumitra Gajbhiye 14 Blow air across surface. Reduce humidity Decrease pressure.

Thermometer

How to increase the range of a thermometer. capillary tube longer or liquid with lower expansivity or smaller bulb with less volume or increase diameter of tube. What happen to range if smaller bulb is used, with smaller volume of liquid? (range) increases and less expansion/increase in volume (of mercury per unit temperature rise) How to increase the sensitivity of a thermometer. capillary tube thinner/finer or liquid with higher expansivity or larger bulb with more volume of liquid or smaller bulb with same volume of liquid. State what is meant by a linear scale. same distance moved (by thread) for same temperature change State and explain the two features of a liquid-in-glass thermometer that are necessary for linearity statement 1: bore of constant (cross sectional) area explanation: idea of same movement / change in length of liquid / thread AND for same increase in volume / expansion (of liquid) statement: (liquid has) constant thermal expansion explanation: liquid moves same distance for each C temperature rise State what is meant by range. difference between the maximum temperature and minimum temperature it can measure State what is meant by sensitivity. Physics Past Paper Common Questions By Vasumitra Gajbhiye 15 distance moved by the thread per C OR per unit temperature change If a larger bulb is used, with more of the same liquid what happens to its sensitivity. greater sensitivity volume increase (of liquid in second thermometer) is greater or liquid moves a greater distance (for the same temperature increase) If a larger bulb is used, with more of the same liquid what happens to its range. smaller range and either of:  smaller temperature increase for liquid / meniscus to reach end of tube  expands more / greater sensitivity and tube of same length State physical properties that can be used to measure temperature expansion of liquid expansion of solid expansion of gas density (of liquid) (electrical) resistance State two benefits of using a thermocouple thermometer instead of a liquid-in-glass thermometer. large range (measure) high temperatures remote sensing small size OR small mass small thermal capacity suitable for data logging responds quickly OR measures rapidly varying temperatures OR temperature changing continuously State and explain the two features of a liquid-in-glass thermometer that are necessary for linearity. Physics Past Paper Common Questions By Vasumitra Gajbhiye 16 statement: bore of constant (cross sectional) area explanation: idea of same movement / change in length of liquid / thread AND for same increase in volume / expansion (of liquid) statement: (liquid has) constant thermal expansion explanation: liquid moves same distance for each C temperature rise

Others

Suggest how to reduce the loss of thermal energy from the surface of a block. lagging / insulation (around block) OR insulate (the block) raise temperature of block by a smaller amount OR heat for a shorter time OR use lower power heater for same time OR higher power for same temperature rise / shorter time polish the surface of the block OR wrap the block in shiny material OR paint (shiny) white reduce initial temperature of block (to below room temperature) OR raise temperature of room reduce draughts When temperature increase, explain in terms of molecules, why does the internal energy increase. kinetic energy (and potential energy) of molecules increase (hence internal energy increases) State, in terms of molecules, what is meant by an increase in internal energy. increase in kinetic energy of molecules or increase in potential energy of molecules What are the advantages of solar cells. no polluting gases / quiet / low maintenance / can be placed on roofs / clean / cheap to run What are the disadvantages of solar cells. Physics Past Paper Common Questions By Vasumitra Gajbhiye 17 intermittent supply / unattractive / takes up space / uses land / d.c. output What are the disadvantages of hydroelectric power schemes damage to habitats (for fish) / construction is expensive / droughts / flood risk if dam bursts State uses for infrared radiation. remote controls (infrared) sensors / alarms specific electrical appliances thermal imaging State two environmental benefits of the electrically powered bicycle. less noise OR no noise less OR no air / gaseous pollution (from the bicycle) OR does not produce acid rain (the bicycle) uses no / less fossil fuel does not contribute to greenhouse effect OR does not release CO2 What are the consequences of burning coal? air pollution / harmful gases / acid rain CO2 / greenhouse gases / contribution to global warming not renewable damage from mining / drilling or any valid environmental consequence of transport of coal

# 3. Waves

SOUND

Sound waves from a television are diffracted through doorways. Light waves from a television are not diffracted through doorways. Suggest why light waves and sound waves behave differently in this situation. Physics Past Paper Common Questions By Vasumitra Gajbhiye 18 wavelength of light is (much) smaller than width of doorway or wavelength of sound wavelength of sound is similar to width of doorway OR   width of gap for diffraction to occur OR larger wavelength results in greater diffraction ORA How compressions differ from rarefactions. compressions are regions of high pressure in compressions particles are close together than normal. What is rarefaction. region of low pressure where molecules/ particles are further apart. Why sound waves are described as longitudinal. particles vibrate/ oscillate OR compressions/ rarefactions move.

in the direction of travel of the wave. What is meant by transverse wave. particles vibrate at right angle/ perpendicular to wave direction. State how longitudinal waves differ from transverse wave. (longitudinal wave) vibration direction parallel to propagation / energy travel direction transverse wave vibration direction perpendicular to propagation / energy travel direction consists of rarefactions AND compressions State how transverse waves differ from longitudinal wave. particles (in transverse waves) vibrate perpendicular to the direction of travel (of the wave) OR particles in longitudinal waves vibrate parallel to the direction of travel of the wave longitudinal waves have compressions and rarefactions transverse waves have troughs and crests Physics Past Paper Common Questions By Vasumitra Gajbhiye 19 Light

State one use of optic fibres in medicine. Fibre passing to site to be examined / treated. Light travels down optic fibres by multiple total internal reflections at the inner surface in to the body. endoscopy use to view internal organs using cameras. State one use of optic fibres in communication. light encoded optic fibre transmits light. Light travels in fiber. total internal reflection at inner surface or within fibre. What is meant by total internal reflection? Reflection in a more optically dense material where there is no refracted ray OR all light in a more dense material is reflected./ incident ray in more dense material angle of incidence greater than critical angle no light refracted all the light is reflected reflected with i = r What is meant by critical angle? The greatest angle of incidence at which refraction can occur The angle of incidence at which the refracted ray travels along the boundary/ angle of refraction is 90. The angle of incidence/ above which total internal reflection occurs. What is principal focus? Point on the principal axis OR use of term paraxial OR centre line (point) where incident parallel rays meet after passing through lens OR origin of rays that emerge parallel after passing through lens Physics Past Paper Common Questions By Vasumitra Gajbhiye 20 Explain, in terms of the behaviour of light rays, what is meant by principal focus for a thin converging lens. (point) where (parallel) rays (of light) meet (after passing through lens) point) where parallel rays (of light) meet / are focussed (after passing through lens) or (point) through which rays (of light) that emerge parallel pass (before reaching lens) Explain, in terms of the wavefronts, why the light changes direction as it enters the solid. idea of one side of wavefront enters / hits solid first OR wavefront does not all hit the solid all at once; idea of this side slowed down first OR this side delayed relative to other side angle of wave(front) changes OR different parts of wavefront delayed by different amounts State what is meant by focal length distance between principal focus / focal point and optical centre / lens State why an image is virtual? rays do not meet at image / only appear to come from image / do not originate from image / cannot be seen on a screen / light does not pass through the image

State why an image is real?

light passes through it OR can be projected/seen on a screen OR refracted rays cross/meet State properties of the image formed by the mirror. virtual upright same size as object laterally inverted Describe one medical use of Xrays. Treating cancer  absorbed by tumor  tumor killed. X-ray shadowgraph  absorbed by bones  photograph is produced. Physics Past Paper Common Questions By Vasumitra Gajbhiye 21 State one reason why it is necessary to take safety precautions when Xrays are used. can cause burns / (cell) mutation / cell damage / tumours / cancer / damages DNA etc. State two conditions required for light to be totally internally reflected. light (must pass) from medium where it travels slower or to medium where it is faster or from medium with larger refractive index or to medium with smaller refractive index angle of incidence (must be) greater than the critical angle / sin1(1  n)

Digital and Analogue signals

What is meant by digital? consists of signal with two possible states - high and low state / voltage Describe the difference between digital and analogue signals? digital signal: consists of signal with 2 possible states - high and low states / voltages analogue signal: consist of signal with continuously varying voltage so can take any value What are the benefits of digital signals? Digital signals enable an increased rate of transmission of data compared to analogue Due to accurate signal regeneration, the range of digital signals is larger than the range of analogue signals (they can cover larger distances ). OR Longer range due to accurate signal regeneration. The signal can be regenerated so there is minimal noise

Extra data can be added so that the signal can be checked for errors Physics Past Paper Common Questions By Vasumitra Gajbhiye 22 4. Electricity and Magnetism

DC Motor

Describe how the split-ring commutator on an electric motor works. brushes connect to other split ring every half turn reverses direction of current every half turn. Explain the purpose of the split-ring commutator. brushes connect to other split ring every half turn. keeps coil rotating (in the same direction) by changing direction of current (in the coil) every half cycle/180 degrees A split-ring commutator is an important feature of a DC motor. Suggest one reason why the DC motor cannot operate without a split-ring commutator coil does not continue to rotate in the same direction

AC Generator

How AC generators work? (as coil rotates) it cuts (magnetic) field between the magnets This induces an e.m.f. / voltage / p.d. (in the coil) This produces a current in the (coil transferred to the) galvanometer (via the slip rings and carbon brushes) Direction of current flow changes with each 180 degree rotation of coil What is the function of slip ring? (provide) continuous connection while coil rotating State the position of the rotating coil when the alternating output voltage is at a maximum value and explain why the maximum output occurs at this position. (plane of coil) horizontal Physics Past Paper Common Questions By Vasumitra Gajbhiye 23 maximum number of magnetic field lines are cut at fastest rate (coil cutting magnetic field the fastest)

Transformer

Explain how does a transformer works? alternating current in primary coil alternating magnetic field is produced in primary coil field channelled/transferred from primary to secondary by core induced EMF in secondary coil Why transformers do not work on DC current? There is no change in the magnetic field. With an unchanging field passing through the secondary coil, no voltage is induced in it. Why transformers dont work at DC? There is no change of flux. Explain why the power losses in transmission cables are lower when electrical energy is transmitted at higher voltages. smaller current (and same resistance when the power is transmitted and an equal rate) less thermal energy loss / produced (in cables)

Safety

Earthing question. Physics Past Paper Common Questions By Vasumitra Gajbhiye 24 An electrical device has a metal case. Explain the benefit of earthing the metal case. (if) live wire touches metal case prevents electrocution OR metal case cannot become live OR metal case always at earth potential / voltage Explain how a fuse protects a circuit. if current too high fuse melts What is the reason for choosing a particular fuse rating. fuse rating/value above but near (to) normal operating current/ 10 A OR fuse rating/value slightly higher (than) normal operating current /10 if too low it would break / blow / melt when the appliances are operating normally if fuse too high wouldnt break / blow until current was too high which would be dangerous (to people /wires /appliance) Physics Past Paper Common Questions By Vasumitra Gajbhiye 25 If there is high current why is it necessary to use thick wire? thick wires have a smaller resistance less thermal energy generated in wires more efficient OR less risk of fire / insulation melting Why circuit breakers are used? quick response protects against electric shock protects against overheating (easily) re-settable avoids damage to lawnmower State and explain why electrical sockets and plugs used outside in a garden need to be different from those that can be used safely in a room inside a house. conditions (outdoors) may be damp / wet water conducts (electricity) OR clear statement of need for waterproof / outdoor specification (components) State and explain why fuses and circuit breakers are installed in electrical circuits connected to the mains supply. protects components / appliances / circuit / wires / user / mains supply prevents electrical supply overheating / fires / electrocution / shocks excess current / power in circuit / wires OR fuse melts / blows OR circuit breaker opens

Other Theory

What is meant by electromagnetic induction? When magnetic fields cut by a conductor. induce current/emf What is electric field? A region in which an electric charge experiences a force. Physics Past Paper Common Questions By Vasumitra Gajbhiye 26 What is the direction of the electric field? direction of force on a positive charge. What is the direction of the magnetic field? the direction of the force on a N-pole Describe how to demagnetise a bar magnet using alternating current (AC) in a coil. place magnet in coil EITHER (gradually) withdraw magnet with ac (in coil) switched on OR reduce current to zero Describe how to demagnetise a bar magnet? heat magnet to high temperature / red hot hammer the magnet repeatedly / in EW direction

(place) magnet in a coil / solenoid carrying AC. remove magnet from coil OR decrease current (slowly) to zero Describe how the cone of the loudspeaker produces this sound. it / cone vibrates any two from: alternating current (a.c.) (in coil / wire) or alternating magnetic field (neighbouring) air vibrates or vibrations passed on Physics Past Paper Common Questions By Vasumitra Gajbhiye 27 (producing) compressions and rarefactions / vibrations parallel to energy transfer vibrating at 15 000 Hz (this 15000 frequency will be given in question) What is the purpose of variable resistor? To vary the current across name component. Suggest a practical use for LDR. switch on street lights (at night) / turn on security light (at night) When describing the motion of ray of beam in magnetic field or electric field use the word deflect and curve , then state the direction. Earthing is only useful if live wire touches the appliance not when excess current flow into the circuit. Fuse are only useful when excess current flows into the circuit, not when live wire touch the appliance.

# 5. Nuclear Physics

State what is meant by nuclear fusion. joining together of (small / H) nuclei to produce a bigger nucleus of different element / He nucleus or with the release of energy State what is meant by nuclear fission. splitting of a nucleus into (2) parts forming light(er)nucleus State what is meant by background radiation? the radiation that is always present due the surrounding/environment in every day life. What are the sources of background radiation? soil / rocks / earth / cosmic rays / space / Sun / weapons testing / radon / nuclear waste Physics Past Paper Common Questions By Vasumitra Gajbhiye 28 Describe the composition and structure of a neutral atom of uranium235. (very small) nucleus and surrounded by electrons (in orbit / shells) 92 protons or 92 electrons or number of protons = number of electrons protons and neutrons in nucleus 143 neutrons Explain why radioactivity readings are not constant. (radioactive decay is a) random (process) Describe how the americium-241 ionises air alpha (particles emitted from americium) move close to / hit molecules in the air (between the metal plates) removing electrons (out of the molecules) Explain why an extremely high temperature is needed when forcing these two nuclei together. are positively charged / have like charges or need to come close together they repel each other (high temperature produces) high (kinetic) energy / momentum / speed / ability to do large quantity of work -particles ionise the air they pass through less strongly than the same number of -particles. Suggest why this is so. -particles have charge of smaller size -particles have smaller mass -particles have less energy -particles travel faster / less time near to air molecule effect / force on electrons in air molecules less Suggest reasons for using an particle emitter in a smoke detector. alpha particles highly ionizing / more ionising than beta particles or gamma rays AND ionise air more easily Physics Past Paper Common Questions By Vasumitra Gajbhiye 29 alpha particles short range (in air) AND stopped by smoke safer to use and cause less harm because they do not travel out of smoke detector as they have short range. How radioactive sources are stored and handled safely? detail of shielded storage (store in lead lined shield storage) detail of secure storage (store in safe and secure storage) protective clothing minimise exposure by time OR distance OR activity monitoring exposure detail of handling source appropriately for, e.g. use of tongs must be disposed of securely limitation of access to approved personnel procedure in place in case of accident / criminal act to protect people and / or environment Suggest and explain three precautions for the safe use of X-rays. shielding of operator behind screen / lead apron / out of room AND to limit absorb radiation shielding of other parts of patient with lead / shielding of other parts of patient AND to limit absorb radiation limit time of exposure / not too frequent / max number of X-rays per year AND to limit dose limit strength / intensity of X-ray beam AND to limit dose distance from source AND reduces intensity / amount of radiation / exposure State economic and environmental consequences of producing nuclear waste. must be stored with shielding must be stored securely / safely must be transported with shielding Physics Past Paper Common Questions By Vasumitra Gajbhiye 30 must be transported securely expensive to store expensive to transport in case of accident / terrorism could escape to environment / danger to people site of storage uninhabitable for thousands of years State two differences between nuclear fission and nuclear fusion. nuclear fission  nucleus / atom splits (into two) AND nuclear fusion  two nuclei / atoms join together

One from:

nuclear fission large(r) mass (number) OR heavy nuclei / atoms involved OR neutrons involved / emitted} AND nuclear fusion  small(er) mass (number) OR light nuclei / atoms involved OR no neutrons fission in a nuclear reactor AND fusion in Sun / stars fission produces very radioactive / long lasting waste fission makes lighter new elements AND fusion makes heavier new elements fission at normal p / T AND fusion at high p / T fusion produces more energy (than fission) State use of radioactive nuclides in medicine. sterilisation of equipment, treatment of cancer, gamma for diagnosis, radiotherapy NOT any link to X-rays State and explain practical application of gamma rays? suitable application e.g. sterilisation of equipment, medical diagnosis / treatment, thickness control, detecting leaks / cracks, food preservation Physics Past Paper Common Questions By Vasumitra Gajbhiye 31 explanation e.g. destroys bacteria, destroys cancer cells, lower amount of radiation detected if thickness too large, radiation detected at site of leak, destroys microbes in food

# 6. Space Physics

How redshift supports big bang? the furthest galaxies show the biggest red shift (meaning that) the furthest galaxies are moving fastest suggesting that galaxies are moving away from earth (so the) Universe is expanding (extrapolating backwards this suggests that) the Universe started from an initial point Explain why it is summer in the northern hemisphere when it is winter in the southern hemisphere. It is summer in the northern hemisphere as it is tilted towards the Sun. The southern hemisphere is tilted away from the Sun and so it is winter there. How many days are there from one full Moon to the next? 27.5 days How much distance is a light year? 9.5*10^15 m Name the force which causes planets to orbit the Sun. gravity Name the force which keeps the Moon in orbit around the Earth. gravity What shape are planetary orbits? elliptical How is the orbit of a comet different to the orbit of a planet? Physics Past Paper Common Questions By Vasumitra Gajbhiye 32 more highly elliptical The Moon does not emit light. Explain how were able to see the Moon. The moon reflects light form sun. Describe the movement of the Moon. The Moon orbits the Earth, taking 27.5 days to do so From which two elements is the Sun mostly made? Hydrogen and helium What two properties do molecular clouds have that allow them to collapse? They are cold and dense enough to collapse. Explain how stars are formed. When a molecular cloud is cold and dense enough, clumps of it can collapse under the force of gravity. The clump collapse into a spinning sphere of superhot gas, which pulls in more matter from the molecular cloud. It becomes a star once nuclear fusion starts. Explain what is meant by nuclear fusion. Nuclear fusion is where light nuclei fuse (join) together to create a heavy nucleus of different element and some mass turns into energy Why can nuclear fusion only occur at high temperatures? The nuclei all have the same positive charge so need to be moving fast enough to overcome the electrostatic repulsion. Explain what is a protostar. A very young star that is still gathering mass from its parent molecular cloud. Explain what is a main sequence star. A stable part of a stars life cycle when it is burning hydrogen in its core before moving onto another stage of its life cycle once it has used up 12% of its hydrogen. Explain what is a red giant A star with a starting mass of less than eight solar masses that is burning helium in its core. Its shell of hydrogen has expanded and cooled. Physics Past Paper Common Questions By Vasumitra Gajbhiye 33 Explain what is a white dwarf. The final stage of a star that started with less than eight solar masses and has run out of fuel. Explain what is a supernova. An exploding star that began life with more than 8 solar masses and has run out of fuel. Explain what is a neutron star. A collapsed star composed almost entirely of neutrons when a star with more than 8 solar masses reaches the end of its life. Explain what is a black hole. This is the final stage in the life cycle of a star that started with more than 8 solar masses. It has enough mass left over after exploding as a supernova to collapse to a point where gravity is so strong that not even light can escape. Calculate the age of the universe from this graph.

Step 1: find the Hubbles constant. using d/v

d/v = 60000/3000 = 20 km/s per million light years. Step 2: convert this Hubbles constant to per seconds by dividing this Hubbles constant by speed of light in Km.

20 / 9.5*10^12 = 2.105263158*10^-12 per second. Step 3: find the reciprocal of this value to fin age of universe in seconds. Physics Past Paper Common Questions By Vasumitra Gajbhiye 34 1 / 2.105263158*10^-12 = 4.75*10^17s

Step 4: convert it to years by dividing by (60*60*24*365)

4.75*10^17 / (60*60*24*365) = 15.1*10^9 years = 15.1 billion years.

What do we call a large group of star? galaxy  Why do these groups form? Gravity What causes the redshift in the light arriving from distant galaxies? The galaxies are moving away; the wavelength is redshifted/increased/ stretched; What two pieces of evidence suggest big bang? Red shift and Cosmic microwave background radiation. What does the big bang theory describe? Origin of the universe. What do scientists believe is the origin of CMBR? Radiation produced shortly after big bang. Why was the discovery of CMBR so important to the scientists believing the Big Bang theory to be correct? Provides evidence for big bang. Can only be explained using big bang. Explain what is meant by the Big Bang theory. Universe began at a (very) small (initial) point. explosion causing Universe to expand Why scientists cannot answer the question why the universe was created? no evidence. involve religious believes. What is redshift? Increase in observed wavelength of light. Why it is better to use the most recent value of Hubbles constant than older ones? Physics Past Paper Common Questions By Vasumitra Gajbhiye 35 data more reliable accept data is more accurate or improved equipment / techniques more technology is insufficient or data obtained from more (distant) galaxies accept a wider range of data accept data closer to the line of best fit or data less scattered accept no anomalous result(s) accept all data fits the pattern What is blueshift? decrease in observed wavelength of light and increase in frequency of light. Describe the life history of a star like sun. formed from dust/gases pulled together by gravity massive so very large gravitational forces (pulling inwards) hydrogen  helium / fusion releases energy [not fission or just nuclear] high temperature creates high pressure (pushing outwards) long period when forces balance then expands  red giant / red star then contracts to (dense) white dwarf / white star

Transcript for:Key Concepts in Physics for Exams

Transcript for:
Key Concepts in Physics for Exams