A2 Physics definitions according to Mark scheme, Papers of Physics

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42. Molton in o Ctrele Define the radian. angle (sublended) where arc (lenglh) Is equal lo radius M1 (angle subtended) at the centre of a circle al With reference to velocity and acceleration, describe uniform circular motion. constanl speed or constan! magnilude of velocity ‘acceleration (always) perpendicular to velocity State what is meant by centripetal acceleration. ‘acceleration perpendicular to velocity a1 |e. 0 ‘ Te HS State what is meant by a field of force. tegion (of space) Bq where a particle experiences a force 51 State what Is meant by a line of force in a gravitational fleld. either direction of force on a (small test) mass or direction of acceleration of a (small lest) mass a1 By reference to the pattern of the lines of gravitational force near to the surface of the Earth, explain why the acceleration of free fall near to the Earth's surface is approximately constant. Any three from: * the lines are radial * pear the surface the lines are (approximately) parallel * — parailel lines so constant field strength * constant field strength hence constant acceleration of free fall State what is meant by a gravitational force. BS force acting between two masses or force on mass due to another mass or force on mass In a gravitational eid State the equation for the gravitational force F between two point masses m, and m, that are separated by a distance r. State the meaning of any other symbols you use. F=(Gmimjir M1 where G is the gravitational constant Al Define gravitational field. force per unit mass Bt Define gravitational field strength. (gravitational) force per unit mass at| the acceleration of free fall. Explain why, at the surface of a planet, gravitational field strength is numerically equal to acceleration = Fim, field strength = Fim, so equal BI presence of two large masses nearby. Explain how it is possible for the gravitational field strength to be zero despite the (gravitational) elds trom the Earth and Moon are in opposite directions Bt (resultant Is zero where gravilational) fields are equal {in magnitude) Bi Explain how a satellite may be in a circular orbit around a planet. gravkational force (ot attraction between satelite and planet) fowides Js centripetal force (on saletfle about the planet) BI A geostationary satellite orbits the Earth. The orbit of the satellite Is circular and the period of the orbit Is 24 hours. (i) State two other features of this orbit. Uses a property (of a subsiance) thol chonges wih lemperature at explain why two thermometers may not give the same temperature reading for an abject. = lomparnture scale assumes Onear change of propeny wih temperature «physical properbes may not vary bnearly wih Lemparature + ogteas only af fixed pownls Any ? points az Explain what is meant by the statement that two bodies are in thermal equilibrium. no net energy transfer between the bodies or bodies are al the same temperature Bi 0) Define specific heat capacity. (thermal) energy per unil mass (lo cause lemperature change) at (ihenmal) energy per unit change In tempersture 51 State what is meant by specific Jaten! heat. (thermal) energy per (unit) mass {lo change stale) (heal transfer during) change of stale at constant temperature BI Define specific latent heat of fusion. (uermal) energy per unit mass (lo cause change of stale) (energy transfer qunng) change of stale between so8d and Bquid al constant temperature Define specific latent heat of vaporisation. (thermal) energy per unil mass 51 energy to change state between liquid and gas al constant temperature: a1 Explain why, although the power of the heater is changed, the rate of loss of thermal energy to the surroundings may be assumed to be constant. temperature difference (between liquid and sumoundings) does not change 51 State what is observed by the sludent that shows thal the Ice Is melting at a constant rate. ‘Any one from: Bi * ale of increase in mass (of beaker and water) Is constant = level of waler rises al a constant rate = volume of water (In beaker) Increases al a constant rate * constant time between drops * constant rate of dripping During meiting, a solid becomes liquid with little or no change in volume. Use kinetic theory to explain why, during the melting process, thermal energy is required although there is no change in temperature. (during melting.) bonds between atoms/molecules are broken 1 potential energy of aloms/molecules Is Increased Bt nofittle work done so required input of energy Is thermal BI 1 Tded qases the Avogadro constant N,, _ um) number of atoms/nuclei in 12 g of carbon-12 B11] | the mole. amount of substance Mi | containing N (or 6.02 x 10) particles/molecules/atoms | or which contains the same number of particles/atoms/molecules as there are atoms in 129 of carbon-12 At 2] State what is meant by an ideal gas. gas that obeys equation p¥-= constant » T mt symbols p,Vand T explained at Explain how movement of the gas molecules causes pressure in the container. Any 3 trom: * molecule collides with wall + momentum of molecule changes during collision (with wall) + force on molecull so force on wall * many forces acl over surface area of container exeriing a pressure ‘ 53 16 Thermodynamics State what is meant by the internal energy of a system. otal potential energy and kinetic energy (of molecules/atoms) Mt reference to fandom mation of moleculesiatoms: AY By reference to intermolecular forces, explain why the change in internal energy of an ideal gas is equal to the change in total kinetic energy of its molecules. infernal energy = Zé (of molecules) + EEr (of molecules) or no forces between molecules 51 potential energy of malaeules is zero BI The first law of thermodynamics may be expressed as AU = (+q) + (+) where AU is the Increase in internal energy of the system. ‘State the meaning of: +9: thennal energy transfer to system BI #w. work done on system a1 State what is represented by a negallve value of AU. decrease in intemal energy Bi State and explain the total change, if any, in the internal energy of the gas during one complete cycle. 1 (total) change (in internal energy) gas retums to its original temperature a1 47-0807 llobione, Explain what Is meant by the natural frequency of vibration of a system. Frequency al which body will vibrate when there Is na (resultant external) resistive force acting on I OR frequency at which body will vibrate when there Is ne driving force exlemal farce acting on It Bt forced frequency, frequency at which object is made to vibrate/oscillate State, by reference to simple harmonic motion, what is meant by angular frequeney. (1) (anguiar frequency =) 2x « frequency or 2n/period Stale what is meant by simple harmonic motion. acceleration (directly) proportional to displacement 81 acceleration In opposte direction to displacement or acceleration (directed) towards equilibrlum position Bt symbols used to represent physical quantities. State the defining equation for simple harmonic motion. Identify the meaning of each of the a=-wix m1 a= acceleration, x= displacement from equilibrium position and «= angutar frequency State what is meant by damping. Al {oss of (total energy (of system) at due to resistive forces a1 State one similarity and one difference between the electric field due to a point charge and the gravitational field due to a point mass. similarity - any one point trom: + both have an inverse square variation + both decrease with distance * both are radial 81 difference — any one point from: * gravitational fleld always towards (Ihe mass) * electric fleld can be lowards or away from (the charge) at Define electric potential at a point. WORK dane per unl charge Bt work done (on charge) In moving posillive charge from Infinity (lo the point) Bt State the relationship between electric potential and electric field strength at a point. field strength = potenttat gradient 1 ‘sign included or directions discussed AL 19. Capactance State what is meant by the capacitance of a parallel plate capacitor. charge /poteptial M1 charge Is on one plate, polential Is p.d. between he plales Al stores energy, not charge. ‘equal and opposite charges on the plates so no resultant charge: Suggest why, when the capacitor Is connected across the terminals of a battery, the capacitor Bt +ve and ve charges separated so energy stored Bt State three functions of capacitors in electrical circuits. 10 any three points from: ‘smoothing timing/(time) delay tuning oscillator blocking d.c. ‘surge protection ‘temporary power supply Show that the combined capacitance C of the capacitors is given by ded atat ae &l- 1. Cc V=VytVo+ V5 either Q/C=Q/C, + Q/C,+Q/E3 or V/Q = Vi/Q + Vo/Q + V¥3/Q and so 1/€ = 1/C, +1/C,+ 1/C, Show that the combined capacitance C; of the two capacitors is given by C,=C,+ Cc, 2) p.d, actos both capacitors = E Gr=Qi+Q a1 GrE = GiE + GoE hence Or = Gi + CG; a1 State what is meant by a magnetic fled. region where there is a force exerted on M1 ‘@ current-carrying conductor or @ moving charge or @ magnetic matertallmagnellc pole Define magnetic flux density, 11 force Is (always) perpendicular to the velocity direction of motion at magnetic force proviges the centripetal force of force perpendicular to motion causes circular motion a1 magnitude of force (due to the magnetic field) is constant or no work done by force: or the force does not change the speed i Explain the use of a uniform magnetic field and a uniform electric field for the selection velocity of charged particles. You may draw a diagram if you wish. of the electric and magnetic fields normal to each other BI velocity of particle normal to bath felds Bt forces (on particle) due to fields are in opposite directions BI forces are equal for particles with a particular speed/for a selected speeditor speed given by v= Etq}/Atq) Bt Explain why a constant voltage V,, is developed between the faces charge carters moving normal to (magnetic) Nekd Bi charge carriers experience a force normal to J (and 8) 81 charge bulld-up sets up electric field across the slice or build-up of charges results in a p.d. across the slice 81 charge stops building up/V, becomes. constant when Fy = Fe Define magnetic flux. flux density x area ‘where funk is normal to area aL or ux density area x sing (m1) where @ fs angle between Nux direction and (plane of) area. (aN) State what is meant by the magnetic flux linkage of a coil. 13 (magnetic) flux density * area Bi magnetic flux density normal to area Bt or reference to cross-sectional area or x sin (angle between 6 and A) x inumber of tums on coll Bt State Faraday’s law of electromagnetic induction. (induced) €.m.1, proportional to rate mt of change of (magnetic) fux (linkage) at State Lenz's law of electromagnetic induction. ‘direction of induced e.m_t. Lu Such as to (produce eftects that) oppose the change that caused it at “at: Bice Corrents, fy Teference to heating effect, explain what is meant by the root-mean-square (rams. value of an alternating currefit. the sleady current Mi or the direct current thal produces. the same heating effect (as the alternating current) at State what is meant by rectification. [conversion (rom a.c) toc. | Smoothing ® The reduction in the variation of the output voltage or current by adding a single capacitor with capacitance C is connected In parallel with a load resistor of resistance R 14 Describe two phenomena associated with the photoelectric effect that cannot be explained using a wave theory of light. two from: + there Isa frequency below witich electrons are nol ejected * Maximum energy of electron depends on Kequency * maximum energy of electrons does not depend on iniensity * _ emission of electrons Is Instantaneous 82 Electromagnetic radiation of a single constant frequency is incident on a metal surface. This causes an electron to be emitted. Explain why the maximum kinetic energy of the electron is independent of the intensity of the incident radiation. + frequency determines energy af photon + Iniensily determines number of pholons (per unifltime) + inlensity does nol determine energy af a photon Any two points, f mark each Ba kinetic energy (of the electron) depends on the energy af one phaton at Describe the appearance of a visible line emission spectrum, as seen using a diffraction grating. mostly darkidark background BI coloured lines 81 grating. Explain why this spectrum contains a number of dark lines, The spectrum of the light emerging from the cloud of cool gas is viewed using a diffraction elecirons (in gas atomsimolecules) Interact with pholons Bt photon energy causes electron to move to higher energy levevio be excited Bt photon energy = difference in energy of (etectron} energy levels at when electrons de-excile, pholons emitted in all directions (so dark fine) Explain how the emission spectrum provides evidence for the existence of discrete energy levels for the electron in a hydrogen atom. 16 * energy of photon has a corresponding frequency * change in eleciran energy level emis a single photon * photon energy = diference in energy levels * discrete frequencies must have come from discrete energy gaps * discrete energy changes imply discrete energy levels Any three poinis, 1 mark each Ba State whal Is meant by the de Broglie wavelength. particie/electron has a wavelength (associated with it) BI dependent on fs momentum or whenvbecause particle is maving QB. enor Phust BI State what is meant by radioactive decay. unstable nucteus 81 emission of parficlesiphatons Bt emission ts spontaneous or (particles‘radiation) are lonising 81 Radioactive decay is both a random and a spontaneous process. (a) State what is meant by: (i) random (ii) spontaneous. \) | cannot predict when a (particular) nucleus will decay or cannot predict which nucleus will decay next Bt @) | not affected by extemal/ environmental factors: Bi Explain what is meant by the binding energy of a nucleus. (minimum) energy required to separate the nucleons Mt to infinity Al Define radioactive decay constant. v7 8 particle interacting with ils antiparticle so thal mass Is converted into energy 81 State the names of the particles involved in the annihilation process. electron(s) and positron(s) a Positrons are not naturally present in the body. Explain how positrons come to be present in the body during PET scanning. introduction of tracer (info the body) Mi containing a B* emitier AL Explain how positrons cause the emission of gamma-radiation from the body during PET scanning. Positron Interacts with electron a (palr) annihitalion occurs BI mass of particles converted Into gamma photons: BI Explain how the gamma photons are used to produce an image. Any 3 from: BS the two gamma photons travel in oppasite directions gamma photons detected (outsise body /by detectors) gamma photons arrive {al detector) af different times determine location of production (of gamma) image of tracer concentration in tissue produced 24. Nedical Phuscs Explain how X-rays are produced for use in medical diagnosis. electrons are accelerated (by an applied p.d.) BI ‘electrons hil target Bt 3Crays produced when electrons decelerate Bt State, for an X-ray image, what is meant by: 19 contrast. ‘difference in degrees of blackening at State how, in a modern X-ray tube, the intensity of the X-ray beam and its hardness are controlled. intensity: vary flament currentip.d, across filament Bi hardness: vary accelerating potential difference Bt State the purpose of computed tomography (CT scanning). lo produce a 3-dimensional image of structure/body 81 Outline the principles of CT scanning. X-rays (are used) ‘scanning in sections ‘scanning from many angles: 81 image of each section is 2-dimensional a1 ‘scanning repeated for many sections or images of many sections combined together Bt Explain the principles of the generation of ultrasound waves for use in medical diagnosis. quartz crystal 51 altemating p.d. across crystal causes il to vibrate Bi Tesonance occurs when trequency of p.d ‘Matches nalural trequency of crystal et ‘atural frequency of crystal & In ultrasound range 81 Outline the use of ultrasound to obtain diagnostic information about internal body structures. 20