Cambridge A Level Physics 9702 — 2002 Oct/Nov Paper 6 · Variant 1

TIME 45 minutes INSTRUCTIONS TO CANDIDATES Write your name, Centre number and candidate number in the spaces at the top of this page. Answer all of the questions in any two Options. Write your answers in the spaces provided on the question paper. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You may lose marks if you do not show your working or if you do not use appropriate units. CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Level PHYSICS 9702/6 PAPER 6 Options OCTOBER/NOVEMBER SESSION 2002 45 minutes Candidates answer on the question paper. No additional materials. This question paper consists of 18 printed pages and 2 blank pages. SPA (NH/PW) S21693/4 © CIE 2002 [Turn over Candidate Centre Number Number Candidate Name FOR EXAMINER’S USE

2 9702/6 O/N/02 Data speed of light in free space, c = 3.00 × 108 m s–1 permeability of free space,
0 = 4 × 10–7 H m–1 permittivity of free space, 0 = 8.85 × 10–12 F m–1 elementary charge, e = 1.60 × 10–19 C the Planck constant, h = 6.63 × 10–34 J s unified atomic mass constant, u = 1.66 × 10–27 kg rest mass of electron, me = 9.11 × 10–31 kg rest mass of proton, mp = 1.67 × 10–27 kg molar gas constant, R = 8.31 J K–1 mol–1 the Avogadro constant, NA = 6.02 × 1023 mol–1 the Boltzmann constant, k = 1.38 × 10–23 J K–1 gravitational constant, G = 6.67 × 10–11 N m2 kg–2 acceleration of free fall, g = 9.81 m s–2

3 9702/6 O/N/02 [Turn over Formulae uniformly accelerated motion, s = ut +
 at 2 v2 = u2 + 2as work done on/by a gas, W = pV gravitational potential, φ = – simple harmonic motion, a = –
2x velocity of particle in s.h.m., v = v0 cos
t v = ±
resistors in series, R = R1 + R2 + . . . resistors in parallel, 1/R = 1/R1 + 1/R2 + . . . electric potential, V = capacitors in series, 1/C = 1/C1 + 1/C2 + . . . capacitors in parallel, C = C1 + C2 + . . . energy of charged capacitor, W =
 QV alternating current/voltage, x = x0 sin
t hydrostatic pressure, p = qgh pressure of an ideal gas, p =
 <c2> radioactive decay, x = x0 exp(– t) decay constant,  = critical density of matter in the Universe, q0 = equation of continuity, Av = constant Bernoulli equation (simplified), p1 +
 qv2 1 = p2 +
 qv2 2 Stokes’ law, F = Arv Reynolds’ number, Re = drag force in turbulent flow, F = Br2qv2 qvr  3H0 2 8G 0.693 t
 Nm V Q 40r Gm r ( ) x x 0 2 2 −

4 9702/6 O/N/02 Answer all of the questions in any two Options. The Options are as follows: Option A Astrophysics and Cosmology questions 1, 2 and 3 Option F The Physics of Fluids questions 4, 5 and 6 Option M Medical Physics questions 7, 8 and 9 Option P Environmental Physics questions 10, 11 and 12 Option T Telecommunications questions 13, 14 and 15 Option A Astrophysics and Cosmology 1 Give an estimate of the time for light to travel (a) from the Sun to Earth, time = … [1] (b) from the nearest stars (other than the Sun) to Earth, time = … [1] (c) across the Milky Way galaxy. time = … [1] For Examiner’s Use

5 9702/6 O/N/02 [Turn over 2 (a) Explain what is meant by redshift. … … … …[3] (b) Suggest why line spectra, rather than continuous spectra, are used to study redshift. … … …[2] (c) Outline three problems associated with observations of electromagnetic radiation at the Earth’s surface. 1. … … 2. … … 3. … …[3] For Examiner’s Use

6 9702/6 O/N/02 3 (a) Estimate the critical mean density of matter in the Universe, giving your answer as the average number of nucleons per cubic metre of space. The age of the Universe is about 4.1 ×1017s. number density = … m–3 [5] (b) Current observations suggest that the actual mean density of matter gives rise to a ‘flat’ Universe. (i) Explain why the amount of matter in the Universe is not known with any accuracy. … … … (ii) Describe the likely fate of the Universe if the actual mean density is greater than is currently suggested. … … … [4] For Examiner’s Use

7 9702/6 O/N/02 [Turn over Option F The Physics of Fluids 4 When a body is immersed in a fluid, it experiences an upthrust equal to the weight of fluid displaced. Explain (a) what is meant by an upthrust, … …[1] (b) the origin of the upthrust, … … …[2] (c) two conditions for the upthrust to be independent of the depth of immersion. 1. … … 2. … …[3] For Examiner’s Use

8 9702/6 O/N/02 5 Fluid flow is sometimes illustrated by means of streamlines. (a) Explain (i) what is meant by a streamline, … … (ii) what is meant by a tube of flow, … … (iii) why fluid in a tube of flow cannot pass out through its sides. … … [3] (b) (i) On Fig. 5.1, draw streamlines to illustrate laminar flow round the object shown. Fig. 5.1 For Examiner’s Use

9 9702/6 O/N/02 [Turn over (ii) On Fig. 5.2, draw streamlines to illustrate turbulent flow round the object. Fig. 5.2 (iii) Suggest one change which could have occurred for the flow to become turbulent, rather than laminar. … [4] 6 The arrows in Fig. 6.1 represent the velocity of fluid moving down a pipe. Fig. 6.1 (a) (i) Suggest why the arrows are not all the same length. … … … (ii) Hence explain what is meant by a velocity gradient in the fluid. … … … [4] For Examiner’s Use

10 9702/6 O/N/02 (b) The magnitude F of tangential forces between two parallel layers of fluid of area A, distance ∆x apart and moving with a relative speed ∆v, is given by F = ηA (∆v/∆x), where η is a constant known as the viscosity. A block of glass of weight 1.5 N has a face of area 9.0 ×10–4m2 in contact with a flat vertical surface, as illustrated in Fig. 6.2. Fig. 6.2 The block is held against the surface by a layer of grease of thickness 2.2 ×10–6m. It is found that, after seven days, the glass block has slid down the vertical surface by a distance of 3.0 mm. Using the equation above, calculate the viscosity of the grease. viscosity = … Pa s [3] grease block vertical surface For Examiner’s Use

11 9702/6 O/N/02 [Turn over Option M Medical Physics 7 (a) The quality of an image produced using X-rays depends on sharpness and contrast. State what is meant by, and briefly explain the causes of, (i) sharpness, … … … (ii) contrast. … … … [4] (b) A parallel beam of X-ray photons is produced by an X-ray tube with 80 keV across it. The beam has its intensity reduced to one half of its original value when it passes through a thickness of 1.0 mm of copper. (i) Describe the energies of the X-ray photons in the beam. … …[2] (ii) Determine the linear absorption coefficient µ of the X-ray photons in copper. µ = … mm–1 [2] (iii) Suggest, with a reason, the effect on the linear absorption coefficient if the beam is comprised of 100 keV photons. … …[2] For Examiner’s Use

12 9702/6 O/N/02 8 (a) With reference to the eye, explain what is meant by accommodation. … … …[2] (b) Estimate the change in power of the optical system of an eye when viewing a star and then when reading a book. change in power = …D [3] 9 Explain why the intensity level of a sound may provide a measure of loudness, but care must be taken in the interpretation of such measurements. … … … … … … …[5] For Examiner’s Use

13 9702/6 O/N/02 [Turn over Option P Environmental Physics 10 (a) Distinguish between the functions of a solar cell and a solar panel. solar cell: … … solar panel: … …[2] (b) (i) State one practical use of solar cells. … (ii) Explain, giving numerical values where appropriate, why it is not feasible to replace nuclear reactors with solar cells for the generation of electrical power. … … … … [4] For Examiner’s Use

14 9702/6 O/N/02 11 Fig. 11.1 is an idealised indicator diagram for one cycle of a four-stroke petrol engine. Fig. 11.1 In the changes PQ and XY, the energies involved are 210 J and 130 J respectively. (a) On Fig. 11.1, (i) mark with arrows the directions of the changes PQ, QX, XY and YP, (ii) mark the directions of the transfers of energy. [2] (b) Complete the Sankey diagram of Fig. 11.2 for one cycle of the engine. [3] Fig. 11.2 pressure volume P Y Q X 210 J 130 J 0 0 For Examiner’s Use

15 9702/6 O/N/02 [Turn over (c) (i) Calculate the efficiency of the engine. efficiency = … % (ii) By reference to the second law of thermodynamics, suggest why no engine can achieve 100% efficiency. … … … [5] 12 A student stated that all cars should be driven by electric motors rather than petrol or diesel engines so that pollution would be reduced. Comment on this statement. … … … … …[4] For Examiner’s Use

16 9702/6 O/N/02 Option T Telecommunications 13 (a) Explain what is meant by a digital signal. … … …[2] (b) Music can be recorded and stored digitally on a compact disc (CD). The music is sampled at a frequency of 44.1 kHz, and each sample consists of two 16-bit words, corresponding to the left and right stereo channels. Calculate the total number of bits stored on this CD if its playing time is 1.0 hour. number = … [2] (c) State one advantage and one disadvantage of storing and transmitting music in digital rather than analogue form. advantage: … … disadvantage: … …[2] For Examiner’s Use

17 9702/6 O/N/02 [Turn over 14 Fig. 14.1 shows the variation with time t of the power of a pulse of light on entering and on leaving an optic fibre. Fig. 14.1 (a) Suggest why (i) the output pulse has a smaller area on the graph than the input pulse, … … (ii) the output pulse lasts for a longer time than the input pulse. … … [4] (b) The length of the optic fibre is 1400 m. Use Fig. 14.1 to determine a value for the speed of light in the fibre. Explain your working. speed = … m s–1 [4] 0 1 2 3 4 5 6 7 8 9 10 11 12 t/µs power output pulse input pulse For Examiner’s Use

18 9702/6 O/N/02 15 (a) State a typical value of wavelength for (i) sky waves, wavelength = … m (ii) space waves. wavelength = … m [2] (b) Explain why radio communication via satellite is more reliable than communication using sky waves. … … … … …[4] For Examiner’s Use

CAMBRIDGE INTERNATIONAL EXAMINATIONS NOVEMBER 2002 GCE Advanced Subsidiary Level UNIveRrSITY of CAMBRIDGE Local Examinations Syndicate

Page 1 of 5 Mark Scheme Syllabus Paper 6 A Level Examinations — November 2002 9702 Option A 1 (a) allow 4—15 minutes oe... eeeeeeceeececeeeeeeeeeeteceeeeeneeeeeetees BI [lj (b) allow 2—B years acececccccsseciescsecseeccssscescescescscesesseesasease BI [1] (©) allow 50 k— 150 k years oo... .eeecceeeecscseseseeeeeeeneeeaeeneeeeeenens Bl fl] (If all else fails allow 1 mark for units of minutes, years and k years) 2 (a) relative motion between source and observer sees wavelength appears longer OR colour shifts towards red . Al (due to) receding source … Leececeeeeeessenececceeeeesecseseeeeaeneeees Al [3] (b) all wavelengths are shifted on so UV becomes visible or visible becomes IR - BL [2] alternative: line gives a reference (1) so that shift can be measured (1) (c) e.g. light pollution absorption irregular refraction ete any three, 1 each [3] 3 (a) Hy = 1/(4.1 x 10") = 24x 108 st Cl po = {3x (2.4 x 10)} / {8 x mx 6.67 x 10°} Cl = 1.06 x 10% kgm eee ceeeeeeeteeeeeeeeeeees Cl idea of divide density by 1.66 x 107’ (1 u) . Cl number density = 6.4 Al [5] (b) (i) mention of dark matter Bl limit of observable Universe Bl (allow alternatives to max 2) {ii) expansion will come to a halt Bl then collapse [4]

Page2of5 | _ Mark Scheme Syllabus | Paper A Level Examinations — November 2002 9702 6 Option F 4 (a) force (on body) acting upwards —…sseeeeeeeeeeeeeeeeeeeeeee Bl [lj (b) pressure below object is different from pressure above . BL. (F = pA, so) force up > force down Bl [2] (accept gravitation as origin of pressure for 1 mark acts through CG of displaced fluid for 1 mark) (c) upthrust depends on Ap = pgAh . OR upthrust = weight of fluid displaced - Bl incompressible fluid OR p constant . Bl rigid object (so volume not change)... Bl [3] (first mark may be awarded for any detail anywhere) 5 (a) @) _ path taken by (a particle of) the fluid Bl (ii) _ tube of fluid bounded by streamlines . Bl (iii) streamlines would be crossed by the fluid 4 or streamlines would not be in direction of flow of fluid … Bl [3] (b) @) sketch: smooth lines MI approx. symmetry with closer lines at sides . Al (ij) sketch: eddies behind the object … Bl (iii) e.g. increased (fluid) speed OR decreased density OR increased VisCOSity …ceccseeeeneeeeeaeeeeseneeeeeeee Bl [4] 6 (a) (i) _ friction between layers of fluid oo... fluid in contact with sides is stationary (ii) rate of change of velocity with distance normal to direction of flow of fluid [4] (b) speed = (3 x 10°)/(7 x 24 x 3600) = 4.96x 10°ms! … Cl 1.5 = 79.0 x 10% x (4.96 x 10°) / (2.2 x 10%) . Cl 7 = 74x10°Pas we . Al [3]

Page 3 of 5 Mark Scheme Syllabus | Paper | A Level Examinations - November 2002 9702 6 | Option M 7 (a) sharpness: clear distinction between boundaries . Bl e.g. parallel X-ray beam / point source - Bl contrast: (large) differences in blackening of different regions ... B1 (allow changes in colour) e.g. differences in attenuation coefficient … Bl [4] (b) () max. energy of photon is 80 keV Bl below 80 keV, continuous spectrum with sharp peaks BI [2] (i) I= he” : %=e* . . . Cl w= 0693mm" ... - Al [2] (iii) X-rays are more penetrating . Bl so wissmaller …eceeeeee - BL [PJ 8 (a) ability of eye to form focused images s MI of objects at different distances from eye « Al» [2] (b) star: power = I/oo + 1/L (Lexplained) … book: power = 1/0.25 + I/L (0.25 explained) change in power = 1/0.25 = 4.0D [3] 9 changes in loudness perceived as AI/I oo. .eeeecceeeceeeeeeeeeeeeeee Bl loudness is log. response to intensity OR loudness/sensitivity not linearly dependent on intensity … Bl and LL. measured as 10 Ig(I/Ip) o…eeceeeeeeeeeeees Bl but perceived loudness depends on frequency . Bl and on the individual... : Bl [5]

Page 4 of 5 Mark Scheme | Syllabus | Paper A Level Examinations — November 2002 [9702 6 Option P 10 (a) cell: conversion (of solar energy) to electrical energy panel: conversion (of solar energy) to thermal energy [2] (b) @ e.g. calculator, remote road signs (ii) dc. not a.c. so problems re. distribution vast area of land would need to be covered OR any other relevant qualitative statement (e.g. time of day!) … Bl. for 1 kW need about 10 m” OR for 240 V need several hundred cells in series OR any other appropriate quantitative statement … eee BI [4] 11 (a) (i) correct direction round cycle ...(allow 3 arrows) Bl (ii) correct direction for both energies Bl [2] (b) input with two output arrows 2.0.20... ee ceeeeeeeeceeceeeceeeeeeeeeeeees Mi approximately correct width for each arrow at point of division .. Al , labels e.g. input, (useful) output, losses and energy valuesor% . Al [3] (c) @ efficiency = (useful) output /input oo. eee cece cece eee Cl = 80/210 = 38% di) Enx = (1- T/T) Bl T, cannotbeOK … .. Bl Ty has a practical upper limit BI [5] 12 Electric cars produce less pollution at location electrical energy has to be generated … (resulting in) pollution at power station any other suitable comment e.g. pollution in cities .. (4]

Page 5 of 5 Mark Scheme Syllabus | Paper A Level Examinations — November 2002 9702 6 Option T 13 (a) series of pulses Bl between discrete levels Bl [2] (b) numberof samples per second = 44100 x 2 = 88200 _… number of bits in 1 hour = 88200 x 16 x 3600 = 5.1 x 10° [2] (c) adv: e.g. perfect regeneration possible, regeneration eliminates noise .. Bl disadv: extra circuitry (ADC,DAC etc) .. Bl [2] 14 (a) (i) area represents energy Bl and some loss of light energy in the fibre … Bl {ii) difference in number of reflections along the fibre Bl mean different path lengths Bl [4] <b) speed = 1400/(7.0x 10%) .. Cl « = 2.0x10?ms™ w. Al 7 ws because this represents minimum number of reflections … Bl so is nearest to path length of 1400 mow... e eee eeeee Bl [4] 15 (a) (i) allowl0m - 100m Bl (ii) allow <10m - BL [2] (b) sky waves rely on ionospheric reflection . ionosphere changes in height, density ete .BL space waves used for satellite communication -BL not affected by ionosphere [4] (allow feasible alternatives e.g. effect of hills to max 4)