Cambridge A Level Physics 9702 — 2006 Oct/Nov Paper 6 · Variant 1

This document consists of 20 printed pages. SPA (SJF3680/CG) S98416/2 © UCLES 2006 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Level PHYSICS 9702/06 Paper 6 Options October/November 2006 45 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all of the questions in any two options. You may lose marks if you do not show your working or if you do not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Centre Number Candidate Number Name For Examiner’s Use A F M P T Total

2 9702/06/O/N/06 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 © UCLES 2006

3 9702/06/O/N/06 [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 = – ω2x velocity of particle in s.h.m., v = v0 cos ωt v = ± ω √(x2 0 – x2) 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 ωt hydrostatic pressure, p = ρgh pressure of an ideal gas, p =
 <c2> radioactive decay, x = x0 exp(– λt) decay constant, λ = critical density of matter in the Universe, ρ0 = equation of continuity, Av = constant Bernoulli equation (simplified), p1 +
 ρv2 1 = p2 +
 ρv2 2 Stokes’ law, F = Arv Reynolds’ number, Re = drag force in turbulent flow, F = Br2ρv2 ρvr  3H0 2 8G 0.693 t
 Nm V Q 40r Gm r © UCLES 2006

4 9702/06/O/N/06 Answer all of the questions in any two of the Options. Answer the questions in the spaces provided on the Question Paper. The Options are as follows. Option A Astrophysics and Cosmology questions 1, 2, 3 and 4 Option F The Physics of Fluids questions 5, 6 and 7 Option M Medical Physics questions 8, 9 and 10 Option P Environmental Physics questions 11, 12 and 13 Option T Telecommunications questions 14, 15 and 16 Option A Astrophysics and Cosmology 1 In June 2004, the planet Venus could be seen crossing the disc of the Sun. (a) State what is meant by a planet. … … … [2] (b) Suggest why this observation leads to the conclusion that Venus was less than 1 AU from Earth. … … … [2] For Examiner’s Use © UCLES 2006

5 9702/06/O/N/06 [Turn over 2 (a) Describe what is meant by redshift. … … … … [3] (b) Suggest why stars must be moving at relatively high speeds before redshift can be observed. … … … [2] 3 Hubble’s law may be written in the form v = H0d, where H0 is the Hubble constant. (a) Explain the meanings of the symbols v and d. v … … d … … [2] (b) One estimate of H0 is 60 km s–1Mpc–1. Use this value to estimate the age of the Universe. age = ………………………… s [3] For Examiner’s Use © UCLES 2006

6 9702/06/O/N/06 4 The ultimate fate of the Universe depends on the density of matter in the Universe. This matter consists, in part, of dark matter. (a) Suggest two reasons why dark matter is not visible. 1. … … 2. … … [2] (b) Suggest and explain two reasons why, even if dark matter could be observed, it would not be possible to obtain a reliable estimate for the mean density of matter in the Universe. 1. … … … 2. … … … [4] For Examiner’s Use © UCLES 2006

7 9702/06/O/N/06 [Turn over Option F The Physics of Fluids 5 (a) On Fig. 5.1, draw lines to illustrate the streamline flow of a fluid round the object. [3] Fig. 5.1 (b) State what feature on your drawing indicates that the speed of the fluid is not constant. … … [1] For Examiner’s Use © UCLES 2006

8 9702/06/O/N/06 6 A hollow tube contains some sand. When placed in a liquid, the tube floats upright as illustrated in Fig. 6.1. Fig. 6.1 The centre of mass of the tube and the sand is at C. (a) Explain why the tube remains upright as it floats in the liquid. … … … [2] (b) The tube and its contents have a total mass M. The tube, of uniform cross-section A, floats with length L submerged in a liquid of density ρ. Show that the length L is given by the expression M L = . Aρ [2] For Examiner’s Use © UCLES 2006 C L sand area of cross-section A liquid, density

9 9702/06/O/N/06 [Turn over (c) When placed in water of density 0.99 g cm–3, the length L is 12.1 cm. The tube is then transferred to a liquid of density 1.11 g cm–3. Calculate the change in the submerged length. change in length = ………………………… cm [3] For Examiner’s Use © UCLES 2006

10 9702/06/O/N/06 7 A sphere falls from rest in a viscous fluid. The flow of fluid round the sphere remains laminar. Explain (a) by reference to the forces acting on the sphere, why the sphere reaches a terminal speed, … … … … … … … [5] (b) why the sphere may not fall vertically if it is spinning. … … … … … [4] For Examiner’s Use © UCLES 2006

11 9702/06/O/N/06 [Turn over Option M Medical Physics 8 (a) Outline the use of ultrasound to obtain diagnostic information about internal body structures. … … … … … … … … [4] (b) Suggest and explain why, in many medical applications, the ultrasound probe is made up of a number of crystals. … … … … [3] For Examiner’s Use © UCLES 2006

12 9702/06/O/N/06 9 The eye is capable of adjustment to different environmental conditions. (a) (i) Explain what is meant by accommodation. … … … [2] (ii) Describe how accommodation is achieved in the human eye. … … … [2] (b) The eye can adjust to light intensities ranging from bright sunlight to moonlight. By making reference to the diameter of the pupil of the eye, suggest why the iris cannot be responsible for all of this adjustment. … … … … [3] For Examiner’s Use © UCLES 2006

13 9702/06/O/N/06 [Turn over 10 Fig. 10.1 shows the variation with frequency f of the threshold of hearing of a certain person. Fig. 10.1 (a) Use Fig. 10.1 to determine the range of frequencies within which sounds of intensity 1.6 ×10–10W m–2 may be heard. The threshold intensity at 3.0 kHz is 1.0 ×10–12W m–2. frequency range from ………………………… Hz to ………………………… Hz [4] (b) Fig. 10.1 represents the threshold of hearing for a person with no hearing defect. Suggest two changes to this graph that occur as a result of deafness brought on by old age. 1. … … 2. … … [2] For Examiner’s Use © UCLES 2006 1 10 100 1000 10 000 f /Hz 100 000 0 20 40 60 80 100 120 intensity level / dB

14 9702/06/O/N/06 Option P Environmental Physics 11 (a) Explain the role of the following components in a nuclear reactor. (i) moderator … … … [2] (ii) control rods … … … [2] (iii) reactor vessel … … … [2] (b) During the fission of a Uranium-235 nucleus, 198 MeV of energy is released. Outline how some of this energy is converted to thermal energy in the coolant of a nuclear reactor. … … … … [3] (c) One disadvantage of the use of nuclear reactors for the generation of electrical energy is the difficulty of storing nuclear waste. Suggest two advantages of nuclear power when compared to coal-fired or oil-fired power stations. 1. … … 2. … … [2] For Examiner’s Use © UCLES 2006

15 9702/06/O/N/06 [Turn over 12 A solar cell has a surface area of 2.5 cm2. It produces an e.m.f. of 0.60 V and an output power of 30 mW when sunlight of intensity 960 W m–2 is incident normally on its surface. (a) Calculate the efficiency of the solar cell for the conversion of solar power to electrical power. efficiency = ………………………… [2] (b) (i) Suggest why a solar cell is not used where comparatively large power outputs are required. … … [1] (ii) Suggest how a number of solar cells may be connected to provide both a large e.m.f. and a large current. … … … … [2] For Examiner’s Use © UCLES 2006

16 9702/06/O/N/06 13 Fig. 13.1 shows a Sankey diagram for the production of electrical energy and its use by an electric motor. Fig. 13.1 (a) The cost of the fuel is 5.4 cents per kilowatt-hour of input energy. Calculate the cost of the fuel in order to supply 5.0 kW h of energy to the motor. cost = ………………………… cents [2] (b) With reference to Fig. 13.1, suggest how a desalination plant or a CHP scheme may be developed as an economical proposition. … … … [2] For Examiner’s Use © UCLES 2006 cost of fuel 5.4 cents per kilowatt-hour 68% production losses 2% distribution losses 3% losses in motor 27% useful work in motor

17 9702/06/O/N/06 [Turn over Option T Telecommunications 14 A radio station on Earth transmits a signal of power 2.4 kW in the direction of a geostationary satellite. The power loss between the radio station and the satellite is 170 dB. (a) Explain what is meant by a geostationary satellite. … … … … [3] (b) Calculate the signal power received by the satellite. power = ………………………… W [3] (c) Suggest why the carrier frequency of the signal received by the satellite is changed and the signal is amplified before transmission back to Earth. … … … … [2] For Examiner’s Use © UCLES 2006

18 9702/06/O/N/06 15 (a) Radio communication may be either frequency modulated or amplitude modulated. Explain what is meant by modulation. … … … [2] (b) An amplitude-modulated radio wave is to be used for the broadcast of music having frequencies between 30 Hz and 4500 Hz. The radio station is broadcasting in the long wave waveband (wavelengths between 1 ×103m and 1 ×104m). Determine (i) the bandwidth of the broadcast, bandwidth = ………………………… Hz [1] (ii) the maximum number of radio stations that could operate simultaneously in the same area within the long wave waveband. number = ………………………… [3] For Examiner’s Use © UCLES 2006

19 9702/06/O/N/06 [Turn over (c) On the axes of Fig. 15.1, sketch a graph of a typical power spectrum for the radio station in (b). Label the x-axis with values of frequency. [3] Fig. 15.1 For Examiner’s Use © UCLES 2006 power frequency

20 9702/06/O/N/06 16 (a) Suggest one example of the use, in a communications system, of a wire pair. … … [1] (b) For many applications, wire pairs have been replaced by co-axial cables or optic fibres. Suggest two reasons for this change. 1. … … 2. … … [2] For Examiner’s Use © UCLES 2006 Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2006 question paper 9702 PHYSICS 9702/06 Paper 6 (Options), maximum raw mark 40 This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes must be read in conjunction with the question papers and the report on the examination. The grade thresholds for various grades are published in the report on the examination for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the October/November 2006 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9702 6 © UCLES 2006 Option A – Astrophysics and Cosmology 1 (a) gaseous/rocky/icy/approx. spherical object B1 that orbits the Sun / a star B1 [2] (b) Venus must have passed between Sun and Earth B1 1 AU is (mean) distance between Earth and Sun B1 [2] 2 (a) (light of a particular wavelength as observed) when source is moving away (from observer) M1 has a longer wavelength A1 than when source is stationary (with respect to observer) B1 [3] (b) (extent of) redshift depends on v/c B1 can only be observed when v is significant when compared to c B1 [2] 3 (a) v is speed of separation of (any two) galaxies B1 d is the separation of the galaxies B1 [2] (max 1 mark if refers to Earth) (b) 1 Mpc = 3.09 × 1019 km (allow 3.0 → 3.2) C1 age = 1 / H0 C1 age = (3.09 × 1019) / 60 = 5.2 × 1017 s A1 [3] 4 (a) e.g. dark matter does not emit light dark matter does not reflect light (any two sensible suggestions, 1 each) B2 [2] (b) e.g. estimate of mass unreliable M1 because there are neutrinos A1 e.g. do not know extent of Universe M1 due to redshift / intensity of light A1 [4] (any sensible suggestion (M1) with reason (A1))

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9702 6 © UCLES 2006 Option F – The Physics of Fluids 5 (a) symmetrical pattern ‘above’ and ‘below’ B1 lines closest together at widest part of object B1 smooth lines tending towards initial separation B1 [3] (b) either separation of lines is not constant or path lengths differ B1 [1] 6 (a) centre of buoyancy is above the centre of mass B1 (if displaced sideways) weight and upthrust provide couple to keep tube upright B1 [2] (do not allow argument in terms of metacentre) (b) either force on base = Lρg × A or weight of liquid displaced = ρLAg M1 this equals weight Mg this equals weight Mg A1 hence L = M/Aρ hence L = M/Aρ A0 [2] (c) M/A = Lρ = constant C1 new length = 12.1 × (0.99/1.11) = 10.8 cm C1 change in length = 1.3 cm A1 [3] 7 (a) (apparent) weight acts downwards B1 drag force acts upwards B1 resultant force = weight - kv OR drag ∝ v B1 as speed increases, resultant force / acceleration becomes less B1 (so) speed increases to a constant value B1 [5] (b) fluid is dragged along by the surface of the (spinning) sphere B1 on one ‘side’ speed of fluid is greater than on other M1 this difference in speed creates a pressure difference / difference in drag / turbulence A1 so sphere moves sideways (in direction of lower pressure) A1 [4]

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9702 6 © UCLES 2006 Option M – Medical Physics 8 (a) pulse of ultrasound B1 reflected at boundary (between any two media) B1 reflected pulse detected by (piezo-electric) crystal B1 signal from crystal amplified / processed and displayed B1 [4] (b) crystals are at different orientations B1 signals from all crystals are combined B1 to build up a (2D) image B1 [3] 9 (a) (i) process by which objects at different distances from the eye M1 are brought to a focus (on the retina) A1 [2] (ii) ciliary muscles alter shape of lens B1 this alters the power/focal length of the lens B1 [2] (b) pupil varies in diameter C1 power (intensity) admitted is proportional to diameter2 B1 either variation of diameter is small / small factor or variation of light intensity is large / (very) large factor B1 [3] 10 (a) IL = 10 lg(I/I0) = 10 lg({1.6 × 10-10} / {1 × 10-12}) C1 = 22 dB A1 range is from 100 Hz B1 to 10 kHz B1 [4] (b) e.g. threshold intensity rises upper frequency (limit) decreases lower frequency (limit) rises (any two suggestions, 1 each, max 2) B2 [2] (allow 1 mark for ‘line closes up’ / smaller frequency range)

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9702 6 © UCLES 2006 Option P – Environmental Physics 11 (a) (i) slows down neutrons M1 to enable further fission reactions A1 [2] (ii) absorbs neutrons M1 to control rate of reaction / power A1 [2] (iii) acts as a biological shield B1 maintains coolant around the core / containment vessel B1 [2] (b) kinetic energy of fission fragments B1 causes heating of the core / fuel rods B1 this thermal energy is carried away by the coolant B1 [3] (c) e.g. either minimal / no release of CO2 into the atmosphere or minimal / no release of gases causing global warming no huge storage areas required at the power station maintenance possible whilst on full load (any two suggestions, 1 each, max 2) B2 [2] 12 (a) incident power = 960 × 2.5 × 10-4 = 0.24 W C1 efficiency = (30 × 10-3) / 0.24 = 0.13 A1 [2] (b) (i) large (surface) area required B1 (ii) connect many cells in series for higher voltage B1 connect many cells in parallel for larger current B1 [3] 13 (a) 30% delivered to motor C1 cost = 5.4 × (100/30) × 5 = 90 cents A1 [2] (allow 1 mark for answer 100 cents) (b) (for both,) there is a need to heat water / for heat energy B1 this energy provided from ‘production losses’ (so reducing overall costs) B1 [2]

Page 6 Mark Scheme Syllabus Paper GCE A/AS LEVEL - OCT/NOV 2006 9702 6 © UCLES 2006 Option T – Telecommunications 14 (a) satellite with orbit having period 24 hours B1 orbits above the Equator B1 from west to east / orbits in same sense B1 [3] (b) loss = 10 lg(P2 / P1) C1 -170 = 10 lg(P2 / 2400) C1 P2 = 2.4 × 10-14 W A1 [3] (c) amplified otherwise power too low to be picked up on Earth B1 either frequency changed to prevent swamping / interference of signal received (from Earth) or prevent feedback B1 [2] 15 (a) variations in either amplitude or frequency of a wave B1 either in synchrony with displacement of information signal or in order to carry information on the wave B1 [2] (b) (i) 9 kHz B1 [1] (ii) LW frequency range is 30 kHz → 300 kHz C1 number = 270 / 9 C1 = 30 A1 [3] (c) sketch: carrier frequency as vertical line and two sidebands M1 reasonable symmetry A1 sideband indicating approx. 4500 Hz range B1 [3] (if sidebands shown as vertical lines, allow max. 1 mark) 16 (a) e.g. link between house and exchange for a telephone (any one suggestion, 1 mark) B1 [1] (b) e.g. greater bandwidth less noise less attenuation (any two suggestions, 1 each, max 2) B2 [2]