Cambridge A Level Physics 9702 — 2006 May/June Paper 6 · Variant 1

This document consists of 20 printed pages. SP (SJF3677/CG) S98408/3 © UCLES 2006 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Level PHYSICS 9702/06 Paper 6 May/June 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/M/J/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/M/J/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/M/J/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, 16 and 17 Option A Astrophysics and Cosmology 1 State, by reference to their orbits, two differences between planets and comets in the Solar System. 1. … … … 2. … … … [4] For Examiner’s Use © UCLES 2006

5 9702/06/M/J/06 [Turn over 2 The Universe may be described as ‘open’, ‘flat’ or ‘closed’. (a) State clearly the factor on which the ultimate fate of the Universe depends. … … [2] (b) Fig. 2.1 illustrates the variation with time of the extent of a ‘flat’ Universe. Fig.2.1 (i) On Fig. 2.1, draw a line to show the variation with time of the extent of a closed Universe. [2] (ii) Suggest three reasons why the ultimate fate of the Universe is not known. 1. … … 2. … … 3. … … [3] For Examiner’s Use © UCLES 2006 present time time extent of Universe

6 9702/06/M/J/06 3 A galaxy has been discovered that is 1.3 ×1010 light-years from Earth. Given that the Hubble constant is 60 km s–1Mpc–1, calculate the ratio speed of galaxy speed of light in free space ratio = ………………………… [4] 4 The Hubble Space Telescope is a telescope that was put into Earth orbit. State and explain reasons for and against the development of such telescopes. … … … … … … … … … [5] For Examiner’s Use © UCLES 2006 .

7 9702/06/M/J/06 [Turn over Option F The Physics of Fluids 5 State the principle on which each of the following is based. (a) the equation of continuity, Av = constant … [1] (b) the Bernoulli equation … [1] For Examiner’s Use © UCLES 2006

8 9702/06/M/J/06 6 Fig. 6.1 illustrates one form of filter pump. Fig. 6.1 Water is forced through the nozzle N. (a) With reference to the Bernoulli principle, explain why the air pressure in tube T is below atmospheric pressure. … … … … … [4] (b) Suggest with a reason the change, if any, in the pressure difference produced by the pump when (i) higher speed water emerges from the nozzle, … … … [2] For Examiner’s Use © UCLES 2006 water tube T nozzle N water

9 9702/06/M/J/06 [Turn over (ii) the water is replaced by another liquid of higher density emerging from the nozzle at the same speed. … … … [2] For Examiner’s Use © UCLES 2006

10 9702/06/M/J/06 7 A car is moving along a straight horizontal road at constant speed. (a) Explain why the production of eddy currents behind the car results in an increase in fuel consumption. … … … … [3] (b) A car having a frontal area A is moving through still air of density ρ with speed v. The drag force F acting on the car is given by the expression F =
 CDAρv2, where CD is a constant for the car. (i) Show that the power output P of the car’s engine that is required to overcome drag is given by P = kv3, where k is a constant. [2] For Examiner’s Use © UCLES 2006

11 9702/06/M/J/06 [Turn over (ii) One particular car has a frontal area A of 1.8 m2 and a constant CD of 0.34. The power available to overcome drag in still air of density 1.1 kg m–3 is 84 kW. Calculate the maximum speed vmax of the car. vmax = …………………………… m s–1 [2] (iii) The car in (ii) now moves against a current of air of speed 9.0 m s–1, measured relative to the ground. The air has density 1.1 kg m–3. Calculate the ratio power output to maintain speed vmax against air current of speed 9.0 m s–1 power output to maintain speed vmax in still air ratio = …………………………… [3] For Examiner’s Use © UCLES 2006 .

12 9702/06/M/J/06 Option M Medical Physics 8 (a) Outline the principles of the generation of ultrasonic waves using piezo-electric transducers. … … … … … [4] (b) Suggest and explain one advantage of the use of ultrasound of frequency 1 MHz, rather than 100 kHz, for medical diagnosis. … … … [2] 9 Describe and explain two uses of a laser in clinical therapy. 1. … … … … … … 2. … … … … … … [6] For Examiner’s Use © UCLES 2006

13 9702/06/M/J/06 [Turn over 10 (a) Explain what is meant by the threshold of hearing. State its value for a person with normal hearing. … … … … … [4] (b) A person has an eardrum of area 54 mm2. When listening to music using an earphone, the earphone produces 0.14 µW of sound power at the eardrum. (i) Calculate the sound intensity level (I.L.) at the eardrum. I.L. = ………………………… dB [3] (ii) Comment on the value you have calculated in (i). … …[1] For Examiner’s Use © UCLES 2006

14 9702/06/M/J/06 Option P Environmental Physics 11 (a) Outline the main principles of a pumped-water storage scheme. … … … … … … [4] (b) A reservoir for a pumped-water storage scheme is to be built such that the mean height of the water, of density 1.0 ×103 kg m–3, above the turbines is 95 m. The scheme has an overall efficiency of 75 % and is to provide 78 MW of electrical power for a period of 4.0 hours. Calculate the minimum volume of water that must be stored in the reservoir. volume = ………………………… m3 [4] For Examiner’s Use © UCLES 2006

15 9702/06/M/J/06 [Turn over 12 A machine operates between temperatures of TH and TL. A quantity QH of thermal energy is absorbed at temperature TH and as a result, the machine does a quantity W of mechanical work, as indicated in Fig. 12.1. Fig. 12.1 (a) By reference to the second law of thermodynamics, explain why some thermal energy must be rejected at temperature TL. … … … … [3] (b) State an expression relating TH, TL, QH and W. … [1] (c) A steam engine operates between the temperatures of 120 °C and 40 °C. Calculate the maximum theoretical efficiency of the engine. efficiency = ………………………… [2] For Examiner’s Use © UCLES 2006 temperature TH QH engine mechanical work W temperature TL

16 9702/06/M/J/06 13 Fig. 13.1 shows the variation with time of the electric power demands of a city on two different days, several months apart. Fig. 13.1 (a) Give two possible explanations for (i) the increase in demand between 6 a.m. and 10 a.m., 1. … 2. … [2] (ii) the different average levels of demand on the two days. 1. … 2. … [2] (b) Suggest the effect on the graph of Fig.13.1. if (i) a popular hour-long television programme ends at 8 p.m., … … [1] (ii) there is an exceptionally hot day. … … [1] For Examiner’s Use © UCLES 2006 time power demand mid- night mid- night 4 a.m. 8 a.m. 4 p.m. 8 p.m. noon

17 9702/06/M/J/06 [Turn over Option T Telecommunications 14 (a) Explain what is meant by frequency modulation (FM). … … … [2] (b) A sinusoidal carrier wave has amplitude 12 V and frequency 600 kHz. The frequency of the carrier wave changes by 25 kHz per volt. The carrier wave is used for the transmission of a signal of frequency 3.0 kHz and amplitude 2.0 V. For the frequency modulated carrier wave, state (i) the amplitude, amplitude = ………………………… V [1] (ii) the maximum frequency, maximum frequency = ………………………… kHz [1] (iii) the minimum frequency, minimum frequency = ………………………… kHz [1] (iv) the number of times per second that the frequency of the carrier wave changes from the maximum value, to the minimum value and then back to the maximum value. number = ………………………… [1] For Examiner’s Use © UCLES 2006

18 9702/06/M/J/06 15 Fig. 15.1 shows a block diagram of a circuit used for the encoding of an analogue signal and its transmission in digital form. Fig. 15.1 (a) State the name of the block labelled X (do not use an abbreviation). … [1] (b) Suggest the function of the clock. … … [1] (c) Suggest one advantage of using a high-frequency clock. … … [1] For Examiner’s Use © UCLES 2006 analogue signal sample and hold clock X

19 9702/06/M/J/06 [Turn over 16 Before the development of microwave links and optic fibres, co-axial cables were used widely for telephone communication. (a) Fig. 16.1 shows one type of co-axial cable. Fig. 16.1 State the purpose of the copper braid and how this purpose is achieved. … … … [2] (b) One advantage over co-axial cables of microwave links and of optic fibres is increased bandwidth. Explain why increased bandwidth has led to a reduction in the cost of telephone calls. … … … … [3] Question 17 is on page 20 For Examiner’s Use © UCLES 2006 copper braid copper conductor

20 9702/06/M/J/06 17 (a) State two sources of noise associated with metal cables. 1. … … 2. … … [2] (b) A metal cable has a signal attenuation of 5.8 dB km–1 and the noise power in the cable is 7.6 µW. An input signal to the cable has a power of 2.6 W and the minimum acceptable signal- to-noise ratio is 35 dB. Calculate (i) the minimum acceptable signal power in the cable, power = ……………………………… W [2] (ii) the maximum uninterrupted length of cable for the transmission of this signal. length = ……………………………… km [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 Level MARK SCHEME for the May/June 2006 question paper 9702 PHYSICS 9702/06 Paper 6 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 initially instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. Any substantial changes to the mark scheme that arose from these discussions will be recorded in the published Report on the Examination. 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 minimum marks in these components needed for various grades were previously published with these mark schemes, but are now instead included in the Report on the Examination for this session. • CIE will not enter into discussion or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the May/June 2006 question papers for most IGCSE and GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 1 Mark Scheme Syllabus Paper GCE A – May/June 2006 9702 06 © University of Cambridge International Examinations 2006 Option A - Astrophysics and Cosmology 1 Planet: almost circular orbits B1 all in nearly the same plane B1 Comet: highly elliptical orbits B1 in many different planes B1 [4] 2 (a) (mean) density M1 of matter in the Universe A1 [2] (b) (i) symmetrical curve below given line M1 touching given line at ‘present time’ A1 [2] (ii) H0 not known with any certainty B1 mass of matter in the Universe not known B1 extent of Universe unknown B1 [3] (allow 1 of the last 2 marks for ρ0 not known) 3 1 light-year = 0.306 pc (allow 0.3 pc) C1 1.3 × 1010 light-years = 3.98 × 103 Mpc C1 v = H0d C1 speed = 60 × 3.98 × 103 = 2.39 × 105 km s-1 ratio = (2.39 × 105 x 103)/(3 .0 × 108) = 0.8 A1 [4] 4 e.g. vast expense (M1) money could be spent on humanitarian aid (A1) observations possible that cannot be made on Earth (M1) since atmosphere limits observations (A1) technological/scientific developments on Earth (M1) greater understanding of Universe (M1) leads to ‘spin off’ benefits for individuals (A1) Any sensible comments, 1 each to max 5 B5 [5] Option F - The Physics of Fluids 5 (a) conservation of volume/mass/density or incompressible B1 [1] (b) conservation of energy B1 [1] 6 (a) air near jet is moving at speed OR water in jet is moving at speed B1 higher speed air has a lower OR high-speed water has lower pressure B1 pressure (because) air is dragged along by OR air is drawn into water jet B1 water jet air (outside pump) is not moving OR loss of air reduces pressure B1 [4] (b) (i) air/water in pump has a higher speed M1 so greater pressure difference A1 [2]

Page 2 Mark Scheme Syllabus Paper GCE A – May/June 2006 9702 06 © University of Cambridge International Examinations 2006 (ii) no change in speed of air OR reference to greater ρ in Bernoulli eqn M1 so no change in pressure OR greater pressure difference A1 [2] difference (allow any logical argument based on liquid causing more/less drag on air) 7 (a) eddy currents have kinetic energy OR cause extra drag M1 eddy currents caused by movement of the car OR energy required to overcome drag A1 extra energy (of eddy currents) is derived from car’s fuel A1 [3] (b) (i) power = force × speed B1 so power = ½CDAρv2 × v and A and ρ are constants B1 [2] (ii) 84 × 103 = ½ × 0.34 × 1.8 × 1.1 × vmax 3 C1 vmax = 63 m s-1 A1 [2] (iii) P = ½ × 0.34 × 1.8 × 1.1 × (63 + 9)3 C1 P = 126 kW C1 ratio = 126 / 84 = 1.5 A1 [3] Option M - Medical Physics 8 (a) alternating voltage B1 applied across (piezo-electric) crystal B1 causes crystal to vibrate B1 crystal dimensions such as to give resonance (in US range) B1 [4] (b) wavelength at 1 MHz is shorter B1 so greater detail is possible B1 [2] 9 e.g. used as a scalpel (1) further detail: causes (explosive) vaporisation of intracellular water (1) CO2 laser (1) IR radiation strongly absorbed by water (1) laser beam focused to give high power density (1) no/very little bleeding (1) accurate guidance (1) e.g. repair of retina (1) further detail: focused laser beam onto retina (1) melts tissue and forms a weld (1) (pulsed) ruby or argon laser (1) any two examples: named (1) plus further detail (2) B6 [6] (allow up to two marks for each diagnostic technique) 10 (a) minimum intensity (of sound) detected M1 where intensity = (sound) power per unit area at a stated frequency A1 value is 1 × 10-12 W m-2 B1 at 3 kHz (allow 2 kHz → 3 kHz) B1 [4]

Page 3 Mark Scheme Syllabus Paper GCE A – May/June 2006 9702 06 © University of Cambridge International Examinations 2006 (b) (i) intensity = (0.14 × 10-6)/(54 × 10-6) = 2.6 × 10-3 W m-2 C1 IL = 10 lg (2.6 × 10-3)/(1 × 10-12) C1 = 94 dB A1 [3] (ii) comment e.g. would be perceived as being loud could cause tinnitus over a short period of time could cause deafness over a long period of time higher level than is acceptable in the workplace any appropriate comment, 1 mark B1 [1] Option P - Environmental Physics 11 (a) at times of low usage of electrical power B1 water pumped from low-level to high-level reservoir B1 at times of high/sudden demand for electrical power B1 water released to pass through turbines B1 [4] (b) electrical energy generated = 78 × 106 × 4.0 × 3600 = 1.12 × 1012 J C1 energy to be stored = (1.12 × 1012)/0.75 = 1.5 × 1012 J C1 1.5 × 1012 = ρVgh C1 = 1.0 × 103 × V × 9.8 × 95 V = 1.6 × 106 m3 A1 [4] 12 (a) law: it is impossible to convert all of a given amount of thermal energy into work B1 (that is) W < QH B1 (QH – W ) is energy rejected at temperature TL B1 [3] (b) W/QH = 1 – TL/TH B1 [1] (c) efficiency = 1 – 313/393 C1 = 0.20 A1 [2] 13 (a) (i) e.g. industry setting up people preparing to go to work starting to cook breakfast (allow any two sensible suggestions, 1 each) B2 [2] (ii) e.g. change in temperature with use of heaters/air conditioning holiday or workday with more power used by industry when not on holiday (allow any two sensible suggestions, 1 each) B2 [2]

Page 4 Mark Scheme Syllabus Paper GCE A – May/June 2006 9702 06 © University of Cambridge International Examinations 2006 (b) (i) sudden increase in demand (as appliances are used) B1 (ii) increased demand in the afternoon B1 [2] (allow any two sensible suggestions in (i) and (ii)) Option T - Telecommunications 14 (a) (instantaneous) displacement of information signal M1 determines the frequency of the carrier wave A1 [2] (b) (i) 12 V B1 [1] (ii) 650 kHz B1 [1] (iii) 550 kHz B1 [1] (iv) 3000 B1 [1] 15 (a) analogue-to-digital converter (do not allow ADC) B1 [1] (b) controls the time at which samples are taken B1 [1] (c) enables higher frequency components in signal to be ‘detected’ B1 [1] 16 (a) electromagnetic shielding for the inner conductor B1 the braid is earthed B1 [2] (b) increased bandwidth means more information can be carried B1 so more calls can be transmitted simultaneously B1 fewer links are required B1 [3] 17 (a) e.g. cross-talk/cross-linking interference/picking up atmospherics/picking up man-made radiation white noise associated with vibrating atoms (any two, 1 each) B2 [2] (b) (i) number of dB = 10 lg (P2/P1) 35 = 10 lg (P/{7.6 × 10-6}) C1 P = 0.024 W A1 [2] (ii) number of dB = 10 lg (2.6/0.024) = 20.3 C1 length = 20.3/5.8 = 3.5 km A1 [2]