Cambridge A Level Physics 9702 — 2002 May/June 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 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 MAY/JUNE SESSION 2002 45 minutes Candidates answer on the question paper. No additional materials. This question paper consists of 20 printed pages. SPA (NH/CG) S14799/3 © CIE 2002 [Turn over Candidate Centre Number Number Candidate Name FOR EXAMINER’S USE

2 9702/6 M/J/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 M/J/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 = ±
√(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
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

4 9702/6 M/J/02 Answer all of the questions in any two Options. 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 The average diameter of the Earth’s orbit around the Sun is 2.99 ×108km. (a) Calculate, to three significant figures, the magnitude, in metres, of the astronomical unit (AU). 1 AU = … m [1] (b) (i) Define the parsec (pc). … … (ii) Use your answer to (a) to calculate the magnitude, in metres, of the parsec. 1 pc = … m [5] For Examiner’s Use

5 9702/6 M/J/02 [Turn over 2 (a) On Fig. 2.1, sketch a graph to show the variation with distance d from Earth of the linear speed v of galaxies. [1] Fig. 2.1 (b) Suggest why your graph implies a finite age for the Universe. … … …[2] (c) Explain why, although most galaxies appear to be moving away from the Milky Way galaxy, it cannot be assumed that the Universe had its origin somewhere in the Milky Way. … … …[2] (d) Explain how your graph of Fig. 2.1 may be used to (i) obtain a value for the Hubble constant, … (ii) estimate the age of the Universe. … … [3] 0 d v 0 For Examiner’s Use

6 9702/6 M/J/02 3 Fig. 3.1 shows the variation with the age of the Universe of its mean temperature. Fig. 3.1 On Fig. 3.1, mark positions at which (a) light elements were formed (mark this position L), [1] (b) decoupling of radiation and matter occurred (mark this position D), [1] (c) the formation of galaxies began (mark this position G). [1] 4 Suggest why the detection of very distant galaxies is a recent development in astronomy. … … … …[3] For Examiner’s Use 10 2 10 4 10 6 10 8 10 10 10 12 10 14 10 16 10 18 10 0 10 12 10 10 10 8 temperature / K age of Universe / s 10 6 10 4 10 2 10 0

7 9702/6 M/J/02 [Turn over Option F The Physics of Fluids 5 (a) Fig. 5.1 illustrates a cross-section through a ship. Fig. 5.1 The point G is the centre of gravity. On Fig. 5.1, (i) mark the approximate position of the centre of buoyancy (label this point B), (ii) draw lines to show the position of the metacentre (label this point M). [2] (b) For stability, the point M must be above the point G. Suggest the effect on the ship of increasing the separation of M and G when the ship is in rough seas. … … …[2] G sea level For Examiner’s Use

8 9702/6 M/J/02 6 An ideal incompressible fluid of density ρ flows along a pipe as shown in Fig. 6.1. Fig. 6.1 The fluid travels at speed v1 where the area of cross-section is A1 and at speed v2 where the area of cross-section is A2. The fluid pressure at these points is p1 and p2 respectively. (a) State formulae, in terms of v1, A1 and ρ for (i) the volume of fluid flowing per unit time along the pipe, … (ii) the mass flow-rate of the fluid. … [2] (b) Derive formulae, in terms of v1, v2, A1, A2 and ρ, for (i) the change in kinetic energy per unit time of the fluid as it flows through the pipe, (ii) the work done per unit time to force the fluid along the pipe. [4] area A1 area A2 v1 v2 pressure p1 pressure p2 For Examiner’s Use

9 9702/6 M/J/02 [Turn over (c) (i) Using your answers in (b), derive the Bernoulli equation p1 + 1 2ρv1 2 = p2 + 1 2ρv2 2. (ii) State one assumption, other than that of an ideal fluid, which you made in your derivation. … … [3] 7 A metal sphere is held just below the surface in a deep vessel containing oil. It is released from rest at time t = 0. (a) On the axes of Fig. 7.1, sketch a graph to show the variation with time t of the speed v of the sphere. [2] Fig. 7.1 (b) By reference to the forces acting on the sphere, describe the motion of the sphere. … … … … … …[5] 0 t v 0 For Examiner’s Use

10 9702/6 M/J/02 Option M Medical Physics 8 (a) Outline the use of ultrasound to obtain diagnostic information about internal body structures. … … … … … … … …[5] (b) The intensity I of a parallel beam of ultrasound is related to its initial intensity I0 and the thickness x of the medium through which it has travelled by the relation I = I0 e–µx where µ is a constant for the medium. Fig. 8.1 shows the constant µ for different media. Fig. 8.1 For Examiner’s Use medium blood bone muscle 2 130 23 µ/m–1

11 9702/6 M/J/02 [Turn over (i) Use the information in Fig. 8.1 to suggest why 1. ultrasound is not used to examine structures within bones, … … … 2. bones may be at risk when using high intensities of ultrasound to treat diseased joints. … … [4] (ii) Determine the ratio fraction of intensity of ultrasound transmitted through 10 mm of muscle fraction of intensity of ultrasound transmitted through 10 mm of bone ratio = … [3] For Examiner’s Use .

12 9702/6 M/J/02 9 A student can only focus clearly on objects which are between 75 cm and 10 cm from his eyes. (a) Name the eye defect from which the person is suffering. …[1] (b) Determine the power of the lenses required so that distant objects may be seen clearly. power = … D [2] (c) Suggest why this student has an advantage over a person with normal vision when a small object, such as the spring in a watch, is to be examined closely. … … …[2] For Examiner’s Use

13 9702/6 M/J/02 [Turn over 10 Fig. 10.1 shows the variation with frequency f of the minimum intensity level I.L. of sound heard by a particular person. Fig. 10.1 (a) Explain what is meant by intensity level. … …[1] (b) Describe, with reference to features of Fig. 10.1, the defects of hearing from which the person is suffering. … … …[2] 0 0.05 0.1 0.5 f / 10 3 Hz I.L. / dB 1 3 10 20 20 40 60 80 100 120 For Examiner’s Use

14 9702/6 M/J/02 Option P Environmental Physics 11 (a) Compare a pumped-water storage scheme and a tidal barrage scheme for the generation of electrical energy. You should include two distinct aspects in your comparison. 1. … … … 2. … … … …[4] (b) A pumped-water storage scheme is used both to pump water and to generate electrical energy. It is capable of pumping water at a rate of 77 m3s–1 to a height of 180 m. The density of water is 1000 kg m–3. (i) Calculate the useful power output of the turbine assembly when it is used as a pump. power = … MW (ii) The same turbine assembly generates 100 MW when the stored water is released at the same rate as when it was being pumped. By reference to your answer in (i), comment on this output power. … … … [5] For Examiner’s Use

15 9702/6 M/J/02 [Turn over 12 A wind generator has blades of length r. Air of density ρ and speed v is incident normally on the plane of the rotating blades. (a) Show that the kinetic energy E of the wind incident normally per unit time on the plane of the rotating blades is given by E = 1 2πr2v3ρ. [3] (b) One particular wind generator has blades of length 12 m. Air of density 1.2 kg m–3 and speed 4.5 m s–1 is incident normally on the generator. Calculate the power output of the generator given that its overall efficiency is 55%. power = … kW [2] (c) Suggest one problem associated with high wind speeds on such a generator, and how the problem is overcome. … … …[2] For Examiner’s Use

16 9702/6 M/J/02 13 (a) Comment on the statement that wind generators are pollution-free. … … …[2] (b) Suggest why there is controversy over the building of wind farms capable of generating the same output as a nuclear reactor. … … …[2] For Examiner’s Use

17 9702/6 M/J/02 [Turn over Option T Telecommunications 14 Fig. 14.1 shows the signal received at the aerial of a radio. Fig. 14.1 (a) State the form of modulation illustrated in Fig. 14.1. …[1] (b) Calculate (i) the frequency of the transmission, frequency = … Hz (ii) the frequency of the modulating waveform. frequency = … Hz [3] 0 voltage time / µs 100 200 300 0 For Examiner’s Use

18 9702/6 M/J/02 (c) On Fig. 14.2, draw a graph to show the variation with frequency f of the signal shown in Fig. 14.1. Show appropriate values on the frequency axis. [3] Fig. 14.2 signal voltage 0 0 f For Examiner’s Use

19 9702/6 M/J/02 [Turn over 15 Railway tracks provide a convenient route for communication cables. However, passing electric trains produce interference (noise) of power 7.3 ×10–5W in a certain co-axial cable. The signal-to-noise ratio in this cable must not fall below 25 dB for the effective transmission of the signal. (a) Show that the minimum effective signal power in the cable is 0.023 W. [2] (b) The cable has a loss of 4.8 dB km–1. Calculate the maximum length of cable which can be used without the need for repeater amplifiers for an input signal of power 5.8 W. length = … km [3] (c) Co-axial cables are being replaced by optic fibres along railway tracks. Suggest two reasons why this is being done. 1. … … 2. … …[2] For Examiner’s Use

20 9702/6 M/J/02 16 (a) State two uses of polar orbiting satellites. 1. … … 2. … …[2] (b) State two uses, other than for television transmissions, of geostationary satellites. 1. … … 2. … …[2] (c) (i) State a typical wavelength used for satellite communication. wavelength = … m (ii) Explain briefly why the transmission frequency from Earth to a satellite is different from the frequency that the satellite transmits back to Earth. … … [2] For Examiner’s Use

CAMBRIDGE INTERNATIONAL EXAMINATIONS JUNE 2002 GCE Advanced Level MARK SCHEME MAXIMUM MARK: 40 SYLLABUS/COMPONENT :9702 /6 PHYSICS (OPTIONS (A2)) BA UNIVERSITY of CAMBRIDGE EE Local Examinations Syndicate

Page 7 Wark Scheme Syllabus | Paper | - 2 A Cevel Examinations — June 2002 S70Z | & | Categorisation of marks The marking scheme categorises marks on the MACB scheme. B marks: These are awarded as independent marks, which do not depend on other marks. For a B-mark to be scored, the point to which it refers must be seen specifically in the candidate’s answer. M marks: These are method marks upon which A-marks (accuracy marks) later depend. For an M-mark to be scored, the point to which it refers must be seen in the candidate's answer. If a candidate fails to score a particular M-mark, then none of the dependent A-marks can be scored. C marks: These are compensatory method marks which can be scored even if the points to which they refer are not written down by the candidate, providing subsequent working gives evidence that they must have known it. For example, if an equation carries a C-mark and the candidate does not write down the actual equation but does correct working which shows he/she knew the equation, then the C-mark is awarded. A marks: These are accuracy or answer marks which either depend on an M-mark, or allow a C-mark to be scored. Conventions within the marking scheme BRACKETS Where brackets are shown in the marking scheme, the candidate is not required to give the bracket information in order to carn the available marks. UNDERLINING In the marking scheme, underlining indicates information that is essential for marks to be awarded.

age Mark Scheme [Syllabus | Paper [ A Level Examinations — June 2002 I70Z 5 Option A 1 (@) 1.50 x 10" m (accept 1.49 x10" m) eects reseeeeeeeeeeeeseen Bl [lt] (b) (i) distance at which 1 AU Mi subtends an angle of 1 second of arc Al (ii) are = 76 . cl 1 arc second = 2n/ (360 x 3600) = (4.85 x 10°) rad cl I pe = (1.5 x t0")/(4.85 x 10%) = 3.09x 10m … Al [5] (accept 3.1 x 10° m) 2 (a) sketch: straight line through origin …----:essecseeeeeeeenecetereeecee BI {Il} {b) galaxies are moving away from each other …----..--seesseeeeeeeees Bl t (so) at one time, must have been close together OR max. speed close to c, So fimite time -…sseeeeceeeeeeeseneneeeeees Bl [2] {c) on sufficiently large scale, Universe is homogeneous OR mentions ‘Cosmological Principle’ Bl so, no matter where positioned, galaxies are moving away B! {2} CC) 0 I (adh (: San EE OOTP SEOESEESO SEITE OSSESOOOOOEOION this is the gradient of the graph... Gi) (div is the time for galaxies to separate i.e.) 1/gradient [3] {allow 1/Hp if Ho stated to be the gradient) 3 (a) allow 10? s— 10‘ Bl fl] (b) allow 10'?s- 10s Lice eee BI fi] (c) later than (b) but about 10! BI 4 e.m. radiation received is very faint cl radiation is absorbed by atmosphere Bl so use detection systems in Earth orbit BI [3]

“Page 3 ark Scheme ylabus Paper ‘evel Examinations — June 6 Option F 5 (a) (b) 6 (a) (b) (c) 7 (a) (b) ® (ii) ) ii) @ (i) @ (ii) reasonable position reasonable construction wit restoring couple increases (i) ship is more stable Qa) so ship less likely to move with the waves or more likely to act as rigid wall against waves (1) any two, | each max 2 Ay PAW, ... By Va occ ccccceccccccecceeeccesueecceeecennsetecsseseeeecseceseneueuersass Cl YepAw, - pAwi . Al work done = pAV . Cl PrAM1 - prAr2 - Al {allow answer to {i) without comment for 2/2) PIA = pada, = Ypdr? - Yaad now 4\y, = Aw2 Pi - Pr = Apr? - py, assumption: horizontal flowistreamfine/non-viscous graph: curve from origin approaches/reaches constant speed weight, upthrust and drag act on sphere …-- sees cee eesneseeeeeee saa eceeeee Bt accelerating force = (apparent) weight - drag OR = weight -—upthrust— drag oo... eee eeeeeee ee eeeeeee Bl as speed increases, drag increases so acceleration decreases …-- reaches a constant/terminal speed (2] {2 (2] (4} (3) [2] 5]

age Wark Scheme Syllabus faper evel Examinations — June Option M 8 (a) pulse of ultrasound reflected (at boundaries) Bl {on return, detected and) processed Bl time delay gives depth …:eeee . Bl strength of echo indicates nature of boundary » BI {5] (b) (i) 1. (high « means) low penetration (do not allow ‘absorbed’) also much reflection (at muscle/bone interface) 2. ultrasound absorbed in bone causes a heating effect [4] Gi) o)msscie = €™ (Wheoe = &™ substitution of value for x or use of indices ratio = 2.9 {3] 9 (a) short sight / myopia BI [Ij (b) power = - 1/0.75 + l/oo Cl =-133D [2] {c) there is greater magnification …csesesseeeescneneseeeneeeereeeesaanees Bl because able to focus when closer to CYC …eceeeeceeeteeeeee seco ae eeeeeee Bl [2] 10 (a) LL. = 10 Ig(i/fo) with fy explained 1) (b) loss of sensitivity at about 3 KHZ …:.eseeeeeeeeeeeeceeeneeeeueeensseeetes Bl loss of hearing at higher frequencies (- cut-off should be about 15kHz)...B1 [2] Option P 11 (a) e.g. energy from tidal flow / stores excess electrical energy …B2 dependent on time of tides / available to meet peak demands … B2 [4] (b) (@) 77 ms! = 77x10 kgs... / energy = mgh power = 77x 10° x 9.8 x 180 = 140MW

Page 5 Mark Scheme Syllabus | Paper K Laver Examinations = Jane 2002———| 6707 6 11 (b) (ii) 12 (a) (b) (©) 13 (a) (b) Option T 14 (a) ) @ (ii) {c) Answer in (i) must be greater than 100 MW Bl because water falling has k.e. (or other valid point) .. . Bl (calculation of efficiency as 74% - allow 1/2) mass of air per unit time = xr?pv Bl kinetic energy = Ymv" ... BI E =%nrp .v Mi = Ynr'p? AO E = 0.55 x%xnx12?x 12x45? ch = 13.6kW Al high speeds cause large stresses (in blades etc) .. . BI blades are ‘feathered’ . Bl not true - visual pollution - Bl - pollution during building ... Bl (allow any two valid points — give credit for justifying ‘no pollution’ claim) Many generators required over a large area other valid point e.g. weather dependence etc amplitude modulated 10 waves in 200 ps f= 50kHZ frequency = 5 kHz graph: three vertical lines carrier tonger than equal sidebands frequencies shown correctly (3] [2] [2] [2] f2]

Page & Mark Scheme Syllabus | Paper ‘evel Examinations — June — S702 mn :3 15 (a) number of dB = 10 Ig(P,/P2) 25 = 10 ig (P/(7.3 x 10°) tes m P= 0023 Wolo cceeceeeseeeeesoeeeteeseeeceeeveceevaas AO [2] {b) change in signal power = 10 tg(5.8/0.023) = 24dB length = 24/48 = 5.0km {3] (c) e.g. less interference greater uninterrupted length no cross-talk etc (any valid points, leach) …eceeeeeeeeeeee B2 {2] 16 (a) e.g. weather forecasting prospecting etc (any two valid points, l each) …00 eee B22} (b) ¢.g. weather monitoring telephone communication (any two valid points, leach) … B22] Ce) (i) allow Lom > 20 cm oe ccccceeecccucecuauveccceveareccauaneess (ii) ¢.g. prevent swamping of incoming signal {2]