2012-DSE PHY PAPER 1A, HONG KONG EXAMINATIONS AND ASSESSMENT AUTHORITY HONG KONG DIPLOMA OF SECONDARY EDUCATION EXAMINATION 2012 PHYSICS PAPER 1 8.30 am ~ 11.00 am (2% hours) This paper must be answered in English GENERAL INSTRUCTIONS. (1) There are TWO sections, A and B, in this Paper. You are advised to finish Section A in about 60 minutes, (2) Section A consists of multiple-choice questions in this question paper, while Section B contains conventional questions printed separately in Question-Answer Book B. (3) Answers to Section A should be marked on the Multiple-choice Answer Sheet while answers to Section B should be written in the spaces provided in Question-Answer Book B. The Answer Sheet for Section A and the Question-Answer Book for Section B will be collected separately at the end of the examination. (4) The diagrams in this paper are NOT necessarily drawn to scale. (6) The fast two pages of this question paper contain a list of data, formulae and relationships which you may find useful INSTRUCTIONS FOR SECTION A (MULTIPLE-CHOICE QUESTIONS) (1) Read carefully the instructions on the Answer Sheet. After the announcement of the start of the ‘examination, you should first stick a barcode label and insert the information required in the spaces provided. No extra time will be given for sticking on the barcade label after the ‘Time is up’ announcement. (2) When told to open this book, you should check that all the questions are there. Look for the words "END OF SECTION A’ after the last question, (3) All questions carry equal marks. (4) ANSWER ALL QUESTIONS. You are advised to use an HB pencil to mark all the answers on the Answer Sheet, so that wrong marks can be completely erased with a rubber. You must mark the answers clearly; otherwise you will lose marks ifthe answers cannot be captured. (5) You should mark only ONE answer for each question. If you mark more than one answer, you will receive NO MARKS for that question. (6) No marks will be deducted for wrong answers. Not to be taken away before the ‘end of the examination session 2012-DSE-PHY LA-1 4Section A. “There are 36 questions. Questions marked with * involve knowledge of the extension component. 1. Two metal blocks X and ¥ of the same mass and of initial temperatures 40°C and 30°C respectively are in good thermal contact as shown. The specific heat capacity of X is greater than that of Y. Which statement is correct when a steady state is reached Assume no heat loss tothe surroundings aoc 30% Block X Block ¥ ‘A, The temperature of block 2is higher than that of block ¥. 8. Their temperature becomes te same and is lower than 35°C. C. Their temperature becomes the same and is higher than 35°C. D. Their temperature becomes the same and is equal to 35°C. 2. When patient’s arm is wiped by a piece of cotton soaked with alcohol, the wiped area will feel cool as that patch of alcohol on the skin evaporates. Which statement explains this phenomenon ? ‘The evaporation of alcohol absorbs heat from the patients arm ‘The alcohol on the skin releases latent heat tothe surrounding air. ‘The motion of all the molecules in the patch of alcohol slows down Air molecules remove heat from the patch of aleohol by conduction. por> +3, Amideal gas is contained in a closed vessel of fixed volume. The graph below shows the variation of Pressure p of the gas against its Celsius temperature 0. P 0 8 If the number of gas molecules in the vessel is halved, which graph of the dotted line best shows the relationship between p and 9°? Ap BP 2012-DSE-PHY 18-24, Which of the following descriptions is correct ? A. When water at 25°C is heated to $0°C, both the kinetic energy and potential energy of the water molecules increase B. When water at 25°C is heated to 50°C, only the potential energy of the water ‘molecules increases. C. When water boils at 100°C and turns into steam, the kinetic energy of the water molecules increases. D. When water boils at 100°C and tus into steam, the potential energy of the water molecules increases. s. Fy 6 A TTwo forces F and F; of constant magnitudes act at the same point as shown. When the angle @ between F) and F; increases from 0° to 180°, the magnitude ofthe resultant force A. decreases throughout B. increases throughout ©. decreases and then increases. D. __jnereases and then decreases 6. A-uniform gangplank PQ of a fery smoothly hinged at end P intially rests horizontally on the pie. ‘The gangplank has mass M and length 2m. Its raised by a man on the ferry using a light rope passing a smooth fixed light pulley and connecting to R on the gangplank as shown. is 1.5 m from end P. Which ofthe following correctly describes the force required to raise the gangplark steadily ? initial force required to raise the subsequent force required to ‘gangplank when itis horizontal raise the gangplank A 0.67 Mg ‘greater than 0.67 Mg : B. 0.67 Mg smaller than 0.67 Mg ! c 0.94 Mg greater than 0.94 Mg D. 0.94 Mg smaller than 0.94 Mg 2012-DSE-PAY 1A-3 67. Which of the following graphs (velocity-time and displacement-time) best represent the motion of a ball falling from rest under gravity at a height #7 and bouncing back from the ground two times ? Assume that the collision with the ground is perfectly elastic and neglect air resistance. (Downward ‘measurement is taken to be negative.) a Q) velocity velocity 4 ° ° * 1/7 time displacement ) displacement, @ H #| : ° ° MAL , fi time ()and @) only (() and (4) only Q) and (3) only Q) and (4) only pow> Blocks P and Q of mass m and 2m respectively are connected by a light spring balance and placed on a smooth horizontal surface as shown. If horizontal forces F; and F; (with Fy > F3) act on P and Q respectively and the whole system moves to the left with constant acceleration, what is the reading of the spring balance ? D. 9. An object of mass 0.5 kg is raised vertically from the ground by a motor. The object is raised 2.5 m in 1.5 s with uniform speed. Estimate the output power of the motor. Neglect air resistance. (g-981ms%) 3sW 82W 1.0W 164W pop> 2012-DSE-PHY 14-4 710, UL. +12, A block of mass m resting on a 30° incline is given a slight push and slides down the incline with @ uniform speed. Which of the following statements about the block’s motion on the incline is/are correct ? £2. Sk > (1) There is no net force acting on the block, (2) The frictional force acting on the block is 0.5 mg. G) Ifthe block is given a greater intial speed, it will slide down the incline with acceleration. (1) only 3) only (1) and @) only (2) and (3) only pop ‘A block of mass m initially resting on a rough horizontal surface is pulled along the surface by a horizontal force F increasing from zero. If the frictional force is constant, which graph shows the ere eater A. a B. a a 4 : C. D. 7 a eae A F A bomber aireraft is 1 km above the ground and is flying horizontally at a speed of 200 m s"!. The aircraft is going to release a bomb to destroy a target on the ground. How long before flying over the target should the bomb be released ? Assume that the bomber aircraft and the target are in the same vertical plane and neglect air resistance. (g= 9.81 ms”) A 56s Bo 101s C1438 D. It cannot be calculated asthe horizontal distance between the aircraft and the target is not known, 2012-DSE-PHY 14-5 813. Ona smooth horizontal surface, a circular disk P moving at velocity w along the x direction collides obliquely with an identical disk Q initially at rest as shown below. The mass of each disk is m. Which statements about the collision is/are correct ? (1) Momentum of te system inthe y direction is not conserved. 2) The total kinetic energy of P and Q after collision is, zme ifthe collision is perfectly caste. @) Speed of Q after collision is less than (1) only GB) only (1) and (2) only @)and (3) only pomp i “14, ‘Two satellites move in circular orbits of the same radius R around the Earth (mass M ). The orbits are in two different planes P and Q as shown. Plane P coincides with the Earth’s equator while plane @ is inclined to the equator at 6. Which statement is INCORRECT ? Plane LEN nme The speed of satelite Pis ‘The centripetal force acting on satellite Q is pointing along the plane Q. ‘The acceleration of both satellites is the same in magnitude, ‘The period of satellite Q is longer than that of satellite P. pape 2012-DSE-PHY 14-6 °15, 1 Figure (a) Figure (6) Sem AA seties of particles is uniformly distributed along a slinky spring initially. Figure (a) shows their positions at a certain instant when a travelling wave propagates along the slinky spring from left to Fight. Figure (b) shows their positions 0.1 s later. Which statement is correct ? Particle ¢ is always stationary. Particles @ and i are in phase. ‘The wavelength of the wave is 16 em. The frequency of the wave is 10 Hz. vamp A pulse on a string propagates towards the right end which is fixed = ‘Which of the following represents the reflected pulse ? A. > = B. = D. = 2012-DSE-PHY 1-7 lo17. Accertain monochromatic light passes through medium X as shown below. What isthe refractive index of medium X? (N air medium X air 125 133 1.50 165 pomp 18. A stationary wave is formed on a string fixed at both ends X and ¥. The following is a snapshot of the string at time ¢= 0. ‘The amplitude of vibration at an antinode is A. Which of the following shows the displacement-time graph of point P on the string far one period ? (Upward displacement is taken as positive.) A gptispacement Fe acer | TZN PK pty th 0 > 0 | imo | im A i le L. Lt i. displacement D. 4 ; 7 . time | A aLlLti | 19, Which of the following statements is INCORRECT ? ‘A, In air, the wavelength of infra-red radiation is shorter than that of ultra-violet radiation, B. Visible light travels faster in air than in glass. C. Microwaves travel at the speed of light in a vacuum, D. Both fight and sound exhibit diffraction, 2012-DSE-PHY 1A-8 i"20. For a diffraction grating of 600 lines per mm, the diffracted red light (657 nm) coincides with the diffracted violet light (438 nm) at angle of difraction 52°. What are the respective orders of the diffacted red light and violet light? red violet raceeeeea 3 B 3 4 cettes 2 D4 3 j 21. Ineach of the following diagrams, Lis a concave lens and its two principal foci are denoted by F and : F*, Which ofthe ray diagrams is/are possible ? i w b @ @ é F A. (only B.G)only C— @and @) only D. — @)and (3) only 2 The figure shows the waveforms of sound notes generated by a violin, a piano and a tuning fork. The scale is the same in time and intensity axes forall three waveforms, «uy au 1 ‘Which of the following about the sound notes are correct ? Q) They al have the same pitch (2) The qualities of sound of (11) and (IUD are different. (3) Wis generated by the tuning fork. A. (I)and@) only B. (1) and) only C— Q)and ) only D. — (),@)and G) 2012-DSE-PHY 14-9 2 eee23. Which of the following about ultrasound is INCORRECT ? A. Ultrasound isa longitudinal wave. B. The frequency of ulrasound is greater than 20000 Iz, C. Imai, the speed of ultrasound is faster than the speed of audibie sound. D. Ina, the diffraction effect of ultrasound is less prominent than tht of audible sound 24. P.O, R,Sare charged objects. When two of them are brought close to each other, P and Q repel, R and S algo repel while Q and R atract each other. Which ofthe following descriptions about thet charges is/are possible ? ()—Pand R are negatively charged. @) and S are positively charged. @) Ps positively charged and S is negatively charged, A. (only B. G)only (and Q) only D. — @)and G)only 125, ‘Two point charges +29 and —9 are situated at fixed positions as shown. is the mid-point between the charges. X,Y and Z are points marked on the line joining these two charges. At which point could (0) the resultant electric field due to the two charges be zero ? @) the total electric potential due tothe two charges be zero ? @ @ A 2 x BZ Y c x Zz DO OY Zz k 26, 129 In the above network, the resistance across terminals a and b is 6 Q. If the 12.0 resistor is replaced by a 6 Qresistor, the resistance across terminals a and & becomes 2 2. becomes 4.0. becomes 6 ‘cannot be found as the value of & is unknown. vap> 2012-DSE-PHY 14-10 B27. What will happen ifthe variable resistor is set to zero in the circuit below ? ‘The light bulb will bum out, ‘The light bulb will not light up. The brightness of the light bulb will increase. The brightess of the light bulb will remain unchanged. poe 28, 30 {| 6a In the above circuit, the cell has e.m.f. 12 V and internal resistance 22. What is the current in the 6 resistor ? OSA 1OA 15 204, vas 29. In the figure below, x, Y and Z are three long straight parallel wires with Z placed midway between X and ¥. X and Z carry currents of 1 A in the same direction while ¥ carries a current of 3 A in the ] ‘opposite direction. The magnetic force per unit length experienced by wire X due to wire Z is of magnitude F. Aer 7 1A] 1A 3A ‘The magnetic force per unit length acting on wire Z due to both and Yis A. 2F tothe right. i B. 2Fwtheleft. C. 4F tothe right. D. —4Ftothe left. 2012-DSE-PHY 14-11 “430. An electron enters a region in which both a uniforin electric field £ and a uniform magnetic field B exist. The magnetic field B is pointing into the paper. In which direction should the electric field be applied so that the electron could be undeflected ? electric B. electric field - field etesnon 242 eecuon 322 Or ee Oman i c. D. electron ‘electron, field o> Se om 3 L]+> = ' 7 : ‘A square metal frame of length of side L moving with constant velocity v passes through a region of uniform magnetic field of width 5Z as shown. What is the total time period during which a current is induced inthe fame? ae 7 peas « pn ov-pse2Hy v2 . ne32. A copper rod PQ is placed horizontally as shown below. It is released and then falls vertically, cutting across the magnetic field ofthe Earth pointing out ofthe paper. Neglect air resistance, Which of the following statements is/are correct ? en of the Earth (1) A voltage is induced across PQ. (2) A steady induced current is generated in the rod. (G) Due to the effect of the Earth's magnetic field, the copper rod falls with an acceleration less than the acceleration due to gravity A ()only B. — G)only © Gand @) only D. — Q)and @) only 33 electric Neutral x iron Live Y Zz Earth The figure shows a simple domestic cireuit for an electric iron. ‘The fuse will blow when which of the following points are short-circuited ? i Q) Xandy Q) Yandz : @) XandZ + A (only i B. G)only C.— (i)and (2) only : D. Gand B) only 2012-DSE-PHY 14-13 1634 35, 36. 2012-DSE-PHY 1A-14 The figure shows a schematic diagram of an X-ray tube in which the filament F and the metal target 7 are connected to terminals P and Q of an E.H.T. Which statement is correct ? ‘A. Pisthe positive terminal and X-rays are emitted from 7: B. Ps the positive terminal and X-rays are emitted from F. c the positive terminal and X-rays are emitted from 7. D. isthe positive terminal and X-rays are emitted from F. A certain radioactive isotope X has a half-life of 20 hours. After a time interval of 10 hours, what is the approximate fraction (/) ofa sample of the radioactive isotope X remaining ? Isotopes of an element have different mass number A and neutron number N. Which of the following NA plots correctly shows the relationship of N and A for any given element ? A B. Ny N o—————~4 ot c. D. Ny N o¢$———_——-4 END OF SECTION A 7List of data, formulae and relationships Data molar gas constant ‘Avogadro constant acceleration due to gravity universal gravitational constant speed of light in vacuum charge of electron electron rest mass + permittivity of free space permeability of free space atomic mass unit astronomical unit light year parsee Stefan constant Planck constant Recilinear motion For uniformly accelerated motion v= what s = uta 2 ab + 2as R831 Jmol! Kt Nq=6.02 x 10” mot! g= 9.81 ms” (close to the Earth) G=667x 10" Nv kg? o= 3.0010 ms! = 1.60x10%C m2 9.11 x 10 kg B= 885107? CON p= 40x 107 U= 1.661% 107 kg (Luis equivatent to 931 Mev) AU=1.50 x 10" m ly=946 x 10m pe= 3.09 x 10! m= 3.26 ly =206265 AU = 567% 104 Wm? K* h~ 6.63 x10 Is Mathematics Equation ofa straight line y= mete Are length =o Surface area of cylinder = 2nrh+2m* Volume of cylinder = rh Surface area of sphere = nr? Volume of sphere tu For small angles, sin 9 tan O= O(n radians) Stefan’s law Doppler effect gravitational potential energy Energy and Use of Energy g=2 4 thermal transmittance U-value maximum power by wind turbine Beey de Broglie formula Einstein's photoelectric equation energy level equation for hydrogen ators Rayleigh citron (resolving power) Rayleigh criterion (resolving power) power ofa fens intensity level (4B) Ze pe acoustic impedance ; hh (Zy+2y Tahe* transmitted intensity through ¢ medium 2012-DSE-PHY 1A-15 18fe nergy transfer during heating AL E=mcaT SREY a enrgy transfer during change AD E=tam Sey ‘equation of state for an ideal ges kinetic theory equation molecular kinetic energy 2 ore moment of afore vitational potential energy kinetic energy mechanical power centripetal sceleration Newton’s law of gravitation fringe width in double-slt interference diffraction grating equation ‘equation fora single lens 2012-DSE-PHY 1-16 ps. v=-2 ‘near DA Ds. D6. br. bs Do. D10. F= BQvsin 8 DIL. F=Bllsind BL v= BL DR. aso, pis, p= Hel er pia, p= Hot I pis. e=wae ar pie, eM % Np EL. N=Ne™ B22 1 e EB. A=kN EA, AE=Ame? 9 Coulomb's law electric feld strength due to ® point charge clecrie potential due to ‘a point charge clecric field between parallel plates (umerically) general curtent flow equation resistance and resistivity resistors in series tesistors in parallel, power in a circuit force on a moving charge ina magnetic field force on a curent-carrying ‘conductor in a magnetic field Hall voltage ‘magnetic field due to along straight wire magnetic field inside a long solenoid induced em. ratio of secondary voltage 10 Drimary voltage ina transformer law of radioactive decay halflife and decay constant ‘ activity and the number of undeeayed nuclei rmass-cnergy relationship