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02 AL Physics/M.C./P.1 2002 Hong Kong Advanced Level Examination AL Physics Multiple Choice Questions 1. 4. A Y B C X A block of mass m falls from rest at A onto a vertical light spring of force constant k firmly fixed to the ground. When the block reaches B, it starts to compress the spring until it reaches the lowest position C as shown. Neglecting air resistance and considering the motion of the block from A to C, which of the following statement is/are correct? Two identical blocks X and Y are connected by a light spring and the system is suspended from a fixed support by a light cord as shown. The system is in static equilibrium. If the cord is suddenly cut, what is the magnitude of the acceleration of each block at that instant? A. B. C. D. 2. Acceleration of Y g 2g g 2g (1) The kinetic energy of the block is at a maximum when it is at B. (2) The resultant force acting on the block is zero when it is at C. (3) The maximum compression of the mg spring is greater than . k Two small identical objects P and Q are released from rest from the top of a building 80 m above the ground. Q is released 1 s after P. Neglecting air resistance, what is the maximum vertical separation between P and Q in the air? A. B. C. D. 3. Acceleration of X g g zero zero 5m 10 m 35 m 45 m The SI unit of length, metre, is defined as n times the wavelength of a certain orange-red light emitted from a krypton-86 atom. The number n is of the order A. B. C. D. 104. 106. 108. 1010. A. B. C. D. (1) only (3) only (1) and (2) only (2) and (3) only 5. A bob of mass m is suspended from a fixed support by a light string. A force F is applied to the bob (F is not shown in the figure) so that the string makes an angle with the vertical. What is the minimum value of F required to keep the bob in static equilibrium as shown? 02 AL Physics/M.C./P.2 mg sin mg cos mg sin cos mg sin2 A. B. C. D. 9. 6. P X Q Y R Z An object undergoes a simple harmonic motion with an amplitude A, and its total energy is E. What is the displacement of the object from the equilibrium position 3E when its kinetic energy is ? 4 A. P, Q and R are three identical spheres moving with the same speed along a smooth horizontal track. They undergo head-on elastic collisions with spheres X, Y and Z respectively which are initially at rest. After collision, P continues to move in its original direction, Q becomes stationary while R reverses its motion. After collision, which sphere (X, Y or Z) has the greatest magnitude of B. C. D. A 2 A 4 3A 4 3A 2 10. (1) momentum (2) kinetic energy? A. B. C. D. 7. (2) Y Y Z Z Z Y X Y 0 momentum. kinetic energy. velocity. acceleration. A. B. C. D. A particle P is moving in a horizontal circle in a clockwise direction as shown (top view). The following diagrams show the direction of the acceleration a of the particle. Which of them is/are possible? (1) (2) y Displacement Force Kinetic energy Speed x Acceleration Displacement Displacement Displacement 11. (3) a a a P A. B. C. D. x The graph describes the motion of a simple harmonic oscillator. Which pair of physical quantities is most likely represented by variables y and x? The impulse experienced by an object is equal to its change in A. B. C. D. 8. (1) y (1) only (3) only (1) and (2) only (2) and (3) only P P A thin uniform rod of mass 0.1 kg and length 0.3 m is smoothly hinged at its lower end as shown. It is then released from rest from the vertical position. What is its angular speed, in radian per second, when it becomes horizontal? (Moment of 02 AL Physics/M.C./P.3 inertia of the rod about one end is 3 10-3 kg m2.) A. B. C. D. 15. 6.3 10 14 50 first-order maximum grating incident light central maximum first-order maximum 12. Due to air resistance, changes may occur to a satellite orbiting the earth (assuming nearly circular orbit). Which of the changes below is incorrect? When a certain monochromatic light is passed through a diffraction grating, a pattern of maxima and minima is observed as shown. Which of the following combinations would produce the largest angle between the first-order maxima? A. The total mechanical energy of the satellite will decrease. B. The angular momentum of the satellite about the earth’s center will decrease. C. The linear speed of the satellite will increase. D. The time needed for the satellite to complete one revolution will increase. A. B. C. D. Grating (lines per mm) 200 200 400 400 Colour of light used blue red blue red 13. 16. Q L1 L2 time P The waveforms in the figure show the time variation of two physical quantities P and Q. What is the phase relationship between P and Q? . 2 B. P leads Q by . 4 C. Q leads P by . 2 D. Q leads P by . 4 A. P leads Q by 14. In which of the following the phenomenon of polarization cannot be observed? A. Light reflected from the surface of water. B. Microwaves emitted from a transmitter. C. Light scattered from a clear sky. D. Ultrasonic waves used in sonar. 20 cm In the figure, L1 and L2 are two thin lenses with the same focal length 40 cm placed coaxially 20 cm apart. A beam of light originating from a distant object is incident on L1. Which of the following statements about the final image formed by the system of lenses is correct? A. It is real and formed on the right of L2. B. It is real and formed between L1 and L2. C. It is virtual and formed between L1 and L2. D. It is virtual and formed on the left of L1. 17. A stretched string is 1 m long and is fixed at both ends. Stationary waves of 400 Hz and 450 Hz but no other intermediate frequency can be formed. What is the 02 AL Physics/M.C./P.4 speed of the mechanical waves along the string? 20. X A. B. C. D. 25 ms-1 50 ms-1 100 ms-1 200 ms-1 Y 18. When a source emitting sound waves of a fixed frequency moves towards a stationary observer in air, the pitch of the sound heard by the observer is different from that when the source is at rest. This is due to a change in the In the above figure the solid lines represent part of an electric field due to a fixed point charge Q (not shown in the figure). A charge particle q, subjected only to electric force in the field, travels along the dotted curve shown. Which of the following conclusions can be drawn? (1) number of waves emitted per second from the source. (2) speed of sound in air. (3) wavelength of sound in air. A. B. C. D. A. q is traveling from X to Y. B. The charge of q has the same sign as that of Q. C. q has a greater speed at X than at Y. D. The electric potential at X due to Q is higher than that at Y. (1) only (3) only (1) and (2) only (2) and (3) only 19. The spectra produced by element X, one on earth and the other on a distant star, are compared. 21. Spectrum form element X on earth: Red Green Violet Spectrum from element X on the distant star: What is the most probable reason for the difference in the spectra readings? A. B. C. D. The universe is expanding. The star is approaching the earth. The star is receding from the earth. The star is spinning about its axis. The above figure shows an electron entering a uniform field which may be electric or magnetic. Which of the following descriptions about the subsequent motion of the electron is correct? A. Only in a magnetic field can the electron be deflected by more than 90. B. Only in an electric field does the force depend on the magnitude of the charge on the electron. C. Whether the field is electric or magnetic, the speed of the electron will increase. D. Whether the field is electric or magnetic, the magnitude and direction of the force acting on the electron are constant. 02 AL Physics/M.C./P.5 22. X Y Three identical capacitors, each of capacitance C, form a network as shown. What is the equivalent capacitance between terminals X and Y? A. C 3 B. C 2 2 C. C 3 D. 3C In the above circuit, the d.c. supply has an e.m.f. of 9 V and its internal resistance is negligible. V1, V2 and V3 are three voltmeters with the same finite internal resistance. If V1 reads 4 V, find the reading of V3 and the potential difference across resistor R. A. B. C. D. Voltmeter reading Potential of V3 difference across R 3V 1V 5V 1V 1V 5V 1V 3V 25. A d.c. supply of constant e.m.f. and internal resistance is connected to a variable resistor of resistance R. Which of the following graphs best shows how the total power P delivered by the supply varies with R? 23. A. P A parallel-plate capacitor is first charged by connecting it to a battery. After disconnecting the battery, one of the plates of the capacitor is shifted upward slightly as shown. What would happen to each of the following quantities? 0 B. P V: the potential difference between the plates Q: the magnitude of the charge on each plate C: the capacitance of the capacitor A. B. C. D. V decreased unchanged increased increased Q unchanged decreased decreased unchanged C increased decreased decreased decreased R 0 R C. P 24. 0 9V R S V3 V1 V2 R 02 AL Physics/M.C./P.6 D. A circular frame and a square frame, made from the same type of insulated metal wires, are placed in a uniform magnetic field as shown. When the flux density of the field is increased at a steady rate, the ratio of the induced current in the circular frame to that in the square frame is P R 0 A. B. C. D. 26. A capacitor is discharged through a resistance of 1 k. If the time constant of the discharging circuit is 2 ms, what is the capacitance of the capacitor? A. B. C. D. 1:1 1: :4 2: 29. 0.5 F 1 F 2 F 5 F P Q 27. P Q 60 l R v S A metal rod of length l is inclined at 60 to rail PQ as shown. It is moved across a uniform magnetic field along the direction of the two horizontal rails PQ and RS. If the rod moves with a uniform velocity v and the flux density of the field is B, the e.m.f. induced in the rod is Blv . 2 B. Blv. 2Blv C. . 3 Three long straight parallel wires P, Q and R carrying currents of the same magnitude are situated at the vertices of an equilateral triangle as shown. The currents in wires P and R are directed out of the paper. Which of the following indicates the direction of the force acting on wire P? → ↓ C. ↑ D. ↗ A. B. 30. A steadily running motor draws a current of 2 A from a battery of e.m.f. 5 V. The internal resistance of the battery is negligible. If the resistance of its armature coil is 0.5 , estimate the efficiency of the motor. A. D. R 3Blv . 2 A. B. C. D. 28. uniform magnetic field 60% 70% 80% 90% 02 AL Physics/M.C./P.7 31. 33. I Y1 E Y2 In the circuit shown, the voltages across the resistor and capacitor are respectively fed to the input terminals Y1 and Y2 of a dual trace CRO where E is the common earth terminal. Which of the following pairs of traces could be obtained? (The trace of Y1 is represented by a solid curve and the trace Y2 is represented by a dotted one.) V Which of the following combinations of a cell, an ideal diode and a resistor will give the above I-V relationship, where I and V are the applied current and voltage respectively? A. A. B. B. C. C. D. D. 34. Which of the following is/are the advantage(s) of using negative feedback in an operational amplifier for voltage amplification? 32. To produce an X-ray photon of energy 3.6 10-15 J, the bombarding electrons in the X-ray tube must be accelerated through a potential difference of at least (Given: electronic charge = 1.6 10-19 C) A. B. C. D. 11.3 kV. 22.5 kV. 28.8 kV. 57.6 kV. (1) greater stability (2) larger voltage gain (3) no distortion of the output A. B. C. D. (1) only (3) only (1) and (2) only (2) and (3) only 02 AL Physics/M.C./P.8 35. A beam of red light falls on one electrode of a photocell and electrons are emitted. The red beam is then replaced by a blue one that has the same intensity. Which of the following physical quantities would decrease as a result of this change? A. The maximum kinetic energy of the photoelectrons emitted B. The energy of each photon striking the electrode C. The number of photons striking the electrode per second D. The magnitude of the potential difference across the photocell required to reduce the photo-electric current to zero 36. In which of the following calculations is it necessary to use the Planck constant? (1) Finding the momentum of an electron from its kinetic energy (2) Finding the energy of a photon emitted as a result of the transition of an electron between two energy levels in an atom (3) Finding the maximum kinetic energy of photoelectrons from the wavelength of incident radiation A. B. C. D. (1) only (3) only (1) and (2) only (2) and (3) only 37. A hydrogen atom absorbs a photon of wavelength such that the electron in the ground state (energy level corresponding to n = 1) is brought to an excited state (energy level corresponding to n = 3). What is the maximum wavelength of a photon that can cause ionization of a hydrogen atom in the ground state? A. B. C. D. 8 9 9 8 3 2 2 3 38. P B A 0 T The graph shows the relation between the pressure P and the absolute temperature T of a fixed mass of an ideal gas, which changes from state A to state B along the path AB. Which of the following statements is/are correct? (1) The graph shows that P is directly proportional to T. (2) The volume V of the gas increases. (3) All the points on straight line AB PV satisfy the relation = constant. T A. B. C. D. (1) only (3) only (1) and (2) only (2) and (3) only 39. What is the order of magnitude of the number of molecules in 1 cm3 of air in an atmospheric pressure of 105 Pa and at room temperature? (Given: Universal gas constant = 8.31 JK1 mol-1 Avogrado constant = 6.02 1023 mol-1) A. B. C. D. 1025 1019 1016 1013 40. At 80 C, the r.m.s. speed of the molecules in a fixed mass of an ideal gas is c. If the temperature is increased to 160 C, the r.m.s. speed of the gas molecules would become A. B. C. D. 2c. 1.4c. 1.2c. 1.1c. 02 AL Physics/M.C./P.9 41. on a quiescent collector current of 3 mA and with the base-emitter junction voltage VBE = +0.6 V. What should be the value of the base-bias resistor RB? ln(A/Bq) 5 A. B. C. D. t/s 0 400 The graph above shows how the logarithm of the activity A of a radioactive isotope varies with time t. What is the half-life of the isotope? A. B. C. D. 128 k 144 k 160 k 176 k 44. 50 k 10 k P V1 - 15 V V2 42. Which of the following situations cannot be explained by using Bernoulli’s equation? (1) An object falling with terminal velocity in air (2) The curved path described by a spinning tennis ball (3) The flow of water out of a tank through a small hole near its bottom A. B. C. D. (1) only (3) only (1) and (2) only (2) and (3) only V0 50 k 0V The figure shows an operational amplifier circuit. When V1 = +2.7 V and V0 = -0.9 V, what is the potential at P? A. B. C. D. 0V 0.6 V 2.1 V 2.4 V 45. The diameter of the bore of a capillary tube can be determined by introducing a small quantity of mercury into the capillary. It is possible to measure the length of the mercury thread to within 2% and the mass of the mercury used to within 4%. Assuming negligible error in the density of mercury, the percentage error in the calculated diameter of the capillary bore is at most 43. + 6V RB C B +15 V 10 k 200 s 55 s 24 s 0.42 s A. B. C. D. E 0V The figure shows a typical voltageamplifier circuit built from a transistor with current gain 80. It operates normally - End of Paper - 2%. 3%. 4%. 6%. 02 AL Physics/M.C./P.10 Question No. Key Question No. Key 1. 2. 3. 4. 5. D (17) C (58) B (55) B (25) A (66) 26. 27. 28. 29. 30. C (88) D (69) A (18) A (43) C (88) 6. 7. 8. 9. 10. D (43) A (89) C (20) A (36) C (75) 31. 32. 33. 34. 35. C (38) B (88) C (30) A (53) C (51) 11. 12. 13. 14. 15. B (43) D (33) A (51) D (81) D (52) 36. 37. 38. 39. 40. B (30) A (46) D (23) B (72) D (48) 16. 17. 18. 19. 20. A (26) C (40) B (69) D (33) C (25) 41. 42. 43. 44. 45. B (75) A (66) B (70) C (52) B (37) 21. 22. 23. 24. 25. A (31) B (91) D (61) D (29) C (34)