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99 AL Physics/M.C./P.1 1999 Hong Kong Advanced Level Examination AL Physics Multiple Choice Question 1. 3. A B F Two objects A and B of equal mass m are connected by two identical light springs and are placed on a horizontal smooth surface. A horizontal force F is applied to B so that the system is in equilibrium. If the applied force F is suddenly removed, what are the magnitudes of the acceleration of each object at the instant when force F is removed? A. B. C. D. E. The above figure shows an open wagon moving with negligible resistance in vertically falling rain. An appreciable amount of rain falls into the wagon and accumulates there. What are the effects of the accumulating rain on the speed, momentum and kinetic energy of the wagon? (Ignore the effects of the raindrops hitting the front of the wagon.) Acceleration of A Acceleration of B F zero m zero zero F F m 2m F zero m F F m m A. B. C. D. E. 4. 2. 30 cm 40 cm F horizontal surface A block of mass 5 kg is placed on the inclined surface of the wedge shown above. All contact surfaces are assumed to be smooth. What is the magnitude of the horizontal force F exerted on the wedge so that it remains stationary while the block is sliding down the inclined surface with acceleration? A. B. C. D. E. 0N 18 N 24 N 30 N 32 N speed momentum kinetic energy decreased unchanged decreased decreased unchanged unchanged decreased decreased decreased unchanged unchanged unchanged unchanged increased increased The velocity of an object changes with time but the magnitude of its acceleration remains unchanged. The motion of the object can be (1) simple harmonic motion. (2) parabolic motion of a projectile. (3) uniform circular motion. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 99 AL Physics/M.C./P.2 5. 7. E/J /Nm 10 1 0 v2/m2s-2 1 0 The above graph shows the variation of kinetic energy E with the square of velocity v of a moving mass m. What is the momentum of the mass when it is moving at a speed of 2 ms-1? A. B. C. D. E. 14 20 t/s A turntable of moment of inertia 1.0 10-3 kg m2 is under the action of a torque. The variation of the torque acting about the axis of rotation with time t is as shown. If the turntable is at rest initially, what is its angular momentum at t = 20 s? 1 Ns 2 Ns 4 Ns 8 Ns 16 Ns A. B. C. D. E. 40 kg m2 s-1 100 kg m2 s-1 200 kg m2 s-1 1 105 kg m2 s-1 2 105 kg m2 s-1 6. 2m 8. Q m P A light, rigid rod of length 1 m is hinged smoothly at P at one end. Two small masses m and 2m are fixed to the midpoint and the other end of the rod respectively. The rod is held vertically above P and is released from rest. What is the total rotational energy of the system when the rod rotates to the position vertically below P? (Neglect air resistance) A. B. C. D. E. 2.5 mg 4.5 mg 5 mg 7.5 mg 9 mg P v A small ball-bearing is projected with velocity v from the lowest position P of a vertical circular track which is not smooth. The ball-bearing starts to leave the track at Q. Which of the following diagrams best represents all the forces acting on the ballbearing at Q? A. Q P B. Q P C. Q P 99 AL Physics/M.C./P.3 C. U D. Q 0 x P E. D. Q U P 0 x 9. E. a U 0 x The above graph shows the variation of the acceleration a of a particle with its displacement x from a fixed point. Which of the following graphs shows the variation of its potential energy U with x? 0 x 10. A. U 0 x B. U 0 x A converging light beam is directed towards a convex mirror M. The reflected beam then passes through a convex lens L and forms an image at I. Which of the following about the focal lengths of M and L is correct? A. B. C. D. E. focal length of M more than 4 cm less than 4 cm 4 cm less than 4 cm more than 4 cm focal length of L 2 cm 2 cm 2 cm 4 cm 4 cm 99 AL Physics/M.C./P.4 11. An astronomical refracting telescope is adjusted to view a distant object under normal adjustment. Which of the following statement is/are correct? (1) The first image formed by the objective is real and is smaller than the object. (2) The final image formed by the eyepiece is at the least distance of distinct vision from the eye. (3) If part of the objective is blocked by an opaque obstacle, part of the final image could not be viewed. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 12. In a Young’s double slit experiment, a monochromatic light source of wavelength 700 nm is used and the separation of the slits is 0.1 mm. If 15 bright fringes are observed, what is the angle subtended by those fringes at the centre of the double slit? 15 bright fringes angle subtended at the centre of the double slit A. B. C. D. E. 4.8 5.2 5.6 6.0 6.4 13. Two dippers S1 and S2 1.2 cm apart are attached to a vibrator. They vibrate in phase in a ripple tank and generate waves of wavelength 0.8 cm. S1 S2 1.2 cm Which of the following statements is/are correct? (1) S1 and S2 are positions of antinodes. (2) There is only one point between S1 and S2 which is always stationary. (3) The separation between two nearest antinodes between S1 and S2 is 0.4 cm. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 14. On a straight road, a car and an ambulance move with uniform speeds u1 and u2 respectively (with u2 > u1) in the same direction. Initially the ambulance is behind the car and it overtakes the car after some time. The siren on the ambulance continuously emits a sound of a certain frequency. What is the ratio of the wavelength of sound received by an observer in the car before the ambulance overtakes to that after the ambulance overtakes? (Given: velocity of sound in air = v) A. v u2 v u2 B. v u2 v u2 C. u2 u1 u2 u1 D. v u2 u1 v u2 u1 E. v u2 u1 v u2 u1 99 AL Physics/M.C./P.5 15. Students A and B are standing 5 m apart. A shouts to B and the intensity level in db recorded by B is x. A then walks away from B so that they are 10 m apart. If A shouts again with the same power, what is the intensity level in db recorded by B? A. B. 1 x 4 1 x 2 (3) If the resistor with resistance R1 is removed, the resulting equivalent resistance is increased. A. B. C. D. E. 18. Which of the following statements about a communication satellite in parking orbit above the earth’s surface is incorrect? x C. log10 4 D. x - 3 E. x - 6 A. It is accelerating towards the centre of the earth at all times. B. It must be in a circular orbit above the earth’s equator. C. It is always vertically above the same place on the earth’s surface. D. It must be rotating in the same sense and with the same angular speed as the earth. E. It is at a height where its gravitational potential energy is numerically equal to its kinetic energy. 16. A V R The above circuit can be used to find the resistance of the resistor R. Which of the following statements is/are correct? (1) The current passing through the ammeter is in fact larger than that passing through R. (2) The ratio of voltmeter reading to ammeter reading is in fact smaller than the resistance of R. (3) The circuit is suitable for measuring high resistance. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 17. Three resistors of resistance R1, R2 and R3 are connected in parallel. It is known that R1 > R2 > R3. The equivalent resistance of this combination is R. Which of the following statements is/are correct? (1) Energy dissipated in moving 1 C of charge through the resistor of resistance R1 is greater than that through R3. (2) R is smaller than R2. 19. R1 P R3 R2 Q S In the above circuit, the battery has constant e.m.f. and negligible internal resistance. If switch S is closed, what would happen to the electric potential at P and at Q? A. B. C. D. E. Potential at P increased increased unchanged decreased decreased Potential at Q increased decreased unchanged increased decreased 99 AL Physics/M.C./P.6 20. Each of the following three students states a conclusion after learning the formulae P = IV, P = V2/R and P = I2R in electricity. Which of these conclusion is/are correct? (1) The power dissipated by any electric appliance can be calculated from P = IV. (2) The power dissipated by a kettle is inversely proportional to its resistance as P = V2/R. (3) The power consumed by a running motor cannot be calculated from P = I2R. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 21. Which of the following statements about electric field lines is incorrect? A. They are closest where the field is strongest. B. They are always perpendicular to equipotential lines. C. They always point from high electric potential to low electrical potential. D. Work has to be done in moving an electron along the direction of a field line. E. They tend to attract one another. 22. A charged capacitor of capacitance 47 F is connected to a voltmeter. The voltmeter reading drops from 8 V to 2 V in 7.8 s. Find the resistance of the voltmeter. A. B. C. D. E. 60 k 80 k 120 k 166 k 240 k C. The conduction electrons in the wire are accelerated momentarily in the opposite direction to that of the electric field. D. The conduction electrons collide with one another, giving out heat energy. E. The current in the wire is proportional to the average drift velocity of the electrons. 24. 45 V 2 F 2 F Output 8 F 0V 0V Three capacitors are connected to a 45 V supply as shown in the above circuit. The voltage at the output is A. B. C. D. E. 5V 15 V 30 V 36 V 40 V 25. A capacitor is charged by a constant current. Which of the following graphs shows the time variation of the energy stored in the capacitor during the charging process? A. energy time B. energy 23. A resistance wire is connected across the terminals of a battery. Which of the following statements is incorrect? A. Before connection to the battery, the conduction electrons in the wire move randomly. B. After connection to the battery, an electric field is set up along the length of the wire. time C. 99 AL Physics/M.C./P.7 energy B. C. time D. energy D. E. time E. energy time 27. Which of the following graphs correctly shows the variation of the magnetic flux density B along the axis of a long solenoid carrying a steady current with its length l? 26. S E C R A. B To CRO 0 l B. B In the above circuit, a capacitor C is charged from a battery E and then completely discharged through a resistor R using a vibrating reed switch S. The waveform displayed on the screen of the CRO with suitable time base should be 0 l C. B A. 0 l 99 AL Physics/M.C./P.8 D. A. B. C. D. E. B 0 (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) l 30. E. long straight wire carrying 6 cm 6 cm an a.c. A B current B 0 search coil To CRO l (1) Boltzmann constant k times absolute temperature T (2) Planck constant h times frequency (3) Electronic charge e times potential difference V The figure shows a long straight wire carrying an a.c. current which lies on the plane of the paper. When a small search coil is placed at B such that the plane of the coil is on the paper, the length of the trace on the CRO is 2 cm (with the time base of the CRO switched off). If the search coil is moved to A, the length of the trace would be A. B. C. D. E. A. B. C. D. E. 28. Which of the following products is/are measured in joules? (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 29. 31. For which of the following does the force between two objects vary inversely as the square of the distance between their centres? S 2V 0.5 cm. 1 cm. 2 cm. 4 cm. 8 cm. L B neon lamp In the above circuit, a coil L of large inductance, a 2 V light bulb B, a switch S and a 2 V battery are connected in series. A neon lamp is connected across L. Which of the following statements is/are correct upon the opening of switch S? (1) A large e.m.f. is induced across coil L. (2) The neon lamp lights up momentarily. (3) Light bulb B continues to light up until the neon lamp dies out. (1) Two equal masses joined by a rubber band under tension. (2) Two long straight parallel conducting wires carrying steady electric currents. (3) The earth and a satellite in its orbit. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 99 AL Physics/M.C./P.9 32. C. ultra-violet D. visible light E. X-rays L R The above figure shows an a.c. circuit in which a variable resistor R is connected in series with an air-cored inductor L of negligible resistance. The a.c. supply has constant r.m.s. voltage and its frequency can be varied. Which of the following methods, on its own, can increase the r.m.s. voltage across the variable resistor R? (1) Inserting an iron core in the inductor L. (2) Increasing the frequency of the a.c. supply. (3) Increasing the resistance of R. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 33. The following are energy values for hydrogen. X Y Z mean kinetic energy of hydrogen gas molecules at room temperature ionization energy of a hydrogen atom photon energy of a particular line in the visible emission spectrum of hydrogen Which of the following shows the correct ascending order (the least first) of these energy values? A. B. C. D. E. X<Z<Y X<Y<Z Y<Z<X Z<Y<X Z<X<Y 34. When an electron in an atom falls from an excited state to the ground state, which of the following forms of radiation is not emitted? A. infra-red B. gamma-ray 35. A B P Q C Two long, straight, parallel conducting wires P and Q are positioned as shown. The same current flows through both wires and is directed into the plane of the paper. Points A, B and C on the plane of the paper are equidistant from both wires where C is the mid-point between the wires. Which of the following statements is/are correct? (1) The magnetic field strength at C is greater than that at A. (2) The directions of the magnetic field at A and at B are the same. (3) The magnetic field strength at B will increase if the current flowing in the wires increases. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 36. A coil of metal wire is placed on a plane perpendicular to a uniform magnetic field. The coil is rotated through 180º about a diameter as shown. 180 The total charge circulated in the coil due to the induced current is independent of A. the area of the coil. B. the flux density of the magnetic field. 99 AL Physics/M.C./P.10 C. the number of turns of the coil. D. the resistance of the coil. E. the time taken for the flux change. 39. p/kPa B A 37. C Y T/K 0 A fixed mass of an ideal gas undergoes the process ABC as shown in the pressuretemperature diagram. Which of the following deductions from the diagram is incorrect? X S V 4V Two metallic containers X and Y of volume V and 4V respectively are connected by a narrow tube as shown. Initially the tap S is closed and an ideal gas is contained in X at a pressure of 400 kPa while container Y is evacuated. The tap S is then opened and when equilibrium is finally reached A. the gas pressure in X is 100 kPa. B. there are still gas molecules moving through the tap S. C. the product of pressure and volume of the gas in X is equal to that in Y. D. the density of gas molecules in X is greater than that in Y. E. the gas molecules in Y on average move faster than those in X. A. The volume of the gas at C is greater than that at B. B. No work is done by the gas when it changes from A to B. C. Work is done by the gas on the surroundings when it changes from B to C. D. Heat energy is transferred to the gas when it changes from A to B. E. Heat energy is extracted from the gas when it changes from B to C. 40. K 38. Which of the following descriptions about ideal gas is/are correct? (1) An ideal gas obeys Boyle’s law only under high temperature and low pressure. (2) The molecules of an ideal gas have no size. (3) The internal energy of an ideal gas consists of kinetic energy only. 0 The above graph shows the variation in maximum kinetic energy K of photoelectrons with the frequency f of the incident radiation on a metallic surface. If radiation of twice the intensity is used, which of the following graphs (dotted line) shows the variation of K with f? A. A. B. C. D. E. f (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) K 0 B. f K 0 f 99 AL Physics/M.C./P.11 A. C. K 0 D. f B. K C. 0 E. f K D. 0 f E. 41. Three sinusoidal signals V1, V2 and V3 are applied in pairs to the X- and Y- inputs of a CRO and the resulting Lissajous figures are as shown. X-input Y-input Lissajous figures 42. N V1 V2 100 V2 V3 0 If V1 and V3 are applied to the X- and Yinputs respectively, the Lissajous figure should look like 100 Z For stable nuclides, the number of neutrons N when plotted against the number of protons Z would give points lying within the above shaded region. Which of the following statements is/are correct? (1) The heavy stable nuclides have more neutrons than protons. (2) Unstable nuclides decay to produce new nuclides closer to the shaded region. 99 AL Physics/M.C./P.12 (3) Unstable nuclides above the shaded region usually decay through emission. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 43. Carbon-14 is radioactive and undergoes decay with a half-life of about 5 600 years. A GM-tube together with a scaler are used in an experiment to determine the concentration of carbon-14 in a piece of excavated wood. To find an accurate value for the activity of the excavated wood, the experimenter should (1) prepare a sample of pure carbon-14 from the piece of excavated wood. (2) take a count over as long a period of times as possible. (3) take a second count without the presence of the excavated wood. A. B. C. D. E. (1) only (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 44. Which of the following are reasonable estimates of the density and volume of an adult human? A. B. C. D. E. Density/kgm-3 100 100 1 000 1 000 10 000 Volume/m3 1 0.1 0.1 0.01 0.01 45. Which of the following will give rise to a systematic error in experimental measurement? (1) using a slow-running stop watch in keeping time (2) ignoring the background counts in radioactive decay measurements (3) uncertainty in locating the sharpest image position in an optics experiment A. (1) only B. C. D. E. (3) only (1) and (2) only (2) and (3) only (1), (2) and (3) 99 AL Physics/M.C./P.13 Question No. Key Question No. Key 1. 2. 3. 4. 5. A C A D C 26. 27. 28. 29. 30. A B E C D 6. 7. 8. 9. 10. C B A E A 31. 32. 33. 34. 35. B B A B D 11. 12. 13. 14. 15. A C B A E 36. 37. 38. 39. 40. 16. 17. 18. 19. 20. C D E E E 41. 42. 43. 44. 45. 21. 22. 23. 24. 25. E C D B B This item was deleted B D E A D C D C C