2007 Hong Kong Advanced Level Examination

07 AL Physics/M.C./P.11

AL Physics

Multiple Choice Questions

07 AL Physics/M.C./P.11

The figure shows a weight W supported by two light rigid rods P and Q. The rods are smoothly hinged to the wall and mounted in the same vertical plane. Which of the following descriptions about the rods is correct?

rod P rod Q

A. in compression in tension

B. in compression in compression

C. in tension in tension

D. in tension in compression

A wedge of mass M is fixed to the ground. A block of mass m slides down the wedge with constant velocity as shown. What is the normal reaction exerted by the ground on the wedge?

A. (M + m)g

B. Mg + mg cos q

C. Mg + mg cos2q

D. Mg + mg cos q sin q

3. An object is projected vertically upwards from the ground. If air resistance is taken into account, which of the following graphs best shows the variation of the velocity v of the object with time t, starting from the moment when the object leaves the ground (t = 0) up to the time when it returns to the ground (t = T)?

4. An aircraft flies with a constant speed in a horizontal circle of radius 10 km. If its wings slant at an angle of 21.8° to the horizontal, find the speed of the aircraft.

A. 280 ms-1

B. 200 ms-1

C. 140 ms-1

D. 100 ms-1

5. In which of the following situations does the person concerned experience ‘weightlessness’?

(1) an astronaut in a spacecraft which is coasting in outer space with its rocket engines shut off

(2) an astronaut in a spacecraft which is decelerating to make a soft landing on the moon

(3) a parachutist descending with a constant velocity in the air

A. (1) only

B. (3) only

C. (1) and (2) only

D. (2) and (3) only

A particle performs simple harmonic motion along a straight line between P and Q as shown. The particle passes the equilibrium position O and travels to the right at time t = 0. It passes point X the first time after 3 s and it passes X the second time after a further 2 s. After what further time will the particle pass X the third time?

A. 16 s

B. 14 s

C. 12 s

D. 10 s

7. Which of the following statements about simple harmonic motion in one dimension is/are INCORRECT?

(1) The amplitude of oscillation must be small.

(2) The acceleration is always directed towards a fixed point.

(3) The frequency of oscillation is independent of the amplitude.

A. (1) only

B. (2) only

C. (1) and (3) only

D. (2) and (3) only

8. Which of the following best gives the orders of magnitude of the wavelengths of ultra-violet radiation and microwaves in air?

ultra-violet radiation microwaves

A. 10-8 m 10-2 m

B. 10-8 m 10-5 m

C. 10-10 m 10-2 m

D. 10-10 m 10-5 m

9. A diver at a depth of x below the water surface looks up and finds that the sky appears to be within a circle of radius r. The critical angle of water in this case is given by

A. tan-1 (r/x).

B. sin-1 (r/x).

C. tan-1 (x/r).

D. sin-1 (x/r).

10.

A beam of monochromatic light falls at normal incidence on a diffraction grating. Third-order diffracted beams are found at angles of 45° to the incident direction. What is the highest order of diffracted beam that can be observed?

A. 3rd order

B. 4th order

C. 5 th order

D. 6 th order

11. In a Young’s double-slit experiment using monochromatic light of wavelength 550 nm, the fringes are observed through the eyepiece of a travelling microscope at a distance of 1.0 m from the double slits. If .the separation between the first and the fifth dark fringes is 5.0 mm, find the slit separation.

A. 0.3 ´ 10-4 m

B. 1.1 ´ 10-4 m

C. 4.4 ´ 10-4 m

D. 5.5 ´ 10-4 m

12. An object is placed at the focus of a concave lens of focal length 10 cm. What is the magnification of the image formed?

A. 0.5

B. 1.0

C. 2.0

D. infinite

13. The figure shows two small charged spheres P and Q suspended by identical nylon threads from a fixed point O. At equilibrium, the threads OP and OQ make angles a and b (a < b) with the vertical.

Which of the following conclusions must be correct?

(1) Both P and Q carry positive charges.

(2) The charge on P is greater than that on Q in magnitude.

(3) The mass of P is greater than that of Q.

A. (1) only

B. (3) only

C. (1) and (2) only

D. (2) and (3) only

14.

The above figure gives the electric field strength (in arbitrary units) at various points near an isolated point charge +Q. Which of the following correctly gives the electric field strength (in the same arbitrary units) at X and at Y?

electric field electric field

strength at X strength at Y

A. 72 30

B. 72 36

C. 90 30

D. 90 36

15.

In the above figure, XYZ is a small right-angled triangular metal frame moving with a constant velocity across a rectangular region PQRS with a uniform magnetic field pointing into the paper. Which of the following graphs best shows the variation of the current I induced in the frame with time t?

16.

The above figure shows the V-I characteristic curves of resistance wire X and filament bulb Y. If they are connected in series with a 12 V d.c. supply of negligible internal resistance, estimate the voltage across the bulb Y.

A. 3V

B. 4V

C. 5V

D. 6V

17.

Which of the following is/are correct for the above circuit at steady state?

(1) The current in the circuit is zero.

(2) The voltage across C is independent of its capacitance.

(3) The voltage across C is independent of the resistance of R.

A. (1) and (2) only

B. (1) and (3) only

C. (2) and (3) only

D. (1), (2) and (3)

18.

Four long straight current-carrying wires perpendicular to the plane of the paper are arranged at the comers of a square PQRS as shown. The same current I flowing in the same direction along the wires at P, Q and S while the current flowing along the wire at R is in the opposite direction. If the wire at P experiences no net force, find the current flowing in the wire at R.

B. I/2

D. 2I

19.

A segment of a vertical wire 0.50 m long carrying a current of 8.0 A is placed in the earth magnetic field. The direction of the field dips at an angle of 20° to the horizontal. If the resulting magnetic force on the wire is 7.5 ´ 10-5 N, fmd the flux density of the earth magnetic field.

A. 6.4 ´ 10-6 T

B. 1.8 ´ 10-5 T

C. 2.0 ´ 10-5 T

D. 5.5 ´ 10-5 T

20. A beam of charged particles passes through crossed uniform electric and magnetic fields without deflection. If the electric field is removed, the beam will split up into several beams. This splitting may be due to the particles having different

(1) charges

(2) masses

(3) incident velocities

A. (1) only

B. (3) only

C. (1) and (2) only

D. (2) and (3) only

21.

In the above figure, a solenoid P and a metal ring Q are arranged coaxially and close to each other. A sinusoidal a.c. varying with time t as shown in the graph is supplied to solenoid P. Which of the following descriptions is INCORRECT?

A. From 0 to t1, the current in Q is in opposite sense to that in P.

B. From tl to t2, Q is attracted towards P.

C. The force on Q is at a maximum at time tl.

D. The force on Q is zero at time t2.

22.

A rectangular coil of 50 turns is being rotated at 300 revolutions per minute in a uniform magnetic field. The field is perpendicular to the coil’s central axis in the plane of the coil. If the maximum flux linking each turn of the coil is 5.1 ´ 10-3 Wb, the maximum e.m.f. induced in the coil is

A. 0.2 V

B. 1.3 V

C. 4.0 V

D. 8.0 V

23. An electric motor driven by a constant voltage d.c. supply is used to raise a load. If the load is increased, how will each of the following change correspondingly?

(1) speed of rotation of the armature coil

(2) current in the armature coil

(3) back e.m.f. in the armature coil

(1) (2) (3)

A. decrease unchanged increase

B. unchanged increase unchanged

C. decrease increase unchanged

D. decrease increase decrease

24. A radioactive source consists of 64 ´ 1012 atoms of nuclide P of half-life 2 days. Another source consists of 8 ´ 1012 atoms of nuclide Q of half-life 3 days. After how long will the number of active nuclei in the two sources be equal? (Assume that the daughter nuclides of both P and Q are stable.)

A. 6 days

B. 9 days

C. 12 days

D. 18 days

25.

A student used a simple pendulum to measure the acceleration due to gravity g. He measured the time (t) for 20 oscillations using various length L of the pendulum. A plot of t2 against L deviates from the ‘theoretical’ graph (the dashed line). Which of the following could be a reason?

(1) He used a stop watch which runs consistently too fast.

(2) He neglected the radius of the pendulum bob when measuring L.

(3) He miscounted the number of oscillations such that the time for only 19 oscillations was taken to be t.

A. (1) only

B. (2) only

C. (2) and (3) only

D. (1), (2) and (3)

26. Two children P and Q are travelling on kateboards with frictionless rollers towards each other as shown. Both are moving at a speed of 1.2 ms-1. The mass of each child together with a skateboard is 30 kg. Initially P holds a ball of mass 1.0 kg, he then throws the ball straight towards Q at a horizontal velocity of 15 ms-1. After child Q catches and keeps the ball, what is his velocity? (All velocities are relative to the ground.)

A. 0.74 ms-1 to the right

B. 0.74 ms-1 to the left

C. 0.68 ms-1 to the right

D. 0.68 ms-1 to the left

27.

Suppose a space craft is launched with an initial speed v and it eventually enters a circular orbit near the earth’s surface. If the launching speed was increased to 2v, the spacecraft would (Neglect air resistance.)

A. revolve uniformly in a circular orbit around the earth with a longer period.

B. revolve uniformly in a circular orbit around the earth with a shorter period.

C. revolve in an elliptical orbit around the earth with a longer period.

D. leave the earth and travel to outer space.

28. It is known that a geostationary communication satellite is at a height of 5.6R above the earth’s surface where R is the radius of the earth. Which of the following is the best estimate for the separation between the moon and the earth?

A. 50 R

B. 60 R

C. 150 R

D. 180 R

29. A uniform heavy rope hangs freely from a support. The support is made to oscillate horizontally with a small amplitude so as to send transverse waves down the rope. A standing wave is set up as these waves are reflected at the free end. Which of the following statements is/are correct?

(1) The tension is the same throughout the rope.

(2) The wavelength is the same throughout the rope.

(3) The frequency of oscillation is the same at all vibrating points of the rope.

A. (1) only

B. (3) only

C. (1) and (2) only

D. (2) and (3) only

30.

A beam of unpolarized light of intensity I passes normally through two polaroids P and Q aligned parallel to each other. The polarizing axis of each polaroid is represented by an arrow. The polarizing axis of P is vertical while that of Q makes 60° with the vertical. What is the intensity of the transmitted beam detected by the observer, assuming that the only absorption mechanism is due to polarization?

31. Which of the following statements about the decibel (dB) are correct?

(1) A ten-fold increase in sound intensity is equivalent to an increase of 10 dB in sound intensity level.

(2) The sound intensity level in a noisy restaurant is about 40 dB.

(3) The threshold of pain is about 120 dB in sound intensity level.

A. (1) and (2) only .

B. (1) and (3) only

C. (2) and (3) only