THERMODYNAMICS

Baptist Lui Ming Choi Secondary School

Mock Examination (2001 - 2002)

Form 7 Physics (Paper II) Date : 6 / 3 / 2002

Time : 1 : 30 – 4 : 30 p.m.

P.T.O.

Time Allowed : 3 hours

SECTION A

There are 45 questions in this section. Answer ALL questions. Each question is followed by four suggested answers. Select thebest answer in each case. Where necessary, take g to be 10 m s-2 and take c to be 3 x 108 ms-1.

1. Which is not a base SI unit?

A. Kelvin

B. metre

C. radian

D. second

2. It is given that x = 50 ± 2, y = 10 ± 1 and p = 3x – 4y. What is the correct value of p?

A. 110 ± 2 B. 110 ± 4

C. 110 ± 6 D. 110 ± 10

3. It is given that x = 10 ± 2, y = 30 ± 6 and q = 3xy. What is the correct value of q?

A. 900 ± 360 B. 900 ± 120

C. 900 ± 36 D. 900 ± 24

SECTION A - Multiple-choice Questions - Answer ALL Questions

SECTION B - Answer Any THREE Questions

The answer sheet for Section A and the answer book for Section B must be handed in separately at

the end of the examination.

INSTRUCTIONS FOR SECTION A

1. Read carefully the instructions on the Answer Sheet and insert the information required

(including the Q.P. Code) in the spaces provided.

2. All the answers should be marked on the Answer Sheet.

3. Note that you may only mark ONE answer to each M.C. question. Two or more answers will

score NO MARKS.

4. All questions carry equal marks. No marks will be deducted for wrong answers.

5. When told to open this book, check that all the questions are there. Look for the words “END

OF SECTION A” after the M.C. questions and “END OF PAPER” after the last question in

Section B.

6. Useful Formulae Sheet in Advanced Level Physics is given to you as reference only. Don't

write anything on it and do return it back after the examination.

Form 7 Physics II (2001 - 2002) Page 2

To Be Continued

4. A sphere is projected downwards from P with a speed of 20 m/s at an angle of 30to the horizontal. Thesphere rebounds from the ground, first at Q and then at R. If the collisions are perfectly elastic, which ofthe following statements is/are correct?

(1) The horizontal distance between P and Q is half QR.

(2) After rebounding at Q, the maximum height h of the ball rises 30 m from the ground.

(3) The vertical component of the velocity of the sphere at Q is 26.5 m/s.

A. (1) only

B. (3 ) only

C. (1) and (2) only

D. (2) and (3) only

5. The table tennis ball is aimed to shoot at the target held by an electromagnet by adjusting the angle between the barrel of the gun and the horizontal as shown. The target will be released at the same timewhen P leaves the barrel of the toy gun. Which of the following determine(s) the value of

(1) The speed of the ball on leaving the toy gun.

(2) h, the vertical height of the target above the level of the ball P.

(3) l, the horizontal distance of the ball P from the target.

A. (1) only B. (3) only

C. (1) and (2) only D. (2) and (3) only

6.

30°

Radius of path = 500 m

The diagram shows the front view of an aeroplane of weight 1.0 x 105 N flying in a horizontal path ofradius of curvature 500 m in air. The angle of tilt is 30°. Calculate the speed of the aeroplane.

A. 17.0 ms-1 B. 53.7 ms-1

C. 93.1 ms-1 D. 2890 ms-1

NOT TO SCALE

Form 7 Physics II (2001 – 2002) Page 3

P.T.O.

7. A stunt man riding on a motor-cycle is ready to travel round the vertical ‘loop-the loop’. As he passespoint X the speed of the motor-cycle is still increasing. At X, the direction of acceleration of the stuntman is

A. along the tangent XT.

B. along the radius XO.

C. between XT and XO.

D. between XT and XV.

8. A simple pendulum is undergoing a forced oscillation. When it is at resonance, which of the followingquantities of the pendulum is /are in phase with the applied force?

(1) Displacement

(2) Acceleration

(3) Velocity

A. (1) only

B. (3) only

C. (1) and (2) only

D. (2) and (3) only

9. A horizontal mass spring system, when placed on a smooth surface, can undergo S.H.M. with a period T inair. If the whole system is put into water and set into vibration, which of the following is true?

A. The period of the new motion is less than T.

B. The amplitude of the new vibration decreases at a constant rate.

C. The velocity of the new vibration at points of maximum displacement decreases at a constant rate.

D. The rate of dissipation of energy of the system is constant.

10. A mass m moving with velocity u collides totally inelastically with a mass M, initially at rest, and theystick together after impact. What fraction of the initial kinetic energy of mass m is lost during thecollision?

A. m / M

B. (M – m) / M

C. m / (M – m)

D. M / (M + m)


To Be Continued

11. A mass m strikes a smooth surface with speed u and rebounds with velocity v, α and β are the angles thatthe paths of m make with the surface before and after impact. Which of the following statements is/arecorrect?

α β

u

v

smooth surface

A. It must be an elastic collision as the surface is smooth.

B. u must be equal to v because the surface is smooth.

C. The change in momentum of the mass m perpendicular to the surface is mv sinβ - mu sin α.

D. The change in momentum of the mass m perpendicular to the surface is mv sinβ + mu sin α.

12. Huygens’ Principle stated: ‘Each point on a (i) is (ii) source of (ii) ’. Which response gives thephrase needed to complete the sentence?

(i) (ii) (iii)

A. ray a secondary wavelets

B. ray an individual ray

C. wavefront a secondary wavelets

D. wavefront an individual wavelets

13. A small amplitude progressive wave in a stretched string has a velocity of 20 ms-1 and a frequency of 100Hz. What is the phase difference between two points 2.5 cm apart along the string?

A. π / 4 B. π / 2

C. 3π / 4 D. π

14. Young’s fringes are investigated using radar waves of wavelength 30 mm. The fringes spacing is 300mm. If the detector is placed 1 m further away from the slits, the fringe spacing becomes 900 mm.How far apart are the slits?

A. 30 mm

B. 50 mm

C. 300 mm

D. 500 mm

15. Infrared ray of a certain frequency passes through water (refractive index 1.31), strikes onto a germaniumsurface (refractive index 4.09) and is reflected. At what angle of reflection will the radiation be mostplane polarised?

A. 17.8°

B. 18.7°

C. 52.6°

D. 72.2°


P.T.O.

L

Q

Q

θ

narrow slit

soundwave

16. Sound waves pass through a narrow slit. A series of loud (L) and quiet (Q) fringes is observed on theother side. The angle between the slit normal and the first quiet fringe is θ. If θ becomes larger, whatproperty of the waves must have increased?

A. amplitude

B. frequency

C. width of slit

D. wavelength

17. The average sound level of human speech is 70 dB. How many people , talking simultaneously, wouldproduce a sound level of 86 dB?

A. 16 B. 24

C. 32 D. 40

18. Ultrasonic waves rather than audible sound waves are used in scanners to examine the internal organs ofpatients. Which of the following correctly explain(s) this?

(1) Ultrasonic waves have shorter wavelengths and they give a clearer picture of the organ underinvestigation compared with audible sound waves.

(2) Ultrasonic waves can penetrate greater distance through the tissues than audible sound waves.

(3) Ultrasonic waves can travel in vacuum.



19. A microscope consists of an objective of focal length 1.5 cm and an eyepiece of focal length 3.0 cm. Thelenses are placed 16 cm apart. To obtain the best view, the distance between the observer’s eye and theeyepiece should be

A. As close as possible. B. 1.5 cm

C. 3.4 cm D. 3.7 cm

20. Which of the following methods can increase the angular magnification of a compound microscope whichconsists of two converging lenses?

(1) Moving the object closer to the objective lens, but keeping their separation greater than the focallength of the objective.

(2) Moving the eyepiece so that it is almost in the same position as the intermediate image formed by theobjective lens.

(3) Replacing the objective lens with a longer focal length.

A. (1) and (2) only B. (2) and (3) only

C. (1) only D. (3) only


To Be Continued

21. Which of the following statements about stationary waves and progressive waves set up in the air is/arecorrect?

(1) The wavefront of a progressive wave moves forward with a velocity equal to that of the particle atthe same position as the wavefront.

(2) All particles between two adjacent nodes in a stationary wave have the same phase.

(3) Air particles in both types of waves are undergoing simple harmonic motion.



22. A tall vertical cylinder is filled with water and a tuning fork vibrating at 400 Hz is held over its open end.The water is slowly run out and the first resonance of the air column is heard when the water level is 0.21m below the top of the cylinder. Neglecting end corrections, how far from the top will the water level bewhen the next resonance is heard?

A. 0.63 m B. 0.84 m

C. 0.95 m D. 1.05 m

23. Which of the following statements gives a satisfactory explanation to the cause of beats when two sourcesof slightly different frequencies emit waves together?

A. One source has a greater amplitude than the other.

B. A standing wave is set up between the two sources.

C. There are constructive and destructive interferences occurring periodically at the receiver.

D. The two sources are not in phase.

24. Consider the earth to be a perfect sphere of uniform density rotating about the polar axis. Which of thefollowing statements is / are correct?

(1) Observed gravity at the equator increases if the earth rotates slower.

(2) Observed gravity at equator is greater than that at the pole.

(3) Observed gravity at the pole increases if the radius of the earth increases and the density remainsunchanged.

A. (1) only

B. (2) only

C. (1) and (3) only

D. (2) and (3) only

25. The escape speed on the earth is v. For a planet with density four times of that of the Earth and withradius twice of that of the Earth, the escape speed from the planet is

A. v / 2

B. v2

C. 2v

D. 4v


P.T.O.

26. Both P and R are metal spheres with insulated stands as shown in the figure. P is positively charged andR is earthed. Which of the following is / are correct?

+ +

++

++

P

R

(1) Both electric field and electric potential at R is zero.

(2) No net charge appears on R.

(3) Electric field points from P to R.



27. In the figure, capacitors C1 , C2 and C3 of identical capacitance C are charged by a dry cell. Which of thefollowing statements is / are true?

(1) Number of charge stored by C3 is equal to the sum of the number of charge stored by C1 and C2.

(2) Voltage across C3 is equal to the voltage across C1.

(3) The capacitance of the system is 2.5 C.



28. A parallel-plate capacitor of capacitance C is charged by a battery and the energy stored in the capacitor isE. The connections of the battery are then removed. If the plate-separation is doubled, the electricalenergy stored in the capacitor will

A. decrease to E / 4. B. decrease to E / 2.

C. remain the same. D. increase to 2 E.

29. Which of the following physical quantities will be increased when the voltage across a metal wire isincreased?

(1) Number of conducting electrons

(2) Speed of electrical signal

(3) Drift velocity of conducting electrons




To Be Continued

30. A circular coil of wire with diameter 5.0 cm is placed so that its plane is at right angles to a magnetic fieldof flux density 3.0 x 10-3 T. The coil is then rotated through 90o so that its plane is parallel to themagnetic field. What is the magnitude of the change of magnetic flux through the coil due to thisrotation?

A. 5.9 x 10-6 Wb B. 1.2 x 10-5 Wb

C. 2.4 x 10-5 Wb D. 4.7 x 10-5 Wb

31. The magnetic field at one end P of a solenoid of length L, is 0.016 T. N is the other end of that solenoid.Q is a point outside and on the axis of the solenoid. Q is at a distance L away from N. The magneticfield at Q is 2 x 10-3 T. If an identical solenoid is connected to N and same current flows in these twosolenoids, find the magnetic field at Q.

A. 0.014 T B. 0.016 T

C. 0.018 T D. 0.032 T

32. Two parallel wires carry identical currents in the same direction. The wires are viewed from the ends asshown below.

wires

Which of the following diagrams best represent the magnetic field in the region near the wires?

A. B.

C. D.

33. An electric meter draws a small current through coil of wire sitting inside a radial magnetic field. Thefront of the coil is labeled X-Y and the magnetic poles of the radial magnetic field as shown in thediagram.

The main reason for using a radial magnetic field in the meter is to

A. allow the torque to remain constant as the meter needle moves across the scale.

B. allow the divisions on the scale to be in a uniform linear pattern.

C. produce a uniform magnetic field between the opposite poles.

D. allow the torque on X-Y to act always in the same direction.


P.T.O.

34.

When a CRO is connected to a circuit, the trace obtained is shown in the above figure. To which of thefollowing circuits has the CRO been connected?

A. B.

C. D.

35.

The circuit of an op-amp has an output potential of 3V. What is the current flowing through the 2 kΩresistor?

A. 0.5 mA B. 0.75 mA

C. 1.0 mA D. 1.5 mA

36. The diagram represents an operational amplifier. The open circuit gain of the amplifier is 105 , Vn is 5µV and

Vi is -3µV.

The output voltage Vo is

A. 0.2 V B. 0.3 V

C. 0.8 V D. 9.0 V


To Be Continued

37.

The above graph shows the distribution of speed (v) of the molecules in a constant mass of gas. Which of the

following statements is/are correct?

(1) The value v = c at which the peak of the curve occurs increases when the temperature drops.

(2) Provided that the temperature does not change, the kinetic energy of each molecule is fixed.

(3) The peak of the curve drops when the temperature rises.

A. (1) and (3) only B. (1) and (2) only

C. (3) only D. (1) only

38. The below figure shows the potential energy U, of a pair of atoms as a function of their separation, r, fortwo solids, X and Y. From the graphs, it can be deduced that

(1) the equilibrium separation of the atoms in Y is greater than that in X.

(2) Y is stiffer than X.

(3) the energy required to separate two atoms of X from equilibrium to infinity is more than that of Y.



39. If the piston of a syringe is pulled outwards quickly, which of the following changes is INCORRECT?

A. The pressure of the gas decreases.

B. The average speed of the molecules increases.

C. The density of gas inside the syringe decreases

D. Work done by the gas is positive.

40. An atom emits light of wavelength 122 nm and 103 nm when one of its electrons returns to its ground statefrom its first and second excited states respectively. Find the wavelength of light emitted when theelectron transits from the second excited state to the first excited state.

A. 112 nm B. 113 nm

C. 225 nm D. 661 nm


P.T.O.

41. The electron-volt is a unit of

A. potential difference.

B. charge.

C. energy.

D. power.

42. The Figure shows a photoelectric cell. C is the emitter and A is the collector. To increase the maximumspeed of the electrons,

EM waveC

A

(1) light of higher frequency is used.

(2) the distance between C and A is decreased.

(3) the light intensity is increased.

A. (1) only

B. (3) only

C. (1) and (2) only

D. (2) and (3) only

43. A radioactive waste of initial activity 200 Bq is put into an isolated room everyday morning. The activityof the radioactive source increases to a steady value even if the radioactive waste is discharged to the roomeveryday. If the half life of the radioactive waste is 2 days, determine the activity at the steady state.

A. 683 Bq B. 231 Bq

C. 200 Bq D. 100 Bq

44. Which of the following conclusions can be deduced from the Gold-foil Scattering Experiment?

(1) Electrons exists in different orbits.

(2) Alpha particles are helium nuclei.

(3) The positive nucleus in an atom is confined in a very small region.



45. A helium atom, a hydrogen atom and a neutron have masses 4.003 u, 1.008 u and 1.009 u respectively.Assuming that hydrogen atoms and neutrons fuse together to form a helium nucleus, the binding energy ofa helium nucleus is (Given that 1 u ≡ 934 MeV)

A. 7.21 MeV B. 28.95 MeV

C. 462.2 MeV D. 924 MeV

END OF SECTION A


To Be Continued

SECTION B

Answer any THREE questions from this section. Write your answers in the ANSWER book provided.

1. (a)

A light spring of natural length L and force constant k is hanged from a fixed point O. When a heavy smallbead of mass m is hanged to the free end of the light spring, the spring is extended by an extension e to P.Then the bead is pulled down a further distance of A to Q and released from rest. Take P as the referencelevel (displacement is zero at P) and downward as positive in the following.

(i) By considering the forces acting on the bead, show that the subsequent motion is a S.H.M.

(ii) Sketch , for one cycle, three separate graphs to show how the displacement, velocity and acceleration ofthe bead vary with time. Comment on their phase relationship. (No mathematical derivation isrequired.)

(iii) Find the expressions for the kinetic energy, potential energy and total energy of the system (bead andspring) as a function of displacement.

(iv) Sketch , for one cycle, on the same graph showing how the kinetic energy, potential energy and totalenergy of the system (bead and spring) vary with displacement. Comment on the values of the energy.

(10 marks)

(b) Describe an experiment to verify that a simple pendulum undergoes S.H.M. (6 marks)

2. (a) Explain qualitatively the cause and apparent result of Doppler effect.

Give one daily example of Doppler effect. (2 marks)

(b) A source is emitting sound wave of frequency fs. Assume Sound wave travels with a velocity of c in air.Deduce the expression for the Doppler effect (i.e. apparent frequency) for the following cases,

(i) An observer moves towards a stationary source with a velocity of vo.

(ii) A source is moving towards a stationary observer with a velocity of vs. (4 marks)

(c) Using results in (b) or otherwise, explain how the speed of an approaching aircraft may be measured by usingmicrowave radiated from a stationary station on the ground. Derive an expression relating the speed of theaircraft to the change in frequency between the emitted signal and that received signal at the station.

(4 marks)

(d) With the aid of a diagram, describe an experiment to find the speed of sound in air by using Kundt’s tubetogether with a loudspeaker. State any precautions which should be taken in the experiment and explainwhat would be observed.

(6 marks)

e

A

me

m

O

P

Q

ke < A

A + e < L


P.T.O.

3. (a) (i) A simple a.c. amplifier can be constructed from a NPN transistor in common-emitter configuration.Draw a circuit diagram to show how you would construct this amplifier. You should include in yourdiagram a d.c. bias circuit, a base resistor Rb, a load resistor RL and blocking capacitors. State typicalvalues for the components used.

(ii) What are the functions of the blocking capacitors?

(iii) Derive from first principles the voltage gain of this amplifier to be G =b

L

R

Rβ− . State assumption(s)

in your derivation.

(iv) Draw the Input-Output Voltage Characteristic of the amplifier and discuss the physical significance ofthe shape. Also, show how an a.c. source can be amplified without distortion.

(12 marks)

(b) Compare and contrast the differences in characteristics between a NPN transistor amplifier and anon-inverting operational amplifier. (2 marks)

(c) A student argues that the use of amplifiers to increase the magnitude of small a.c. signal is actually notnecessary. Since a step-up transformer with the number of secondary coil greater than that of the primarycoil can step up voltage easily, in most cases amplifiers can be substituted by step-up transformers withappropriate turn ratio. Do you agree with his argument? Explain your reasoning.

(2 marks)

4. (a) (i) Define magnetic flux linkage.

(ii) Explain why a search coil with C.R.O. can be used to measure varying magnetic field.

(iii) Describe an experiment to investigate the magnetic field strength surrounding a long current-carryingstraight wire with a search coil and a C.R.O.

(8 marks)

(b) (i) Account for the attractive force between two long wires with current in the same direction.

(ii) Hence, or otherwise, define the unit of current, ampere.

(4 marks)

(c) In discovering isotopes, J.J. Thomson created a mass spectrometer. One key feature of this apparatus was avelocity selector. The velocity selector combined the use of an electromagnet, a pair of electric plates, anda screen with a hole in it.

(i) Draw a labeled diagram showing the arrangement of the main parts of the velocity selector.

(ii) Explain why only charged particles of certain velocity can pass the hole in the velocity selector andshow that the velocity depends on the ratio of the electric field and magnetic field.

(4 marks)


To Be Continued

5. (a) (i) What are the microscopic meanings of temperature and gas pressure of an ideal gas in kinetic theorymodel?

(ii) Derive 2

3

1cNmPV = for ideal gas in a cubic container, which relates the macroscopic physical

quantities, namely gas pressure P and volume V; and the microscopic physical quantities, namely

number N, mass m and the r.m.s. speed 2c of gas molecules.

(iii) Now, the ideal gas is put in a container and a cycle of operations is illustrated in the PV graph of thegas as shown in Figure 5.1. If the initial state is (1), describe all the processes in a cycle and state ifthere is any change in the internal energy U, energy transfer due to heating Q and work done W in acomplete cycle.

Figure 5.1

(10 marks)

(b) (i) Describe and explain the speed of running water if the month of the tap is covered by half.

(ii) Figure 5.2 shows a small polythene ball spinning in a steady stream of air ejected out of a nozzle N.

The ball is observed to be stationary in mid air as shown. The nozzle and the direction of the air

stream make an angle θ with the horizontal.

Figure 5.2

Copy Figure 5.2 to your answer book and draw the spinning sense and the free body diagram of the ball

stating all nature of the force(s). Hence, or otherwise, explain why the ball can stay in mid air as in the

figure.

(6 marks)

END OF PAPER

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