ce physics 2002 paper1(e)

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香港考試局 保留版權 Hong Kong Examinations Authority All Rights Reserved 2002 2002-CE-PHY 1–1 HONG KONG EXAMINATIONS AUTHORITY HONG KONG CERTIFICATE OF EDUCATION EXAMINATION 2002 PHYSICS PAPER 1 8.30 am – 10.00 am (1½ hours) This paper must be answered in English 1. Answer ALL questions in Section A and any FOUR questions in Section B. 2. Write your answers in the answer book provided. For Section A, there is no need to start each question on a fresh page. 3. Some questions contain parts marked with an asterisk (*). In answering these parts, candidates are required to give paragraph-length answers. In each of these parts, one mark is allocated to assess candidates’ ability in effective communication. 4. Take g = 10 m s –2 . 5. Unless otherwise specified, numerical answers should be either exact or correct to three significant figures. 6. Unless otherwise specified, all the cells are assumed to have negligible internal resistance. 7. The last page of this question paper contains a list of physics formulae which you may find useful. 2002-CE PHY PAPER 1

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Page 1: Ce Physics 2002 Paper1(E)

香港考試局 保留版權

Hong Kong Examinations Authority All Rights Reserved 2002 2002-CE-PHY 1–1

HONG KONG EXAMINATIONS AUTHORITY

HONG KONG CERTIFICATE OF EDUCATION EXAMINATION 2002

PHYSICS PAPER 1

8.30 am – 10.00 am (1½ hours) This paper must be answered in English

1. Answer ALL questions in Section A and any FOUR questions in Section B. 2. Write your answers in the answer book provided. For Section A, there is no

need to start each question on a fresh page. 3. Some questions contain parts marked with an asterisk (*). In answering

these parts, candidates are required to give paragraph-length answers. In each of these parts, one mark is allocated to assess candidates’ ability in effective communication.

4. Take g = 10 m s–2 . 5. Unless otherwise specified, numerical answers should be either exact or

correct to three significant figures. 6. Unless otherwise specified, all the cells are assumed to have negligible

internal resistance. 7. The last page of this question paper contains a list of physics formulae

which you may find useful.

2002-CE PHY PAPER 1

Page 2: Ce Physics 2002 Paper1(E)

2002-CE-PHY 1–2 – 1 – 保留版權 All Rights Reserved 2002

Section A (30 marks) Answer ALL questions in this section. 1. (a)

Figure 1 shows an ambulance. Explain why the word

AMBULANCE is printed in the form as shown in the figure. (2 marks)

(b) Figure 2 shows the structure of part of a pair of binoculars, which

consists of two triangular prisms. (i) Copy Figure 2 into your answer book and complete the

path of the ray. (1 mark)

(ii) Give one advantage of using triangular prisms over plane

mirrors in making binoculars. (1 mark)

Ray Figure 2

Figure 1

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2. Figure 3 shows a set-up to study the relation between the volume and

temperature of a column of air trapped in a uniform capillary tube by a drop of paraffin oil. Figure 4 shows the position of the paraffin oil when the temperature of the water is 25°C. A half-metre rule is used to measure the length of the air column in cm.

(a) Write down the length of the air column as shown in Figure 4.

(1 mark)

(b) Estimate the length of the air column when the temperature of the water is increased to 80°C.

State one assumption in your calculation.

(3 marks)

Stirrer

Half-metre rule

Capillary tube

Water 0 cm

Air columnParaffin oil Thermometer

Figure 3

Figure 4

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3.

Figure 5

A man holds a ball of weight 60 N with his hand. The weight of the forearm and hand of the man is 20 N, and the biceps muscle in the upper arm exerts an upward force F on the forearm. The horizontal distances of these forces from the elbow joint are shown in Figure 5. (a) Find the moment of the weight of the ball about the elbow joint .

(1 mark)

(b) Find the magnitude of F . (2 marks)

(c) Some weight-lifting champions are known to have their biceps

muscles a few millimetres further away from the elbow joint than usual. Explain how this feature can help such athletes in lifting heavy weights.

(2 marks)

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4. A wave is generated on a string. Figure 6 shows the shape of the string at a

certain instant. At this instant, both particles P and Q are moving downwards.

(a) State the kind of wave generated on the string (transverse or

longitudinal, travelling or stationary). (2 marks)

(b) Find the wavelength of the wave. (1 mark) (c) Describe the motions of particles P and Q at a quarter of a period

later. (2 marks)

0.3 m

Equilibrium position P

Q

Figure 6

Page 6: Ce Physics 2002 Paper1(E)

2002-CE-PHY 1–6 – 5 – 保留版權 All Rights Reserved 2002

5. Two identical loudspeakers S1 and S2 are connected to a computer. The

set-up generates a sound of frequency 200 Hz. Mary and Susan stand at positions P and Q respectively in front of the loudspeakers, where PS1 = 6.10 m, PS2 = 8.65 m and QS1 = QS2. The speed of sound in air is 340 m s–1.

(a) Find the wavelength of the sound emitted by the loudspeakers.

(2 marks)

(b) (i) Find the path difference at P from S1 and S2. (1 mark)

(ii) Explain whether Mary will hear a loud or a soft sound.

(2 marks)

(c) The set-up now generates sound of frequencies 200 Hz and 400 Hz alternately. Susan predicts that constructive and destructive interference will occur alternately at Q. Explain whether Susan is correct or not.

(2 marks)

Computer

P (Mary)

Q (Susan)

S1

S2

Figure 7

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6.

A soft-iron rod is inserted into a solenoid AB, which is connected to a

battery and a switch S. Initially S is open. An aluminium ring is also inserted into the rod and placed beside the solenoid as shown in Figure 8. S is now closed.

(a) State the polarity at end B of the solenoid.

(1 mark)

*(b) Explain why the aluminium ring will move away from the solenoid.

(4 marks)

Soft-iron rod

A B

S Aluminium ring

Figure 8

Page 8: Ce Physics 2002 Paper1(E)

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Section B (60 marks) Answer any FOUR questions in this section. Each question carries 15 marks. 7. In a science project competition, a student constructs a hand-dryer. He

connects an electric fan of rating ‘20 W, 24 V’ and a heating coil to a 24 V power supply (see Figure 9). When switch S is closed, the fan will operate at its rated value.

(a) Are the fan and the heating coil connected in series or in parallel ?

Explain your answer. (2 marks)

(b) If the output power of the heating coil is 200 W, find (i) the operating resistance of the heating coil, (ii) the total current drawn from the power supply when S is closed.

(4 marks)

(c) The student designs a circuit to control the operation of the dryer. A light bulb and a light dependent resistor (LDR) are installed at the positions shown in Figure 10.

S

24 V

Heating coiland fan Figure 9

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(c) (continued) When the hands are inserted, the light beam from the bulb cannot

reach the LDR and the dryer is turned on. When the hands are removed, the dryer is turned off. A thermistor is used to protect the hand-dryer from overheating. Figure 11 shows an incomplete diagram of the circuit.

(i) Construct a truth table for a NOR gate.

(2 marks)

(ii) Copy Figure 11 into your answer book and complete the circuit using an LDR, a thermistor and a variable resistor.

(3 marks)

*(iii) Explain how the thermistor can protect the hand-dryer from overheating.

(4 marks)

0 V

24 V

Figure 11

5 V

Heating coil and fan

Page 10: Ce Physics 2002 Paper1(E)

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8. A car is travelling with a speed u on a road. The stopping distance of the car includes two parts :

1. the thinking distance l (i.e. the distance travelled after the driver

has seen a danger and before the brakes are on). 2. the braking distance s (i.e. the distance travelled after the brakes

have been put on). Figure 12 shows the variations between l and s with u. (a) Find the slope of the straight line in Figure 12 and state its physical

meaning. (3 marks)

(b) Assume that the deceleration a of the car remains unchanged at

different speeds. Write down an equation relating u, s and a. Using Figure 12, find the value of a.

(3 marks)

5 10 15 20 25 0

20

40

60

Speed u/m s–1

Distance/m

Figure 12

l

s

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(c) A boy was hit by the car when he was crossing a zebra-crossing.

Figure 13 shows a sketch of the accident drawn by the police. Let d be the distance between the car and the boy at the moment the driver first observed the boy. The driver applied the brakes and a skid mark 36.0 m long was left on the road. After hitting the boy, the car travelled a distance of 19.7 m before coming to rest. You may neglect the change in speed of the car during the impact.

(i) Write down the braking distance of the car. (1 mark)

(ii) Using Figure 12, estimate the value of u.

(1 mark)

(iii) Estimate the thinking distance and the value of d. (3 marks)

*(iv) The speed limit of the road is 50 km h–1 (i.e. 13.9 m s–1).

If the car is travelling at this speed, explain whether it would hit the boy.

(4 marks)

36.0 m

19.7 m

Point of impact u

Figure 13

d

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9. Yunnan Guoqiao-mixian (雲南過橋米線 ) is a famous Chinese food. In preparing the food, the first step is to cook a pot of chicken soup : A pot of water containing chickens is heated over a high flame until it boils. A low flame is then used to keep the soup boiling for 3 hours.

(a) Explain why the temperature of the boiling soup remains

unchanged, even though it is being heated. (2 marks)

(b) (i) The power output of the low flame is 300 W. If 70% of

the energy supplied is lost to the surroundings, calculate the mass of soup that would be vaporized after being heated for 3 hours. Assume the specific latent heat of vaporization of the soup is 2.26 × 106 J kg–1.

(3 marks) (ii) Explain why it is undesirable to use a high flame to keep

the soup boiling. (1 mark)

(c) Customers ordering the food are served with the following :

a bowl of hot soup with a layer of oil on the surface, a dish of thin slices of raw meat, and a bowl of pre-cooked mixian (noodles) (see Figure 14).

Figure 14

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(c) (continued)

The meat is first put into the soup. After a while, the mixian is also added.

(i) Explain why the meat has to be sliced into thin pieces.

(1 mark) (ii) What is the purpose of adding a layer of oil to the bowl ?

(2 marks)

(iii) The following data are given :

Mass of the soup = 1 kg Initial temperature of the soup = 97°C Specific heat capacity of the soup = 4200 J kg–1 K–1

Mass of each slice of meat = 0.02 kg Initial temperature of the meat = 27°C Specific heat capacity of the meat = 3500 J kg–1 K–1

For health reasons, the meat has to be heated to a minimum temperature of 82°C. Estimate the maximum number of slices of meat that can be added to the soup.

State one assumption in your calculation.

(4 marks)

(iv) A customer first places the mixian into the soup before adding the meat. Explain why this is undesirable.

(2 marks)

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10.

Iodine-131 ( )I131

53 is a radioisotope which decays by emitting a β-particle

and γ rays. It is used in hospitals to test the kidneys of patients. During the test, an iodine-131 solution is injected into the bloodstream of a patient. As the blood passes through the kidney, iodine-131 will be absorbed by the kidney and eventually excreted out of the body with urine. If the kidney is not functioning properly, both the absorption and excretion rates of iodine-131 will decrease. A γ -detector is placed near the kidneys of the patient to detect the activity of the radiation coming from the kidneys (see Figure 15).

(a) Using X to denote the daughter nucleus, write down an equation

for the decay of an iodine-131 nucleus. (2 marks)

(b) Explain why the β-particles emitted by iodine-131 fail to reach the

detector. (1 mark)

(c) The half-life of iodine-131 is 8 days. (i) State the meaning of ‘half-life’.

(2 marks)

(ii) For safety purposes, the activity of iodine-131 solution in the test should not exceed 1.5 × 108 disintegrations per second. When an iodine-131 solution is prepared, its activity is 6 × 108 disintegrations per second. How many days after preparation would the solution be suitable for the test ?

(2 marks)

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(c) (continued) (iii)

Figure 16 shows the variation of the activities of the radiation detected from the right and left kidneys of a patient with time. Which kidney do you think is not functioning properly ? Explain your answer.

(3 marks)

*(iv) Besides iodine-131, technetium-99m is another radioisotope which is also used in the kidney test. Technetium-99m emits γ radiation only and its half-life is 6 hours. Which of these two sources do you think is more preferable for use in the kidney test ? Explain your answer.

(5 marks)

Time/min

Activity/disintegrationsper second

0

Figure 16

Right kidney

Left kidney

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11. (a) A visitor stands at a distance 30 cm in front of the peephole (see

Figure 18 on next page). (i) In Figure 18, draw the refracted rays of the three incident

rays and the image formed. (4 marks)

(ii) Find the magnification of the image formed. (2 marks)

(b) Suggest one reason to explain why the concave lens inside the peephole cannot be replaced by a convex lens. (2 marks)

(c)

Figure 19 shows the top-view of the peephole. The metal tube will

only allow Kitty to see those images formed in the shaded region. Now a visitor stands at a point P and Kitty cannot see him through the peephole.

(i) Explain, by drawing a ray diagram in Figure 20, why

Kitty cannot see the visitor. (3 marks) (ii) The lens is now replaced by another concave lens of a

shorter focal length and Kitty can just see the visitor at P. In Figure 20, locate the image observed and find the focal length of this lens. (4 marks)

Kitty designs a simple peepholewhich is installed at an entrance doorto identify visitors (see Figure 17).The peephole consists of a metal tubewith a concave lens of focal length10 cm fixed inside.

Figure 17

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Candidate Number

Centre Number

Seat Number

Total Marks on this page

If you attempt Question 11, fill in the first three boxes above and tie this sheet into your answer book.

END OF PAPER

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This is a blank page.

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Useful Formulae in Physics (a) Relationships between initial velocity u, uniform acceleration a, final velocity v and displacement travelled s after time t : v u + at=

s ut + at=12

2

2 2 2v u + as= (b) Potential energy gained by a body of mass m when raised through a height h is mgh. (c) Kinetic energy of a body of mass m moving with speed v is

12

2mv .

(d) Power = force × velocity (e) Equivalent resistance of two resistors R1 and R2 : (i) in series R + R= 1 2

(ii) in parallel R R

R R=

+1 2

1 2

(f) Power = potential difference × current

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2002 Physics 1 2. (a) 4.7 cm (b) 5.57 cm 3. (a) 21 Nm (b) 480 N 4. (b) 0.2 m 5. (a) 1.7 m (b) (i) 2.55 m 7. (b) (i) 2.88 Ω (ii) 9.17 A 8. (a) 0.7 s (b) 6.4 m s–2 (c) (i) 36.0 m (ii) 21.6 m s–1 (iii) 15.0 m, 31.3 m 9. (b) (i) 0.430 kg (c) (iii) 16 10. (c) (ii) 16 11. (a) (ii) 0.25 (b) (ii) 6 cm