Ce Physics 2002 Paper1(E)

2002-CE HONG KONG EXAMINATIONS AUTHORITY
PHY
HONG KONG CERTIFICATE OF EDUCATION EXAMINATION 2002
PAPER 1

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.

Take g = 10 m s–2 .
4.

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.

香港考試局保留版權
Hong Kong Examinations Authority
All Rights Reserved 2002

2002-CE-PHY 1–1

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

1. (a)

Figure 1

Figure 1 shows an ambulance. Explain why the word
AMBULANCE is printed in the form as shown in the figure.
(2 marks)

(b)

Ray
Figure 2

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)

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

2.
Half-metre rule

Capillary tube

Stirrer
Paraffin oil
Thermometer
Air column
Water
0 cm

Figure 4
Figure 3

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)

2002-CE-PHY 1–3 Go on to the next page
–2–

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)

2002-CE-PHY 1–4 –3–

4.

Q

Equilibrium
P position

0.3 m

Figure 6

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)

–4–

5.
S1
P (Mary)

Q (Susan)
Computer

S2

Figure 7

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)

2002-CE-PHY 1–6 –5–

6.
Soft-iron rod

A B

Aluminium ring
S

Figure 8

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)

–6–

Section B (60 marks)
Answer any FOUR questions in this section. Each question carries 15 marks.
24 V
7.

S
Heating coil
and fan Figure 9

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.

2002-CE-PHY 1–8 –7–

(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.

5V

24 V

0V
Heating coil
and fan
Figure 11

(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)

–8–

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.

Distance/m

60

40 s

20
l

0 5 10 15 20 25
Speed u/m s–1
Figure 12

(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)

2002-CE-PHY 1–10 –9–

(c)

Point of
impact u

36.0 m

d
19.7 m

Figure 13
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)

The speed limit of the road is 50 km h–1 (i.e. 13.9 m s–1).
*(iv)
If the car is travelling at this speed, explain whether it
would hit the boy.
(4 marks)

– 10 –

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

2002-CE-PHY 1–12 – 11 –

(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)

– 12 –

10.

( I)
131
is a radioisotope which decays by emitting a β-particle
Iodine-131 53
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)

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

2002-CE-PHY 1–14 – 13 –

(c) (continued)

(iii) Activity/disintegrations
per second

Right kidney

Left kidney

0
Time/min
Figure 16

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)

– 14 –

11. Kitty designs a simple peephole
which is installed at an entrance door
to identify visitors (see Figure 17).
The peephole consists of a metal tube
with a concave lens of focal length
Figure 17
10 cm fixed inside.

(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)

2002-CE-PHY 1–16 – 15 –

Total Marks
Candidate Number Centre Number Seat Number 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

2002-CE-PHY 1–17 – 16 –

This is a blank page.

2002-CE-PHY 1–18 – 17 –

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

12
s = ut + at
2

v 2 = u2 + 2 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
mv .
2

Power = force × velocity
(d)

(e) Equivalent resistance of two resistors R1 and R2 :

in series = R1 + R2
(i)

R1 R2
in parallel =
(ii)
R1 + R2

Power = potential difference × current
(f)

2002-CE-PHY 1–19 – 18 –

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

2.88 Ω
7. (b) (i)

(ii) 9.17 A

8. (a) 0.7 s

6.4 m s–2
(b)

(c) (i) 36.0 m

21.6 m s–1
(ii)

(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

2002-CE-PHY 1–20 – 19 –

Ce Physics 2002 Paper1(E)

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