06 AL Physics/Essay/P.1
HONG KONG ADVANCED LEVEL EXAMINATION
AL PHYSICS
2006 Essay Type Question
1. (a) A horizontal spring-loaded gun and a small wooden block are fixed on the same horizontal level, and the gun is aimed at point O as shown. (Neglect air resistance and the length of the gun.)
B ball bearing compressed spring
O
D small wooden block
A
Due to gravity, the ball bearing shot from the gun reaches a point A at a distance D below O . In order to hit the block at O , explain why the gun should be tilted to aim at a point B vertically above O , with OB slightly greater than D . (3 marks)
(b) The wooden block is replaced by an iron block and the gun is fixed horizontally as shown below. With an electromagnet and the apparatus available in a school laboratory, you are required to design an experiment by modifying the set-up so that the block can be hit by the bearing at A . ball bearing compressed spring
O
D small iron block
A
(i) Describe the experiment.
(ii) Could the bearing hit the block if the force constant of the spring is larger? Explain.
(iii) Explain how the vertical distance, D , and the corresponding time taken, t , would be affected
(I) if a heavier ball bearing is used;
(II) if the gun is not firmly fixed and it experiences horizontal recoil when the compressed spring hits the bearing.
(10 marks)

06 AL Physics/Essay/P.2
(c) A cannon ball fired by hypothetical powerful cannon at a certain initial horizontal velocity would orbit near the earth’s surface in a circular path.
Explain how this hypothetical case can be achieved. How would the respective magnitude and the direction of the cannon ball’s velocity and acceleration change with time? The earth is treated as a uniform sphere of radius 6400 km. (Neglect air resistance and the earth’s rotation.) (3 marks)
2. (a) (i) State the principle of superposition of waves.
(ii)
A free end
B incident wave propagating from left to right
On a string with a free end B , the incident wave generated by a vibrator propagates from left to right and its waveform at a certain instant is as shown. Draw the corresponding reflected wave and the resultant wave.
Draw a similar labelled diagram at a quarter of a period later and explain the formation of a stationary wave in this set-up.
(5 marks)
(b) Describe and explain an experiment to show the interference phenomenon of sound waves using two loudspeakers. State ONE precaution of the experiment. (5 marks)

06 AL Physics/Essay/P.3
(c) On 26 December 2004 at 6:58 a.m. an undersea earthquake in the Indian
Ocean near Sumatra, Indonesia produced tsunami waves which devastated the shores of several countries in the region.
Tsunami waves have wavelengths of over 100 km and speeds of several hundred km/h on open ocean. Assume that the speed of the tsunami waves is constant on the ocean. Explain the following using your knowledge of the properties of waves:
(i) At about 9:00 a.m., tsunami waves reached Sri Lanka, which is about
1500 km from the earthquake epicentre (

), while The Maldives at about
2500 km from the epicentre was struck by tsunami waves at about 10:20 a.m.
(ii) Although Phuket, in Thailand was sheltered from the epicentre by
Sumatra of Indonesia, it was still affected by tsunami waves.
(iii) The amplitude of tsunami waves when reaching the shore from the open ocean can build up to more than 10 times. (Assume that the energy carried by tsunami waves is directly proportional to the product of the wave speed and the square of the wave amplitude.)
(6 marks)
3. (a) (i) What is an electric field? Describe an experiment to show the electric field patterns between
(I) two parallel straight electrodes; and
(II) a straight electrode and a point electrode.

06 AL Physics/Essay/P.4
(ii) Explain why electric field lines never cross.
(5 marks)
(b) A horizontal copper disc is suspended by a thread from the ceiling. A bar magnet underneath the disc is then set in uniform rotation as shown. thread
N S copper disc bar magnet
(i) Describe and explain what happens in the above set-up. What would the result be if the bar magnet and the copper disc are interchanged?
(ii) Suggest ONE possible change that would happen to the copper disc if it is fixed. Explain.
(4 marks)
(c) (i) With the aid of a diagram, explain how a d.c. motor works.
(ii) Explain why a motor is sometimes connected in series with a ‘starting’ resistance which is reduced gradually after the motor is switched on.
(7 marks)
4. (a) Carbon-14 dating is a powerful tool for archaeological chronologies.
Radioactive carbon,
14
C, is a naturally-occurring isotope of carbon formed in the upper atmosphere. The half-life of
14
C is 5568 years.
(i) Describe how
14
C is produced in the upper atmosphere and eventually enters the food chain.
(ii) Briefly explain the principle and assumption(s) of carbon-14 dating.
(7 marks)
(b) (i) Coal was formed millions of years ago. Can the age of coal be found by using carbon-14 dating? Explain briefly.
(ii) Since about 1890, the industrial use of fossil fuels has released a large amount of carbon dioxide into the atmosphere. State and explain how this industrial effect influences the concentration of
14
C in living organisms.
(5 marks)

06 AL Physics/Essay/P.5
(c) (i) Explain, in terms of nuclear binding energy, why nuclear fission can be used as a source of energy.
(ii) State the differences in the uranium fuel and neutrons used in a nuclear reactor and in an atomic bomb.
(4 marks)
5. (a) (i) In the circuit below, the input voltage V in
is varied between 0 V and 9 V.
Sketch the graph of the collector-emitter voltage V
CE
against V in
. Explain the various parts of your graph in terms of the characteristics of an n-p-n transistor.
9 V
R
L
V in
R
B
B
C
E
0 V
(ii) Referring to your graph in (a)(i), describe how a transistor can be used as a ‘switch’. State TWO advantages of transistor switching.
(8 marks)
(b) (i) Draw the necessary modification(s) to the circuit in the above diagram and explain the modification(s)/adjustment required so that it can be used as a linear voltage amplifier for small varying signals. Show that the voltage gain for varying signals is
 
R
L
/ R
B
, where

is the current gain of the transistor.
(ii) Due to a faulty component in the voltage amplification circuit, V
CE
always equals 9 V no matter what V in
is. If the transistor functions properly, suggest TWO possible reasons for the fault and what measurement can identify the origin of the fault.
END OF PAPER
(8 marks)