Mock-CE PHY PAPER 1 Name Class Class number MOCK EXAMINATION PHYSICS PAPER 1 Question-Answer Book (1¾ hours) This paper must be answered in English 1 Write your Name, Class and Class number in the spaces provided on the this cover. 2 This paper consists of TWO sections, Section A and Section B. Section A carries 54 marks and Section B carries 36 marks. 3 Answer ALL questions in each section. Write your answers in the spaces provided in this Question-Answer Book. Supplementary answer sheets will be supplied on request. Write your Name on each sheet and fasten them with string inside this book. 4 Some questions contains 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. Section A Question No. 1 2 3 4 5 6 7 8 9 Section A Total Teacher's Use Only Marks 5 Unless otherwise specified, numerical answers should be either exact or correct to 3 significant figures. 6 Take g = 10 m s 2. 7 Unless otherwise specified, all the cells are assumed to have negligible resistance. Section B Question No. 10 11 12 13 Section B Total Marks
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 1 s ut at 2 2 2 2 v u 2as (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 1 mv 2. 2 (d) Power = force velocity (e) Equivalent resistance of two resistors R 1 and R 2 : (i) in series = R 1 + R 2 (ii) R1R2 in parallel R R 1 2 (f) Power = potential difference current SECTION A (54 marks) Answer ALL questions in this section and write your answers in the spaces provided. Question No. 1 2 3 4 5 6 7 8 9 Marks 4 5 6 6 6 8 5 6 8 1 Figure 1 shows a compact fluorescent lamp. Figure 1 Figure 2-1 -
Figure 2 is the enlarged image showing the specifications of the lamp: 20 W 220 240 V 50 60 Hz Page total In Hong Kong, the mains voltage is 220 V. (a) Find the operating current of the lamp. (b) Find the operating resistance of the lamp. 2 John produces a wave by flicking an elastic string. He produces 2 complete waveforms every second. Figure 3 shows the shape of the elastic string at a certain time t. Figure 3 (a) Is the wave produced transverse or longitudinal? (1 mark) (b) Find the wavelength and the amplitude of the wave. (c) In Figure 3, draw the waveform at time t + 0.125 s. - 2 -
3 Jane wants to find the focal length of a convex lens. She uses the lens to project the image of a distant building on a screen. She measures the distance between the lens and the image and finds it 15 cm. (a) State a property of the image. (1 mark) (b) What is the focal length of the lens? (1 mark) She then uses the lens to form the image of a nearby object on a screen. She puts the object 20 cm from the lens. The object is 10 cm high. (c) In Figure 4, use a scale of 1 cm to 10 and draw a ray diagram to locate the image. Hence find the magnification of the image. (4 marks) Figure 4-3 -
4 A fire breaks out in a building. A resident is waiting for rescue on the 8th floor. The firemen arrive soon and open a large air cushion below the resident (Figure 5). The resident (mass 60 kg) jumps down onto the cushion. Figure 5 (a) If each storey of the building is 3.5 m high, find the speed of the resident at the moment when he reaches the cushion. The cushion is 3 m thick when inflated. (b) After reaching the cushion, the resident slows down and comes to a stop after 0.2 seconds. Calculate the average net force acting on the resident during this period. (c) The resident later says that he crawled close to the floor when moving in the smoke-filled building. Comment on whether he acts correctly. - 4 -
5 It is found that passengers taking New York Hong Kong flight would receive radiation equivalent to that of three X-ray scans (about 20 Sv for each X-ray scan). The high radiation of New York Hong Kong flight is due to the long flight time and also the high flight altitude. (a) Sv is a unit of radiation dose. What does the dose mean? (b) What kind of radiation may the passengers receive inside the plane? (1 mark) (c) State a main source of this background radiation. (1 mark) (d) A nuclear plant is another source of nuclear radiation. Do you agree with the use of nuclear energy? Give two reasons to support your position. - 5 -
6 Figure 6 In Figure 6, the roller-coaster Dragon in Ocean Park of mass 1500 kg is about to travel down a track from rest at a point A which is 110 m above ground level. Take the potential energy at ground level as zero. (a) Find (i) the potential energy of the cart at point A, (ii) the speed of the cart at a point B which is 89 m above ground level, assuming friction is negligible. (4 marks) (b) The actual speed of the cart at B is less than that in part (a)(ii). Describe the energy change as the cart moves from A to B. - 6 -
6 (c) In Figure 7, complete the following free-body diagram for the cart when it is going downhill. cart weight Figure 7 7 Figure 8 Figure 8 shows the structure of a loudspeaker. The coil is wound round the S-pole of a cylindrical magnet. Attached to the cone, the coil is free to move inside the magnet. (a) The coil is connected to an a.c. power supply. What happens to the cone when the supply is switched on and a current flows into the coil from A? (1 mark) *(b) Describe the working principle of the loudspeaker. (4 marks) - 7 -
8 Read the following passage about electric light bulbs and answer the questions that follow: The structure of a light bulb is very simple. At the base, it has two metal contacts, which connect to the mains circuit. The metal contacts are attached to two stiff metal wires, which are attached to a thin metal filament. The filament is held in the middle of the glass bulb. The glass bulb is filled with an inert gas, such as argon. The filament in a light bulb is made of a long, thin wire of tungsten metal. The filament for a 60-W bulb can be as long as 2 m, but it is made into a coil of less than 3 cm long. Tungsten has the highest melting point (3422 C) among all metals. When the bulb is connected to a power supply, an electric current flows through the filament. The current heats up the filament. When the filament is hot enough, it gives out visible light. For tungsten, it emits a large amount of visible light when its temperature reaches about 2200 C. At such an extreme temperature, some tungsten will change into vapour. If the inside of the bulb is a vacuum, tungsten becomes vapour easily and the filament will disintegrate in a short time. This greatly reduces the life of the bulb. Today inert gases such as argon are used to fill the bulbs. The gas makes vaporization of tungsten much slower. Besides, it does not react with tungsten. This extends the life of the bulbs. Source: HowStuffWorks http://science.howstuffworks.com/light-bulb2.htm (a) You are given two light bulbs, A and B. Bulb A has a thinner filament than bulb B. Write down the relationship between the resistance and the length and cross-sectional area of the filament. Hence state which bulb has a lower resistance. The filaments are of the same material and length. (b) State an advantage of using tungsten over other metals for making the bulb filament. (1 mark) - 8 -
8 (c) But tungsten normally catches fire at the temperature mentioned in the passage. Explain why this does not happen inside the bulb. (1 mark) (d) Describe the energy change in a light bulb, hence explain whether the light bulb is an efficient source of light. 9 Many Chinese dim sums are cooked by steam. In order to keep the food warm, a dim sum cart is used as shown in Figure 9. There is a heater inside the cart to boil water and the food steamers are made of bamboo. food steamer Figure 9 (a) List one advantage of cooking by steam. (1 mark) (b) State the process by which energy is transferred from the heater to the food steamers at the top. (1 mark) - 9 -
9 (c) A student says that the food inside the steamers at the top is hotter than that at the bottom. Comment on this statement. (d) Explain why the food steamer is made of bamboo. (e) If the power of the heater is 200 W, how much water at 100 C will be boiled away in each minute? (Given: Specific latent heat of vaporization of water = 2.26 10 6 J kg 1.) - 10 -
SECTION B (36 marks) Answer ALL questions in this section and write your answers in the spaces provided. Question No. 10 11 12 13 Marks 5 7 9 15 *10 You feel hot and sweat (Figure 10). When you turn on a fan, you will feel cooler than when the fan is not turned on. Explain why. (5 marks) Figure 10-11 -
11 Figure 11 shows an induction cooker. Figure 11 Under the plastic plate of the cooker are some coils. A high-frequency a.c. flows through the coils. The rapidly changing magnetic field produces a strong eddy current inside metal pots placed on the plastic plate. The heating effect of the eddy current cooks the food inside the pot. (a) Can one use the cooker to cook rice in a clay pot? Explain briefly. (b) The power of the above induction cooker is 1500 W. A family uses it to make hot pot and switches it on for 4 hours. If each unit of electricity costs $0.9, what is the cost of electricity for using the cooker? (c) What happens to the heating effect of the cooker if (i) the frequency of the a.c. is lowered; (ii) coils with more turns are used? (d) The induction cooker makes use of eddy current. But in some situations eddy current should be avoided. State one such situation. (1 mark) - 12 -
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12 Figure 12 shows two loudspeakers, A and B, connected to the same signal generator. The generator produces sound waves at 500 Hz. Initially, only A is switched on. The speed of sound is 340 m s 1. Figure 12 (a) Figure 13 shows the displacement-time graph of an air molecule at P. Figure 13 Figure 14 (i) Indicate the values for t 1 and t 2. (ii) In Figure 14, draw the displacement-distance graph of the sound wave along AP at t = 0.002 s. (5 marks) (b) Then B is also switched on. One can hear a series of loud and faint sounds when walking across in front of the loudspeakers. What happens to the loudness of sound heard at P? Explain briefly. (3 marks) - 14 -
(c) Page total In daily life, one cannot hear similar changes in loudness when walking across in front of the loudspeakers of a hi-fi system playing a song. Explain why. (1 mark) - 15 -
13 Figure 15 Figure 15 shows the set-up of a data-logging experiment on a horizontal table to investigate impacts. Two trolleys, A and B, collide with each other and their motions are recorded by motion sensors. The mass of trolley A and trolley B is 0.69 kg and 1.38 kg respectively. The velocity-time graphs captured by motion sensors for trolleys A and B are shown in Figures 16 and 17 respectively. For the shaded region, Mean value of y = 0 For the shaded region, Mean value of y = -0.59 Figure 16 Velocity-time graph for trolley A For the shaded region, Mean value of y = 0.54 For the shaded region, Mean value of y = 0.22 Figure 17 Velocity-time graph for trolley B *(a) Describe the motions of trolleys A and B before and after the collision. (5 marks) - 16 -
(b) In Figures 16 and 17, what is the physical meaning of the area bounded by the curve and the horizontal axis? (1 mark) (c) (i) Do the results support the conservation of momentum? Show your calculations. (3 marks) (ii) Give one source of error and one suggestion for improvement. (d) Calculate the total kinetic energy of the trolleys before and after the collision. Hence explain briefly if the collision is elastic. (4 marks) - 17 -
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