Name: __________________________________ ( ) Class: _____

HWA CHONG INSTITUTION END-OF-YEAR EXAMINATION 2009

PHYSICS Paper 2 Level: Secondary Four Duration: 1 hour 45 mins

Do not open this booklet until you are told to do so. INSTRUCTION TO CANDIDATES Write your name, index number and class on the top of this page. Answer the questions in Section A and B in the spaces provided. All workings must be shown. In Section B, for Question 11 answer ‘EITHER’ or ‘OR’. INFORMATION FOR CANDIDATES In Sections A and B the intended marks for each question or part of a question are given in brackets [ ]. Any working should be done in the space provided. When necessary, take acceleration due to gravity to be 10 m/s2. ___________________________________________________________________________________

This question paper consists of 17 printed pages, including this page.

SECTION A (40 Marks)

Answer all the questions in this section. 1. A ball of mass M is tied to the ceiling by a string A. Another string C pulls the

ball horizontally towards the left such that string A makes an angle of 30o to the vertical as shown in the diagram below. The ball is at rest.

ceiling

string C

string A

30o

a) On the diagram above draw and label in the forces acting on the ball. [1]

b) If the tension in string A is 3.0 N, using a scale diagram or otherwise, find the tension in string C and the weight of the ball. [2]

c) What is the mass M of the ball? [1]

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2. A student is investigating projectiles. He fires two identical balls, A and B, simultaneously. Their trajectories are shown in the sketch below. The balls A and B land at the same instant at the target, T.

Horizontal A

Vb 45o

Va

B T

a) If Vb = 20 m s-1, find the horizontal component of Vb. [1]

b) Explain why the horizontal component of Vb equals Va. [2] _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ c) If the time the balls take to hit the target T is 7.0 s find the vertical

distance between the balls initially. [2]

d) If balls A and B have a mass of 200 g each, calculate the total energy

each ball has at the beginning of the trajectory? [2]

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3. A uniform meter rule is placed on a pivot at its centre of gravity. Two 2.0 N weights are hung from the meter rule as shown. The meter rule is balanced.

a) Calculate the upward pressure exerted by the pivot on the ruler if the weight of the ruler is 1.0 N and the area of contact between the pivot and ruler is 0.10 mm2. [2]

The pivot and both the weights are moved to the left to a new position as shown below.

b) Where should a 0.50 N weight be placed to restore the balance of the

ruler? [2]

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4. a) The diagram shows a transverse wave moving to the right along a

spring, at a particular instant.

On the diagram, i) draw the new position of the wave as seen at the next instant. [1] ii) draw the direction of movement of particle X; [1] b) The following table gives information about the wavelength and output

power of some types of laser used in a hospital.

Type of laser Wavelength/m Output power/ W Excimer 3.2 x 10-7 20.0 Argon 4.9 x 10-7 2.0 Dye 5.5 x 10-7 0.5

Helium-neon 6.3 x 10-7 0.005 Nd-YAG 10.6 x 10-7 50.0

Visible light has wavelengths ranging from 4.0 x 10-7 to 7.0 x 10-7 m.

iv) State the laser which emits infrared radiation? [1]

_______________________________________________________________

iv) State one medical use of infrared radiation. [1]

_______________________________________________________________

iv) Calculate the frequency of light from the helium-neon laser. [2]

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5. William makes a glass of hot tea. After a while, he adds some ice cubes into the tea. William uses a temperature sensor to measure the temperature of the tea. The figure below shows the temperature-time graph obtained.

a) Explain why the temperature of the tea increases from R to S. [2]

_______________________________________________________________ _______________________________________________________________

_______________________________________________________________ _______________________________________________________________ b) Estimate the temperature of the surroundings. [1]

_______________________________________________________________

c) Another method to cool the hot tea without adding ice cubes is by leaving the cup of hot tea in the room to cool by evaporation.

Explain how evaporation causes cooling. [2]

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________ _______________________________________________________________

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6. The dehumidifier shown below is turned on for a few hours in a closed room. Water vapour in the incoming wet air condenses and 1.50 kg of water is collected in the water tank.

Part A of the

dehumidifier Part B of the dehumidifier

wet air in dry air out coiled tube metal fins

pump water tank

air fan

Given: - specific latent heat of vaporization of water is 2.26 x 106 J kg-1 - density of air is 1.30 kg m-3 - volume of air is 400 m3 in room - specific heat capacity of the air is 1.03 x 103 J kg-1K-1

Assuming that all the energy released in Part B of the dehumidifier is used to raise the temperature of the air inside the room, calculate

a) the thermal energy loss by the water in condensing, [1] b) the increase in temperature of the air in the room. [2]

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7. a) How can a polythene strip be charged? [1]

_______________________________________________________________ _______________________________________________________________

b) If the polythene strip is charged negatively by the method you have

just described above, explain the charge movement when the polythene strip is charged. [1]

_______________________________________________________________

_______________________________________________________________

c) A negatively charged polythene strip is brought near the left end of an

uncharged metal bar. This makes the plastic strip suspended near the right end of the metal bar move away from the metal bar.

i) How does the charged polythene strip affect the electrons in the metal bar? Explain your answer. [2]

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________ _______________________________________________________________

ii) Why does the plastic strip move away from the right end of the metal bar? [2]

_______________________________________________________________

_______________________________________________________________

______________________________________________________________

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8. A student wishes to design an electromagnet to pick up metal debris on the laboratory floor. In his design he uses insulated copper wire to form a coil wound on a plastic core connected to a 2.0 V cell and a switch as shown below.

Excess insulated copper

a) Add an arrow on the wire AB above to show the direction of the current when the switch is closed. [1]

b) On the diagram indicate the North pole of the electromagnet formed.

[1]

c) The student found that the electromagnet formed is too weak to pick up the metal pieces. Without changing the cell and length of the wires used, state and explain two ways on which the student can increase the strength of the magnetic field produced. [3]

_______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________

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SECTION B (30 Marks) 9. a) A balloon is filled with air and is attached to a puck. It releases air

through a hole at the bottom of the pluck. The balloon puck then moves on a horizontal straight track (see Figure a below) and its velocity-time graph is shown in Figure b.

velocity/m s-1

time/s 0

0.50

1.0 1.4

i) Explain why the motion of the balloon puck changes at t = 1.0 s. [2]

_______________________________________________________________ _______________________________________________________________ _______________________________________________________________

ii) If the balloon is filled with less air and its initial velocity is still 0.50 m s-1, sketch the corresponding velocity-time graph of the balloon puck in Figure b. [2]

b) Figure c shows Player X trying to block the ball from Player Y in a

volleyball game. Standing on the ground with his arms fully stretched upwards, Player X’s hands are 2.25 m above the ground. In order to block the ball, Player X has to jump up such that his hands reach a height of 3.00 m.

Figure a

Figure c

3.00 m

Figure b

Player Y

2.25 m

Player X

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i) Using Newton’s laws of motion, explain why Player X in Figure c can gain an initial speed to leave the ground vertically. [2]

_______________________________________________________________ _______________________________________________________________ _______________________________________________________________

_______________________________________________________________

ii) Player X jumps up vertically and his hands can just reach a height of 3.00 m. Calculate the initial speed of Player X at the instant he leaves the ground. Assume that air resistance is negligible. [2]

iii) Player Z is a teammate of Player X. His hands can also reach a height of 2.25 m when his arms are fully stretched upwards but he is heavier than player X. If he jumps up such that his hands just reach a height of 3.00 m, explain whether the initial vertical speed of Player Z will be the same as Player X. [2]

_______________________________________________________________ _______________________________________________________________ _______________________________________________________________

_______________________________________________________________

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10. Two filament lamps are designed to work from a 9.0 V supply but they have different characteristics. The graph shows the current-potential difference relationship for each lamp.

The two lamps are connected in parallel with a 9.0 V supply as shown.

a) What is the current through each lamp and what is the total current drawn from the 9.0 V battery? [2]

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b) Calculate the total resistance of the circuit. [1]

c) Which of the two lamps is brighter? Give a reason for your answer. [2]

_______________________________________________________________ _______________________________________________________________ _______________________________________________________________ d) Explain how the graph shows that the resistance of the lamps increases

with temperature rise. [2] _______________________________________________________________ _______________________________________________________________ _______________________________________________________________

A lighting engineer wishes to design an electrical circuit to light up two rooms, Room 1 and 2, as shown below. The lamps to be connected, Lamps A and B, are shown in their respective rooms.

Live wire

9.0 V

Neutral wire

Room 1 Lamp A

Room 2 Lamp B

e) Complete the circuit above so that the lamps can be operated separately. [2]

f) Add a suitable fuse to protect the electrical circuit. [1]

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Answer EITHER 11. a) An optical fibre carries coded information in the form of pulses of

light. The optical fibre consists of a thread of glass whose core is surrounded by glass of a different material of different refractive index called the cladding. The light source, usually a light emitting diode (LED), emits infrared radiation. The radiation passes through a lens and enters the fibre as shown in the diagram (not drawn to scale) below.

The position of the LED

core

cladding

cladding lens

Two light rays from LED

The LED, which acts as a point source is placed 5.0 cm from a converging lens of focal length 5.0 cm.

i) What is meant by the focal length of a lens? [1] _______________________________________________________________ _______________________________________________________________

ii) Complete drawing the two light rays from the LED (shown in the diagram above) as they pass through the lens into the core of the fibre. [2]

iv) State what happens to the frequency and wavelength of the light (either

increase, decrease or unchanged) as it enters the fibre. [2]

Frequency – ________________ Wavelength – ________________

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iv) As the fibre bends, the light will continue to travel in a straight line until it reaches the side of the core where it should be totally internally reflected at the boundary with the cladding. Explain what is meant by the term critical angle for a boundary between two media. [2]

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________ _______________________________________________________________

v) The core has a refractive index of 1.48. Will the refractive index of the

cladding be smaller or larger than 1.48? Explain your answer. [2] _______________________________________________________________

_______________________________________________________________ _______________________________________________________________

vi) Explain why the light may not be totally internally reflected if a section of the fibre is bent sharply as shown below. [1]

Light ray

Optical fibre

_______________________________________________________________ _______________________________________________________________ _______________________________________________________________

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OR 11. b) The diagram below shows two circuits linked by a core.

Core Lamp

S

i) When S is closed the lamp gives out a momentary flash. Explain why

this happens. [3]

_______________________________________________________________ _______________________________________________________________ _______________________________________________________________

_______________________________________________________________ _______________________________________________________________ ii) Explain what alteration to the circuit is needed so that the lamp can

light up continuously. [2] _______________________________________________________________

_______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________

A transformer is used to light up a 12 V 96 W lamp. The primary coil has 200 turns and is connected to a mains supply of 240 V. iii) Calculate the number of turns of the secondary coil so that the lamp

can be optimally lighted. [2]

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iv) Calculate the current taken from the mains supply if the efficiency of

the transformer is 100%. [2] v) The soft iron core of the transformer becomes warm after some time.

Explain why this occurs. [1] _______________________________________________________________ _______________________________________________________________

End of Paper