2012 OLevel Science Physics Paper 2 Questions and Answers

7/30/2019 2012 OLevel Science Physics Paper 2 Questions and Answers

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O-LEVEL 2012

QUESTIONS AND SUGGESTED ANSWERS

1. The figure below illustrates the regions of electromagnetic spectrum. They are arranged inascending order of their wavelengths.

(a) State the differences in the wave properties between the waves in A and C with soundwaves.

1. The waves in the region A and C are transverse waves while sound waves are

longitudinal waves.

2. The waves in the region A and C travels approximately at the speed of light, 3 x 108ms-1, in air while sound waves travels approximately 330ms -1 in air.

Other acceptable answer(s)

1. Waves in A and C do not require a medium to travel (or can travel in vacuum) while

sound waves require a medium to travel (or cannot travel in vacuum).

2. Waves in A and C consist of electric fields and magnetic fields that oscillate 900 to

each other while sound waves consist of particles.

(b) For region B

(i) Name this region

Ultraviolet Ray

(ii) Name one of the uses for the wave mentioned in bi)Sunbed

Other acceptable answer(s)

1. Sterilisation of medical equipments

2. For the first 30 minutes, a train travels at a constant speed of 60ms -1. For the next 10 minutes,it decelerates constantly until it comes to rest. The mass of the train is 2.4 x 10 5 kg.

Calculate the followings,

(a) distance travelled in the first 30 mins

Distance = area under the graph

= 60 x 30 x 60

= 108 km.

Gamma A B Visible Light C Microwave Radio

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(b) Deceleration of the train

(c) Braking force exerted on the train

F = ma

= (240000)(0.1)

= 24000 N

(d) The work done against braking force

W.D = F x //d

//d = area under v-t graph

= x 60 x 10 x 60

= 18 km

W.D = 24000 x 18000

= 432 MJ

3. A pure substance has a melting point of 500C. The temperature of the substance has beencooled from 800C to 300C.

(a) On the figure below, sketch a temperature-time graph to illustrate the temperaturechange of the substance.

0

10

20

30

40

50

60

70

80

0 0.2 0.4 0.6 0.8 1 1.2

Temperature(0C)

Time (s)

Temperature against time graph


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(b) Describe any changes to the arrangement and the motion of the molecules of thesubstance.

(i) as the temperature drops from 800C to 510C,

Arrangement of molecules:

The arrangements of the molecules will remain at closely packed that is less dense

than that of solid.

Motion of molecules:

The molecules will lose energy to vibrate less vigorously, hence having lesser

capability to slide past each other.

(ii) as it freezes at 500C

Arrangement of molecules:

The arrangement of the molecules will change from closely packed to very closely

packed.

Motion of molecules:

The motion of the molecules changes from being able to slide past each other to

vibrate about its fixed position.

4. A virtual and enlarged image of an object has been produced by a thin converging lens.(a) Which of the diagrams below will be able to illustrate the correct ray diagram?

Correct: D

(b) When light travel from air to glass, the light will refract more if it has a shorter wavelength.

The diagram below shows the refraction of red light through a lens.


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(i) State the differences between the wavelength of red and blue light.

The wavelength of blue light is shorter than that of red light.

(ii) In the figure above, draw the rays of blue light when it passes through the lens.

5. The figure below shows the wiring in a plug.

(a) In the safety aspect, explain why the switch is connected to the live wire rather than the

neutral wire.

Live wire connects the circuit to the high potential point of the main supply. Hence, switch

has to be placed on the live wire to control the operation mode of the appliance through

the supply of potential difference to the appliance and the connection of high potential

point to the appliance.

Acceptable answer

Since the live wire is connected to the current source of the main supply. Hence, by

placing the switch at the live wire, it can isolate the current from the appliance when

necessary.

6. The figure below shows the setup of a DC solenoid and a bar magnet.

(a) When the switch is on, explain why the bar magnet moves away from the iron core.

When the switch is on, the current from the DC supply will generate magnetic field to

align the domains in the iron core. This would cause the iron bar to be magnetised. Hence,

by using Right Hand Grip Rule, it can be found that the right hand side of the iron core toexperience an induced South pole. Since unlike poles repel, it will cause the bar magnet

to move away.


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(b) The switch is then turned off and the bar magnet has been replaced by an iron rod. Stateand explain what will happen when the switch is now turn on.

When the switch is on, the current flow in the solenoid will generate magnetic field and

align the domains in the iron core. By using Right Hand Grip rule, it will induce a South

Pole at the right hand side of the iron core.With the magnetic field produced by the ironcore and the solenoid, it will cause the domains in the soft iron bar to get aligned and

hence causing the left hand side of the iron bar to experience an induced North Pole. As

such, it causes a force of attraction between the solenoid and the iron bar, causing it to

get nearer to the solenoid.

7. A vertical cylindrical tube which has a cross sectional area of 0.25 cm2 and contain a column ofliquid of length 12.4cm. The density of the liquid is 0.80 g/cm3.

Calculate

(a) Mass of liquid

M = x V

= 0.80 x (0.25 x 12.4)

= 2.48g= 0.00248 kg

(b) Weight of liquid

W = mg

= 0.00248 x 10

= 0.0248 N

(c) Pressure on the base of the tube

992 Pa


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8. The figure below shows a circuit with various components.

(a) Calculate(i) Current in Z

IZ = 2.5 1.7

= 0.8 A

(ii) Voltage across Z

VZ = 9.0 3.0= 6.0 V

(iii) Resistance of Z

VZ = IZ x RZ

6.0 = 0.8 x RZ

RZ = 7.5

.

(b) Charge flowing through Y in 5 minutes.

QY= IYx tY

= 1.7 x (5 x 60)

= 510 C

(c) Total effective resistance of the circuit.

Vtotal = Itotal x Rtotal

9.0 = 2.5 x R total

Rtotal = 3.6

9.0 V

9.0 VVoltmeter 1

3.0V

Voltmeter 2

2.5A

Ammeter 1

1.7AAmmeter 2

X

Y

Z


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9. The figure below shows a uniform ruler that is pivoted at 35cm.

(a) On the figure above, draw an arrow to illustrate the weight of the ruler.

(b) Calculate the weight

Sum of anti-clockwise moment = Sum of clockwise moment

(4 x 0.25) = (W x 0.15) + (2 x 0.45)

W = 0.667 N

Section B

10. The figure below shows a pendulum which consist of a metal sphere.

35cm

10cm

80cm

50cm

W

F

O

X


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(a) Draw a free body diagram of the sphere when it is at the highest point.

(b) The pendulum is now free to swing. Explain why the metal sphere will move and it is ableto move past its lowest point, O.

After the external force F has been removed, all the potential energy of the sphere will be

converted to kinetic energy. Hence, it will start to move when it is being released. Due to

the law of conservation of energy, total energy at O = total energy at X. Since all the

potential energy at X will be converted to kinetic energy at O, the ball will possess

maximum kinetic energy at O, causing it to move past point O.

(c) Mass of sphere is 200g. When it is being shifted from O to X, the vertical distance movedis 3.0 cm. Given that the free fall is 10 ms -2, calculate the followings.

(i) Work done in shifting the sphere.

W.D = F x //d

= W x 0.03

= 0.2 x 10 x 0.03

= 0.06 J

(ii) Maximum speed of the sphere during its oscillation.

By conservation of energy, all the work done will be converted into kinetic energy,

hence,

W.D = x m x v2

0.06 = x 0.2 kg x v2

v = 0.775 ms-1

(d) A student uses two different methods to determine the period of the pendulum.

In the first method, she only measure the time for one oscillation

In the second method, she measures twenty oscillations and calculates the average time

taken for one oscillation.

Explain why the second method will give a more accurate result.

By measuring the time taken for twenty oscillations and calculating the average time

taken for one oscillation, she is able to reduce the random error incurred in her reaction

time. However, in the first method, the reaction time can be significant and hence,

inducing a large percentage error.

F


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11. (a) A fridge has a maximum power of 80 W when it is being connected to a 240V powersupply. On average, it uses 0.39 kWh of energy every 24 hours.

Calculate,

(i) Maximum currentPmax = Imax x Vmax

80 = Imax x 240

Imax = 0.333 A

(ii) Average power

Eaverage = Paverage x t

0.39 = Paverage x 24

Paverage = 16.25 W

(b) In the cooling system of a fridge, a volatile liquid is used to be pump through the metalpipes and outside the food compartment.

(i) In the freezing compartment, the liquid will be changed into a vapour.

With the scenario mentioned above, state the changes in the arrangement of the

molecules and suggest why energy is needed to vaporise a liquid.

The arrangement of the molecule will change from closely-packed to far apart.

Energy is absorbed to overcome the forces of attraction between the molecules

such that the molecules are able to far apart from each other.

(ii) The vapour will be pumped to the outside of the fridge where it can be compressedto form liquid, causing the liquid to be heated. It will then be passed through the

metal tube which is attached with black metal plates.

Using the idea of thermal energy transfer, explain how the energy is lost to the

surroundings.

The metal tube and the black metal plates are good conductor of heat as they are

able to conduct heat away from the liquid through particle vibration and electron

diffusion processes. In addition, the black metal plate is a good absorber and

emitter of heat, hence it can absorb energy from the metal tube and radiate it out

to the surrounding efficiently.


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12. Under the earths surface, there are two layers of rocks, rock A and B respectively. Rock A has alayer that is 2.5km thick and it is on top on rock B. Geologists are trying to find all oil bearing

rocks. An explosion would generate a wave to travel into the earth.

Such explosion would cause part of the wave to be reflected at the boundary back towards the

surface and the rest to enter rock B. Wave reflected will be detected by a microphone.

(a) Explain what transverse wave is.

Transverse wave is a wave that travels perpendicularly to its direction of vibration. It is a

progressive wave that is able to transmit and distribute energy.

(b) The time taken for the wave to be reflected is 1.6s. Calculate the speed of wave in rock A.

()

(c) Given that the speed of wave in rock B is greater than that of A and the number ofcomplete wave cycles per unit time is the same in both rock A and B. Suggest and explain

the similarities and differences between the frequency and wavelength between rock A

and B.

Since the frequency is defined as the number of complete vibrations per second, and it is

the same between A and B, it shows that frequency of wave in A and B are the same. By

using the formula v = f x , the wavelength of the wave in B is larger than that of A as

the frequency is constant while the speed of wave in B is larger than that of A.

2012 OLevel Science Physics Paper 2 Questions and Answers

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