2 section a answer all the questions in this section

8/14/2019 2 Section a Answer All the Questions in This Section.

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2Section A

Answer all the questions in this section.

For

Examiners

Use

1 Fig. 1.1a shows a series of eight electronic timers, positioned at an equal interval of20 m from each other along a straight road. A car, starting from rest, is driven alongthe road. All timers are started the moment the car starts moving, and each timer isstopped when the front of the car passes it.

Fig. 1.1b shows the data collected from timers A to F.

(a) The car is undergoing uniform acceleration for the first 100 m.

(i) Define what is meant by uniform acceleration.

.....

.[1]

(ii) Explain how the results show that the car is accelerating in the first 100 m.

...

..

...

.[2]

(b) Calculate the average speed of the car in the first 100 m.

average speed = [2]

(c) The car moves at a constant speed once it passes 100 m. Deduce the timerecorded by timer G and timer H.

timer G = timer H = ..[1]

electronic timer time (s)A 4.3B 6.0C 7.4D 8.5E 9.5F 10.5

Fig. 1.1bFig. 1.1a


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2 Fig. 2.1 shows a remote control toy helicopter of mass 1.5 kg rising upwards at aconstant acceleration of 2.0 m/s2. Take g = 10 N/kg.

(a) On Fig. 2.1, draw all the forces acting on the toy helicopter. [2]

(b) Calculate the force generated by the propeller.

force generated by propeller = [2]

(c) When the toy helicopter reaches at height of 10 m, it hovers at this elevation.

(i) What can you say about the forces acting on the toy helicopter at thismoment?

....

....[1]

(ii) At the height, the propeller suddenly stops turning. Using the principle ofconservation of energy, find the speed at which the helicopter is falling whenit is 5 m above the ground.

speed = [3]

Fig. 2.1


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3 Fig. 3.1 shows a cat in a diving bell of volume 12 m3. As the bell is lowered into thewater, the water level rises to fill 1 m of the bell.The temperature of the air remainsconstant. Take g= 10 N/kg and density of water is 1000 kg/m3.

(a) Explain, in terms of the molecules of air, why the pressure inside the diving bellincreases as it is being lowered.

....

....

...

....[2]

(b) Determine the pressure in the diving bell when the diving bell is filled with 1 m ofwater.

pressure = [2]

(c) Calculate the volume of the diving bell when it is under water. State the formulathat you use in your calculation.

volume = [2]

1m

Fig. 3.1

atmospheric pressure(100 000 Pa)


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4 Fig. 4.1 shows two incident rays of light on the top facets of a diamond and a glassrespectively.

Diamond has a refractive index of 2.4 and glass has a refractive index of 1.5.

(a) Determine the critical angle for diamond.

critical angle of diamond = [2]

(b) Given that the critical angle of glass is 41.8, complete the path of light ray in eachof the materials shown in Fig. 4.1 as they leave the facets, explain which material,diamond or glass, gives more glitter.

.................................................................................................................................

......

.................................................................................................................................

......

...

..[3]

(c) Determine the speed of light in the diamond.

speed = [2]

Fig. 4.1

top facets

bottom facets


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6

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5 The spraying of pesticides with crop sprayers makes use of electrostatic principles. Aspray gun charges the tiny droplets of pesticide as they leave the nozzle as shown inFig. 5.1.

(a) In terms of electron transfer, explain how does the spray gun make the dropletsof pesticides positively charged?

.................................................................................................................................

.................................................................................................................................

..[2]

(b) Explain why the droplets of pesticides must be charged for this task.

.................................................................................................................................

.................................................................................................................................

..[2]

(c) Small amount of electric charges can move about in the plants. What type ofcharges will be attracted to the surface of the leaves by the positively chargeddrops? Show the distribution of charges in Fig. 5.2.

Type of charges attracted to the surface: [2]

leaf

Fig. 5.2

+

+

+

spray guns

Fig. 5.1Fig. 5.1


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7

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Use6 Fig. 6.1 shows a cell of e.m.f. 12.0 V is connected in series with a 250 resistor and

a thermistor. The graph on the right shows how the current reading on the ammeter ofthe thermistor varies with temperature.

(a) State the current reading at the lower fixed point and the upper fixed point.

current reading at lower fixed point =

current reading at upper fixed point= . [1]

(b) Determine the resistance of the thermistor at 80 C.

resistance = [2]

(c) Explain how the voltmeter reading will change as the temperature drops from

100 C to 0 C.

..

..

..

.....[2]

Fig. 6.1

current/ mA

temperature /C0 20 40 60 80 1000.00

0.20

0.40

0.60

0.80

1.00


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7 Double insulation and earth wires protect the user of the electrical appliance. Circuitbreakers and fuses are safety features installed in our homes to protect the electricalappliance.

(a) Explain how the double insulation protects the user of electrical appliance.

...

...

...

..........[2]

(b) Fig. 7.1 shows the inside of a circuit breaker under normal conditions.

Using Fig. 7.1, explain what happens when there is a sudden surge in current.

...

...

...

...

..........[2]


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8 A student sets up a simple apparatus to study the current flowing from terminal X toY through a solenoid as shown in Fig. 8.1.

(a) The student claims that this apparatus can be used to measure magnitude of direct

current when it is connected across XY. Explain how this works.

.

.

.

.

....[3]

(b) Suggest 2 ways to increase the sensitivity of this set up.

1 ....

2 .....[2]

(c) Another student connects a centre-zero galvanometer across XY. He then uses aspring and sets magnet vibrating up and down vertically. Describe and explainwhat is likely to be observed on the galvanometer.

...

...

...

...

..[3]

scale

Fig. 8.1

S

N

pivot

pointer

X

Y


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10Section C (30 marks)

Answer all the questions in from this section. Question 11 has a choice of parts to answer.

For

Examiner

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9 Fig. 9.1 shows a thermocouple thermometer. Junction A of the thermocouple is inmelting ice.

(a) Suggest suitable metals for the wire P and wire Q.

wire P = wire Q = .... [1]

(b) What would be the millivoltmeter reading when junction B is placed in anotherbeaker containing melting ice? Give a reason for your answer.

...

...

...

..[2]

(c) When junction B is placed in steam of a boiling water, the millivoltmeter readingreads 25 mV. What is the temperature of the junction B when the millivoltmeterreads 7.5 mV?

temperature =............[2]

(d) State two key advantages of using thermocouple thermometer.

...

...

...

..[2]

Fig. 9.1

beaker ofmelting ice

wire Q wire P

junction A

junction B


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11

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Examiners

Use(e) A heater which supplies thermal energy of 1.2 kJ every second is completely

immersed in the beaker of melting ice at 0 C. The beaker contains 150 g of iceand 250 g of water.

Calculate the amount of time required to raise the temperature of the beaker

and its content to room temperature of 30 C.

You may make use of the following information:

Specific heat capacity of water is 4 200 J/(kgC)

Specific heat capacity of ice is 2 100 J/(kgC)

Heat capacity of beaker is 67 J/C

Specific latent heat fusion of water is 3.36 x 105 J/kg

Specific latent heat vaporisation of water is 2.26 x 106 J/kg

time taken =[3]


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12For

Examiner

Use10 During the construction of a tunnel for MRT, an engineer faces the challenge of theneed to locate the position of possible hard rocks in water.

In water

He employs echolocation method where a pulse of ultrasound from the ship is

reflected by the hard rock as shown in Fig. 10.1.

(a) What is meant by ultrasound?

...

...[1]

(b) Describe how the vibrations of the emitter produces waves of ultrasound andsuggest how these waves are subsequently detected by the sensor.

...

...

...

...

...

...

..[3]

hard rock

ultrasound emitter and sensor

water surface

Fig. 10.1


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(c) The wavelength of the ultrasound is 0.03 m and its speed in water is 1 500 m/s.Calculate the frequency of this ultrasound.

frequency = [2]

(d) Fig. 10.3 shows the trace on the screen of a cathode ray oscilloscope (c.r.o.)of the transmitted and the reflected pulse. The time base setting on the c.r.o. is20 ms/cm.

Determine the depth of the hard rock in water.

depth = [2]

(e) Describe one other application of the ultrasound.

.

.....

...

...

..[2]

1cm

Fig. 10.3


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14For

Examiner

Use11EITHER

Lasik (laser-assisted in situ keratomileusis) has become a popular refractive surgery forcorrecting myopia commonly known as short-sightedness for many teenagers and youngadults. Many patients choose Lasik as an alternative to wearing corrective eyeglasses or

contact lenses.

The surgery involves the use of laser (light amplification by stimulated emission ofradiation) to permanently remove some of the corneal tissue and thereby changing theshape of the cornea. The technology has advanced such that now it requires less time forthe patient's recovery, and the patient feels less pain overall.

Fig. 11.1 shows the information about the wavelength and the output power of some typesof laser.

The visible spectrum has wavelengths ranging from 4.0 x 10-7 m to 7.0 x 10-7 m.

(a) Which laser emits ultraviolet radiation?

....[1]

(b) Describe the medical uses of ultraviolet radiation.

.

........

.

........

.......[2]

(c) Calculate the frequency of light from the HeNe laser. State clearly any constantused.

frequency = [2]

types of laser wavelength /m output power /WExcimer 1.93 x 10-7 20.0Argon 4.98 x 10-7 2.0

Krypton 5.68 x 10-7 0.5HeNe 6.33 x x 10-7 0.005Yag 10.6 x 10-7 50.0

Fig. 11.1


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(d) During a lasik treatment, light from the Excimer laser is used to treat a patients eye.This laser fires 15 short pusles of light. Each pulse lasts 0.5s.

Calculate the energy given out by the laser during the treatment.

energy = [2]

(e) Despite this advancement in technology, not all short-sighted patients can undergolasik treatment. They still need to rely on the traditional diverging lens to help them tosee far objects. Fig. 11.2a shows the condition of short-sightedness where the imageformed is in front of the retina.

On Fig. 11.2b, complete the light path to show how the use of a diverging lens can helpto allow a distant object to get focus on the retina. Explain how the diverging lensachieve this.

..

.............

..

.............

............[2]

(f) Describe the image formed on the retina.

............[1]

converginglens

retina

Fig. 11.2a

diverging

lens

Fig. 11.2b


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ORFig. 11.3a shows a newspaper cutting from Straits Time on 15 Jul 2009 of a newlyinstalled off-shore wind farm. The world has seen a rise in the number of off-shore windfarms as the wind is more reliable at sea.

Fig. 11.3b shows a simple setup to illustrate how wind power can be used to generate

electricity.

(a) Explain the term 5 MW.

.........

....[1]

(b) Explain the term how the electricity can be generated when the blades turn.

..

.........

..

.....[2]

Following a one-year delay, the 5-MW turbine was

installed 45 kilometres north of the island of Borkum,Germany. -- PHOTO: AFP

Wind farm gets 5-MW turbine

Fig. 11.3a Fig. 11.3b


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(c) State the purpose of the iron rod.

.........

.......[1]

(d) State one advantage of a rotating magnet over a rotating coil generator.

.........

.......[1]

(e) A transformer is used to step up the voltage from 50 kV to 300 kV.

(i) Determine the turn ratio for this transformer.

turn ratio=..[2]

(ii) Assuming that this transformer is 100% efficient, calculate the current in thesecondary coil.

current=..[2]

(iii) In practice, the transformer is hardly 100% efficient. Suggest a possible reasonfor this.

.......[1]

2 section a answer all the questions in this section

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