jc2 preliminary examinations h2 physics 9749 ......h2 physics 9749 paper 1 23 sep 2020 1 hour...

River Valley High School Pg 1 of 19 H2 Physics 9749

JC 2 Preliminary Examinations 2020

RIVER VALLEY HIGH SCHOOLJC2 PRELIMINARY EXAMINATIONS

H2 PHYSICS 9749 PAPER 1

23 SEP 2020

1 HOUR

CANDIDATE NAME CENTRE NUMBER S

INDEX NUMBER

CLASS 1 9 J INSTRUCTIONS TO CANDIDATES DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO. Read these notes carefully. Write your name, class and index number above. There are thirty questions in this section. Answer all questions. For each question, there are four possible answers, A, B, C and D. Choose the one you consider correct and shade your choice in soft pencil on the separate Optical Answer Sheet. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done on the Question Paper. The use of an approved scientific calculator is expected where appropriate. Hand in the Optical Answer Sheet. _________________________________________________________________________

This document consists of 19 printed pages.



Data speed of light in free space, c = 3.00 108 m s–1

permeability of free space, O = 4 10–7 H m–1

permittivity of free space, O = 8.85 10–12 F m–1

(1/(36 )) 10–9 F m–1

elementary charge, e = 1.60 10–19 C

the Planck constant, h = 6.63 10–34 J s

unified atomic mass constant, u = 1.66 10–27 kg

rest mass of electron, me = 9.11 10–31 kg

rest mass of proton, mp = 1.67 10–27 kg

molar gas constant, R = 8.31 J K–1 mol–1

the Avogadro constant, NA = 6.02 1023 mol–1

the Boltzmann constant, k = 1.38 10–23 J K–1

gravitational constant, G = 6.67 10–11 N m2 kg–2

acceleration of free fall, g = 9.81 m s–2



Formulae

uniformly accelerated motion 212

s ut at

2 2 2v u as

work done on/by a gas W p V hydrostatic pressure p gh gravitational potential rGm temperature T / K = T / C + 273.15

pressure of an ideal gas 231 c

VNmp

mean translational kinetic energy of an ideal gas molecule 32

E kT displacement of particle in s.h.m. txx sin0 velocity of particle in s.h.m. tvv cos0

22

0 xx

electric current AnvqΙ resistors in series 1 2R R R resistors in parallel 1 21/ 1/ 1/R R R

electric potential rQV

04

alternating current/voltage txx sin0

magnetic flux density due to a long straight wire d

B2

0I

magnetic flux density due to a flat circular coil rN

B20 I

magnetic flux density due to a long solenoid InB 0 radioactive decay )exp(0 txx

decay constant 21

2lnt



For each question, there are four possible answers, A, B, C and D. Choose the one you consider correct and shade your choice in soft pencil on the separate Answer Sheet. 1 Which of the following series of units have the prefixes in descending order of power?

A terahertz, kilohertz, gigahertz

B picometre, micrometre, centimetre

C megawatt, microwatt, milliwatt

D centiseconds, milliseconds, nanoseconds 2 The following are graphs of various quantities plotted against time for an object dropped

from a stationary balloon high in the atmosphere. Which of the following statements most accurately describes the graphs?

A Graph 1 is acceleration against time and graph 3 is resultant force against time.

B Graph 1 is acceleration against time and graph 4 is resultant force against time.

C Graph 3 is acceleration against time and graph 1 is velocity against time.

D Graph 3 is acceleration against time and graph 2 is velocity against time.



3 Object A moving with an initial velocity u has a head-on elastic collision with a stationary object B. After the collision, the velocity of object A is v and that of the object B is w. Taking the masses of the object A and object B to be equal, which one of the following statements is wrong?

A Object A and object B have equal kinetic energy after the collision since the collision is elastic.

B Kinetic energy of object A before the collision is the same as the kinetic energy of object B after the collision.

C u2 = v2 + w2

D u = v + w 4 A lorry carries 2000 kg of sand and moves with constant acceleration in a straight line.

The sand is slowly flowing out of the bottom of the lorry while the lorry is in motion. Which of the graphs below best represents the variation of its momentum p with time t?

A

B

C

D

t

p

0

p

t 0

p

0 t

0

p

t



5 A simplified diagram below represents the trunk of a person bent forward, with the spine at an angle of 70o to the vertical. The back muscle exerts a tension T and makes an angle of 8.0o to the spine. The weight of the person’s trunk which is 400 N, acts at the point along the spine where the back muscle is attached. What is the tension T in the back muscle?

A 140 N B 380 N

C 980 N D 2700 N 6 A measuring cylinder contains an ice cube of volume 1.00 cm3 floating on sea water.

density of ice = 0.920 g cm3 density of water = 1.00 g cm3 density of sea water = 1.03 g cm3 Ignoring evaporation, which of the following best describes the change in volume of the liquid in the measuring cylinder when the ice cube has completely melted?

A no change B increase by 0.03 cm3

C decrease by 0.03 cm3 D increase by 0.08 cm3

weight of trunk: 400N

tension T

pivot at hip joint

70o

8.0o



7 The diagram shows a lift system in which the elevator (mass m1) is partly counterbalanced by a heavy weight (mass m2).

At what rate does the motor provide energy to the system when the elevator is rising at a steady speed v? ( g = acceleration of free fall )

A 1

2m1v

2

B 1

2m1 m2 v 2

C m1gv

D m1 m2 gv



8 A model aeroplane X has a mass of 0.50 kg and has a control wire OX of length 10 m attached to it when it flies in a horizontal circle with its wing horizontal. The wire OX is at an angle of to the vertical and fixed to a point O as shown in the diagram below.

Aeroplane X takes 2.0 s to fly once round its circular path. What is the tension T in the control wire?

A 25 N B 49 N

C 99 N D 200 N 9 The distance between star P and star Q is 400 times that between star Q and star R.

The gravitational pull of star P on star Q is 170 times that of star Q on star R. How many times is the mass of star P greater than that of star R?

A 6.8 104 B 7.4 105

C 1.2 107 D 2.7 107

O

T

10 m



10 Satellite A and B are orbiting around Sun and both satellites have the same kinetic energy. Satellite A has a larger mass than satellite B. Which of the following statements is false?

A Satellite A has a larger period.

B Satellite A has a larger orbital radius.

C Satellite A has a smaller total energy.

D Satellite A has a smaller angular velocity.

11 The two curves shown below connect points that have the same temperature for a fixed mass of an ideal gas. What is the ratio

r.m.s. speed of the molecules at temperature T2 r.m.s. speed of the molecules at temperature T1

?

A 1

B √2 C 2

D 4

V / m3

p / 105 Pa



12 The temperature of a hot liquid in a container of negligible heat capacity falls at a rate of 4.0 K per minute just before it begins to solidify. The temperature then remains steady for 25 minutes by which the liquid has all solidified. What is the value of the ratio

specific heat capacity of liquid specific latent heat of fusion ?

A 0.01

B 0.04

C 25

D 100

13 One mole of an ideal monatomic gas is confined in a cylinder fitted with a frictionless

piston. When 90 J of heat are supplied and the gas is allowed to expand at constant pressure, the temperature rises by 4.5 K. What heat input would be required to raise the temperature of the same amount of gas by the same amount at constant volume?

A 90 J

B 56 J

C 34 J

D 18 J



14 The graph below shows the variation with time of the velocity of a 5.0 kg oscillating mass.

What is the maximum restoring force acting on the mass as it oscillates?

A 0.041 N B 0.050 N

C 0.079 N D 0.15 N 15 An object mass m oscillates in simple harmonic motion between two spring as shown

below. The amplitude of the motion is xo.

What is the ratio elastic potential energy of the two springs

kinetic energy of mass when the mass is

xo2

from

its equilibrium?

A 1

3 B 1

2

C 1 D 3



16 A plane-polarised light of intensity I is incident normally on the face of a Polaroid P whose polarising plane is θ with respect to the plane-polarised light.

If the intensity of light emerging from P is

12

I, what could be the value of θ?

A 60o B 180o

C 225o D 270o 17 The diagram represents the pattern of stationary waves formed by the superposition of

sound waves from a loudspeaker and their reflection from a metal sheet (not shown). W, X, Y, Z are four points on the line through the centre of these waves. Which statement about these stationary waves is correct?

A The kinetic energies of the particles at W and Z are the greatest.

B A node is a quarter of a wavelength from an adjacent antinode.

C The oscillations at X are in phase with those at Y.

D The air particles oscillate perpendicular to the line WZ.

I



18 Monochromatic light is incident on a pair of narrow slits a distance of 0.10 mm apart. A series of bright and dark fringes are observed on a screen a distance of 2.0 m away. The distance between adjacent bright fringes is 8.0 mm. What is the path difference between the light waves from the two slits that meet at the second order dark fringe?

A 2.0 107 m

B 4.0 107 m

C 6.0 107 m

D 8.0 107 m

19 X and Y are two identical conducting spheres separated by a distance d. X has a charge +6 μC and Y has a charge –2 μC. The electric force between them is F (i.e. attractive). The spheres are touched together and are then returned to their original separation d. The force between them now is nearest to

A F B F

C

3F

D 3F



20 The figure below shows two electrons P and Q, moving between two parallel charged plates with different velocities VP and VQ respectively. If VP is greater than VQ, which of the following correctly compares the potential energies and accelerations of P and Q?

potential energy acceleration

A greater for P equal for both

B greater for P greater for Q

C greater for Q equal for both

D greater for Q greater for P

21 In the diagram of an oscilloscope shown below, the shaded area represents a section through the electron beam which is generated near P, deflected and accelerated at Q and focused at R. The tube contains no gas.

Which of the following statements about the current along PQR is true?

A It has the same value at P, Q and R.

B It decreases from P to Q but becomes very large at point R.

C It decreases between P and Q, then increases to reach the same value at R as at P.

D It increases between P and Q, then decreases to reach the same value at R as at P.

RP Q



22 Two cells are connected to two load resistors of resistance 3.0 Ω. The electromotive

force (e.m.f.) and the internal resistance of each of the cells is shown.

What is the potential difference across the load resistors?

A 3.4 V

B 3.6 V

C 3.9 V

D 7.7 V



23 In the circuit below, P is a potentiometer of total resistance 10 Ω and Q is a fixed resistor of resistance of 20 Ω. The battery has an e.m.f. of 6.0 V and negligible internal resistance. The voltmeter has a very high resistance. The slider on the potentiometer is moved from X to Y and a graph of voltmeter reading V is plotted against slider position.

Which graph is obtained?

A B

C D

6.0 V

2

6

slider position X Y

V

0

4

6

slider position X Y

V

0

4

6

slider position X Y

V

0

2

6

slider position X Y

V

0



24 The figure below shows case X and Y in which a charged particle moves in a helical path through a uniform magnetic field B.

Which of the following statements is correct?

A Only the charged particle in case X is negatively charged.

B Only the charged particle in case Y is negatively charged.

C Both charged particles in case X and Y are positively charged.

D Both charged particles in case X and Y are negatively charged. 25 The diagram shows a mass spectrometer in which singly-charged positive ions of mass

1.93 1025 kg pass through slits S1, S2 and S3 before entering the main chamber. Between S2 and S3, the ions pass through a velocity selector in which an electric field of intensity 20 kV m−1 and a magnetic field of flux density 0.25 T are applied. The selected ions are deflected by a uniform magnetic field of flux density 0.40 T, within the main chamber and arrive at the point P.

What is the distance between P and slit S3?

A 0.24 m B 0.39 m

C 0.48 m D 0.77 m

case X case Y



26 An electromagnet produces a uniform field from left to right in the gap between its poles. The gap has sides 0.050 m 0.080 m and there is no field outside the gap. A circular coil of radius 0.100 m, has 40 turns and it surrounds all of the magnetic flux as shown below.

The ends of the coil are connected together so that an induced e.m.f. in the coil produces a current in the coil. The magnetic flux density of the electromagnet fall linearly from 0.15 T to zero in a time of 3.0 s. What is the average induced e.m.f. in the coil as the magnetic flux density decreases?

A 0.20 mV B 8.0 mV

C 50 mV D 63 mV 27 In the figure below, the switch K is used to close the circuit of solenoid X.

Which of the following statements is correct?

A Coil Y is repelled by X.

B There is no current flow along QR.

C No flux change occurs in coil Y.

D A momentary current flows from the straight wire segment R to Q.

X Y

Q RK



28 A lamp is rated at 60 W for a 240 V a.c. power supply. The lamp is connected to the power supply. What is the peak current through the lamp?

A 0.25 A B 0.35 A

C 4.0 A D 5.7 A 29 The energy level diagram below shows the three lowest energy levels in the magnesium

atom.

What is the wavelength of the radiation that is produced when the energy level of the atom falls from the E3 level to the E1 level.

A 0.954 nm B 0.992 nm

C 1.02 nm D 31.9 nm 30 The intensity of a beam of monochromatic light is halved while the number of photons

released per unit time is the same. Which one of the following represents the corresponding change if any in the momentum of each photon of the radiation?

A halved

B one quarter of original

C the same

D doubled

END OF PAPER

E / eV 0

49.7

88.7

1303 E1

E2

E3

River Valley High School Page 1 of 24 H2 Physics 9749JC 2 Preliminary Examinations 2020

RIVER VALLEY HIGH SCHOOLJC 2 PRELIMINARY EXAMINATIONS

H2 PHYSICS 9749 / 2 PAPER 2

14 SEPTEMBER 2020

2 HOURS


INDEX NUMBER

CLASS 1 9 J INSTRUCTIONS TO CANDIDATES DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO. Read these notes carefully. Write your name, centre number, index number and class in the spaces at the top of this page and on all work you hand in. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected whereappropriate. Candidates answer on the Question Paper. No Additional Materials are required. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question.

FOR EXAMINERS’ USE Paper 2

1 / 72 / 123 / 94 / 105 / 126 / 107 / 20

Deduction

Paper 2 / 80

This document consists of 24 printed pages.



permeability of free space, 0 = 4 10–7 H m–1

permittivity of free space, 0 = 8.85 10–12 F m–1

= (1/(36 )) 10–9 F m–1












Formulae uniformly accelerated motion 221 atuts

2 2 2v u as

work done on / by a gas W p V hydrostatic pressure p gh gravitational potential = GM / r temperature T / K = T / C + 273.15


VNmp

mean translational kinetic energy of an ideal gas molecule kTE23

displacement of particle in s.h.m., x = x0 sin t velocity of particle in s.h.m., v = v0 cos t = )( 220 xx electric current, I = Anvq resistors in series, 1 2R R R resistors in parallel, 1 21/ 1/ 1/R R R

electric potential, rQV

04

alternating current/voltage, x = x0 sin t

magnetic flux density due to a long straight wire, d

B2

0 I

magnetic flux density due to a flat circular coil, rNB

20 I

magnetic flux density due to a long solenoid, InB 0

radioactive decay, x = x0 exp (t) decay constant,

21

2lnt


Answer all the questions in the space provided

1 (a) State two conditions under which the following equation can be used to determine the displacement of an object in motion.

s =12 at

2

1. ..…………………………………………………..............……………………….. ..…………………………………………………..............……………………………… 2. ..…………………………………………………..............……………………….. ..…………………………………………………..............……………………….. [2]

(b) A ball is thrown with an initial velocity v at angle to the horizontal, as shown in

Fig. 1.1.

Fig. 1.1

The variation with time t of the height h of the ball is shown in Fig. 1.2.

Fig. 1.2


(i) Sketch the vertical component of the velocity of the ball with respect to time in Fig. 1.3.

Fig. 1.3 [2]

(ii) Hence, by using (b)(i), find the initial vertical velocity of the ball.

vertical velocity = ................................m s1 [1]

(iii) Air resistance acting on the ball is actually not negligible. State and explain

the effect of air resistance on the time taken for the ball to reach maximum height.

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

……………………………………………………………………………….. [2]

v / m s1

t / s


2 (a) A force F acting on an object moving in the straight line. Derive the expression

P Fv where P is the power delivered to the object and v is the velocity of the object.

[1]

(b) A car of mass 1500 kg can generate a constant power of 52.0 10 W to the

wheels. The resistive forces can be taken to be constant at 5000 N at all speeds.

(i) The car travels on along a horizontal surface ground. Calculate the maximum speed the car can attain.

maximum speed = ........................... m s1 [2]

(ii) The car travels up a 10 slope.

Determine the new maximum speed the car can attain.

maximum speed = ........................... m s1 [3]


(iii) Describe the energy conversion when the car is driven at its maximum speed when it is going up a slope.

……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………… [2] (c) The car is driven over the top of a hill, the cross-section of which can be

approximated by a circle of radius R = 250 m as shown in Fig. 2.1.

Fig. 2.1

Determine the maximum speed the car can be driven without losing contact with the road at the top of the hill.

maximum speed = ........................... m s1 [4]

R


3 (a) Star P of mass M and star Q of mass m follow circular orbits of radii r and R respectively, centred on their common centre of mass O as shown in Fig. 3.1.

not drawn to scale

Fig. 3.1

(i) Write down an expression for the gravitation force experienced by each star in terms of M, m, r and R.

[1] (ii) Using Fig. 3.1, explain why M is of a bigger mass compared to m. ……………………………………………………………………………………... …………………………………………………………………………………….... ……………………………………………………………………………… [2]

P Q O r

R


(iii) Write down the expressions for the centripetal acceleration experienced by star P and star Q in terms of M, m, r and R. Show your working clearly.

[2] (iv) The period of rotation of star P is equal to the period of rotation of star Q.

By considering the circular motion of each star about their common centre of mass, show that the period T of rotation of the stars is given by

= 4π2(R + r)3

G(M + m)

[2] (b) A rocket is currently travelling at 830 km/h at O.

Calculate the minimum speed for the rocket to escape completely from star P and star Q’s gravitational field. Additional information given: m = 1.50 × 1023 kg M = 4.50 × 1023 kg R = 1.2 × 106 km r = 4.0 × 105 km

minimum speed = ........................... m s1 [2]

T


4 (a) State what is meant by stationary waves.

..…………………………………………………..............………………….........……..

..…………………………………………………..............………………………...........

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

(b) A loudspeaker producing sound of constant frequency is placed near the open

end of the pipe, as seen in Fig. 4.1.

Fig. 4.1

A movable piston is at a distance x from the open end of the pipe. Distance x is increased from x = 0 by moving the piston to the left with a constant speed of 0.75 cm s1. The speed of the sound in the pipe is 330 m s1.

(i) Explain how a stationary wave can be formed in the pipe.

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

……………………………………………………………………………….. [2]

(ii) A much louder sound is first heard when x = 6.0 cm. Determine the

frequency of the sound in the pipe.

frequency = ................................ Hz [3]


(iii) After a time interval, a second much louder sound is heard. Calculate the time interval between the first and second louder sound.

time = ................................ s [2]

(iv) The actual time interval measured is different from that calculated in (b)(iii), despite no experimental errors. Suggest why this is so.

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

……………………………………………………………………………….. [1]


5 (a) A power supply of electromotive force (e.m.f.) 8.7 V and negligible internal resistance is connected by two identical connecting wires to three filament lamps, as shown in Fig. 5.1.

Fig. 5.1

The power supply provides a current of 0.30 A to the circuit. The filament lamps are identical. The I-V characteristic for one of the lamps is shown in Fig. 5.2.

Fig. 5.2


(i) State and explain the I-V characteristic of the filament lamp.

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

……………………………………………………………………………….. [3] (ii) Determine the resistance of each connecting wire.

resistance = ................................

[2]

(iii) The resistivity of the metal of the connecting wires does not vary with

temperature. On Fig. 5.2, sketch the I-V characteristic for one of the connecting wires.

[1]


(b) The potentiometer shown in Fig. 5.3 is used to measure the e.m.f. and internal resistance of battery E2. The wire AB is 80.0 cm long and has a resistance of 15.0 Ω. E1 is a driver cell of 3.0 V with an internal resistance of 0.50 Ω. R1 and R2 have resistance of 20.0 Ω and 5.0 Ω respectively.

Fig. 5.3 When the switches S1 and S2 are both open, the galvanometer has zero deflection when AJ is 63.1 cm in length. When both switches are closed, the balanced length is 12.5 cm.

(i) Show that the e.m.f. of E2 is 1.00 V.

[3]

R1

R2

E1 = 2.0 V

E2

S2

S1

A B J

E1


(ii) Hence, or otherwise, determine the internal resistance of E2.

resistance = ................................ Ω [3]


6 (a) An alternating current generator has a coil of area 0.090 m2 and consists of 8 turns of wire. This coil rotates in a uniform magnetic field at a constant rate. The variation with time of the induced e.m.f. in the coil is shown in Fig. 6.1.

Fig. 6.1

(i) State Faraday’s Law of electromagnetic induction.

……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………… [1] (ii) Use Fig. 6.1 to estimate the maximum magnetic flux linkage through the

coil. Explain your working.

maximum magnetic flux linkage= ........................... Wb [2]

induced e.m.f. / V

-30.00

-20.00

-10.00

0.00

10.00

20.00

30.00

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14time / s


(b) (i) Use your answer in (a)(ii) to determine the magnetic flux density of the magnetic field.

magnetic flux density = ........................... T [2]

(ii) Calculate the angular frequency of the rotation.

angular frequency = ........................... rad s1 [1]

(c) The angular frequency of the rotation can be varied.

In Fig. 6.2, sketch the variation with angular frequency of the maximum induced e.m.f.

Fig. 6.2 [1]

maximum induced e.m.f.

angular frequency


(d) The coil in (a) is connected to a pair of slip-rings which produces an alternating current at the output terminal. The circuit is closed with a resistor of resistance 12 . Ignore the resistance of the coil in the generator.

(i) Calculate the root-mean-square current through the resistor.

root-mean-square current = ........................... A [2]

(ii) Determine the mean power output of the resistor.

mean power output= ........................... W [1]


7 Photomultiplier tubes Photomultiplier tubes (PMTs) are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. These detectors multiply the current produced by incident light by as much as 100 million times, in multiple dynode stages, enabling individual photons to be detected when the incident amount of light is low. Fig. 7.1 shows a schematic diagram of a PMT.

Fig. 7.1 Principle of operation of a PMT Photomultipliers are typically constructed with an evacuated glass housing (using an extremely tight and durable glass-to-metal seal like other vacuum tubes), containing a photocathode, several dynodes, and an anode. Incident photons strike the photocathode material, which is usually a thin vapor-deposited conducting layer on the inside of the entry window of the device. Electrons are ejected from the surface as a consequence of the photoelectric effect. These electrons are directed by the focusing electrode toward the electron multiplier, where electrons are multiplied by the process of secondary emission. The PMT consists of a number of electrodes called dynodes. Each dynode is held at a more positive potential, by approximately 100 volt, than the preceding one. A primary electron leaves the photocathode with the energy of the incoming photon, or about 3 eV for "blue" photons, minus the work function of the photocathode. A small group of primary electrons is created by the arrival of a group of initial photons. The primary electrons move toward the first dynode because they are accelerated by the electric field. They each arrive with approximately 100 eV kinetic energy imparted by the potential difference. Upon striking the first dynode, more low energy electrons are emitted, and these electrons are in turn accelerated toward the second dynode. The geometry of the dynode chain is such that a cascade occurs with an exponentially-increasing number of electrons being produced at each stage. This last stage is called the anode. This large number of electrons reaching the anode results in a sharp current pulse that is easily detectable, signaling the arrival of the photon(s) at the photocathode approximately 50 nanoseconds earlier.


The detected current depends on two factors: the number of electrons ejected from the photocathode (which in turn depends on the number of incoming photons and on their energy), and the Quantum Efficiency η of the photomultiplier. The Quantum Efficiency is defined as the number of electrons collected at the anode per unit time relative to the number of incident photons per unit time on the photocathode expressed as a percentage. Fig. 7.2 shows the graph of photocathode responsivity R versus wavelength of incident light and some of Quantum Efficiency (QE) lines of a metal used as photocathode in the PMT. The intersections of the graph and the QE lines show the Quantum Efficiencies at various wavelengths. For example, when the graph and the QE lines intersect at M as shown in Fig. 7.2, it means that the number of electrons collected at the anode per unit time is 10% of the total number of incident photons per unit time when a light of 510 nm is incident on the photocathode.

Fig 7.2

M


(a) (i) Explain what is meant by the term photoelectric effect. …………………………………………………………………………………….... ……………………………………………………………………………… [1] (ii) State the wavelength that allows the photocathode to achieve its optimum

responsivity.

wavelength = ........................... nm [1] (iii) With reference to Fig. 7.2, explain how the threshold frequency of

photocathode material can be determined. ……………………………………………………………………………………... …………………………………………………………………………………….... ……………………………………………………………………………… [2] (iv) The photocathode has a threshold frequency of 4.76 1014 Hz.

If a photomultiplier detects radiation of 450 nm, calculate the maximum speed of the photoelectron emitted from the photocathode.

maximum speed = ........................... m s1 [3] (v) Explain clearly why the photocathode used in a photomultiplier should

preferably be one with a low work function. ……………………………………………………………………………………... …………………………………………………………………………………….... ……………………………………………………………………………… [1]


(b) Light of wavelength 610 nm is now incident on the PMT.

(i) Given that the detected current from the PMT is 7.8 104 A, calculate the number of electrons per unit time reaching the anode.

number of electrons per unit time = ........................... s1 [2] (ii) Hence, using Fig. 7.2, calculate the number of incident photons per unit time

on the photocathode.

number of incident photons per unit time = ........................... s1 [1] (iii) From Fig. 7.2, the photocathode responsivity of the PMT can be estimated

to be 4.8 mA/W. Use your understanding of current and power, suggest the meaning of 4.8 mA/W.

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


(c) (i) The relationship between Responsivity R and Quantum Efficiency η is stated as

η Rhceλ

where λ is the wavelength of the incident light, e is the charge of an electron. Using Fig. 7.2, show that for the photocathode used in the PMT, this relationship is true when η is 5 %.

[1] (ii) Using the equation given in (c)(i), complete Fig. 7.3.

η / % λ / nm R / mA W1

3 300

3 400

3 500 12

3 600

3 700 17

Fig. 7.3

[3] (iii) Hence, plot the line η = 3 % on Fig. 7.2. [2]


(d) (i) Photomultipliers are usually shielded by a layer of soft iron at cathode potential. The external shield must also be electrically insulated. Suggest why photomultipliers are magnetically shielded and electrically insulated.

…………………………………………………………………………………….... ……………………………………………………………………………… [1] (ii) Suggest a possible application of photomultiplier that can be used in the

industry. …………………………………………………………………………………….... ……………………………………………………………………………… [1]

END OF PAPER


RIVER VALLEY HIGH SCHOOLJC 2 PRELIMINARY EXAMINATIONS

H2 PHYSICS 9749 / 3 PAPER 3

17 SEPTEMBER 2020

2 HOURS


INDEX NUMBER

CLASS 1 9 J INSTRUCTIONS TO CANDIDATES DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO.

FOR EXAMINERS’ USE

Section A – do all questions

1 / 5 2 / 8 3 / 7 4 / 7 5 / 7 6 / 8 7 / 9 8 / 4 9 / 5

Section B – do ONE question only 10 / 20 11 / 20

Deduction

TOTAL / 80

Read these notes carefully. Write your name, centre number, index number and class in the spaces at the top of this page and on all work you hand in. Candidates answer on the Question Paper. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all questions. Section B Answer one question only. You are advised to spend one and half hours on Section A and half an hour on Section B. The number of marks is given in brackets [ ] at the end of each question or part question.

This document consists of 27 printed pages and 1 blank page.



permeability of free space, 0 = 4 10–7 H m–1

permittivity of free space, 0 = 8.85 10–12 F m–1

= (1/(36 )) 10–9 F m–1












Formulae uniformly accelerated motion 221 atuts

2 2 2v u as

work done on / by a gas W p V hydrostatic pressure p gh gravitational potential = GM / r temperature T / K = T / C + 273.15


VNmp

mean translational kinetic energy of an ideal gas molecule kTE23

displacement of particle in s.h.m., x = x0 sin t velocity of particle in s.h.m., v = v0 cos t = )( 220 xx electric current, I = Anvq resistors in series, 1 2R R R resistors in parallel, 1 21 / 1 / 1 /R R R

electric potential, rQV

04

alternating current/voltage, x = x0 sin t

magnetic flux density due to a long straight wire, d

B2

0 I

magnetic flux density due to a flat circular coil, rNB

20 I

magnetic flux density due to a long solenoid, InB 0

radioactive decay, x = x0 exp (t) decay constant,

21

2lnt


Section A

Answer all the questions in the space provided

1 (a) The spring constant k of a spring may be determined by using the extension of the spring and load applied, using the apparatus shown in Fig. 1.1.

Fig. 1.1

Give one example each of a systematic error and one example of a random error

which could occur in this experiment.

..…………………………………………………..............………………………………

..…………………………………………………..............………………………………

..…………………………………………………..............………………………………

……………………………………………………………………………………… [2]

metre rule

load


(b) The work done by a force on a mass is to be calculated using the following formula.

W = Fscosθ The following measurements with their uncertainties are made. force applied F: (0.60 ± 0.01) N displacement s: (0.750 ± 0.001) m angle of force to horizontal θ: (30 ± 1) º

Determine the percentage uncertainty of the work done by the force.

percentage uncertainty = ................................ [3]


2 Mass X of 220 g and mass Y of 600 g are connected by an inelastic string that passes over a frictionless pulley as shown in Fig. 2.1. The system is released from rest. Mass X slides on the smooth tabletop and hits a vertical board that is attached to a spring that is firmly attached to a fixed triangular block.

Fig. 2.1

(a) In Fig. 2.2, draw the free-body diagrams of mass X and Y after they are released

from rest. Label the forces clearly.

Fig. 2.2

[2]

(b) (i) Show that the magnitude of the acceleration of mass X is 7.2 m s2 just before it hits the spring.

[2]

Y

X

Y

board

X


(ii) Calculate the tension in the string just before mass X hits the spring.

tension = ........................... N [1]

(iii) Calculate the resultant force on the two masses just before mass X hits the spring.

resultant force = ........................... N [1]

(c) A student calculates the speed of mass X and the board immediately just after the collision using the conservation of linear momentum since both objects move at the same speed at that instant. Explain whether you agree with the method used by the student.

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


3 Fig. 3.1 shows a picture frame hanging symmetrically by two cords by a nail fixed to a wall.

Fig. 3.1

(a) (i) State the conditions for the picture frame to be in equilibrium ………………………………………………………………………….................. ………………………………………………………………………….................. …………………………………………………………………………......... [1] (ii)

Sketch a vector triangle to represent the equilibrium of forces acting on the picture frame.

[2]

nail

cord

50º 50º


(b) The mass of the picture frame is 1.0 kg. Use your diagram in (a) to determine the tension in the cord.

tension = .............................. N [2]

(c) The cord breaks at a maximum tension of 10 N. Determine the minimum angle between the cord and the horizontal top of the picture frame.

angle = ................................ o [2]


4 A sound wave passes through some air particles. The vertical lines in Fig. 4.1 show positions of the air particles at an instant in time.

Fig. 4.1

The sound is then captured by a microphone connected to a cathode-ray oscilloscope (CRO). The time-base setting of the CRO is 2.0 ms per division. A portion of the image of the CRO is shown in Fig. 4.2.

Fig. 4.2

(a) (i) Determine the frequency of the sound.

frequency = ........................... Hz [1]

(ii) Take the speed of the sound to be 300 m s-1.

Determine the wavelength of the sound.

wavelength = ........................... m [1]

(b) (i) On Fig. 4.1, mark a region of wave which shows centre of compression with ‘C’ and a region of wave which shows centre of rarefaction with ‘R’.

[1]

(ii) Use your answer in (a)(ii) to determine the distance between C and R you have marked on Fig. 4.1.

distance between C and R = ........................... m [1]

P


(c) With reference to the frequency you have determined in (a)(i), describe the motion of the particle P labelled in Fig. 4.1.

……………………………………………………………………………….................... ……………………………………………………………………………….................... ……………………………………………………………………………….................... ………………………………………………………………………………........... [3]

5 A beam of red laser light is incident normally on a diffraction grating.

(a) Diffraction of the red laser light occurs at each slit of the grating. The light emerging from the slits are coherent.

Explain what is meant by the following terms with reference to the situation given:

(i) diffraction

..…………………………………………………..............………………………..

……………………………………………………………………………….. [1]

(ii) coherent

..…………………………………………………..............………………………..

……………………………………………………………………………….. [1]


(b) The wavelength of the laser light is 650 nm. The angle between the two third order diffraction maxima is 68, as illustrated in Fig. 5.1.

Fig. 5.1

(i) Determine the angle between the two second order maxima.

angle = ................................ [2]

(ii) Determine the maximum order that can be observed from.

order = ................................ [2]

(iii) The red laser light is replaced with blue laser light. State and explain the change, if any, to the angle between the third order diffraction maxima.

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

……………………………………………………………………………….. [1]


6 Fig. 6.1 shows how the electric potential V between two small spherical charged insulators C and D varies along the distance d joining their centres. The electric potential is a maximum at point P. The distance from point P to the centre of C and centre of D is x and y respectively. The distance between the two insulators is very large compared to the radii of the insulators.

Fig. 6.1

(a) Using Fig. 6.1, sketch the variation with distance d of potential V for charged

insulator D only. [1] (b) Using Fig. 6.1, state and explain the signs of the charge of insulators C and D.

…………………………………………………………………………………….............

…………………………………………………………………………………….............

……………………………………………………………………………………… [2] (c) Explain why the graph has a maximum at point P.

…………………………………………………………………………………….............

…………………………………………………………………………………….............

……………………………………………………………………………………… [2]

P

d / m

V / V

D C x

0 0

y


(d) By considering the electric field strength at P, determine the ratio

magnitude of charge of Cmagnitude of charge of D

in terms of x and y.

[3]


7 The setup in Fig. 7.1 shows the top view of a 12 V D.C supply connected in series with a metal rod PQ of mass 30 g and length 0.50 m.

Fig. 7.1 The rod has a resistance of 24 and lies in a region of a uniform magnetic field. The magnetic field strength B is 1.0 T and the direction of the field is perpendicular to and acts into the plane of the page. The two ends of the rod rest on the conducting rails and are free to move in the plane of the rails. The frictionless connecting rails are very long and have negligible electrical resistance. The rod is initially at rest.

Fig. 7.2 shows the side view of the setup. The conducting rails are inclined at an angle of 30o above the horizontal. The switch is closed and current is flowing in the conducting rail as shown in Fig. 7.2.

30o

rod I

B = 1.0 T

Q

Y

I Conducting rail

Fig. 7.2

12 V

rod

Q

Conducting rail

switch

P

Y

Z

Conducting rail

magnetic field acts vertically downwards

magnetic field acts into the plane

conducting rail

12 V

rod switch conducting rail

P Z

Q Y

top view

conducting rail

rod

I

I

Q

Y

B 30o


(a) On Fig. 7.2, draw the forces acting on the rod. Label the forces clearly. [1]

(b) Calculate the initial acceleration of the rod when the switch is closed, and state its

direction.

initial acceleration = ........................... m s2 direction of acceleration: ...................................................... [4]

(c) Using laws of electromagnetic induction, state and explain how the speed of the rod will vary as it moves along the slope.

…………………………………………………………………………………….............

…………………………………………………………………………………….............

…………………………………………………………………………………….............

…………………………………………………………………………………….............

…………………………………………………………………………………….............

…………………………………………………………………………………….............

…………………………………………………………………………………….............

……………………………………………………………………………………… [4]


8 Fig. 8.1 shows a magnet dropped from rest through A: a plastic pipe B: a copper pipe C: a solenoid tightly wound using insulated copper wire. An ammeter is connected to the solenoid in series. A, B and C have the same dimensions. A B C

Fig. 8.1

(a) List, from the fastest to the slowest, which pipe will the magnet fall through first. ____ , ____, _____

[1]

(b) There is a time difference the magnet takes to fall through B and C. Explain why this is so.

……………………………………………………………………………….................... ……………………………………………………………………………….................... ……………………………………………………………………………….................... ………………………………………………………………………………........... [3]

A


9 Fig. 9.1 shows a typical X-ray spectrum emitted when accelerated electrons hit a metal target.

Fig. 9.1

(a) Briefly explain the formation of the continuous spectrum.

…………………………………………………………………………………….............

…………………………………………………………………………………….............

…………………………………………………………………………………….............

……………………………………………………………………………………… [2] (b) Explain the formation of the Kβ line.

…………………………………………………………………………………….............

…………………………………………………………………………………….............

…………………………………………………………………………………….............

……………………………………………………………………………………… [2] (c) Suggest why the Kα line has a higher intensity than the Kβ line.

…………………………………………………………………………………….............

……………………………………………………………………………………… [1]

X-ray intensity

wavelength

Kα

Kβ


Section B

Answer one question from this Section in the spaces provided.

10 (a) (i) Clearly distinguish between temperature and heat.

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

……………………………………………………………………………….. [2]

(ii) Explain why a piece of metal at room temperature feels cool to the touch

while a piece of wood at room temperature does not.

..…………………………………………………..............………………………..

..…………………………………………………..............………………………..

……………………………………………………………………………….. [2]

(b) A student carries out an experiment to determine the specific latent heat of

vaporisation of a liquid. Some liquid in a beaker is heated electrically as shown in Fig. 10.1.

Fig. 10.1

Energy is supplied at a constant rate to the heater. When the liquid is boiling at a constant rate, the mass of liquid evaporated in 5.0 minutes is measured. The power of the heater is then changed and the procedure is repeated. Data for the two power ratings are given in Fig. 10.2.

power of heater / W

mass evaporated in 5.0 minutes / g

50.0 70.0

6.5 13.6

Fig. 10.2

to electrical circuit

heater

liquid


(i) Suggest

1. how it may be checked that the liquid is boiling at a constant rate,

..…………………………………………………..............………………………..

……………………………………………………………………………….. [1]

2. why the rate of evaporation is determined for two different power ratings.

..…………………………………………………..............………………………..

……………………………………………………………………………….. [1]

(ii) Calculate the specific latent heat of vaporisation of the liquid.

specific latent heat of vaporisation = ................................ J g1 [3]

(c) (i) State what is meant by an ideal gas.

..…………………………………………………..............………………………..

……………………………………………………………………………….. [1]

(ii) State what is meant by the internal energy of an ideal gas.

..…………………………………………………..............………………………..

……………………………………………………………………………….. [1]


(iii) Two thermally insulated vessels are connected by a narrow tube fitted with a valve that is initially closed. One vessel, of volume 16.8 103 cm3, contains an ideal gas at a temperature of 300 K and a pressure of 1.75 105 Pa. The other vessel, of volume 22.4 103 cm3, contains the same ideal gas at a temperature of 450 K and a pressure of 2.25 105 Pa. When the valve is opened, the gases in the two vessels mix, and the temperature and pressure become uniform throughout.

1. Show that the final temperature of the gases is 380 K.

[2] 2. Determine the final pressure of the gases.

pressure = ................................ Pa [2]


(d) A fixed mass of an ideal gas undergoes a cycle PQRP of changes as shown in Fig. 10.3.

Fig. 10.3

(i) State the change in internal energy of the gas during one complete cycle PQRP.

change in internal energy = ................................ J [1]

(ii) Calculate the work done on the gas during the change from P to Q.

work done = ................................ J [2]


(iii) Some energy changes during the cycle PQRP are shown in Fig. 10.4.

change work done on gas / J heating supplied

to gas / J increase in

internal energy / J

P Q

Q R

R P

………………

0

………………

600

720

480

………………

………………

………………

Fig. 10.4

Complete Fig. 10.4 to show all of the energy changes. [2]


11 Fig. 11.1a shows a U-tube of uniform cross-sectional area A containing liquid of density ρ. The total length of the liquid column is L. The liquid is displaced by distance x from the equilibrium level as shown in Fig. 11.1b.

Fig. 11.1a Fig. 11.1b

(a) (i) By considering the pressure difference between the two water levels, write down an expression for the restoring force in terms of A, ρ, x and g where g is the acceleration of free fall.

[1]

(ii) Hence show that the magnitude of acceleration a of the liquid column caused by this force is

a 2gxL

[2]

L

x equilibrium level

P


(iii) Use the expression in (a)(ii) to explain why point P on the liquid surface will move in a simple harmonic motion.

……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………… [3]

(iv) The length of the liquid column L is 40.0 cm. Determine the period of the oscillation T.

T = ........................... s [3]

(b) It was assumed that viscosity in the liquid is negligible. Fig. 11.2 shows the variation with time t of the displacement x.

Fig. 11.2

(i) Sketch in Fig. 11.2, the variation with time t of the displacement x when viscosity of the liquid is not negligible.

[2]

displacement x

time t

‐1.5

‐1

‐0.5

0

0.5

1

1.5

0 5 10 15 20


(ii) The mass of the liquid in the column is 500 g. The maximum displacement x is 3.5 cm. Use your answer in (a)(iv) to determine the maximum kinetic energy of the liquid.

maximum kinetic energy = ........................... J [2]

(iii) Sketch in Fig. 11.3, for the variation with displacement x of

1. the kinetic energy of the liquid. Label it EK

[2]

2. the potential energy of the liquid. Label it EP.

[1]

Fig. 11.3

kinetic energy

displacement, x 0


(c) The U-tube is now placed in contact with an oscillator moving sideways as shown in Fig. 11.4. The oscillator causes the U-tube to oscillate. The frequency of oscillator can be varied.

Fig. 11.4

Fig. 11.5 shows the variation with the oscillator’s frequency of the amplitude of the water level.

Fig. 11.5

(i) Use your answer in (a)(iv) to determine the value f0.

f0 = ........................... Hz [1]

(ii) Explain why there is a peak in the amplitude in Fig. 11.5.

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

(iii) On Fig. 11.5, sketch the variation of the amplitude when the liquid in the tube is replaced by another liquid with higher viscosity. [1]

End of Paper

amplitude

frequency f0

x


BLANK PAGE

River Valley High School Pg 1 of 7 H2 Physics 9749JC2 Prelimimary Examination 2020

Solutions to MCQ

1 D 11 C 21 A 2 C 12 A 22 C 3 A 13 B 23 A 4 D 14 C 24 D 5 D 15 A 25 C 6 B 16 C 26 B 7 D 17 B 27 A 8 B 18 C 28 B 9 D 19 D 29 B 10 C 20 A 30 A

A 8

B 7

C 8

D 7


1. Ans: D Centi (102), milli (103), nano (109)

2. Ans: C The object dropped from a great height will be experiencing a decreasing acceleration due to to increase in air resistance acting on it. As a result, the velocity will be increasing at a decreasing rate until it reaches a constant value.

3. Ans: A C: 1/2mu2 + 0 = 1/2mv2 + 1/2mw2 u2 = v2 + w2 D: mu + 0 = mv + mw u = v + w A: Wrong statement B: For elastic collison between two equal masses where one of the mass is initially at rest, the masses will exchange speed such that the mass that is initially at rest will move off with same speed as colliding mass.

4. Ans: C

5. Ans: D Let L be the distance from hip joint pivot to centre of mass. Applying principle of moment at the hip joint pivot,

70sin8 sin70

8400 6.7522700 N

o o

o

o

sinTL WL

Tsin

W

p

t

1. “constant acceleration” constant tv

means constant increase in v 2. but “burns fuel” means mass is

decreasing at the same time 3. p = mv, although there is a constant

increase in v, there is also a decrease in mass at the same time so it will be a curve rather than straight line graph.


6.

Ans: B For an ice cube floating on sea water, its weight = upthrust, so 0.920 g cm-3 x 1.00 cm3 x g = 1.03 g cm-3 x volume of sea water displaced x g So volume of sea water displaced = 0.893 cm3 let the volume of water from melted ice be v , by conservation of mass, we have 0.920 g cm-3 x 1.00 cm3 = 1.00 g cm-3 x v v = 0.920 cm3 So volume of liquid increases by 0.920 – 0.893 = 0.03 cm3

7. Ans: D work done required by the motor = net potential gain by the system = m1gx m2gx , where x is the distance raised and fallen by m1 and m2 respectively. Hence the rate the motor provides energy is m1 m2 gv

8. Ans: B Horizontal component of tension provides centripetal force, so

T sin30o mr 2, where 22

, and r 10sin30o

T sin30o 0.5 10sin30o 2

T 49 N

9. Ans: D

Between Earth and Moon, Fg = GMeMm/r2 --- (1) Between Sun and Earth, 170Fg = GMeMs/(400r)2 --- (2) Solving (1) and (2), MsMe = 2.7 x 107

10. Ans: C Since satellites are orbiting around the sun, the energies of the satellites can be represented by Ep = GMsM/r, Ek = GMsM/2r and Etotal = GMsM/2r. Since satellite A has a larger mass than satellite B and both satellites have the same kinetic energy, GMsMA/2rA = GMsMB/2rB MA/rA = MB/rB → rA is larger than rB. (Option B is true) By Kepler’s 3rd law, since T2 is proportional to r3, TA is larger than TB. (Option A is true) Since ω = 2π/T, ωA is smaller than ωB. (Option D is true) Using Etotal = GMsM/2r and MA/rA = MB/rB, both satellites should have the same total energy (Option C is false)


11. Ans: C

Since product of pV for T2 is four times that of T1, complied with the fact that pV = nRT, T2 is four times that of T1. Since 𝑚〈𝑐 〉 𝑘𝑇, 𝑐 ∝ √𝑇

𝑐𝑐

𝑇𝑇

21

12. Ans: A

The rate of heat loss of the hot liquid is constant during cooling before solidification and during the freezing During cooling:

𝑃𝑡 𝑚𝑐∆𝜃 𝑃 1 𝑚𝑐 4.0

During freezing: 𝑃𝑡 𝑚𝑙

𝑃 25 𝑚𝑙

𝑃 1𝑃 25

𝑚𝑐 4.0𝑚𝑙

𝑐𝑙

125

14.0 0.01

13. Ans: B

∆𝑈 32 𝑛𝑅∆𝑇32 1 8.31 4.5 56.1 𝐽

At constant volume, there is no work done on the gas, hence the heat input will be equal to the increase in internal energy.

14. Ans: C

Using v0 x0, 3 212

x0 giving x0 5.730 cm

Using a0 2x0, a0

212

2

5.730 1.571 cm s1

Hence maximum restoring force = 5.0 x 1.571 102 = 7.9 102 N


15. Ans: A

Let the total energy of the oscillating system be E 02 21

2m x .

Since potential energy of the system is 2 212

m x , when x 12

x0 , the potential energy is

E4

. Then the kinetic energy would have to be 3E4

. Hence ratio is 13

16. Ans: C

Using Malus’ Law, I2 I cos2

gives 45o, 135o, 225o, 315o

17. Ans: B Adjacent antinodes are half a wavelength apart. Hence a node is a quarter of a wavelength from an adjacent antinode. A: W and Z are nodes, hence the kinetic energies of the particles are those positions are zero. C: X and Y are in adjacent segments hence they are antiphase with respect with each other. D: The air particles oscillate parallel to direction of propagation.

18. Ans: C

𝑥 𝜆𝐷𝑎 ⇒ 𝜆𝑎𝑥𝐷

0.1 10 8.0 102.0 4.0 10 𝑚

At the second order dark fringe, the path difference will be 1.5 times of the wavelength, 6.0 10 𝑚

19. Ans: D Inititally, electric force on each sphere F = (6 x 106)(2 x 106)/4π𝜀 d2. [attractive] After the spheres touch each other, the total amount of change is 4 x 106 C. Hence, each sphere will receive 2 x 106 C. Hence, F1 = (2 x106)(2 x106)/4π4π𝜀 d2 = F/3 [repulsive]

20. Ans: A Fnet = Fe = qE since E is constant and same charge →Fe is constant →acceleration constant UP = qφp and UQ = qφQ The potential at Q is greater than P, since charge is negative, therefore UP > UQ.


21. Ans: A Since 𝐼 𝑛𝐴𝑣𝑞 and the current, drift velocity and charge of each charge carriers remain the same, the reason why the number density is decreasing along the strip has to be because the cross-sectional area is increasing.

22. Ans: C p.d across load resistors: .. . 9.0 3.857 𝑉

23. Ans: A Potential difference across P is 2 V. Hence the expected potential as the slider is moved from X to Y is 6 to 4 V.

24. Ans: D Using Fleming’s left hand rule, it can be used to explain that both are negative charged particles.

25. Ans: C When ions pass through velocity selector, Eq = Bqv 20000q = 0.25qv v = 80000 m s1 When ions are at main chamber, Bqv = mv2/r d = 2r = mv/Bq = 2(1.93 x 1025)(80000)/(0.40)(1.6 x 1019) = 0.48 m

26. Ans: B

BANt

0 0.15 0.050 0.080 40

3.0

0.0080 V

27. Ans: A

By Lenz’s law, coil Y would produce an induced magnetic field to oppose the increase flux. Hence X and Y would repel.


28. Ans: B Using

P VrmsIrms

Irms 60240

0.25

Hence I0 Irms 2 0.25 2 0.35A

29. Ans: B Using E3 – E1 – hc/λ λ = hc / (E3 – E1) = hc / (1303 49.7)(1.6 x 1019) = 0.992 nm

30. Ans: A Intensity = Power / Area = Energy / (Time)(Area) = Nhf/tA = Nhc / λtA → λ is inversely proportional to intensity. Since intensity is halved, then λ is doubled. Using λ = h/p, momentum of photon is halved when λ is doubled.

River Valley High School Page 1 of 6 J2 H2 Physics 9749Preliminary Examinations 2020

RVHS JC2 H2 Physics Preliminary Examinations Paper 2 Mark Scheme

1 (a) 1. Zero initial velocity 2. Uniform acceleration

B1 B1

(b)

(i) Line with negative gradient; equal length above and below x-axis 1.5 and 3.0 s marked

B1 B1

(ii) s = ½ (u + v) t 11 = ½ (0 + v)1.5 v = 14.7 m s-1

A1 (b) (iii) Shorter time

Greater downward acceleration on the ball. M1 A1

2 (a) work done = F x , where x is the distance moved by the object B1 in a unit time,

work done = time taken time taken

F x , but velocitytime taken

x

So P Fv A0 (b) (i) at maximum speed, driving force = resistive force

(BOD for net force = 0) C1

max

-1

resistive force

200000 5000maximum speedmaximum speed 40 m s

Pv

A1

(ii) max

0

resistive force sin

200000 5000 1500 9.81 sin10maximum speed

P mgv

C1

M1

-1maximum speed 26 m s A1 (iii) From chemical potential energy to gravitational potential energy B1 and thermal energy

(BOD: work done due against friction) B1

(c) normal contact force – weight provides centripetal force B1 for contact normal contact force > 0 B1 2

2

vmg N mr

vN mg mr

When N > 0 2

0

250 9.8149.5

vmg mrv rg

B1 maximum speed = 49 m s-1

(accept both 49 and 50) A1


3 (a) (i)

F = GMm

(R + r)2

B1

(ii) M has a slower speed due to its smaller orbital radius and hence has a smaller acceleration. By Newton’s second law, for the same gravitational force between M and m, M must be of a bigger mass. Alternatively, since both masses experience the same gravitational force (N3L) same centripetal force since r is smaller than R, M has to be larger than m. *Can use centre of mass to explain?

B1 B1

or B1 B1

(iii) For star P,

GMm

(R + r)2 = Mrω2

Centripetal acceleration for star P = Gm(R + r)2

= rω2 --- (1) For star Q, GMm

(R + r)2 = mRω2

Centripetal acceleration for star Q = GM(R + r)2

= Rω2 --- (2)

A1

A1

(iv) Gravitational force on each star provides for their individual centripetal

force. Adding (1) and (2),

G(M + m)(R + r)2

= (R + r)ω2 = (R + r) 2πT

2

=4π2(R + r)3G(M + m)

C1

A1

(b) Let mr be mass of rocket.

loss in Ek of rocket = gain in gpe of rocket 0.5mrv2 0 = 0 mr (GM/r + Gm/R)] 0.5mrv2 = Gmr [(4.50 × 1023/4.0 × 108) + (1.50 × 1023)/(1.2 × 109)]] 0.5mrv2 = Gmr (1.25 × 1015) v = 408 m s1

C1 A1

T


4 (a) Stationary waves are waves whose waveform does not advance and there are no translation of energy.

B1B1

(b) (i) The sound wave produced by the loudspeaker travels down the pipe and gets reflected at the piston. The incident wave and reflected wave have the same frequency and speed and are travelling in opposite directions hence Superpose/meet to form a stationary wave.

B1

B1

A0 (ii) Wavelength of stationary wave = 0.24 m

f = v / λ = 330 / 0.24 = 1400(1375 Hz)

C1

M1 A1

(iii) t = d / v = 12 / 0.75 = 16 s

M1 A1

(iv) The actual wavelength was longer due to end corrections. B1

5 (a) (i) When p.d. V increases, current I through the filament lamp also increases, with decreasing I-V ratio. As I increases, power dissipated increases (P = I2R). Heat is generated and hence equilibrium temperature increases. (This is because as electrons drift through the metal, they collide with the metal lattice, transferring energy to them) As equilibrium temperature increases, the lattice ions vibrate more vigorously, hindering the flow of ‘charge carriers’, therefore increasing the resistance.

B1 B1 B1

(ii) E = I (3R + 2r) 8.7 = 0.30 (3 (2.5/0.3) + 2r) r = 2.0 Ω

M1 A1

(iii) Straight line passing through (2.0, 0.10) and (4.0, 0.20) B1 (b) (i) 𝑉 𝐸

𝑉63.180.0 15.0

15.0 20.0 0.5 3.0

.. .

. . . =0.9998 V

C1 C1 A1

(ii) 𝑉

12.580.0 15.015.0 0.5 3.0

12.580.0 15.015.0 0.5 3.0

C1


𝑉 5.05.0 𝑟 1.00 By solving, r = 6.0 Ω

C1

A1

6 (a) (i) magnitude of induced e.m.f. in a conductor is directly proportional to the rate of change of magnetic flux linkage.

B1

(ii) Recognise that the value is given by area under the graph from t = 0 to t = 0.025 s

C1

Show substitution using trapezium rule or equivalent. (When integration is used, the function used must be clear) Acceptable range 0.38 0.04 Wb

A1

(b) (i) 0.38 = B 0.090 8 C1 B = 0.53 Wb

A1

(ii) 2 200.10 rad s-1

B1

(c) Straight line through origin

B1

(d) (i) V0=I0 R, so I0 =

2412

= 2.0 A C1

Irms =

2.0 1.42 A

or equivalent method *expression needs to be updated, quite misleading.

A1

(ii) mean power = 0 0 0 24 2.0 24

2 2 2P I V

W

or equivalent method

B1


7 (a) (i) The photoelectric effect refers to the emission of electrons from a metal surface when the surface is irradiated with electromagnetic radiation of a high enough frequency.

B1

(ii) Allow 380 nm or 390 nm A1

(iii) Threshold frequency is determined when there is no responsivity from

photocathode/ no release of photoelectrons. From Fig. 7.2, threshold wavelength is approximately 640 mm. Threshold frequency is found by using speed of light divided by threshold wavelength (or 630 nm) *Statement to be updated

B1

B1

(iv) Using hc/λ = work function + Ek, max, hc/(450 x 109) = h (4.76 x 1014) + 0.5(9.11 x 1031)v2 v = 5.27 x 105 m s1*

B1

C1A1

(v) Using a low work function photocathode will allow electrons to be

emitted easily with photons of larger wavelength. B1

(b) (i) Current = nq/t

7.8 x 104 = (n/t)*(1.6 x 1019) n/t = 4.88 x 1015 s1

C1A1

(ii) Number of photons per unit time

= 4.88 x 1015 (100) = 4.88 x 1017

A1

(iii) 4.8 mA of current is detected from photocathode when 1 W of power of EM radiation is incident on it.

B1

(c) (i) Use wavelength = 225 nm, R = 9.0 mA/W and wavelength = 540 nm,

R = 22 mA/W to correctly determine η at 5 %. B2

(ii) Correct computation of values with maximum values of 2sf

To deduct one mark for one wrong calculation.

η / % λ / nm R / mA W1

3 300 7.2

3 400 9.7

3 500 12

3 600 14

3 700 17

A2

(iii) Correct plotted points with best-fit curve B2


(d) (i) If there is little magnetic shield, magnetic field will curve electron paths,

steer the electrons away from the dynodes. The voltage used in PMT is higher than 1000V and must be electrically insulated for safety reason. Accept any reasonable answer.

B1

(ii) Use in eye devices to measure interruption of light.

To detect radiation. Measure intensity and spectrum of light emitting materials in

laboratory. https://en.wikipedia.org/wiki/Photomultiplier_tube#Usage_considerations

B1


RVHS JC2 H2 Physics Preliminary Examinations Paper 3 Mark Scheme

1 (a) Systematic error: forgetting to subtract the original length of the spring Random error: parallax error when reading the extension of the spring Any other logical answers.

B1

B1

(b)

(i) W = Fscosθ W = (0.60)(0.750)(cos30) 0.3897 𝐽 Max W = (0.61)(0.751)(cos29) 0.4007 𝐽 Min W = (0.59)(0.749)(cos31) 0.3788 𝐽 Uncertainty of W = 0.0110 = 0.01 Percentage uncertainty = 0.01 / 0.39 * 100% = 2.6 %

C1

C1

A1

2 (a)

Fig. 2.2 T: tension of string N: normal contact force on X WX: weight of X WY: weight of Y 1 mark for correct FBD for each mass

B2

(b) (i) For X,

T = mXa --- (1) For Y, WY – T = mYa --- (2) Solving (1) and (2), 0.600 x 9.81 = (0.220 + 0.600) a a = 7.2 m s2

C1

A1

(ii) T = 0.22 x 7.2 = 1.58 N B1 (iii) Resultant force = 0.600 x 9.81 = 5.89 N B1

X Y T

T

WX

WY

N


(c) The collision is not perfectly inelastic at there are external forces acting on either object such as tension force on X and the force between the fixed block at table top. Need to identify the correct external forces acting on the objects

B2

3 (a) (i) resultant force on frame is zero and resultant torque is zero about any point

B1

(ii) Triangle forms a closed loop and direction of arrows are correct B1 angles of vectors are correct B1 (b)

sin50o W / 2T

or equivalent

jc2 preliminary examinations h2 physics 9749 ......h2 physics 9749 paper 1 23 sep 2020 1 hour...

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