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YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE
Candidate Name ………………………………….……… CTG ……………….…
YISHUN JUNIOR COLLEGE JC 2 Preliminary Examinations 2009
PHYSICS 9745/1 HIGHER 2
2 September 2009
Paper 1 Multiple Choice Wednesday 1 hour 15 minutes
Additional Materials: Optical Mark Sheet
INSTRUCTIONS TO CANDIDATES
Do not open this booklet until you are told to do so. Write your name and CTG on the Optical Mark Sheet in the spaces provided. Shade your CTG and OMR Register Number in the space provided. There are forty questions in this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Optical Mark Sheet. Read the instructions on the Optical Mark Sheet carefully. INFORMATION FOR CANDIDATES Each correct answer will score one mark. A mark will not be deducted for a wrong answer.
Any rough working should be done in this booklet.
This question paper consists of 22 printed pages.
9745/1/JC2Prelims/YJC2009
2
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, s = ut + 2
1at2
v2 = u2 + 2as
work done on/by a gas, W = pV hydrostatic pressure, p = g h gravitational potential,
r
Gm
Displacement of particle in s.h.m. x = xo sin t velocity of particle in s.h.m., v = vo cos t =
)( 22 xxo
resistors in series, R = R1 + R2+……….
resistors in parallel,
R
1
........
11
21
RR
electric potential,
r
Q
o4
alternating current/voltage, x = xo sin t
transmission coefficient T = exp(2kd)
where k = 2
2 )(8
h
EUm
radioactive decay, x = xo exp(–t)
decay constant, =
2
1
6930
t
.
=
=
V =
9745/1/JC2Prelims/YJC2009
3
1 A driver cell of voltage VD is used to determine the voltage VT of a test cell via a
potentiometer. The driver cell is labelled with a value (1.5 0.3) V. The resistance wire
has a length L of (0.980 0.001) m.
At balance condition, the balance length, d, is found to vary between 22.7 cm and 23.3
cm. Given that L
d
V
V
D
T , which is the correction expression for VT?
A (0.35 0.08) V
B (0.4 0.08) V
C (0.3 0.2) V
D (0.35 0.21) V
2 With reference to question 1, which of the following is the best way of reducing the
percentage uncertainty of d?
A Adding a resistor in parallel with driver cell.
B Adding a resistor in series with driver cell.
C Adding a resistor in parallel with test cell.
D Adding a resistor in series with test cell.
Driver Cell, VD
Resistance wire of length L
G
Test Cell, VT
Balance length, d
9745/1/JC2Prelims/YJC2009
4
3 A multiple exposure photograph is taken for a sphere dropping vertically. The time
interval between each pair of successive exposures is always the same.
Taking downwards as positive, which graph best represents, the motion of the body over
this period?
A B
C D
acceleration
time
acceleration
time
velocity
time
time = 0 s
displacement
time
9745/1/JC2Prelims/YJC2009
5
4 A skateboarder glides along a straight road and throws a balloon vertically upwards.
If effects of air resistance are significant, which diagram best represents the trajectory
of the ball seen by a stationary observer?
A B
C D
9745/1/JC2Prelims/YJC2009
6
5 The specific heat capacity of a liquid, c, can be determined using electrical methods.
If the heat loss to the surroundings is significant but not accounted for during the
experiment, how would the experimental value of c be affected?
A It will be overestimated.
B It will be underestimated.
C It will vary randomly with time.
D It will not be affected.
6 An ideal gas of volume V at pressure p undergoes the cycle of changes shown in the
graph.
At which points are the gas coolest and hottest respectively?
coolest hottest
A X Y
B Y X
C Z X
D Z Y
p / 105 Pa
V / 10–3 m3
4
1
1 5
Y X
Z
9745/1/JC2Prelims/YJC2009
7
7 Four different composite rods of uniform thickness are to be balanced horizontally on a
knife-edge. Each rod is made up of 50% material A and 50% material B, where B is
denser than A. Which scenario is unlikely to occur?
A B
C D
8 A horizontal plank of uniform density is supported by a metal cable as shown in the
diagram. The cable joins at Q, the midpoint of the plank, and R is the midpoint of
cable QS. What is the direction of the reaction force exerted by the hinge pin on the
plank?
A PQ B PR C RP D PS
P Q
R
S
hinge pin
plank
cable
Material A Material B
Legend:
9745/1/JC2Prelims/YJC2009
8
9 In each of the four diagrams below, a force is applied horizontally on crate P so that
both crates P and Q accelerate along a frictionless surface. If m and a denote unit
mass and acceleration respectively, which scenario corresponds to the largest force
exerted by Q on P?
A B
C D
10 Which of the following scenarios involves an object (in bold) having the greatest
resistance to change in motion?
A Bringing a car to a stop from 20 m s1.
B Raising a 5.0 kg block through a vertical height of 1.0 m from the ground.
C Steering an aircraft into a runway at a constant speed.
D Stopping an alpha particle using a thick sheet of paper.
2m m
a
Q P
3m m
0.5a
Q P
m m
3a
Q P
2m m
2a
Q P P
9745/1/JC2Prelims/YJC2009
9
11 A person pulls a loaded trolley such that both move at constant velocity.
Which of the following statements about work done is correct?
A Work done on the trolley by the cord is zero because the trolley is moving at
constant velocity.
B Work done on the person by the ground is positive.
C Work done on the person by the cord is positive.
D Work done on the trolley by the ground is positive.
12 A spring of spring constant k is compressed by a length x. When released, it projects a
smooth metal sphere of mass m up a 30 slope.
Determine the maximum height h which the ball rises.
A mg
kx
4 B
mg
kx
2 C
mg
kx
4
2
D mg
kx
2
2
h
30
cord trolley
9745/1/JC2Prelims/YJC2009
10
13 A car is travelling at constant speed v on a road in a hilly region as shown. The tops
and bottoms of the hills have radii of curvature R. At which position is the driver most
likely to feel weightless?
A At the top of a hill when gRv
B At the top of a hill when gRv
C At the bottom of a hill when gRv
D At the bottom of a hill when gRv
14 A child whirls a ball at the end of a rope, in a uniform circular motion. Which of the
following statements is not true?
A The speed of the ball is constant.
B The resultant acceleration of the ball is constant.
C The momentum of the ball is tangential to the path of travel.
D The rate of change of momentum of the ball is perpendicular to the path of
travel.
9745/1/JC2Prelims/YJC2009
11
15 A rocket blasts away from Earth. Which of the following graphs best represents the
gravitational force, g on the rocket with respect to the distance, r from the surface of
the Earth?
A B
C D
16 Which of the following explains why free hydrogen atoms are abundant in the Sun but
not on Earth?
A The mass of the Earth is lighter.
B The escape velocity of hydrogen atoms on Earth is higher.
C The internal energy of hydrogen atoms on Earth is lower.
D Most of the hydrogen atoms on Earth have undergone nuclear fusion.
g
r
g
r
g
r
g
r
9745/1/JC2Prelims/YJC2009
12
17 The following diagram is used as a reference to Questions 17 and 18. It shows the
trace produced by a sound wave on a c.r.o. The time base is calibrated at 4.0 ms cm1.
The vertical sensitivity is set at 1.0 mV cm1.
What is the frequency of the sound wave?
A 0.063 Hz B 63 Hz C 89 Hz D 180 Hz
18 The vertical deflection of the waveform can be adjusted on the c.r.o. using a knob to
change the vertical sensitivity. The intensity of the original sound wave increases and
at the same time, the vertical sensitivity is adjusted to 2.0 mV cm-1, such that the same
waveform (in above diagram) is replicated on the c.r.o. screen. What is the new
intensity in terms of the original intensity Io?
A 0.25 Io B 2.0 Io C 2.8 Io D 4.0 Io
19 In a fairground shooting game, a player is firing at a moving target by using a gun that
fires by itself at random timings. The player has to point the gun in a fixed direction,
while the target moves from side to side in simple harmonic motion.
At which region should the player take a fixed aim to score the greatest number of hits
on the target?
A 3 B 1 or 5 C 2 or 4 D 1, 3 or 5
1 cm
1
target
2 3 4 5
9745/1/JC2Prelims/YJC2009
13
f
amplitude
f
a
f
amplitude
fo f
amplitude
ao
fo
f
amplitude
fo f
amplitude
fo
20 A pendulum is constructed from a fixed length of light thread and a spherical,
polystyrene bob of low density. It is forced to oscillate in air at different frequencies f.
The following diagram shows how the amplitude of its oscillation varies with f.
The experiment is repeated in a partial vacuum. Which graph best represents the
variation with f of the amplitude?
A
B
C
D
21 Under which conditions will the bright fringes of a double-slit light interference pattern
be farthest apart?
distance between
slits distance from slits
to screen wavelength of
source
A small large short
B small large long
C large small short
D large small long
ao
ao ao
9745/1/JC2Prelims/YJC2009
14
22 The diagram shows the formation of the first order spectrum when parallel rays of
monochromatic light fall perpendicularly on a sub-standard diffraction grating PQR. For part of the grating between P and Q, the angle of deviation is constant and the
diffracted rays emerge parallel. However, from Q to R, falls progressively as shown in the graph.
Which graph best shows how the grating interval d varies with x, the distance from
P?
A
d
P x
Q R 0
B
d
P x
Q R 0
C
d
P x
Q R 0
D
d
P x
Q R 0
P x
Q R
graph diagram
x
falling
parallel P
R
Q
0
mono-chromatic
light
9745/1/JC2Prelims/YJC2009
15
23 An isolated point charge produces an electric field with magnitude E at a point 2.0 m
away from the charge. What is the distance from the charge when the field
magnitude is E/4?
A 0.50 m B 1.0 m C 4.0 m D 8.0 m
24 An electron is moved in a uniform electric field of strength E.
What is the work done against the electric force when the
electron moves a distance s along the path?
A + e E s cos 60
B + e E s sin 60
C e E s cos 60
D e E s sin 60
25 The diagram shows a rectangular block with dimensions t 2t 3t.
Electrical contact can be made to the block between opposite pairs of faces (for
example between the face labelled P and its opposite face).
Between which two faces would the maximum electrical resistance be obtained?
A The face labelled P and its opposite face.
B The face labelled Q and its opposite face.
C The face labelled R and its opposite face.
D The resistance is the same, whichever pair of faces is used.
E
60
s
t
2t
3t
P Q
R
9745/1/JC2Prelims/YJC2009
16
26 Which of the following shows the I – V characteristics of a thermistor?
A B
C D
27 Visible light of various frequencies emitted from hydrogen gas is irradiated onto a
calcium plate in a photoelectric experiment to determine their corresponding stopping
potential VS. The graph shows two plots P1 and P2 corresponding to two longest
wavelengths of light.
Which point on the graph shows the possible result when the next lower wavelength is
used?
V
I
V
I
V
I
V
I
VS / V
P1
f / Hz
P2
A
B C
D
9745/1/JC2Prelims/YJC2009
17
28 A power supply is connected to a set of four identical resistors. Which of the following
arrangements corresponds to the maximum power delivered across PQ?
A B
C D
29 Which unit is equivalent to weber?
A volt second –1
B tesla metre –2
C kilogram metre 2 ampere
D joule ampere –1
P Q P Q
P Q P Q
9745/1/JC2Prelims/YJC2009
18
30 Two long, parallel wires X and Y carry currents of I and 2I respectively.
The wire experiences
A attractive forces of same magnitude.
B attractive forces, but force on Y is greater than force on X.
C repulsive forces, but force on Y is greater than force on X.
D repulsive forces, but force on X is greater than force on Y.
31 A uniform magnetic flux of flux density 0.52 T passes at an angle of 60 to a horizontal
thin rod as shown.
When the metre-long rod is moved vertically upwards at a speed of 0.75 m s –1, what is
the magnitude of e.m.f. induced in the rod?
A 0 V
B 0.20 V
C 0.34 V
D 0.39 V
B = 0.52 T
60
2 I
I X
Y
0.75 m s –1
9745/1/JC2Prelims/YJC2009
19
32 The magnetic flux linkage through a coil varies with time as shown.
Which graph shows the variation with time of the e.m.f. generated by the coil?
A B
C D
e.m.f.
time
e.m.f.
time
e.m.f.
time
e.m.f.
time
flux linkage
time
9745/1/JC2Prelims/YJC2009
20
33 A rectifier is connected in series with load P and an alternating voltage supply as shown in
the figure below.
What is the value of the r.m.s. voltage across load P?
A 0.18 Vo B 0.35 Vo C 0.50 Vo D 0.71 Vo
34 In the diagram shown, the average power dissipated across a 2.0 resistor is 50 W.
What is the r.m.s. potential difference across the primary coil of the ideal transformer?
A 20 V B 40 V C 200 V D 400 V
P
Vin Vin / V
t / s Vo
240
2000 turns
50 turns
2.0
t 2t 3t 4t
9745/1/JC2Prelims/YJC2009
21
35 A photon of energy 3.5 10–19 J falls on the cathode of a photocell. The work function
energy of the cathode is 3.1 10–19 J.
What is the stopping potential?
A 0.24 V
B 0.25 V
C 0.40 V
D 0.46 V
36 The diagram shows the electron energy levels for four different isolated atoms A, B, C
and D.
Which atom can produce radiation of the shortest wavelength when atoms in the ground
state are bombarded with electrons of energy W?
37 Which of the following statements about the energy gap of an intrinsic semiconductor is
incorrect?
A The energy gap is the energy separation between the bottom of the conduction
band and the top of the valence band.
B The energy gap usually carries a magnitude in electron volts.
C The energy gap can vary between different elements under Group IV of the
periodic table.
D The energy gap can be reduced by introducing dopant atoms.
A
W
B C D
Ground state
9745/1/JC2Prelims/YJC2009
22
38 Which of the following is not a necessary condition for lasing action?
A Population inversion occurs between a metastable state and a lower lasing
state.
B Photons that trigger stimulated emission must carry the same energy as the
difference between a metastable state and a lower lasing state.
C The atoms of the lasing medium must stay at the ground state long enough for
external energy source to cause excitation.
D Emitted photons are confined long enough between two reflecting surfaces to
allow them to stimulate further emission for other excited atoms.
39 Which of the following best associates with decay constant of a radioactive source?
A It increases with number of radioactive nuclei.
B It increases with temperature.
C It is independent of time elapsed.
D It is independent of the element.
40 The count rate observed from a radioactive source at three different timings are as
follows:
t / s count rate / s –1
0 1600
6.0 X
8.0 100
What is the value of X?
A 150 B 200 C 300 D 400
~ END OF PAPER 1 ~
9745/2/JC2 Prelims/YJC2009
YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE
Candidate Name ………………………………. CTG ……….…
YISHUN JUNIOR COLLEGE JC 2 Preliminary Examinations 2009
PHYSICS 9745/2 HIGHER 2
20 August 2009 Paper 2 Thursday
1 hour 15 minutes
INSTRUCTIONS TO CANDIDATES Write your name and CTG in the spaces at the top of this page. Answer all questions. Write your answers in the spaces provided on the question paper. For numerical answers, all working should be shown clearly. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question.
This question paper consists of 14 printed pages.
For Examiner’s Use
1 /9
2 /9
3 /9
4 /9
5 /9
6 /15
Penalty
Total /60
Candidates answer on the Question Paper. No Additional Materials are required.
2
9745/2/JC2 Prelims/YJC2009
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, s = ut + 2
1at2
v2 = u2 + 2as
work done on/by a gas, W = pV
hydrostatic pressure, p = g h
gravitational potential,
r
Gm
Displacement of particle in s.h.m. x = xo sin t
velocity of particle in s.h.m., v = vo cos t
= )( 22 xxo
resistors in series, R = R1 + R2+……….
resistors in parallel,
R
1
........
11
21
RR
electric potential,
r
Q
o4
alternating current/voltage, x = xo sin t
transmission coefficient T = exp(2kd)
where k = 2
2 )(8
h
EUm
radioactive decay, x = xo exp(–t)
decay constant, = 2
1
6930
t
.
=
=
V =
3
9745/2/JC2 Prelims/YJC2009
For Examiner’s
Use
1 (a) Define work done on a body.
……………………………………………………………………………………….................
……………………………………………………………………………............................... [2]
(b) A skier starts from rest at A, and glides down a smooth slope. The dimensions of the
slope and the skier’s motion are illustrated in Fig.1.1. The skier passes through B, C, D,
E and reaches point F, R metres away from the cliff.
The effect of air resistance can be ignored in this scenario.
(i) Draw an arrow on Fig.1.1 to show the net force acting on the skier
1. at B (label as FB),
2. at E (label as FE). [2]
(ii) Show that the skier’s speed at C is 22 m s –1.
[2]
(iii) The skier leaves C at an angle of 35 above horizontal. Calculate R.
R = ………………… m [3]
B
A
C
D
E
F
R
30 m
5 m
10 m
skier
Fig. 1.1
4
9745/2/JC2 Prelims/YJC2009
For Examiner’s
Use
2 (a) (i) State the principle of conservation of momentum.
………………………………………………………………………………………..............
……………………………………………………………………………........................ [2]
(ii) In a science-fiction movie, a superhero in mid-air throws a heavy fridge towards a
villain on the ground. Using the answer in (a)(i), explain why the superhero cannot
remain stationary after the throw.
………………………………………………………………………………………..............
……………………………………………………………………………........................ [1]
(b) In a telematch, players need to catch as many eggs as possible, without breaking them,
using a big piece of towel. The egg is thrown towards the players one at a time.
(i) Discuss why a towel is suitable for performing the task described in (b).
………………………………………………………………………………………..............
…………………………………………………………………………….............................
……………………………………………………………………………........................ [2]
(ii) At a particular instant, an egg of mass 20 g reaches a piece of towel at a speed of
8.0 m s1.
1. Determine the impulse acting on the egg when it reaches the towel.
impulse = ……………………… N s [2]
2. Calculate the average force exerted by the towel in the attempt to bring the egg
safely to a stop in 1.5 s.
average force = ……………………… N [2]
5
9745/2/JC2 Prelims/YJC2009
For Examiner’s
Use
3 Hummingbirds (see Fig. 3.1) can hover around flowers by beating their wings at a frequency
between 20 to 80 times per second. It can be assumed that the air molecules around the birds
vibrate at the same frequency.
Fig. 3.1
(a) Deduce why a person who stands near a hovering hummingbird may hear a buzzing
sound.
………………………………………………………………………………………........................
………………………………………………………………………………………........................
………………………………………………………………………………………........................
……………………………………………………………………………............................... [2]
(b) A bird-watcher is initially 2.0 m from a hummingbird. To pick up a louder buzz, the bird-
watcher moves nearer to the bird by a distance x. Determine the value of x in metres for
an increased intensity of 60%.
x = ……………… m [3]
6
9745/2/JC2 Prelims/YJC2009
For Examiner’s
Use
(c) It is assumed that for a hummingbird which beats its wings at 75 times per second, the air
molecules around it can vibrate in simple harmonic motion at an amplitude of 5.0 10-9 m.
(i) Determine the maximum speed of vibration of the air molecules.
speed = …………………….. m s1 [2]
(ii) Calculate the distance covered by an air molecule over the duration in which the
hummingbird beats its wings for 1800 times.
distance = …………………….. m [2]
7
9745/2/JC2 Prelims/YJC2009
For Examiner’s
Use
4 (a) X-rays are emitted when a metal target placed in vacuum is bombarded with high energy
electrons. The variation with wavelength, , of the relative intensity of the X-rays is shown
in Fig. 4.1.
On the horizontal axis of Fig. 4.1, indicate the wavelength corresponding to the maximum
photon energy associated with the following processes:
1. Slowing down of the high energy electrons (label as A)
2. Electron transitions between the deep-lying energy levels of the atoms (label as B)
[2]
(b) Experimental results on alpha-decay indicate an inverse relationship between the kinetic
energy E of the alpha-particles and the half-life t½ of the radioactive source.
For observed E between 4 to 9 MeV, t½ varies between 1020 and 10–7 seconds.
(i) Show, with appropriate calculations, that E and t½ cannot be related in the form of
E =
21t
k , where k is a constant. [1]
relative intensity
wavelength,
Fig. 4.1
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(ii) The concept of quantum tunnelling is used to account for this inverse relationship.
An illustration used in conjunction with this concept is shown in Fig. 4.2. The
wavefunction of a 10-MeV alpha-particle is shown and the shaded region
represents the potential barrier encountered by the alpha-particle.
Fig. 4.2
1. Explain what is meant by quantum tunnelling.
………………………………………………………………………………………..........
……………………………………………………………………………........................
……………………………………………………………………………........................[2]
2. Deduce from Fig. 4.2, why the alpha-particle has a non-zero probability of
tunnelling through the potential barrier.
……………………………………………………………………………........................
……………………………………………………………………………........................
……………………………………………………………………………........................[2]
3. Using Fig. 4.2, suggest why a radioactive source which emits 20-MeV alpha-
particles would have a shorter half-life compared to a source which emits 10-
MeV alpha particles.
………………………………………………………………………………………..........
………………………………………………………………………………………..........
……………………………………………………………………………........................
…………………………………………………………………………….......................[2]
distance from centre of nucleus / 10–15 m
En
erg
y / M
eV
30
20
10
Inside nucleus
outside nucleus
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5 (a) When Uranium-235 nuclei are fissioned by slow moving neutrons, the following reaction takes place:
cbYInU 10239
13153
10
23592
Identify the particle c and state the number b of such particles produced in the reaction.
b = ………………… [1]
c = ………………… [1]
(b) The binding energy per nucleon of U-235, I-131 and Y-102 are 7.6 MeV, 8.5 MeV and 8.6 MeV respectively. Calculate the energy released by 1.0 kg of Uranium.
energy released = ………………… J [3]
(c) In all nuclear plants, radioactive wastes are being produced. One of the radioactive
wastes Iodine-131( I13153 ) decays spontaneously with a half-life of 8.02 days.
(i) Calculate the decay constant for Iodine-131.
decay constant = ………………… s-1 [2]
(ii) Another radioactive product Strontium-90 ( Sr90
38 ) has a half-life of 28.8 years.
Explain why I13153 and Sr90
38 were among the most hazardous isotopes.
…………………………………………………………………………………………...........
…………………………………………………………………………………………...........
…………………………………………………………………………………………...........
……………………………………………………………………………....................... [2]
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6 (a) Mobility of charge carriers in a metallic conductor refers to the ease which the charge carriers are able to move through the conductor. Suggest why the charge mobility is inversely related to the resistivity of the conductor.
………………………………………………………………………………………........................
………………………………………………………………………………………........................
……………………………………………………………………………............................... [1]
(b) A sample of silicon is doped with small amount of impurities such as boron or phosphorus which will easily give rise to holes or electrons respectively as majority charge carriers. These impurities are also known as dopants. Fig. 6.1 shows the mobility of the electrons and holes with respect to doping density.
Figure 6.2 shows how the resistivity of an extrinsic semiconductor varies with the doping density.
100
10
1
0.1
0.01
0.001 1014 1016 1018 Fig.
6.5
n-type
p-type
Fig. 6.1
1014 1016 1018 1020
Fig. 6.2
1020
Doping density / cm3
Mo
bili
ty /
cm
2 V
1 s
1
Re
sist
ivity
/
cm
Doping density / cm3
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(i) A n-type semiconductor has a cross-sectional area of 0.25 cm2. Using Fig. 6.1 and Fig. 6.2, calculate the resistance per unit length when the mobility of the electrons is 1200 cm2 V1 s1.
resistance per unit length = ………………… cm1 [3]
(ii) Using Fig. 6.1 and Fig. 6.2, state how the mobility of the charge carriers and the resistivity of the semiconductors vary as doping density increases.
………………………………………………………………………………………..............
……………………………………………………………………………....................... [1]
(iii) Explain the apparent contradiction between (a) and (b)(ii).
………………………………………………………………………………………..............
………………………………………………………………………………………..............
………………………………………………………………………………………..............
…………………………………………………………………………….............................
……………………………………………………………………………....................... [2]
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(c) Fig. 6.3 shows how the conductivity, , of a n-type semiconductor varies with the reciprocal of the temperature, T1. [Conductivity = 1/resistivity]
Fig. 6.4 shows the typical band diagram of a n-type semiconductor. Electrons can transit from either the valence band or the donor level to the conduction band.
(i) Label ‘P’ and ‘R’ beside the arrows shown in Fig. 6.4 to match the regions P and R in Fig. 6.3. [1]
(ii) Explain your answer to (c)(i).
………………………………………………………………………………………..............
………………………………………………………………………………………..............
………………………………………………………………………………………..............
…………………………………………………………………………….............................
……………………………………………………………………………....................... [2]
P
Q
R
Fig. 6.4
Valence Band
Conduction Band
T1/(103 K1)
electron
Fig. 6.3
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(d) When a suitable p-type semiconductor is joined with a n-type semiconductor, it is found that it can act as a solar cell. The I-V characteristic is shown in Fig. 6.5.
Fig. 6.6 shows a magnified version of curve in Fig. 6.5 indicating a particular light level irradiating onto the solar cell.
(i) Estimate the maximum power obtainable from the solar cell using Fig. 6.6.
maximum power = …………………….. W [2]
Fig. 6.6
I/A
V/ V
Fig. 6.5
Voltage / V
Cu
rre
nt /
A
Fig. 6.5
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(ii) Discuss if the estimated value in (d)(i) is equal to the maximum power irradiated by the sun onto the solar cell.
………………………………………………………………………………………..............
………………………………………………………………………………………..............
………………………………………………………………………………………..............
………………………………………………………………………………………..............
………………………………………………………………………………………..............
…………………………………………………………………………….............................
……………………………………………………………………………....................... [3]
~ END OF PAPER 2 ~
9745/3/JC2Prelims/YJC2009
YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE YISHUN JUNIOR COLLEGE
Candidate Name ………………………………. CTG ……….…
YISHUN JUNIOR COLLEGE JC 2 Preliminary Examinations 2009
PHYSICS 9745/3 HIGHER 2
28 August 2009 Paper 3 Friday
2 hours
INSTRUCTIONS TO CANDIDATES Write your name and CTG in the spaces at the top of this page. Answer all questions. Write your answers in the spaces provided on the question paper. For numerical answers, all working should be shown clearly. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question.
This question paper consists of 22 printed pages.
For Examiner’s Use
Section A
1 /9
2 /9
3 /12
4 /10
Section B
5 /20
6 /20
7 /20
Penalty
Total /80
Candidates answer on the Question Paper. No Additional Materials are required.
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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, s = ut + 2
1at2
v2 = u2 + 2as
work done on/by a gas, W = pV
hydrostatic pressure, p = g h
gravitational potential,
r
Gm
Displacement of particle in s.h.m. x = xo sin t
velocity of particle in s.h.m., v = vo cos t
= )( 22 xxo
resistors in series, R = R1 + R2+……….
resistors in parallel,
R
1
........
11
21
RR
electric potential,
r
Q
o4
alternating current/voltage, x = xo sin t
transmission coefficient T = exp(2kd)
where k = 2
2 )(8
h
EUm
radioactive decay, x = xo exp(–t)
decay constant, = 2
1
6930
t
.
=
=
V =
3
9745/3/JC2Prelims/YJC2009
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[Turn over
Section A Answer all the questions in this section.
1 (a) State the base units associated with upthrust.
base units = …………………........ [1]
(b) A block of copper is suspended in air from an inelastic cord. The tension, T, in the cord is
measured using a force gauge as shown in Fig. 1.1. The copper block is next submerged
fully into a beaker of seawater (see Fig. 1.2). The new measurement of the tension from
the gauge is T.
(i) Suggest a reasonable value of the density of sea water.
density = ………………… kg m-3 [1]
(ii) Explain why T is greater than T.
……………………………………………………………………………....................... [1]
(iii) The densities of the copper block and the seawater are c and s respectively. The
volume of the block is V. Derive an expression for the tension T in terms of c, s
and V.
[2]
Gauge
Copper Block
Fig. 1.1
Gauge
Fig. 1.2
Beaker of seawater
Cord
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(iv) Hence, deduce how the volume of the block can be estimated using the force
measurements from the set-up in Fig. 1.1 and Fig. 1.2.
……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…… [2]
(c) An iron block of 200 kg is initially suspended vertically using two identical ropes as shown
in Fig. 1.3. Each cord can withstand a maximum tension of 1100 N. Both cords are
shifted slowly apart so that the angle increases at the same rate (see Fig. 1.4).
Calculate the maximum value of attained before the cords break.
maximum = ……………….. [2]
Iron Block
Fig. 1.3
Ropes
Fig. 1.4
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2 (a) Wave–particle duality is the concept that all matter and energy exhibit both wave-like and
particle-like properties. An electron diffraction tube shown in Fig. 2.1 can be used to show
the wave nature of particles.
Electrons are accelerated from rest at the filament towards the target by a potential
difference of 4500 V.
(i) Calculate the speed of the electrons before they reach the target.
speed = ………………..… m s-1 [2]
(ii) Calculate the wavelength associated with the electrons.
wavelength = …………………… m [2]
Fig. 2.1 Fig. 2.2
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(iii) When the electrons pass through the graphite target, a diffraction pattern is
observed on the screen as shown in Fig. 2.2. The first-order maximum of the
electron diffraction pattern occurs at an angle of 10 from the straight-through
position.
Calculate the separation of the atoms in the graphite.
separation = …………………… m [2]
(b) State three evidences from the photoelectric effect experiment that can be used to show
the particulate nature of electromagnetic radiation.
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
……………………………………………………………………………................................. [3]
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3 (a) An electron can be made to undergo uniform circular motion by applying a field.
(i) Sketch on Fig. 3.1 an electric field that enables the electron to move in a circular path. [2]
(ii) Sketch on Fig. 3.2 a magnetic field that enables the electron to move in a circular path. [2]
(b) Kepler’s third law states that the square of period, T2, of any planet orbiting around the
Sun is proportional to the cube of their mean distance, r3, from it.
Kepler’s third law led to the discovery of new planets such as Neptune in 1846.
(i) Derive Kepler’s third law from Newton’s law of gravitation.
[3]
(ii) State an assumption made in deriving the answer to (b)(i).
…………………………………………………………………………………………...........
……………………………………………………………………………........................ [1]
v
Fig. 3.1
v
Fig. 3.2
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(iii) The Earth is at a distance of 1.50 x 1011 m from the Sun. Calculate the distance of
Neptune from the Sun given that Neptune’s orbital period about the Sun is 165
times that of the Earth.
distance = …………………… m [2]
(iv) State the work done by the gravitational force of the Sun to keep the Earth in orbit.
Explain your answer.
………………………………………………………………………..…………....................
……………………………………………………………………………………..................
……………………………………………………………………………........................ [2]
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4 (a) Blue diamond, a stable form of carbon (group IV element), is a naturally occurring p-type
semiconductor which contains some boron atoms (group III element). Explain
qualitatively how this example of p-type doping changes the conduction properties of
carbon.
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
…………………………………………………………………………………………....................
……………………………………………………………………………................................. [3]
(b) A junction is formed when a p-type and a n-type semiconductor are joined together.
A sinusoidal alternating current (a.c.) source is connected across the p-n junction as
shown in Fig. 4.1.
(i) Explain how the junction acts as a rectifier when the switch in Fig. 4.1 is closed.
……………………………………………………………………………..……....................
…………………………………………………………………………………………...........
…………………………………………………………………………………………...........
…………………………………………………………………………………………...........
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
……………………………………………………………………………........................ [4]
p-type n-type
switch a.c. source
resistor
Fig. 4.1
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(ii) When the switch is closed, power is supplied from the a.c. source at 60 Hz with a
root-mean-square voltage of 220 V. Draw a graph with labelled axes to represent
the time variation of the potential difference across the resistor. Indicate the peak
voltage and the period on the graph.
[3]
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Section B Answer two questions in this section.
5 (a) (i) Explain what is meant by the internal energy of a gas.
……………………………………………………………………………………….…….…. ……………………………………………………………………………….....…….…. [2]
(ii) The pressure of ideal gas, p, is related to its density, , by the equation 2
31 cp where 2c is the mean square speed of the molecules.
Show that the internal energy of an ideal gas is directly proportional to its thermodynamic temperature.
[3]
(b) Explain, using the kinetic theory of matter, why
(i) the specific latent heat of vaporisation is higher than the specific latent heat of fusion for the same substance,
……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………….....…….…. [3]
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(ii) cooling effect accompanies evaporation.
……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………………….…….…. ……………………………………………………………………………….....…….…. [3]
(c) An engine contains 5.2 10–3 mol of gas at volume 5.0 10–5 m3 and pressure 6.0 105 Pa.
(i) Assuming ideal gas behaviour, calculate the temperature of the gas.
temperature of gas = ……..……….… K [2]
(ii) The gas is then heated at constant volume, raising its temperature by 800 K. This is done by supplying 85 J of energy to the gas.
1. The molar heat capacity, cv, of the gas at constant volume is the energy needed to raise the temperature of unit amount of gas by unit temperature. Calculate cv.
molar heat capacity = ……..……….… J mol–1 K–1 [2]
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2. Determine the final pressure of the gas.
final pressure of gas = ……..……….… Pa [2]
(iii) During the power stroke of the engine, the gas expands by doing 62 J of work, while no thermal energy enters or leaves the gas.
1. State the first law of thermodynamics.
……………………………………………………………………………………….…….…. ……………………………………………………………………………….....…….…. [1]
2. By applying the law to this process, calculate the change in the internal energy of the gas during the power stroke.
change in internal energy = ……..……….… J [2]
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6 (a) State the laws of electromagnetic induction.
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………............................... [3]
(b) A magnet is released from rest from the top of a copper pipe as shown in Fig. 6.1.
(i) Explain why the time taken for the magnet to fall is considerably longer than when
the magnet is released from the same height without the copper pipe.
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………........ [3]
Fig. 6.1 retort stand
copper pipe
magnet
h
15
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(ii) The copper pipe is replaced by a solenoid as shown in Fig. 6.2. The ends of the
solenoid are connected by a wire.
Explain why the time taken for the magnet to fall is shorter as compared to that
when the copper pipe was used.
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………...............
………………………………………………………………………………………........ [3]
Fig. 6.2 retort stand
connecting wire
magnet solenoid
h
16
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(c) For the experiment in (b)(i), the variation with time t of the velocity v of the magnet is
shown in Fig. 6.3.
(i) Define displacement.
………………………………………………………………………………………........................
………………………………………………………………………………………........................
………………………………………………………………………………………........................
……………………………………………………………………………................................. [2]
(ii) State the magnitude of the net force acting on the magnet just before it leaves the
pipe.
……………………………………………………………………………................................. [1]
0.0
1.0
2.0
3.0
4.0
5.0
0.0 0.5 1.0 1.5 2.0 2.5
Fig. 6.3
v / m s –1
t / s
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(iii) Using Fig. 6.3, estimate the value of h shown in Fig. 6.2.
h = ……..……….… m [2]
(iv) Using Fig. 6.3, sketch on Fig. 6.4, the variation with time t of the displacement s of
the magnet. [3]
Fig. 6.4 0.0 0.5 1.0 1.5 2.0 2.5
s / m
t / s
Fig. 6.4
18
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(v) The copper pipe is now placed on the table as shown in Fig. 6.5. The magnet is to
be released from the same height as in (b)(i).
Fig. 6.6 shows a predicted v – t graph for the motion of the magnet.
Discuss, with appropriate calculation why the velocity values of P and Q are
incorrect.
……………………………….………………………………………………........................ ………………………………………………………………………………………............... ……………………………….………………………………………………........................ ………………………………………………………………………………………............... ………………………………………………………………………………………........ [3]
0.0 0.5 1.0 1.5 2.0 2.5
P
Q
Fig. 6.6
v / m s-1
t / s
4.0
0.6
0.47
Fig. 6.5
retort stand
copper pipe
magnet
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7 (a) Some of the energy levels in atomic hydrogen are shown in Fig. 7.1.
Fig. 7.1
(i) Calculate the minimum wavelength of the radiation that could be emitted from
atomic hydrogen.
wavelength = ………………… m [3]
(ii) Sketch the pattern of the visible line emission spectrum of hydrogen. This takes
place when electrons fall to the -3.40 eV level. Mark the red and violet ends of the
spectrum.
[3]
(b) A considerable amount of light can be obtained by connecting 240 V alternating voltage
across a pickle. The emission spectrum is most intense at wavelengths 589.0 nm and
589.6 nm.
(i) Explain how the existence of electron energy levels in atoms gives rise to emission
line spectra.
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………................................. [3]
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(ii) Fig. 7.2 shows the emission spectra of three different elements. Deduce the
element present in the pickle.
……………………………………………………………………………………….......................
……………………………………………………………………………………….......................
……………………………………………………………………………................................. [2]
Fig. 7.2
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(c) On Fig. 7.3, monochromatic light of wavelength 300 nm is irradiated onto an aluminium
target. When the switch is closed, the variable resistor is adjusted to a value of 760 to
obtain zero current on the ammeter.
(i) Determine the potential difference across the 40.0 resistor.
potential difference = ………………… V [2]
(ii) Hence, calculate the threshold frequency of the aluminium target.
frequency = ………………… Hz [3]
A
40.0
3.00 V
Fig. 7.3
light
target switch
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(iii) The switch is now open in Fig. 7.3. Sketch a graph to show the variation with time
of the photoelectric current for each of the following cases:
1. The intensity of the light source is increased at a constant rate. [2]
2. The frequency of the light source is decreased at a constant rate. [2]
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