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Transcript
```F.7 Physics
P. 1 /16
SKH LAM WOO MEMORIAL SECONDARY SCHOOL
Mock Examination (2004-2005)
F.7 Physics Paper II
Name:
Class:
Marks:
( )
Date: 21-2-05 (Mon)
Time Allowed: 3 hours
Instructions: 1. Total marks of the paper: 93
2. Section A – Multiple-choice Questions – Answer ALL Questions
Section B – Answer any THREE Question
3. Take g  10 ms2 unless otherwise stated.
Section A (45 marks)
1. All questions carry equal marks.
3. You should mark only ONE answer for each question. If you mark more than
4. No marks will be deducted for wrong answers.
1. In order to support a load W, four light hinged rods P, Q, R
and S are connected and mounted in a vertical plane.
Which rods are in compression and which in tension?
in compression
in tension
A.
R, S
P, Q
B.
Q, R
P, S
C.
Q, R, S
P
D.
P, Q
R, S
2. In a nuclear reactor, fast moving neutrons released in fission events can be slowed
down through elastic collisions with nuclei of some substances. You may assume
the nuclei are free particles and both gravitational and electric forces can be ignored.
Which of the following substances are most effective in slowing down the
neutrons?
B. Iron-56
C. Boron-11
D. Hydrogen-1
F.7 Physics
P. 2 /16
3. A body is projected with initial speed u at elevation  with the horizontal. Which
graph represents the variation of its speed v with time t?
A.
B.
C.
D.
4. For no spilling of water, the minimum speed of a bucket of water at the highest
point when whirled in a vertical circle is 2 ms-1. The radius of the circle is
A. 0.1 m
B. 0.2 m
C. 0.4 m
D. 0.8 m
5. A point mass P slides down from rest as shown
in the figure. It starts to leave the sphere when
 is
A. 41.8
C. 70.5
B. 48.2
D. 90
6. All three systems represented as p, q and r in the diagrams below show simple
harmonic motion.
spring
string
spring
Frictionless slider
p
q
In which system will the period be independent of the mass of body?
A. p only
B. r only
C. q and r only
D. p, q and r
r
7. A mass m slides on a frictionless horizontal
surface at speed vo. It strikes a light spring of
force constant k attached to a rigid wall as shown.
After a completely elastic encounter with the
spring the mass moves in the opposite direction.
In terms of k, m and vo, how long is the mass m in contact with the spring?
A.

2
mvo
k
B. 
m
k
C. 2
m
k
D. 2
k
mvo
F.7 Physics
P. 3 /16
8. A string suspended from a ceiling is wrapped around a uniform
cylinder of mass 1 kg and radius 0.1 m, as shown.
What is the acceleration of the cylinder when it rolls down the
string? (Given: moment of inertia of the cylinder about an axis
1
through its centre and along the length of the cylinder is mr 2 )
2
A. 1.0 ms-2
C. 5.0 ms-2
B. 3.3 ms-2
D. 6.7 ms-2
9. A ring, a thin circular disc and a square disc have equal masses IA, IB, IC are the
respective moment of inertia of the three objects.
2R
2R
IA
IB
IC
2R
ring
circular disc
square disc
Rotating about the axis through their centres of mass and perpendicular to their
surfaces,which of the following sequences arranges IA, IB and IC in ascending
order?
A. IA< IB< IC
B. IA< IC< IB
C. IB< IA< IC
D. IB< IC< IA
10. The orbital path of the Earth around the Sun is elliptical in shape. Which of the
following about the Earth can be explained by the law of conervation of angular
momentum?
(1) The axis of spinning of the Earth remains fixed in direction.
(2) The angular speed increases when it moves closer to the Sun.
(3) The period of the rotation of the Earth around the Sun remains the same year
after year.
A. (3) only
C. (2) and (3) only
B. (1) and (2) only
D. (1), (2) and (3)
11. A satellite skimming over the surface of the Earth follows a circular orbit. By what
factor must the speed of the satellite be increased so that it may escape from the
Earth permanently?
A. 2
C. 2 2
B. 2
D. 4 2
F.7 Physics
P. 4 /16
12. The following figure shows an apparatus for measuring the speed of light c. Light
is incident at P on one face of an octagonal mirror M and then traverses a path
PQRS, of total length L, before being reflected again from another face of M.
M is rotated about its axis of symmetry as indicated and its angular velocity is
adjusted until the light emerges in the same direction as when M is stationary.
What is the smallest angular velocity at which this condition is achieved?
A.  c / 8 L
B.  c / 4 L
C.  c / 2 L
D.  c / L
13. A slit of width d is illuminated
normally by parallel monochromatic
light of wavelength  . A converging
lens L of focal length f projects the
diffraction pattern on to a screen S in
its focal plane.
The intensity of illumination on the screen is greatest at O and first becomes zero
at a distance x from O. The quantities d,  , f and x are related by the equation
A. x  d / f
B. x  f / d
C. x  d / f
D. x  1 / df
14. Two identical narrow slits S1 and S2 are illuminated by light of wavelength 
from a point source P.
l1
l2
l3
l4
If, as shown in the figure above, the light is then allowed to fall on a screen, and if
m is a positive integer, the condition for destructive interference at Q is that
A. l3  l 4  (2m  1) / 2
B. l3  l 4  m
C. (l1  l3 )  (l 2  l 4 )  (2m  1) / 2
D. (l1  l3 )  (l 2  l 4 )  m
F.7 Physics
P. 5 /16
15. A thin biconvex lens is placed on a flat glass plate. The arrangement is illuminated
with monochromatic light and observed through a partially reflecting plate as
shown below.
Which one of the following diagrams could illustrate the observed pattern of dark
fringes?
A
B
C
D
16. The figure below shows a beam of initially unpolarised light passing through three
polaroids P1, P2 and P3. The polarising axis of each polaroid is shown by an arrow.
Polaroids P1 and P2 are fixed, with their polarising axes at 30o to one another, and
P3 can be set with its polarising axis at a variable angle  to that of P1.
30o

P1
P2
P3
For what values of  do intensity minima of the emergent light occur?
A. 30o, 120o, 210o, 300o
B. 90o, 120o, 270o, 300o
C. 90o, 270o
D. 120o, 300o
17. Two glass tubes as shown are identical in
all respects except that one of them has
one end closed.
If the air columns in the tubes are caused
to oscillate in their fundamental mode,
what do these oscillations have in common?
(1) Same number of vibrational antinodes
(2) Same wavelength
(3) Same wave speed
A. (1) only
B. (3) only
C. (1) and (3) only
D. (1), (2) and (3)
F.7 Physics
P. 6 /16
18. A man stands near a railway track when a train approaches and then passes him.
The train sounds its whistle all the time. The highest note and the lowest note the
man hears are of frequency 110 Hz and 90 Hz respectively. The actual frequency
of the whistle is
A. 95 Hz
B. 99 Hz
C. 100 Hz
D. 105 Hz
19. The figure shows an object O placed at the focus of a converging lens L. A
concave mirror M is arranged on the other side of L and is 80 cm from it.
If the focal length of L is 60 cm and the final image formed by this system is at
infinity, what is the focal length of M?
A. 20 cm
B. 30 cm
C. 40 cm
D. 70 cm
20. A sample of an ideal gas initially having internal energy U1 is allowed to expand
adiabatically performing external work W. Heat Q is then supplied to it, keeping
the volume constant as its new value, until the pressure rises to its original value.
The internal energy is then U2.
The increase in internal energy , U1 – U2 equal to
A. W
B. Q
C. Q – W
D. W – Q
F.7 Physics
P. 7 /16
21. Two vessels X and Y of volumes VX and VY, connected by a tube of negligible
volume and kept at temperatures TX and TY respectively, contain the same ideal
number of molecules of X
gas. What is the value of the ratio
?
number of molecules of Y
A.
VY TY
V X TX
B.
C.
V X TY
VY TX
D.
VY TX
V X TY
V X TY
VY T X
22. The charge-to-mass ratio for an electron is 1.76  1011 C kg-1. What is the ratio of
the electrostatic force on an electron situated in an electric field of intensity
200Vm-1 to the gravitational force on the Earth surface?
A. 2.8  10 13
C. 3.52  1012
B. 20
D. 3.52  1013
23. A charged particle is accelerated across the gap between two parallel metal plates
maintained at a certain potential difference in a vacuum.
Assuming there is no gravitational force, the energy acquired by the charged
particle in crossing the gap depends on
(1) the potential difference between the plates.
(2) the charge of the charged particle.
(3) the width of the gap.
A. (1) only
B. (1) and (2) only
C. (2) and (3) only
D. (1), (2) and (3)
24. In discussing electric fields, the terms electric field strength, electric potential and
potential gradient are used. Which one of the following statements about these
terms is correct?
A. Unit potential gradient exists between any two points if one joule of work
is done in transporting one coulomb of charge between the points.
B. The electric potential at a point is the force on unit positive charge placed at
that point.
C. Electric field strength at a point is the work done in bringing unit positive
charge from infinity to the point.
D. The potential gradient at a point is numerically equal to the electric field
strength at that point.
F.7 Physics
P. 8 /16
25. The diagram shows a network of three resistors. Two
of these, marked R, are identical. The other one has a
resistance of 5.0  .
The resistance between Y and Z is found to be 2.5  .
What is the resistance between X and Y?
A. 0.21 
B. 0.53 
C. 1.9 
D. 4.8 
Y
R
5.0 
X
R
Z
26. Three capacitors of equal capacitance of 3  F are joined to the terminals of a 12V
battery. What are the charges carries by C1 and C3?
Charges on C1
Charges on C3
A.
6 C
12  C
B.
12  C
12  C
C.
12  C
24  C
D.
24  C
24  C
27. An electron moves in a circular path in a uniform magnetic field of flux density
1mT. If an  -particle of the same speed follows an identical path, what must be
the magnetic field? Given that mass of an  -particle is 7200 times that of an
electron.
A. 3600 mT in opposite direction
B. 1800 mT in opposite direction
C. 1800 mT in the same direction
D. 3600 mT in the same direction
28. X and Y are identical flexible conducting ribbons, suspended from
points P and Q. The bottom parts of the ribbons lie in dishes of a
conducting liquid at R and S.
When a current 2I is passes from R to P through X, and a
current I is passes from Q to S through Y, which of the diagrams
best represents the shapes assumed by the ribbons (if the ribbons remain in contact
with the conducting liquid at R and S)?
F.7 Physics
P. 9 /16
29. A plane coil of wire containing N turns each of area A is
placed so that the plane of the coil makes an angle  with
the direction of a uniform magnetic field of flux density B.
The coil is now moved through a distance x in time t to
the position shown dotted in the figure.
What is the e.m.f. induced in the coil?
A. zero
B. NABx/t
C. NBx(cos  )/t
D. NABx(cos  )/t
plane of coil

x
B
30. An aluminium ring hangs vertically from a thread with its axis pointing east-west.
A coil is fixed near to the ring and coaxial with it.
N
W
E
S
What is the initial motion of the aluminium ring when the current in the coil is
switched on?
A. remains at rest
B. moves towards S
C. moves towards W
D. moves towards E
31. An ammeter is connected in series with an electric motor which is running freely,
of the ammeter will
A. increase to a higher value.
B. decrease to a lower value.
C. increase to a maximum value and then decrease.
D. decrease to a minimum value and then increase.
32. The sinusoidal p.d. V1 shown in the figure applied across a
resistor R produces heat at a mean rate W. What is the mean
rate of production of heat when the square-wave p.d. V2
shown in the figure is applied across R?
A. W / 2
C. 2W
B.
D.
V1
V0
time
-Vo
2W
V2
4W
V0
time
-Vo
F.7 Physics
P. 10 /16
33. In the circuit shown in figure a, the r.m.s. currents I1, I2 and I3 are altered by
varying the frequency f of the oscillator. The output voltage of the oscillator
remains sinusoidal and has a fixed amplitude.
I3
I1
I2
Figure a
Figure b
Which curves in figure b indicate correctly the variations with frequency of the
current I1, I2 and I3?
I1
I2
I3
A.
B.
C.
D.
R
R
Q
Q
P
Q
P
R
Q
P
R
P
34. In an LCR series circuit the frequency of the a.c. supply is adjusted so that the
current registered is a maximum. The values of capacitance and inductance and
frequency remain unchanged but the resistance is increased by a factor of four.
The current will
A. stay the same.
B. increase by a factor of two.
C. increase by a factor of four.
D. decrease by a factor of four.
35. In the circuit shown, when the transistor is conducting, the p.d. VBE between the
base and the emitter is 0.7 V and the minimum p.d. VCE between the collector and
the emitter is 0.2 V. Assume that the current amplification factor of the transistor is
100. Determine the collector current Ic.
A. 2.7 mA
2k
Ic
B. 2.9 mA
4k
6V
C. 20 mA
D. 37.5 mA
1.5 V
5V
F.7 Physics
P. 11 /16
36. An input voltage (Vin) of 2.0 V is applied to an ideal
operational amplifier connected as shown.
The current flowing through the 8 k resistor is
A. 0.80 mA from X to Y
B. 0.80 mA from Y to X
C. 1.0 mA from X to Y
D. 1.0 mA from Y to X
37. The following figure shows the variation of potential energy U between two atoms
with distance r separating them in a solid.
Which of the following statements is/are correct?
(1) The atoms will experience a repulsive force when r < b.
(2) The atoms will experience an attractive force when r > a.
(3) The atoms are at equilibrium separation when r = a.
A. (1) only
B. (3) only
C. (2) and (3) only
D. (1), (2) and (3)
38. A steel bar has a radius of R1 for half its length and a radius of R2 = R1 / 2 for the
other half. When subject to axial loading, what is the ratio e1 : e2 of the elastic
energy densities in the two parts of the bar?
A. 1 : 16
B. 1 : 4
C. 1 : 2
D. 1 : 2
39. The Thomson’s apparatus is used for measuring the charge-mass ratio e/m.
When the accelerating voltage is V, the radius of the electrons path in the magnetic
field is r. What will be the radius if the accelerating voltage is 4V? Assume the
electrons emitted from the cathode by thermionic emission have zero initial
velocity.
A. 2 r
B. 2 r
C. 2 2 r
D. 4 r
F.7 Physics
P. 12 /16
40. A monochromatic beam of blue light falls on one electrode of a photo-cell and
electrons are emitted. The light beam is then replaced by a red light delivering the
same energy per second to the cell. Which one of the following quantities
increases as a result of this change?
A. The maximum kinetic energy of the electrons emitted.
B. The number of photons striking the metal per second.
C. The work function of the metal.
D. The magnitude of the p.d. required across the cell to reduce the current to
zero.
41. In an X-ray tube, the penetrating power of the X-ray beam emitted can be
increased by
(1) increasing the p.d. between the anode and the cathode.
(2) decreasing the cathode to anode distance while maintaining the same p.d.
between them.
(3) raising the temperature of the cathode.
A. (1) only
B. (3) only
C. (1) and (3) only
D. (1), (2) and (3)
42. The potential difference across different parts of a circuit are applied to a CRO.
The p.d. across the purely resistive portion A is applied to the X-plates while the
p.d. across the portion B with unknown impedance is applied to the Y-plates. An
elliptical trace is displaced on the screen of the CRO as shown. What is the power
factor of the circuit between the portion B?
A. 0.86
B. 0.75
C. 0.66
D. 0.48
43.
3
He is an isotope of helium. The masses of a proton, a neutron and a
2
2
2
3
He
nucleus are 938.3 MeV/c , 939.6 MeV/c and 2808.5 MeV/ c respectively. The
binding energy of 3 He is
A. zero.
B. 7.7 MeV.
C. 9.0 MeV.
D. 930.6 MeV.
F.7 Physics
P. 13 /16
44. When fission occurs in a heavy nucleus, the two nuclei produced
(1) are stable.
(2) contains more protons than neutrons.
(3) have more binding energy per nucleon than the original nucleus.
A. (1), (2) and (3)
B. (1) and (2) only
C. (1) only
D. (3) only
45. A student attempts to measure the diameter of a steel ball by using a metre rule to
measure four similar balls in a row.
0
1
2
3
4
X
The positions on the scale are estimated to be
5
cm
Y
X is 1.0  0.2cm
Y is 5.0  0.2cm
What is the diameter of a steel ball together with its associated uncertainty?
A. 1.0  0.05cm
B. 1.0  0.1cm
C. 1.0  0.2cm
D. 1.0  0.24cm
End of Section A
Section B (48 marks)
1. (a) Derive an expression for the kinetic energy of a body of mass m, and hence
explain its meaning, by considering the body to be linearly accelerated from
rest to a velocity v.
(2 marks)
(b) Show that an analogy exists for rotational motion and hence define the
physical quantity "moment of inertia".
(3 marks)
(c) How would you differentiate experimentally between a hollow and a solid
cylinder, which both have the same dimensions and mass? Give the theory of
(4 marks)
(d) Describe, and give the theory of, an experiment to measure the moment of
inertia of a flywheel.
(7 marks)
F.7 Physics
P. 14 /16
2. (a) Explain the physical origin for the production of acoustic resonance in a
measuring cylinder with the help of a tuning fork, an open pipe and water.
(3 marks)
(b) Consider the case of a fundamental note emitted from the measuring cylinder,
state the characteristic features for the
(i) phase,
(ii) amplitude, and
(iii) motion
of the air particles inside the cylinder.
Also describe how the frequency of the tuning fork can be determined
experimentally.
(5 marks)
(c) Describe an experimental procedures to find the speed of sound waves from
the results of producing
(i) resonance effect, and
(ii) interference effect.
(8 marks)
3. (a) Describe and explain briefly the methods adopted in the measurement of
(i) a steady magnetic field using a Hall probe, and
(ii) an alternating magnetic field using a search coil.
Compare the different physical mechanisms in these two methods and derive
any necessary mathematical expressions.
(11 marks)
(b) Comment briefly on the main factors that might affect the accuracy of the
measurements.
(5 marks)
4. (a) Draw a circuit which can be used to observe the periodic variations of current
and applied a.c. voltage for a capacitor. Also explain quantitatively the phase
relationship between current and voltage.
(3 marks)
(b) Explain how a combination of R-L can be used in high frequency and low
frequency filters in loudspeakers.
(3 marks)
(c) (i) Describe an experiment to study the phase difference in a series R-L-C
circuit between the r.m.s. current and constant r.m.s. source voltage as the
frequency changes.
(4 marks)
(ii) Explain the changes in phase difference and power of the circuit by using
phasor diagrams.
(6 marks)
F.7 Physics
P. 15 /16
5. (a) (i) Using a practical example, demonstrate what is meant by ‘the conservation
of mechanical energy’.
(ii) By means of a further practical example, show that in ‘real-life’ situations
mechanical energy is often not conserved.
(3 marks)
(b) Derive Bernoulli’s equation for fluid flow:
1
(6 marks)
P  hg  v 2  a constant .
2
(c) Explain why Bernoulli’s equation is not strictly applicable to
(i) a gas, and
(ii) a viscous liquid flowing through a narrow tube.
(3 marks)
(d) With the aid of diagrams and Bernoulli’s equation, explain the observed
effects of
(i) the motion of a spinning ball, and
(ii) the mixing of coal gas and air in a bunsen burner.
(4 marks)
—
End of Paper —
Title of the publication: 1991 Paper II (1), 1987 Paper II(1)
Date of making this copy: 15/1/2005
This material has been copied under a licence issued by HKEAA. You are not permitted to make any
further copy of this work, or to make it available to others. It is important to understand and respect
F.7 Physics
P. 16 /16
1.
No.
(letter)
1
A
2
D
3
C
4
C
5
B
6
B
7
B
8
D
9
D
10
D
No.
(letter)
11
A
12
B
13
B
14
C
15
A
16
D
17
B
18
B
19
A
20
C
No.
(letter)
21
C
22
C
23
B
24
D
25
C
26
C
27
A
28
A
29
A
30
D
No.
(letter)
31
A
32
C
33
D
34
D
35
B
36
D
37
A
38
A
39
B
40
B
No.
(letter)
41
A
42
C
43
B
44
D
45
B
F.7 Physics
P. 17 /16
F.7 Physics
P. 18 /16
2
1A
1A
F.7 Physics
P. 19 /16
(c)
3. (a) (i)
diagram
If a conductor carrying a current I is placed in a magnetic field B,
a magnetic force qvB then acts at right angles to the direction of
the magnetic field and the current.
This force causes the charge carriers to be pushed upward for
½
½
F.7 Physics
P. 20 /16
positive charge carriers or downwards for negative charge carriers,
½
thus increasing their concentration towards one side of the conductor.
As a result, a p.d. VH ( and an electric field ) is produced across
the conductor.
½
When the electric force qE is equal to the magnetic force qvB,
the charge carriers are in equilibrium.
½
i.e.
qE = qvB
since qE =
VH
,
d
q
VH
= qvB
d
VH = Bvd
For a conductor of cross-sectional area A carrying current I
½
and having n charge carriers per unit volume, I = nAqv.
BId
BI
Therefore we have VH =
=
nqt
nAq
½
½
If n, t, I are known, B can be found by measuring VH
½
In practice, the Hall probe is first calibrated by a standard magnetic
field before measurement if absolute value is required.
½
Before the measurement, make sure the p.d. of the Hall probe is
zero by adjusting the ‘balance’ control.
½
If the Hall p.d. connections X and Y on the slab are not directly
opposite each other, a p.d. will exist between them even in the
(a) (ii)
absence of a magnetic field.
During the measurement, the Hall probe should be rotated until
a maximum voltage is obtained,
otherwise only a component of magnetic field is measured.
The current through the conductor should be kept constant all
the time since VH varies with current.
A search coil consists of N turns of wire enclosing an area A.
When it is exposed to a changing magnetic field component B
perpendicular to the coil, it produces an induced e.m.f. across PQ
½
proportional to the rate of change of B.
½
½
½
P
B = B0 sinwt
diagram
Q
 = - NA
Area A
dB
dt
½
½
F.7 Physics
P. 21 /16
i.e.
(b) (i)
 = -wNAB0 cos wt
 = -V0 cos wt
where V0 = wNAB0
Connect the coil PQ to a CRO.
A sinusoidal signal will be seen on the CRO.
Rotate the coil until the amplitude of the signal is a maximum.
i.e. the orientation of the coil is perpendicular to the magnetic field.
The amplitude is proportional to B0.
Again the search coil need to be calibrated if absolute
measurement is required.
The following might affect the accuracy of the measurement:
1. The probe may not be exactly perpendicular to the field.
2. The area of the probe restricts the spatial resolution
if there is magnetic field gradient along the area.
3. The change in temperature affect the mobility of
½
½
½
½
½
11
1
1
the charge carriers significantly.
Thus an increase in temperature increases the Hall voltage as well.1
(b) (ii) The accuracy might be affected by:
1.
sensitivity of the CRO to give large amplitude trace.
1
2. stray fields which could be comparable to field being measured. 1
5
4.
F.7 Physics
(c) (i)
P. 22 /16
(c) (ii)
5.
.
F.7 Physics
P. 23 /16
F.7 Physics
P. 24 /16
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