Physics Stage 3 Exam 2012

Western Australian Certificate of Education
Examination, 2012
Question/Answer Booklet
PHYSICS Please place your student identification label in this box
Stage 3
Student Number: In figures
In words
Time allowed for this paper

Reading time before commencing work: ten minutes
Working time for paper: three hours
Materials required/recommended for this paper

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Number of additional
This Question/Answer Booklet
answer booklets used
Formulae and Data Booklet (if applicable):
To be provided by the candidate
Standard items: pens (blue/black preferred), pencils (including coloured), sharpener,
correction tape/fluid, eraser, ruler, highlighters
Special items: non-programmable calculators approved for use in the WACE examinations,
drawing templates, drawing compass and a protractor
Important note to candidates

No other items may be taken into the examination room. It is your responsibility to ensure that
you do not have any unauthorised notes or other items of a non-personal nature in the
examination room. If you have any unauthorised material with you, hand it to the supervisor
before reading any further.
Copyright © School Curriculum and Standards Authority 2012
Ref: 12-130
*PHY3* PHY3
PHYSICS 2 STAGE 3
Structure of this paper
Number of Number of Suggested

Marks Percentage
Section questions questions to working time
available of exam
available be answered (minutes)
Section One:
Short response 11 11 50 54 30
Section Two:
Problem-solving 7 7 90 90 50
Section Three:
2 2 40 36 20
Comprehension
Total 100
DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF

Instructions to candidates
1. The rules for the conduct of Western Australian external examinations are detailed in
the Year 12 Information Handbook 2012. Sitting this examination implies that you
agree to abide by these rules.
2. Write your answers in this Question/Answer Booklet.
3. When calculating numerical answers, show your working or reasoning clearly. Give
final answers to three significant figures and include appropriate units where applicable.

When estimating numerical answers, show your working or reasoning clearly. Give final
answers to a maximum of two significant figures and include appropriate units where
applicable.
4. You must be careful to confine your responses to the specific questions asked and to
follow any instructions that are specific to a particular question.
5. Spare pages are included at the end of this booklet. They can be used for planning
your responses and/or as additional space if required to continue an answer.
● Planning: If you use the spare pages for planning, indicate this clearly at the top
of the page.
● Continuing an answer: If you need to use the space to continue an answer, indicate
in the original answer space where the answer is continued, i.e. give the page
number. Fill in the number of the question(s) that you are continuing to answer at the
top of the page.
6. The Formulae and Data booklet is not handed in with your Question/Answer Booklet.
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STAGE 3 3 PHYSICS
Section One: Short answers 30% (54 Marks)
This section has eleven (11) questions. Answer all questions.
When calculating numerical answers, show your working or reasoning clearly. Give final answers
to three significant figures and include appropriate units where applicable.
When estimating numerical answers, show your working or reasoning clearly. Give final answers
to a maximum of two significant figures and include appropriate units where applicable.
Spare pages are included at the end of this booklet. They can be used for planning your
responses and/or as additional space if required to continue an answer.
● Planning: If you use the spare pages for planning, indicate this clearly at the top of the page.
● Continuing an answer: If you need to use the space to continue an answer, indicate in the
original answer space where the answer is continued, i.e. give the page number. Fill in the
number of the question(s) that you are continuing to answer at the top of the page.
Suggested working time: 50 minutes.
Question 1 (3 marks)
The diagram below shows a string 250 cm long vibrating in its fundamental mode between two
fixed points.
a c
The string is vibrating with a frequency of 100 Hz.

For each of the positions a, b, and c, indicate whether these are nodes or antinodes, and
calculate the speed of the wave.
a:
b:
c:
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PHYSICS 4 STAGE 3
The figure below shows three simplified absorption spectra for ionised calcium. Many of the
absorption lines and the background colour have been removed. In all three spectra the same
two absorption lines, ‘a’ and ‘b’, are shown. The top spectrum is an example of a spectrum
recorded in a laboratory on Earth; the lower two have been recorded from two different galaxies.
a b
Our Sun’s calcium absorption spectrum

as seen from Earth.
λ(nm) 390 410
a b

The calcium absorption spectrum of
Galaxy NGC 2903.
λ(nm) 390 410
a b
The calcium absorption spectrum of
Galaxy NGC 3147.
λ(nm) 390 410
(a) Explain why absorption spectra appear as dark lines on an otherwise continuous
electromagnetic spectrum. (3 marks)
(b) Which galaxy is further away from Earth? Justify your answer. (3 marks)
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STAGE 3 5 PHYSICS
The two diagrams below show wavefronts incident on gaps of different width. On each diagram
draw five (5) wavefronts to show how the waves behave after they have passed through the gap.
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PHYSICS 6 STAGE 3
The diagram below shows a section lengthwise through a bird whistle capable of making sounds
over a large range of frequencies. The frequency can be changed by moving the plunger inside
the whistle. The longest length of the whistle is 8.7 cm.
8.7 cm
Plunger

You should assume that air at 25°C is in the whistle.
Determine the distance moved by the plunger when changing the fundamental note from 18 kHz
to 21 kHz, and draw a diagram of the fundamental wave in the whistle.
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STAGE 3 7 PHYSICS
The diagram below shows a side view of a laptop computer resting on an outdoor table. The
mass of the base of the laptop is 2.00 kg and the mass of the screen is 600 g. They are both
22.0 cm long. There is an angle of 50.0° between the horizontal and the screen. The computer is
blown over by wind.
Assume that the base and screen both have a uniform mass distribution.
Wind
22
cm
50°
22 cm
Calculate the minimum single equivalent wind force on the centre of the screen needed to tip the
laptop over.
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PHYSICS 8 STAGE 3
The diagram below shows a tenpin bowler propelling a bowling ball which has a velocity of
11.5 m s−1 when released. The distance from the bowler’s shoulder to the top of the ball is
0.700 m and the ball has a diameter of 0.250 m. The ball has a mass of 6.00 kg.
The bowler approaches the lane at 3.00 m s−1.
3 m s−1

0.700 m
(a) Calculate the tension in the bowler’s arm, due to the bowling ball, as the ball is released.
You should assume the ball is released horizontally from the lowest point. (4 marks)
(b) Draw an arrow on the diagram to show the direction of the force exerted on the bowler’s
arm by the shoulder joint. (1 mark)
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STAGE 3 9 PHYSICS
An electron moving with an initial velocity u, has initial kinetic energy EKi . It enters a uniform
electric field with field strength E, as shown in the diagram below. The electron’s final kinetic
energy EKf is equal to 4EKi.
u v
e−
The electric field strength is now doubled. If another electron, having initial kinetic energy EKi
enters the field, determine this electron’s final kinetic energy in terms of EKi.
You should ignore the effects of gravity.
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PHYSICS 10 STAGE 3
A GPS system uses the signals from four satellites to establish a position on the Earth’s surface.
The satellites have an orbital period of 12.0 hours but they are in different planes of orbit. Each
satellite has an atomic clock that allows a signal to be emitted at prescribed intervals. The time
difference between the four signals is used by the receiver to establish a position.
(a) By equating the relationship for centripetal force and gravitational force show that the
orbital velocity of each satellite is close to 3.90 × 103 m s−1. (5 marks)
2�r
Hint: v =
T
Show all your workings.

(b) The manufacturers of the satellites deliberately build in a correction to the rate at which
the clocks tick so that they run a little fast before they are put into orbit. Explain why
they do this. (2 marks)
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STAGE 3 11 PHYSICS
A uniform beam of length 2.00 m and mass 1.00 kg sits horizontally on a table. Two balls, A and
B, are initially stationary on the left edge of the beam. Ball A has a mass of 2.00 kg and Ball B
has a mass of 0.250 kg. This is summarised in Diagram 1 below.
Side view Front view
Ball B Ball A Ball A

1m
Ball B
Diagram 1
Beam
Table
Ball A is pushed to the right and begins to move toward with a constant velocity, v. This is shown
in Diagram 2 below.
Front view
v
Ball B
Ball A
Diagram 2 Beam
Table
Determine, in terms of v, the time at which Ball B begins to move.
Hint: Consider the positions of the balls at the moment that Ball B begins to move.
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PHYSICS 12 STAGE 3
Your use of appropriate significant figures will be assessed in this question.
The photograph shows a motorcyclist riding around a roundabout on a flat road.

(a) Show that the angle between the motorcyclist and the road is independent of the mass
of the motorcyclist. Draw a vector diagram to assist your answer. (3 marks)
(b) Using an appropriate calculation, estimate the velocity of the motorcyclist in the
photograph. Use the photograph as a guide. (3 marks)
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STAGE 3 13 PHYSICS
Your use of appropriate significant figures will be assessed in this question.
The photograph shows a swimming pool toy that sprays water when the plunger is pressed into
the barrel containing water. A boy, using the toy, sprays water vertically from a height of 1 m and
counts the time from the last drop of water leaving the barrel to it hitting the ground and finds it
to be 3 s.
Plunger Barrel
Estimate the angle at which the toy should be held if it is to be used to spray water from the
surface of a swimming pool onto a person 4 m away. Assume that air resistance is negligible and
show all your workings.
4m
Person with Pool surface Person being

plunger aimed at
Hint: You may need to use the trigonometric identity sin 2θ = 2 sinθ cosθ to answer this question.
End of Section One
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PHYSICS 14 STAGE 3
Section Two: Problem-solving 50% (90 Marks)
This section has seven (7) questions. Answer all questions. Write your answers in the spaces
provided.
● Planning: If you use the spare pages for planning, indicate this clearly at the top of
the page.

Photovoltaic cells are used to generate electricity from sunlight. Photons in sunlight hit the cell
and are absorbed by a semiconducting material and electrons are raised to a higher energy level
and become conducting electrons. A common material in photovoltaic cells is monocrystalline
silicon, which has a band gap energy of 1.1 eV.
A solar panel consists of 72 photovoltaic cells each with dimensions of 0.125 m × 0.125 m.
Under test conditions the panel generates electricity at a rate of 190 W. During a test, 1000 W m−2
falls on a panel, and the energy includes a full range of solar wavelengths.
(a) Calculate the wavelength of electromagnetic radiation absorbed by the silicon, which
causes electrons to become conducting electrons. State which part of the
electromagnetic spectrum this wavelength belongs to. (3 marks)
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STAGE 3 15 PHYSICS
(b) Calculate the efficiency of the solar panel. Assume that there is no gap between the cells
on the panel. (3 marks)
A wind turbine generates electricity at a rate of 2000 kW at a voltage of 690 V. The turbine is
connected to a transformer which increases the voltage to 33 kV before connecting it to the
electricity grid.
(c) Determine the turns ratio for the transformer connected to the wind turbine. (2 marks)
(d) Explain why the voltage is increased before it is transmitted. (3 marks)
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PHYSICS 16 STAGE 3
A and B are two identical very small particles. They are both positively charged with charge
+ Q. They are fixed in position 10 units apart.
(a) On the diagram below draw the resultant electric field around the charged particles.
You should draw at least five (5) field lines around each particle. (3 marks)
A
+Q

+Q
B
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STAGE 3 17 PHYSICS
(b) C and D are two particles with identical mass and volume to A and B but they have
charge –Q. Draw particles C and D on the diagram below so that the four particles will
be in static equilibrium. (3 marks)
A
+Q
+Q
B
(c) On the diagram above draw and label three (3) arrows on particle C to indicate the forces
acting on particle C due to the other three particles. (3 marks)
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PHYSICS 18 STAGE 3
The Kepler NASA mission aims to search for planets orbiting stars in other solar systems.
The star named Kepler 20 has been observed to have several planets orbiting it. Kepler 20 is
950 light-years from Earth.
Information about Kepler 20 and some of the planets orbiting it is summarised in the table below.
Astronomical Orbital period around

Radius Mass
object Kepler 20
Star – Kepler 20 0.944 × radiusSUN 0.912 × massSUN
Planet – Kepler 20b 2.40 × radiusEARTH 290 days
Planet – Kepler 20e 0.87 × radiusEARTH 6.1 days
Planet – Kepler 20f 1.03 × radiusEARTH 19.6 days

(a) A light-year is an astronomical unit of distance. It is defined as the distance travelled
by light in one year. Calculate the distance from Kepler 20 to Earth in kilometres.
(2 marks)
(b) Astronomers express the mass of Kepler 20 as (0.912 ± 0.035) × massSUN.

Calculate the maximum value astronomers expect for the mass of Kepler 20. (2 marks)
(c) Calculate the orbital radius of Kepler 20e around Kepler 20. You should use the mass
for Kepler 20 quoted in the table and assume the orbit is circular. (4 marks)
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STAGE 3 19 PHYSICS
(d) The mass of Kepler 20b is unknown but it has been speculated that it may have a
density similar to that of Earth, 5520 kg m-3. Calculate the surface gravity of Kepler 20b
if its density is 5520 kg m-3. (4 marks)

Reminder:
mass
density = volume

4
volume of a sphere = 3 �r3

The Kepler mission is particularly concerned with finding planets that lie within the
habitable zones of stars. A planet in a star’s habitable zone receives the right amount
of energy from the star to maintain liquid water on its surface, provided it also has an
appropriate atmosphere.
(e) By comparing the Kepler 20 system and our own solar system, suggest which planet
in the Kepler 20 system is most likely to lie in the habitable zone. Explain your answer.
(3 marks)
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PHYSICS 20 STAGE 3
Two parallel metal rails are connected by a resistor. A vehicle made of copper allows current to
flow between the rails and moves from rest at Position I to Position V.
I II III IV V
Top view
B
I II III V
Side view R = 0.750 m

IV
Permanent magnet
(a) The vehicle moves between Position I and Position II in 3.00 s, driven by a 3.00 V,
20.0 mA motor. The energy conversion efficiency of the vehicle is 70.0% and the mass
of the vehicle is 120 g. Ignore air resistance and frictional forces.
Show that the velocity of the vehicle at Position II is 1.45 m s-1. (3 marks)
(b) The motor is switched off at Position II and the vehicle continues to move from Position
II to Position V, and then back through Position IV. The metal rails are 0.170 m apart and
have a radius of curvature of 0.750 m as shown in the diagram. A magnetic field, B, is
arranged so that the field strength acting anywhere between Position IV and Position V is
perpendicular to the rails, and has magnitude 0.550 T.
Calculate the magnitude of the emf induced across the vehicle as it first passes through
Position IV. (4 marks)
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STAGE 3 21 PHYSICS
(c) Draw a labelled free body diagram to show the forces acting on the vehicle at Position IV.
(3 marks)
(d) Sketch a graph of the magnitude (absolute value) of induced EMF versus position as the
vehicle moves from Position IV to Position V and then back again to IV. (3 marks)
Absolute magnitude of induced emf (V)
IV V IV
Position
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PHYSICS 22 STAGE 3
In the diagram below, the arrow represents a stream of electrons, moving with velocity v,
entering a solid copper strip. The electrons are moving in the direction M to N. A magnetic field
of strength B, perpendicular to the strip is switched on.
x x x x x N
x x x x x
x x x x x
x x x x x
x x x x x Magnetic field

d B into page
x x x x x
x x x x x
x x x x x
x x x x x
M
x x x x
(a) Explain why electrons will begin to collect on the right hand edge of the strip and why an
electric field develops across the strip. Express the voltage (V) due to the electric field in
terms of the electric field strength (E) and the distance across the strip (d). (4 marks)
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STAGE 3 23 PHYSICS
The phenomenon of a voltage being produced across a current carrying conductor due to the
presence of a magnetic field is called the Hall effect, and the voltage is termed the Hall voltage.
It is utilised in probes used to measure magnetic field strength.
(b) For the probe in the diagram below draw an arrow to indicate the direction of the
electric field in the strip. (1 mark)
B
Electrons
IB
(c) The Hall voltage can be calculated using the equation V = tne
where
I = electric current
B = magnetic field strength
t = thickness of the strip
n = number of electrons per m3
e = charge on an electron

Calculate the magnetic field strength when V = 2.25 mV, I = 1.80 A, t = 1.25 × 10-4 m and
n = 1.52 × 1025 m-3. (3 marks)
(d) Calculate the magnetic force exerted on the electrons if they are moving with velocity
1.17 m s−1. (2 marks)
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PHYSICS 24 STAGE 3
Below is a photograph of a brick saw on a stand. The saw is powered by a 2.2 kW single
phase AC electric motor that draws current from the 240 V and 50 Hz mains supply. There is a
very tight belt around the shaft of the blade and the shaft of the electric motor and this is how
the spinning motor makes the blade spin. Bricks are cut by placing them on the platform and
pushing them through the spinning blade.
Motor

Spinning blade
Platform
(a) Calculate the current used by the saw when it is operating normally. (2 marks)
(b) Calculate the size of the EMF generated by the coil if the supply is exactly 240 V and
the losses due to inefficiency are 28 V. (2 marks)
(c) When the motor is switched on, it speeds up until it reaches a maximum. Explain how
the EMF generated in the coil restricts the speed of the motor. (4 marks)
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STAGE 3 25 PHYSICS
(d) While the saw is operating it suddenly stops spinning because it gets stuck in a brick. The
current through the saw will (3 marks)
(i) increase.
(ii) decrease.
(iii) remain the same.
Circle your answer and explain your reasoning.

(e) On the axes below sketch the current in the saw when the saw is operating normally
and when it gets stuck in a brick. (3 marks)
Normal operation Stuck in brick

Current
Current
Time Time
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PHYSICS 26 STAGE 3

This page has been left blank intentionally
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STAGE 3 27 PHYSICS
In the diagram below a copper rod is free to slide down two parallel electrical contact rails which
are mounted on an inclined plane. The inclined plane is a strong magnet. The angle, θ,
between the inclined plane and the horizontal can be changed. The electrical contact rails are
connected to a galvanometer.
Copper rod
B (perpendicular to the inclined plane)

v
Electrical contact rails

θ
G
As the rod slides, it first accelerates but eventually reaches a constant, terminal speed.
(a) Explain why a current is detected by the galvanometer when the copper rod moves.
(2 marks)
(b) Explain why there is a force opposing the rod’s motion down the rails. (2 marks)
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PHYSICS 28 STAGE 3
STAGE 3 27 PHYSICS
A group of students investigate the relationship between the terminal speed of the rod and the
A group
angle of students
of inclination. Theyinvestigate relationship
measure the terminal speedbetween
of the the
rod terminal speed
using data of the
logging rod and the
equipment
and the angle of inclination with a protractor. They plot their data on a graph. This graphequipment
angle of inclination. They measure the terminal speed of the rod using data logging is
and the angle
reproduced below.of inclination with a protractor. They plot their data on a graph. This graph is
reproduced below.
1.6
1.4
1.2
Terminal speed (cm s–1)
0.8

0.6
0.4
0.2
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
sin θ
(c) (c) Express

Express the
the value
value of
of terminal
terminal speed,
speed, when sin θθ==0.5
when sine 0.5ininthe
theform
formyy±±∆y,
∆y,where
whereyyisis the
value theofvalue of terminal speed and ∆y is the uncertainty in the measurement.
terminal speed and ∆y is the uncertainty in the measurement. (2 (2 marks)
marks)
(d)Describe the trend in uncertainty for the terminal speed and the sine of the angle θ.
(4 marks)
(d) Describe the trend in uncertainty for the terminal speed and for the sin of the angle θ.
(4 marks)
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____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
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STAGE 3 29 PHYSICS
(e) When drawing the line of best fit the students chose not to include the two largest
terminal speed measurements from their data because they thought these two
measurements were less reliable. Refer to the graph to explain why they thought this.
(3 marks)
(f) Draw a line of best fit onto the graph and determine the gradient of the line. (3 marks)
(mg sinθ)R
(g) The rod’s terminal speed can be calculated from the equation vts = where
l 2B2
m = 44.0 g, R = 1.4 × 10-4 Ω and l = 20.0 cm. Use your value of the gradient to calculate
a value of the magnetic field strength B. If you were unable to determine a value for the
gradient you should use 1.57 cm s−1. (2 marks)
End of Section Two
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PHYSICS 30 STAGE 3
Section Three: Comprehension 20% (36 Marks)
This section has two (2) questions. You must answer both questions. Write your answers in
the spaces provided.
● Planning: If you use the spare pages for planning, indicate this clearly at the top of
the page.

Radio Telescopes and Interferometry
Light Interferometry
An interferometer is a device that can split a light beam into two parts and recombine them to
form an interference pattern after they have travelled over different paths. A light interferometer
can be used to accurately determine wavelengths or distance.
A simplified diagram of an interferometer is shown below. A beam of light is incident on a
half-silvered mirror. Some of the light is reflected from this mirror and is incident on Mirror 1. The
remaining light is transmitted through the half silvered mirror and is incident on Mirror 2. Light
from both mirrors is then reflected back and received at the detector.
An observer at the detector may see an interference pattern consisting of a series of bright and
dark lines. The spacing of the lines depends on the distances the two light beams, arriving at the
detector, have travelled.
Mirror 1
Mirror 2
Light source
Half-silvered mirror
Detector
Resolving Power
The resolving power of a telescope is a measure of its ability to distinguish between objects
separated by a small angular distance. Point like sources that are separated by an angle
smaller than the resolving power of the telescope will not be seen as separate.
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STAGE 3 31 PHYSICS
57.3 × λ
The angular resolution of a telescope can be approximated to R = D
where λ is the wavelength of the observed radiation, D is the diameter of the aperture or lens
used in the telescope and R is the distance between the objects being observed in degrees.
A way of increasing the resolving power of a telescope is to use interferometry. An array of

telescopes arranged in a grid can all look at the same region of the sky. The signals from the
telescopes are combined and the interference pattern can be interpreted to determine the exact
location of a source in the sky.
57.3 × λ
The resolution of an array of telescopes can be calculated using R = B
where B is the distance between telescopes in the array.
The Square Kilometre Array is a radio telescope that will be built in southern Africa and Western
Australia. It is thought that both of these regions offer the best opportunity for observing without
interference from other radio sources. When it is complete it will have a total collecting area of
more than 1 square kilometre and the maximum distance between the central core of receivers
and the most distant will be approximately 3000 km.
(a) Explain why a series of dark and light fringes may be observed at the detector of an
interferometer. (3 marks)
(b) In an interferometer the distance from the half-silvered mirror to Mirror 1 is 1.5 m. The
distance from the half-silvered mirror to Mirror 2 is 1.85 m. The light used in the
interferometer has a wavelength of 694 nm. Calculate the difference in path length
between the light beams arriving at the detector in terms of number of wavelengths.
You should express your answer to 1 significant figure. (2 marks)
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PHYSICS 32 STAGE 3
(c) Two stars, separated by an angle of 0.5°, are both emitting radio waves with a frequency
of 1 × 106 Hz. Can they be seen as separate sources by a telescope with a diameter of
76 m? You should show the calculations you have used to justify your answer. (4 marks)

(d) Determine the resolution of two telescopes, 5 km apart receiving radio waves with a
wavelength of 1.71 m. (2 marks)
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STAGE 3 33 PHYSICS
(e) Give three (3) reasons why radio waves are used to explore very distant regions of the
Universe instead of visible light by comparing the characteristics of the two regions of the
electromagnetic spectrum. (4 marks)
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PHYSICS 34 STAGE 3
Measuring the age of the Universe
In 1929 Edwin Hubble published a claim that the recession velocities of galaxies are proportional
to their distance from any observer in the Universe. The red shift of a galaxy is a measure of its
recession velocity. The plot below shows Hubble’s 1929 data.
1200
1000
Recession velocity ( km s–1)
800
600

400
200
0
0 0.5 1 1.5 2 2.5
–200 Distance (Mpc)
The gradient of the fitted line is 464 km s−1 Mpc−1 and is now known as the Hubble constant, H0.
A parsec is an astronomical unit of distance and a megaparsec, Mpc, is equivalent to
3.086 × 1019 km. Since both kilometres and megaparsecs are units of distance, the simplified
units of H0 are s–1.
The assumption that the relationship between recession velocity and distance is linear, implies
that the value of H0 is constant throughout the Universe. If this is not true then the position that
we collect our data from is unique, the only point in the Universe where the red shift is measured
to be the same in all directions – i.e. the central point of the Universe.
1
The age of the Universe should be equivalent to H . In 1929 the age of the Universe was
0
measured using other methods and determined to be over 10 gigayears. The discrepancy
between the age of the Universe determined from Hubble’s constant and the previously
measured value led to scepticism over the cosmological models based on Hubble’s data and
motivated the development of the ‘Steady State’ model of the Universe.
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STAGE 3 35 PHYSICS
(a) Use the gradient of Hubble’s graph to calculate a value of H0 in yr −1. (3 marks)
(b) Use the plot of Hubble’s data to explain why there would be scepticism about his
proposed relationship between the velocities of the galaxies and the distance from the
observation point. (2 marks)
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PHYSICS 36 STAGE 3
Question 20 (continued)
Later work found that Hubble had confused two different kinds of Cepheid variable stars that
are used for calibrating distances, and also that what Hubble thought were bright stars in distant
galaxies were actually large nebulae where large stars were beginning to form.
Improvements in data collection and astronomical observation techniques have led to revisions
of the value of Hubble’s constant. The table below contains more recent data for Cepheid
variable stars.
Distance (Mpc) Recession velocity (km s−1)

28.60 2120
81.00 5150
129.0 7880

171.0 10 900
235.0 14 800
381.0 20 900
476.0 28 800
(c) Use the data from the table to plot a straight line graph on the grid provided. (4 marks)
(d) Using the graph, calculate the value for Hubble’s constant in yr −1 provided by this set
of data. (3 marks)
(e) Use the value of Hubble’s constant, derived from the data above, to calculate the age of
the Universe in years. (2 marks)
(f) Indicate on your graph the extent of the data collected by Hubble in 1929. Refer to this
to explain why Hubble’s value for the age of the Universe was so different from current
estimates. (3 marks)
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STAGE 3 37 PHYSICS
If you wish to have a second attempt at this item, the graph is repeated at the end of the
Question/Answer Booklet. Indicate clearly on this page if you have used the second graph
and cancel the working on the graph on this page.
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PHYSICS 38 STAGE 3
Question 20
(g) An alternative to the Big Bang model is called the Steady State model, which states
that our Universe looks the same from every spot in it and at every time. A Steady State
Universe has no beginning or end. The Steady State model states that although the
Universe is expanding it does not change its look over time because new matter must be
formed to keep the density equal over time. The implication of the Steady State model for
Hubble’s data is that the Earth is in a unique position in the Universe; i.e. the only point
from which the expansion would look the same in all directions, allowing a linear
relationship between recession velocity of a galaxy and its distance from the observer.
If we were located anywhere else in the Universe, the data would produce a quadratic
relationship between the recession velocities of galaxies and their distances away from
the observer.
The table below shows four key points about the Steady State model. Use this table
to compare the Big Bang model of the Universe with the Steady State model. (4 marks)

Steady State
Big Bang model
model
The Universe
is expanding.
The Universe
has no
beginning
or end.
The Earth is
in a unique
position in
the Universe.
The Universe
does not
change its
look over time.
End
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STAGE 3 39 PHYSICS
Additional working space
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PHYSICS 40 STAGE 3
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STAGE 3 41 PHYSICS
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PHYSICS 42 STAGE 3
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PHYSICS
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43
STAGE 3
ACKNOWLEDGEMENTS
ACKNOWLEDGEMENTS
Section One
Question 2 Data source: University of Washington. (2012). Values of wavelength in

Cepheid variable spectra data. Retrieved January 14, 2012, from
www.astro.washington.edu/courses/labs/clearinghouse/labs/HubbleLaw/ga
laxies.html.
Question 10 Image of a motorcyclist by courtesy of the examining panel.
Question 11 Image of a plunger by courtesy of the examining panel.
Section Two
Question 14 Data source: NASA. (2012). Kepler Mission. Retrieved January 10, 2012,
from http://kepler.nasa.gov/Mission/discoveries/.
Question 17 Image of a brick-saw by courtesy of the examining panel.
Question 18 Data and diagram from: Curriculum Council. (2006). Physics Tertiary
Entrance Examination, 2006. Osborne Park: Curriculum Council,
pp. 24, 26.
Section Three
Question 20 Graph from: Hubble, E. (1929). A relation between distance and radial
velocity among extra-galactic nebulae. Proceedings of the National
Academy of Sciences, 15(3), pp. 168–173. Retrieved January 10, 2012,
from http://apod.nasa.gov/diamond_jubilee/d_1996/hub_1929.html.
Data source: Wright, E.L. (2009). Ned Wright’s cosmology tutorial.

Retrieved January 10, 2012, from
www.astro.ucla.edu/~wright/cosmo_01.htm.
This examination paper – apart from any third party copyright material contained in it – may be freely copied, or communicated on an
intranet, for non-commercial purposes in educational institutions, provided that it is not changed and that the School Curriculum and
Standards Authority is acknowledged as the copyright owner.
Copying or communication for any other purpose can be done only within the terms of the Copyright Act or with prior written
permission of the Authority. Copying or communication of any third party copyright material can be done only within the terms of the
Copyright Act or with permission of the copyright owners.
Published by the School Curriculum and Standards Authority of Western Australia

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Western Australian Certificate of Education

PHYSICS Please place your student identification label in this box

Student Number: In figures

Time allowed for this paper

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Important note to candidates

Structure of this paper

Number of Number of Suggested

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2. Write your answers in this Question/Answer Booklet.

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Section One: Short answers 30% (54 Marks)

This section has eleven (11) questions. Answer all questions.

Suggested working time: 50 minutes.

The string is vibrating with a frequency of 100 Hz.

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Our Sun’s calcium absorption spectrum

λ(nm) 390 410

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λ(nm) 390 410

λ(nm) 390 410

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The bowler approaches the lane at 3.00 m s−1.

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You should ignore the effects of gravity.

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Side view Front view

Ball B Ball A Ball A

Determine, in terms of v, the time at which Ball B begins to move.

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Your use of appropriate significant figures will be assessed in this question.

The photograph shows a motorcyclist riding around a roundabout on a flat road.

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Your use of appropriate significant figures will be assessed in this question.

show all your workings.

Person with Pool surface Person being

End of Section One

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Section Two: Problem-solving 50% (90 Marks)

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Suggested working time: 90 minutes.

Question 12 (11 marks)

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(d) Explain why the voltage is increased before it is transmitted. (3 marks)

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Question 14 (15 marks)

Astronomical Orbital period around

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(b) Astronomers express the mass of Kepler 20 as (0.912 ± 0.035) × massSUN.