Physics 2007
Sample assessment instrument and indicative responses
Supervised assessment
This sample is intended to inform the design of assessment instruments in the senior phase of
learning. It highlights the qualities of the indicative response work and the match to the syllabus
standards.
Criteria assessed
• Knowledge and conceptual understanding
• Investigative processes
• Evaluating and concluding
Assessment instrument
The indicative response presented in this sample is in response to an assessment task.
This is a Supervised assessment set in the contexts of Physics in the home and Making music. It
assesses concepts of heat, sound and electromagnetic radiation.
The assessment items are presented with the responses.
r1895 Rebranded July 2014
Students were supplied with a generic list of equations and physical constants.
Instrument-specific criteria and standards
Standard A
Standard B
Standard C
The student work has the
following characteristics:
The student work has the
following characteristics:
The student work has the
following characteristics:
• reproduction and
interpretation of
complex and
challenging heat, sound
and electromagnetism
concepts, theories and
principles (Q3d ii; 4d i)
•
reproduction and
interpretation of complex or
challenging heat, sound and
electromagnetism concepts,
theories and principles
(Q3c)
•
reproduction of heat, sound
and electromagnetism
concepts, theories and
principles. (Q1a; 3a; 4a)
•
linking and application
of algorithms, concepts,
principles, theories and
schema to find
solutions in complex
and challenging heat,
sound and
electromagnetism
situations.
(Q1d; 2d i; 4d ii)
•
linking and application of
algorithms, concepts,
principles, theories and
schema to find solutions in
complex or challenging
heat, sound and
electromagnetism situations.
(Q1c i; 2c; 3d i; 4c; 6b)
•
application of algorithms,
principles, theories and
schema to find solutions in
simple heat, sound and
electromagnetism situations.
(Q1b; 2a,b; 3b; 4b; 5b)
•
systematic analysis of
primary and secondary
sound data to identify
relationships between
patterns, trends, errors
and anomalies. (Q6a)
•
analysis of primary and
secondary heat data to
identify patterns and trends.
(Q5b, c)
•
analysis of primary and
secondary heat data to
identify obvious patterns.
(Q5a)
•
exploration of scenarios
and possible outcomes
with justification of
conclusions.
(Q6b)
•
explanation of scenarios
and possible outcomes with
discussion of conclusions.
(Q1c ii; 5c)
•
description of scenarios and
possible outcomes with
statements of conclusion.
(Q2d ii)
Evaluating and
concluding
Investigative
processes
Knowledge and conceptual understanding
The responses have been matched to instrument-specific criteria and standards; those which
best describe the response in this sample are shown below. For more information about the
syllabus dimensions and standards descriptors, see
www.qcaa.qld.edu.au/1964#assessment.html.
Physics 2007
Sample assessment instrument and student responses
Page 2 of 12
Queensland Curriculum & Assessment Authority
July 2014
Indicative response — Standard A
The annotations show the match to the instrument-specific standards.
Comments
Question 1
a. State the relationship between temperature and the motion of the
particles of a substance.
b. A particular room contains 60 kg of air. Calculate the amount of heat
(in kJ) that needs to be removed from the room to reduce the
temperature of the air from 29 °C to 24 °C if the specific heat capacity
of air is 1200 J/kg/K.
c. Harry knows that Melia likes her coffee at exactly 75 °C. He decides to
make a cup of coffee for her by mixing together 150 mL of water from
the kettle (assumed to be at 100 °C) and 50 mL of tap water (assumed
to be at 24 °C).
Determine how close the coffee will be to Melia’s preferred temperature.
Next time, should Harry use more or less tap water? Explain your answer.
(It is not necessary to calculate how much more or less water should be
used.)
Note: Assume 1 mL of water has a mass of 1g and the specific heat
capacity of water is 4.2 J/g/°C.
d. 750 g of water at an initial temperature of 23 °C was placed in a kettle
with a power rating of 1.5 kW. The kettle was turned off when 20% of
the water had turned to steam. Determine how long the kettle was
switched on.
Assume the following values:
specific heat capacity of water = 4.2 kJ/kg/K
specific latent heat of fusion of water = 334 kJ/kg
specific latent heat of vaporisation of water = 2260 kJ/kg
Physics 2007
Sample assessment instrument and student responses
Page 3 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
The student
response
demonstrates:
Response:
a. Temperature is a measure of the average kinetic energy of the particles
in a substance. The higher the temperature, the faster the particles
move.
reproduction of heat
concepts, theories
and principles
b. 𝑄 = 𝑚𝑐∆𝑇 = 60 × 1200 × 5 = 360000 𝐽 = 360 𝑘𝐽
c.
application of
algorithms and
theories to find
solutions in a simple
heat situation
i.
𝑄𝑙𝑜𝑠𝑡 ℎ𝑜𝑡 𝑤𝑎𝑡𝑒𝑟 = 𝑄𝑔𝑎𝑖𝑛𝑒𝑑 𝑐𝑜𝑙𝑑 𝑤𝑎𝑡𝑒𝑟
𝑚ℎ𝑜𝑡 𝑐𝑤𝑎𝑡𝑒𝑟 ∆𝑇ℎ𝑜𝑡 = 𝑚𝑐𝑜𝑙𝑑 𝑐𝑤𝑎𝑡𝑒𝑟 ∆𝑇𝑐𝑜𝑙𝑑
150 × 4.2 × (100 − 𝑇) = 50 × 4.2 × (𝑇 − 24)
𝑇 = 81 °𝐶
linking and
application of
algorithms, concepts
and schema to find
solutions in a
complex or
challenging heat
situations
The coffee will be 6 °C above Molly’s preferred temperature.
ii.
explanation of
d. 𝑄𝑡𝑜𝑡𝑎𝑙 = 𝑄ℎ𝑒𝑎𝑡𝑖𝑛𝑔 + 𝑄𝑏𝑜𝑖𝑙𝑖𝑛𝑔 = 𝑚𝑐∆𝑇 + 𝑚𝐿𝑣
possible outcome
with discussion of
conclusion
linking and
application of
algorithms, concepts,
and schema to find
solutions in a
complex and
challenging heat
situation
Next time, Harry should use a little bit more tap water. This would
be mean that more heat would be needed to get the tap water to
the same temperature as the kettle water so the final temperature
would be lower.
= 0.75 × 4.2 × (100 − 23) + 0.2 × 0.75 × 2260
= 243 + 339 = 582 𝑘𝐽
𝑄
𝑡
𝑄 582
= 388 𝑠
∴𝑡= =
1.5
𝑃
𝑃=
Physics 2007
Sample assessment instrument and student responses
Page 4 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
Question 2
a. A clothes iron is plugged into a 240 V power point. Calculate the
resistance of the iron if it draws 9 A of current.
b. Calculate the amount of energy (in megajoules) used by an 850 W
heater running for 2 hours.
c.
An amplifier is connected to a 4 Ω speaker as shown below. The 2 Ω
resistance shown represents the total resistance of all the speaker
cables. Calculate the power output of the speaker.
Note: Assume in this and the following question that the power output of
a speaker is given by the maximum current that can flow through the
speaker.
2 Ω cables
4 Ω speaker
amplifier signal: 50 V
d. A young car owner decides to makes some alterations to turn her car’s
two-speaker stereo system into a quadraphonic (i.e. four speaker)
system by adding some extra speakers. The original sound system
consists of two 4 Ω speakers connected in parallel. The speakers are
powered by a 12 V signal as shown below.
A
12 V
4 Ω speaker
4 Ω speaker
B
The car owner takes two 8 Ω speakers from her home stereo
system and connects them in series with the original circuit at the
points A and B indicated.
i.
Calculate how much the power output of each of the original
speakers will diminish because of this change.
ii.
Compare the power output of the original 4 Ω to the power output
of the new 8 Ω speakers to determine whether or not this new
circuit is an appropriate design for a speaker system.
Physics 2007
Sample assessment instrument and student responses
Page 5 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
The student
response
demonstrates:
application of
algorithms to find
solutions in simple
electromagnetism
situations
linking and
application of
algorithms and
theories to find
solutions in complex
or challenging
electromagnetism
situations
linking and
application of
algorithms, concepts
and theories to find
solutions in complex
and challenging
electromagnetism
situations
Response:
𝑉
240
a.
𝑉 = 𝐼𝑅 ∴ 𝑅 =
b.
𝐸 = 𝑃 × 𝑡 = 850 × (2 × 60 × 60) = 6120000 𝐽 = 6.12 𝑀𝐽
𝐼
=
9
= 27 Ω
c. 𝑅𝑒𝑞 = 𝑅1 + 𝑅2 = 2 + 4 = 6 Ω
𝑉
𝐼=
𝑅
=
50
= 8.3𝐴
6
𝑃 = 𝐼 2 𝑅 = 8.32 × 4 = 280 𝑊
d.
i.
𝑃=
Original power output of each speaker:
𝑉2
𝑅
=
122
4
= 36 𝑊
For new circuit:
Equivalent resistance of parallel resistors:
1
𝑅𝑝
=
1
𝑅1
+
1
𝑅2
1
1
= + =
4
4
1
2
∴ 𝑅𝑒𝑞 = 2 𝛺
Equivalent resistance of new circuit:
𝑅𝑠 = 𝑅1 + 𝑅2 + 𝑅𝑝 = 8 + 8 + 2 = 18 Ω
Total current in new circuit:
𝐼=
𝑉
𝑅
=
12
18
= 0.67 𝐴
This current will be split evenly between the two 4 Ω speakers, so
current in each speaker will be 0.33 A
𝑃 = 𝐼2 𝑅 = 0.332 × 4 = 0.44 𝑊
The power output of the original speakers will decrease by over 35 W or
99%.
ii.
description of
scenarios and
possible outcomes
with statements of
conclusion
Power output of new speakers:
𝑃 = 𝐼 2 𝑅 = 0.672 × 8 = 3.6 𝑊
The power output of the new 8 Ω speakers is much higher than the output
of the original 4 Ω speakers. This is not an appropriate design for a
speaker system.
Physics 2007
Sample assessment instrument and student responses
Page 6 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
Question 3
a.
‘The North geographic pole is a south magnetic pole.’
Identify whether this statement is true or false and give an example of
an observation that could be used to support your answer.
b.
Calculate the magnetic field strength at a distance of 15.0 cm away
from a conducting wire carrying a current of 2.5 A.
c.
Sketch a diagram of a simple DC motor showing the orientation of the
coil when it experiences maximum torque. The diagram should also
clearly indicate the direction of the:
external magnetic field
flow of conventional current
rotation of the coil.
Describe the function and purpose of the split-ring commutator in a DC motor.
d.
A wire loop is contained entirely within a 2.4 T magnetic field, with a
conducting rod free to slide along the wire as shown. (Note: the
external magnetic field is directed into the page.)
×
×
×
×
B = 2.4 T
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
L = 0.62 m
i.
The rod is pushed to the right at a velocity of 1.6 m/s. If the total
resistance of the wire and rod is 5.0 Ω, determine the magnitude of
the induced current that will flow in the loop.
ii.
Determine the direction of the current in the loop (i.e. clockwise or
anticlockwise as viewed in this diagram). Provide reasoning to
support your answer.
Physics 2007
Sample assessment instrument and student responses
Page 7 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
The student
response
demonstrates:
reproduction of
electromagnetism
concepts and
theories
application of
algorithms to find
solutions in simple
electromagnetism
situations
Response:
a.
The statement is true. This is demonstrated by the fact that the north
pole of a suspended magnet will point towards the North geographic
pole so it must be a south magnetic pole.
b. 𝐵 =
𝑘𝐼
𝑟
=
2×10−7 ×2.5
0.15
= 3.3 × 10−6 𝑇
c. Simple DC motor (end view):
reproduction of
electromagnetism
concepts and
theories
reproduction and
interpretation of
complex or
challenging
electromagnetism
concepts, theories
and principles
The purpose of a split-ring commutator is to change the direction of the
current in the coil every half turn. Without the commutator, the motor
would stay stuck in the vertical position.
When the coil gets to the vertical position, the wires swap from one contact
of the commutator to another, reversing the direction of the current. This
reverses the direction of the force on the wires and keeps the coil rotating.
d.
i.
linking and
application of
algorithms, concepts,
principles, theories
and schema to find
solutions in complex
or challenging
electromagnetism
situations
reproduction and
interpretation of
complex and
challenging
electromagnetism
concepts, theories
and principles
EMF = 𝐵𝐿𝑣. 𝑠𝑖𝑛𝜃 = 2.4 × 0.62 × 1.6 × sin(90) = 2.4 𝑉
𝐼=
ii.
𝑉 2.4
=
= 0.48 𝐴
𝑅
5
According to Lenz’s Law, the induced current will be in the
direction that opposes the change that caused it.
The current is induced by the rod sliding to the right; therefore, the
magnetic force on the induced current must be to the left.
Using the right hand palm rule, with the field into the page and force to
the left, the current must go upwards (as pictured) through the rod.
The current will flow anti-clockwise in the loop.
Physics 2007
Sample assessment instrument and student responses
Page 8 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
Question 4
a.
Identify which property of a sound wave is related to the pitch of a
musical note.
b.
Calculate the wavelength of 256 Hz sound waves in air on a day when
the speed of sound is 331 m/s.
c.
A school teacher, concerned about the noise levels at the school
dance, takes some measurements while standing 1.0 m in front of one
of the speakers. She measures the sound intensity produced by this
speaker to be 10 W/m2. She knows that 80 dB is considered a safe
sound level for long-term exposure. How far away from the speakers
should she stand to experience this intensity?
d.
Timpani or kettle drums are drums that are tuned to produce a
particular musical note when struck.
[Note: A photograph of a kettle drum has been omitted due to copyright
restrictions.]
A particular kettle drum which has a diameter of 850 mm is tuned to
produce the note G with a frequency of 98 Hz. A student sprinkles a
fine powder all over the skin of the drum. When the drum is struck,
standing waves are set up in the skin of the drum and the powder
moves to form the pattern shown below.
i.
Interpret the powder pattern on the surface of the drum in terms of
resonance.
ii.
Calculate the speed of the waves moving in the skin of the drum.
edge of drum
powder
Physics 2007
Sample assessment instrument and student responses
Page 9 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
The student
response
demonstrates:
reproduction of
sound concepts
application of
algorithms, to find
solutions in simple
sound situations
Response:
a. Pitch is related to the frequency of a sound wave, i.e. a high frequency
corresponds to a ‘high’ pitch.
𝑣
b. 𝑣 = 𝑓𝜆 ∴ 𝜆 = =
𝑓
331
256
= 1.29 𝑚
c. Safe sound intensity:
𝐼
𝛽 = 10 𝑙𝑜𝑔 � �
𝐼0
𝐼
∴ 80 = 10 𝑙𝑜𝑔 � −12 �
10
𝐼
8
10 =
10−12
8
𝐼 = 10 × 10−12 = 10−4 𝑊. 𝑚−2
Safe distance:
linking and
application of
algorithms and
concepts to find
solutions in complex
or challenging sound
situations
d.
𝐼1 (𝑑1 )2 = 𝐼2 (𝑑2 )2
10 × 12 = 10−4 × (𝑑2)2
10
(𝑑2)2 = −4 = 105
10
�
𝑑2 = 105 = 316 𝑚
i.
reproduction and
interpretation of
complex and
challenging sound
concepts, theories
and principles
The surface of the drum must set up a resonance (i.e. standing
wave) pattern. This would be a pattern of alternating nodes and
antinodes.
Over time, the powder would move away from the antinodes
because of the large amount of movement of the surface and
collect in the nodes. So the powder reveals the pattern of nodes
on the surface of the drum.
The edge of the drum must be a node, since the surface cannot
move (i.e. it is attached to the body of the drum).
ii.
Across the diameter of the drum, the pattern is:
node (edge), antinode, node, antinode, node (centre), antinode,
node, antinode, node (edge)
linking and
application of
algorithms, concepts
and theories to find
solutions in complex
and challenging
sound situation
The distance between successive nodes is ½ λ. Since there are
5 nodes across the drum, the diameter of the drum must be
1
4 × 𝜆 = 2𝜆.
2
∴ 850 𝑚𝑚 = 2𝜆
850 𝑚𝑚
∴𝜆=
= 425 𝑚𝑚 = 0.425 𝑚
2
Given the frequency of the note is 98 Hz:
𝑣 = 𝑓𝜆 = 98 𝐻𝑧 × 0.425 𝑚 = 41.7 𝑚/𝑠
Physics 2007
Sample assessment instrument and student responses
Page 10 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
The student
response
demonstrates:
Question 5
The graph below shows the relationship between the temperature of 100 g of
an unknown substance and the heat added to it.
a. Identify the melting point of the substance.
b. Calculate the specific heat capacity of the liquid state
c. Determine whether the specific latent heat of fusion of this substance is
greater or less than its specific latent heat of vaporisation. Explain your
answer. (It is not necessary to calculate values for the two latent heats.)
180
160
Temperature (°C)
140
120
100
80
60
40
20
0
400
800
1200 1600 2000 2400 2800 3200 3600 4000
-20
analysis of primary
and secondary heat
data to identify
obvious patterns
application of
algorithms, and
theories to find
solutions in simple
heat situations
analysis of primary
and secondary heat
data to identify
patterns and trends
Heat Energy Supplied (J)
Response:
a. The melting point is 40 °C (i.e. where the data flattens out the first
time).
b. Q = mc∆T ∴ c =
Q
m∆T
=
2800J−2000J
100g×(140°C−40°C)
= 0.08 J/g/°C
c. More energy is required to melt 100 g of the substance (at 40 °C) than
is needed to boil 100 g of the substance (at 140 °C).
This means that the specific latent heat of fusion is greater than the
specific latent heat of vaporisation.
explanation of
scenarios and
possible outcomes
with discussion of
conclusions
Physics 2007
Sample assessment instrument and student responses
Page 11 of 12
Queensland Curriculum & Assessment Authority
July 2014
Comments
Question 6
The student
response
demonstrates:
A group of students conduct an experiment to measure the speed of sound using
Kundt’s apparatus. This involves a long closed tube with a speaker connected to
a signal generator at one end. The length of the tube can be changed to find
resonant frequencies by moving a plug up and down the length of the tube. Their
data is shown below.
a. Systematically analyse the data to calculate the speed of sound in air.
Clearly identify any obviously anomalies and deal with these
appropriately.
b. Compare the result for this experiment to the expected value for these
conditions.
Frequency (Hz)
Fundamental
(cm)
709
1000
1163
10.5
4.0
5.0
1st
overtone
(cm)
34.7
22.5
19.5
2nd overtone
(cm)
60.0
59.0
35.0
Air temperature = 24 °C
Response:
a.
systematic analysis
of primary and
secondary sound
data to identify
relationships
between patterns,
trends, errors and
anomalies
f (Hz)
d1 − d0 (cm)
d2 − d1 (cm)
average 1/2
λ (cm)
70
1000
24.2
25.3
24.8
speed of
sound
(m/s)
351
18.5
36.5
18.5
370
1163
14.5
15.5
15.0
349
average:
357
This value is clearly an anomaly. It is expected to be similar to the other value for
1000 Hz, i.e. 18.5 cm. This value has been ignored when calculating the average
½ λ length for this frequency.
linking and
application of
algorithms to find
solutions in
complex or
challenging heat
and sound
situations
exploration of
scenarios with
justification of
conclusions
b. The speed of sound in air at 24 °C is expected to be:
𝑣 = 331 + 0.6 𝑇 = 331 + 0.6 × 24 = 345 𝑚/𝑠
error = 357 − 345 = 12 m/s
𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑒𝑟𝑟𝑜𝑟 =
12
∗ 100% = 3%
345
This experiment has been quite accurate since the speed of sound agrees within
about 3% of the expected value.
Acknowledgments
The QCAA acknowledges the contribution of St Aidan’s Anglican Girls’ School in the preparation
of this document.
Physics 2007
Sample assessment instrument and student responses
Page 12 of 12
Queensland Curriculum & Assessment Authority
July 2014