Sample assessment instrument and indicative responses

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1 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. Students were supplied with a generic list of equations and physical constants. r1895 Rebranded

2 Instrument-specific criteria and standards 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 Standard A Standard B Standard C Knowledge and conceptual understanding The student work has the following characteristics: reproduction and interpretation of complex and challenging heat, sound and concepts, theories and principles (Q3d ii; 4d i) application of algorithms, concepts, principles, theories and schema to find solutions in complex and challenging heat, sound and. (Q1d; 2d i; 4d ii) The student work has the following characteristics: reproduction and interpretation of complex or challenging heat, sound and concepts, theories and principles (Q3c) algorithms, concepts, principles, theories and schema to find solutions in complex or challenging heat, sound and. (Q1c i; 2c; 3d i; 4c; 6b) The student work has the following characteristics: reproduction of heat, sound and concepts, theories and principles. (Q1a; 3a; 4a) algorithms, principles, theories and schema to find solutions in simple heat, sound and. (Q1b; 2a,b; 3b; 4b; 5b) Investigative processes 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) Evaluating and concluding 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) Page 2 of 12

3 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 Page 3 of 12

4 The student response demonstrates: reproduction of heat concepts, theories and principles 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. b. Q = mc T = = J = 360 kj algorithms and theories to find solutions in a simple heat situation algorithms, concepts and schema to find solutions in a complex or challenging heat c. i. Q lost hot water = Q gained cold water m hot c water T hot = m cold c water T cold (100 T) = (T 24) T = 81 C The coffee will be 6 C above Molly s preferred temperature. 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. explanation of possible outcome with discussion of conclusion algorithms, concepts, and schema to find solutions in a complex and challenging heat situation d. Q total = Q heating + Q boiling = mc T + ml v = (100 23) = = 582 kj P = Q t t = Q P = 582 = 388 s 1.5 Page 4 of 12

5 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 amplifier signal: 50 V 4 Ω speaker 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. 12 V A 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. 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. Page 5 of 12

6 The student response demonstrates: algorithms to find solutions in simple algorithms and theories to find solutions in complex or challenging Response: a. V = IR R = V = 240 = 27 Ω I 9 b. E = P t = 850 ( ) = J = 6.12 MJ c. R eq = R 1 + R 2 = = 6 Ω I = V R = 50 6 = 8.3A P = I 2 R = = 280 W d. i. Original power output of each speaker: algorithms, concepts and theories to find solutions in complex and challenging P = V2 = 122 = 36 W R 4 For new circuit: Equivalent resistance of parallel resistors: 1 R p = 1 R R 2 = = 1 2 R eq = 2 Ω Equivalent resistance of new circuit: R s = R 1 + R 2 + R p = = 18 Ω Total current in new circuit: I = V = 12 = 0.67 A R 18 This current will be split evenly between the two 4 Ω speakers, so current in each speaker will be 0.33 A P = I 2 R = = 0.44 W The power output of the original speakers will decrease by over 35 W or 99%. description of scenarios and possible outcomes with statements of conclusion Power output of new speakers: P = I 2 R = = 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. Page 6 of 12

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

7 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. 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. Page 7 of 12

8 The student response demonstrates: reproduction of concepts and theories algorithms to find solutions in simple 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 = = T r 0.15 c. Simple DC motor (end view): reproduction of concepts and theories reproduction and interpretation of complex or challenging concepts, theories and principles algorithms, concepts, principles, theories and schema to find solutions in complex or challenging reproduction and interpretation of complex and challenging 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. EMF = BLv. sinθ = sin(90) = 2.4 V I = V R = 2.4 = 0.48 A 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. Page 8 of 12

9 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. Calculate the speed of the waves moving in the skin of the drum. edge of drum powder Page 9 of 12

10 The student response demonstrates: reproduction of sound concepts algorithms, to find solutions in simple sound algorithms and concepts to find solutions in complex or challenging sound reproduction and interpretation of complex and challenging sound concepts, theories and principles algorithms, concepts and theories to find solutions in complex and challenging sound situation Response: a. Pitch is related to the frequency of a sound wave, i.e. a high frequency corresponds to a high pitch. b. v = fλ λ = v = 331 = 1.29 m f 256 c. Safe sound intensity: d. β = 10 log I I 0 I 80 = 10 log I = I = = 10 4 W. m 2 Safe distance: I 1 (d 1 ) 2 = I 2 (d 2 ) = 10 4 (d 2 ) 2 (d 2 ) 2 = 10 = d 2 = 10 5 = 316 m i. 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). Across the diameter of the drum, the pattern is: node (edge), antinode, node, antinode, node (centre), antinode, node, antinode, node (edge) The distance between successive nodes is ½ λ. Since there are 5 nodes across the drum, the diameter of the drum must be 4 1 λ = 2λ mm = 2λ 850 mm λ = = 425 mm = m 2 Given the frequency of the note is 98 Hz: v = fλ = 98 Hz m = 41.7 m/s Page 10 of 12

11 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.) Temperature ( C) analysis of primary and secondary heat data to identify obvious patterns algorithms, and theories to find solutions in simple heat analysis of primary and secondary heat data to identify patterns and trends Response: Heat Energy Supplied (J) a. The melting point is 40 C (i.e. where the data flattens out the first time). Q b. Q = mc T c = 2800J 2000J = 0.08 J/g/ C = m T 100g (140 C 40 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 Page 11 of 12

12 The student response demonstrates: Question 6 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) 1st overtone (cm) 2nd overtone (cm) systematic analysis of primary and secondary sound data to identify relationships between patterns, trends, errors and anomalies algorithms to find solutions in complex or challenging heat and sound exploration of scenarios with justification of conclusions Response: a. Air temperature = 24 C f (Hz) d 1 d 0 (cm) d 2 d 1 (cm) average 1/2 λ (cm) speed of sound (m/s) average: 357 This value is clearly an anomaly. It is expected to be similar to the other value for 1000 Hz, i.e cm. This value has been ignored when calculating the average ½ λ length for this frequency. b. The speed of sound in air at 24 C is expected to be: v = T = = 345 m/s error = = 12 m/s relative error = % = 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. Page 12 of 12

# Ans Workings / Remarks

# Ans Workings / Remarks 1 A The positive zero error is +0.03 mm. The reading is 1.84 mm. Thus, final reading = 1.84 (+0.03) = 1.81 mm 2 A We can use parallelogram of forces to determine the final resultant