General Instructions s5

2004 Half – Yearly HSC EXAM Weighting: 10%

Physics

Total marks (70) Part I This section has three parts, Part A, Part B and Part C General Instructions  Reading time – 5 minutes Part A  Working time – 2 hours Total marks (15)  Board-approved calculators may be  Attempt Questions 1 – 15 used  Allow about 30 minutes for this part  Write using blue or black pen  Draw diagrams using pencil Part B Total marks (45) A Data Sheet and Periodic Table, and  Attempt Questions 16-23 Formulae Sheets are provided at the  Allow about 1 hour and 10 minutes for back of this paper. this part Section II – Elective Style Part C Total marks (10)  Attempt Question 24 Allow about 20 minutes for this part Part A Total marks (15) Allow about 30 minutes for this part

Use the multiple choice answer sheet. Select the alternative A, B, C or D that best answers the question. Fill in the response oval completely.

Sample 2 + 4 = (A) 2 (B) 6 (C) 8 (D) 9 A B C D

If you think you have made a mistake, put a cross through the incorrect answer and fill in the new answer.

A B C D

If you change your mind and have crossed out what you consider to be the correct answer, then indicate this by writing the word correct and drawing an arrow as follows:

correct A B C D

Outcomes Assessed

H1 evaluates how major advances in scientific understanding and technology have changed the direction or nature of scientific thinking H2 analyses the ways in which models, theories and laws in physics have been tested and validated H3 assesses the impact of particular advances in physics on the development of technologies H5 identifies possible future directions of physics research H6 explains events in terms of Newton’s Laws, Law of Conservation of Momentum and relativity H7 explains the effect of energy transfers and transformation H8 analyses wave interactions and explains the effects of those interactions H9 explains the effects of electric, magnetic and gravitational fields H10 describes the nature of electromagnetic radiation and matter in terms of the particles H11 justifies the appropriateness of a particular investigation plan H12 evaluates ways in which accuracy and reliability could be improved in investigations H14 assesses the validity of conclusions from gathered data and information

2- - Question 1

A panda on Earth, where its weight is 2940 N is transported to Europa, a moon of Jupiter. If the value of the acceleration due to gravity at the surface of Europa is 3.4 ms-2, then the weight of the panda on Europa is

(a) 1020 N. (b) 1940 N. (c) 2940 N. (d) 6830 N

Question 2

The term “g forces” is used to describe accelerations acting on humans because

(a) gravity has a value of 9.81 ms-2 on the surface of the earth. (b) “weight force” cannot be used if you leave earth’s gravitational field. (c) the pioneers of supersonic and space flight found that high g affected humans. (d) it is easier to describe the physiological effects of accelerations in terms of multiple of “g”.

Question 3

The space shuttle is launched into

(a) low earth orbit at high speed. (b) low earth orbit at low speed. (c) geostationary orbit at high speed. (d) geostationary orbit at low speed.

Question 4

A gravitational field

(a) acts on pure masses only. (b) is the result of a massive object acting on a smaller object. (c) is best represented by the sum of all gravitational fields at a point. (d) can be expressed in terms of the gravitational constant, the masses and the distances between them.

Question 5

A spacecraft is travelling at 2.0 X 108 m/s relative to the planet from where it was launched. If the spacecraft is away from the planet for 2 “spacecraft” years, then the elapsed time on the planet is

(a) 0.37 years. (b) 1.3 years. (c) 2.0 years. (d) 2.7 years.

3- - Question 6

By defining the metre in terms of the speed of light,

(a) distance is now relative. (b) the expansion of the universe can no longer be measured. (c) the definition is no longer based on earth-bound measurements. (d) the accuracy of measuring distance is increased due to the technology used.

Question 7

This question refers to the diagrams below:

From such thought experiments, Einstein

(a) developed the atomic bomb. (b) showed that gravity bent light. (c) proved his theories of relativity. (d) demonstrated that light should be constant regardless of the frame of reference.

Question 8

An overland transmission power cable carries 12000 A of current each way with the cables separated by 3.4 metres. The magnitude of the force per unit length acting on these cables is

(a) 0.055 Nm-1. (b) 0.14 Nm-1. (c) 2.5 Nm-1. (d) 7.5 Nm-1

Question 9

At Wonderland (before it closed down) there used to be a ride called “Space Probe 7”. Passengers were seated in a metal cage that fell freely due to gravity from the top of a tower. In the lower end of the tower is a powerful permanent magnet. The motion of the cage in the lower end of the ride

(a) slows down due to Lenz’s law. (b) slows down due to Faraday’s law. (c) speeds up due to Lenz’s law. (d) speeds up due to Faraday’s law.

4- - Question 10

Induction cooktops

(a) warm food using the moisture content of the food. (b) can only use ferromagnetic materials in pots such as iron. (c) generate high AC currents that are dangerous to human health. (d) are more inefficient at transferring heat than radiant cooktops.

Question 11

This question refers to the diagram below.

The purpose of the commutator is to

(a) convert DC into AC. (b) convert AC into DC. (c) allow for the full rotation of the rotor. (d) connect the armature to the supply current.

Question 12

In an experiment to determine how a generated electric current changes as

1. the distance between the coil and magnet is varied 2. the strength of the magnet is varied 3. the relative motion between the coil and the magnet is varied

The following results were obtained:

Graph X Graph Y Graph Z

W W W The label “W” and relationship being investigated is

Graph A B C D W Magnetic Field Distance Speed Speed X Relationship Magnet Strength (2) Distance (1) Relative motion (3) Relative motion (3) W Speed Magnetic Field Magnetic Field Distance Y Relationship Relative motion (3) Magnet Strength (2) Magnet Strength (2) Distance (1) W Distance Speed Distance Magnetic Field Z Relationship Distance (1) Relative motion (3) Distance (1) Magnet Strength (2)

5- - Question 13

Michael Faraday played around with lots of toys. One such set of toys involved permanent magnets and many coils of wire wrapped in linen. With such simple materials, Faraday was able to demonstrate

(a) the motor effect. (b) the principles of a galvanometer. (c) the creation of an electromagnet. (d) the generation of an electric current by a moving magnet.

Question 14

Which alternative below correctly identifies a step-down transformer?

Step-Down Transformers A B C D Voltage Increases Decreases Increases Decreases Current Decreases Decreases Increases Increases No. of turns of wire More Less Less More (primary to secondary)

Question 15

Cross-country electrical cables need certain operating conditions. These include

(a) using an AC source to generate the current. (b) running at low voltage and high current to improve efficiency. (c) running at high voltage and low current to reduce heating losses. (d) the need to be insulated from their pylons due to their high electric fields.

6- - Name / Number: ______Part B Total marks (45) Attempt Questions 16 – 23 Allow about 1 hour and 10 minutes for this part

Answer Questions 16 – 18 in the Part B1 Answer Booklet. Answer Questions 19 – 24 in the Part B2 Answer Booklet.

Show all relevant working in questions involving calculations.

Part B1 – Answer this section in this booklet.

Question 16 (6 marks) Marks

During your course you have performed a first-hand investigation, gather information and analyse data to calculate initial and final velocity, maximum height reached, range, time of flight of a projectile, for a range of situations by using simulations, data loggers and computer analysis.

(a) Describe your investigation. 2

(b) Suggest one modification that may improve the investigation. 1

(c) In one such experiment, a student obtained the following results for a ground-to-ground motion at a 45° angle:

Run Initial speed (m/s) Final speed (m/s) Max height (m) Time of flight (s) 1 2.1 0.1 1.2 0.0034 2 0.4 0.5 0.4 0.058 3 1.2 1.3 1.1 0.17

(i) Explain why this student’s method may not be reliable. 1

(ii) Calculate the value of acceleration due to gravity produced from these results. 2

7- - Question 17 (8 marks) Marks

A 100 kg satellite is in orbit at an altitude of 400 km above the surface of a planet. If the radius of the planet is 4880 km and the mass of the planet is 4.2 X 1020 kg,

(a) Calculate the value of acceleration due to gravity at the altitude of the satellite. 2

(b) If another satellite at an altitude of 100 km has a period of 847 minutes, calculate the period of the 100 kg satellite (in minutes). 2

(c) Explain why a wrench left inside the 100 kg satellite floats. 2

(d) Discuss the stability of this orbit relative to a geostationary orbit. 2

8- - Name / Number: ______Question 18 (8 marks) Marks

Discuss the implications of mass increase, time dilation and length contraction for space travel 8

9- - Name / Number: ______

Part B2 – Answer this section in this booklet.

A motor has 3000 turns of wire in its armature with a total resistance of 40Ω. The wires form the equivalent of a square loop 15 cm on a side. It uses four magnets with a net magnetic field of 0.2T. If the supply voltage is 12V,

(a) Explain how the motor effect works. 2

(b) Calculate the maximum torque generated by the motor. 1

(c) Sketch a graph of how the torque changes over 360°. 2

(d) Explain the relationship between the supply emf and back emf . 2

Describe the application of the motor effect in a loudspeaker. 3

(a) Discuss the advantages and disadvantages of AC and DC generators and relate these to their use. In your discussion, you should address the competition between Westinghouse and Edison to supply electricity to cities. 6

11- - Name / Number: ______

Assess the need for transformers in the transfer of electrical energy from a power station to its point of use. 5

Describe the main features of an AC induction motor using a sketch. 2

12- - Part C Total marks (10) Attempt Question 24 Allow about 20 minutes for this part Start this question on a new sheet of paper.

24. Motors and Generators in Space (10 marks) Marks

A space technology that was trialled in the 1990’s for power generation was the space tether. In 1997, the space shuttle lowered a 20 km copper cable out of its shuttle bay. Unfortunately, the cable broke, cutting the experiment short. If the average strength of Earth’s magnetic field at this altitude is 2.3 X 10-5 T and the shuttle is moving at 27,000 km/hr relative to the ground,

(a) Explain how this technology can be used for electrical power generation. 2

(b) Identify why a geostationary orbit does not produce electricity. 1

(c) Describe one way in which heating effects in the tether be overcome. 1

(d) Calculate the theoretical voltage produce by this tether. 1

(e) Calculate the magnetic flux covered in one minute. 2

(f) Describe the effect on the orbit of the shuttle as the space tether generates an electrical current. 3

End of Exam – Check your answers.

13- - Kambala Year 12 Half-Yearly Examinations 2004 Physics Multiple Choice Answer Sheet Name / Number: ______

Select the alternative A, B, C or D that best answers the question. Fill in the response oval completely. Sample 2 + 4 = (A) 2 (B) 6 (C) 8 (D) 9 A B C D If you think you have made a mistake, put a cross through the incorrect answer and fill in the new answer. A B C D If you change your mind and have crossed out what you consider to be the correct answer, then indicate this by writing the word correct and drawing an arrow as follows: correct A B C D

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14- - HSC Physics Half Yearly Exams 2004 Mapping Grid Question Mark Content Syllabus Targeted Correct Outcomes Performance Band Answer 1 1 9.2.1.3(3) H9 3 A 2 1 9.2.2.5(2) H9 3 A 3 1 9.2.2.9(2) H3, H7 2 A 4 1 9.2.3.2(2) H9 4 C 5 1 9.2.4.5(3) H6 5 D 6 1 9.2.4.8(2) H3, H5, H6 3 B 7 1 9.2.4.4(2) H2, H6 2 A 8 1 9.3.1.4(2) H3, H9 5 C 9 1 9.3.2.5(2) H7, H9 3 A 10 1 9.3.2.4(3) H3, H7 2 B 11 1 9.3.3.2(2) H3, H8 3 C 12 1 9.3.2.2(3) H2, H9 5 D 13 1 9.3.2.1(2) H1, H7, H9 2 A 14 1 9.3.4.2(2) H3, H7 4 D 15 1 9.3.4.3(2) H3, H7 3 A 16(a) 2 9.2.2.2(3) H2, H6 2 16(b) 1 9.2.2.2(3) H2 3 16(c)(i) 1 9.2.2.2(3) H2, H6, H9 4 16(c)(ii) 2 9.2.2.2(3) H2, H9 5 17(a) 2 9.2.3.2(3) H3, H9 5 17(b) 2 9.2.2.5(3) H2, H6 5 17(c) 2 9.2.3.1(3) H6, H9 4 17(d) 2 9.2.3.3(2) H7, H9 3 18 8 9.2.4.12(2) H5, H6, H7, H9 6 19(a) 2 9.3.1.5(2) H3, H7, H9 3 19(b) 1 9.3.1.4(3) H3, H7 5 19(c) 2 9.3.1.34(3) H3, H7 6 19(d) 2 9.3.2.6(2) H7 3 20 3 9.3.1.5(3) H3, H7, H9 3 21 6 9.3.3.4(3) H1, H3, H7, H9 6 22 5 9.3.4.4(3) H1, H3, H7, H9 6 23 2 9.3.5.1(2) H3 4 24(a) 2 9.3.2.4(2) H5, H7, H9 4 24(b) 1 9.2.2.10(2) H7, H9 4 24(c) 1 9.3.4.5(2) H6, H7 3 24(d) 1 9.3.2.4(2) H7, H9 4 24(e) 2 9.3.2.3(2) H7, H9 3 24(f) 3 9.3.2.5(2) H6, H7 5

During your course you have performed a first-hand investigation, gather information and analyse data to calculate initial and final velocity, maximum height reached, range, time of flight of a projectile, for a range of situations by using simulations, data loggers and computer analysis.

(a) Describe your investigation. 2

MARKING GUIDELINES Criteria Marks  States controls, dependent and independent variables AND outlines a 2 basic method.  States controls, dependent and independent variables OR outlines a basic 1 method.

Sample answer: In the investigation, a ball is thrown across a white board marked with lines every 10 cm. A digital video camera is used to capture the motion at 24 frames per second. After recording the video, the video is analysis looking at how the ball changes frame by frame in both the vertical and horizontal planes. The independent variables – time (each frame difference is 1/24 second), initial speed (measured from the first two frames) and launch angle, determine the dependent variables – maximum height, final speed and range.

(b) Suggest one modification that may improve the investigation. 1

MARKING GUIDELINES Criteria Marks  Correctly identifies one modification that may improve the investigation. 1

Sample answer: One modification could be to use a video with higher resolution or faster frame speed.

(c) In one such experiment, a student obtained the following results for a ground-to-ground motion at a 45° angle:

Run Initial speed (m/s) Final speed (m/s) Max height (m) Time of flight (s) 1 2.1 0.1 1.2 0.0034 2 0.4 0.5 0.4 0.058 3 1.2 1.3 1.1 0.17

(i) Explain why this student’s method may not be reliable. 1

MARKING GUIDELINES Criteria Marks  Relates the different values of run 1 to their effect on an average OR 1 identifies that the time values are too small for standard school equipment.

Sample answer: The values in run 1 are not consistent with the other values.

2- - (ii) Calculate the value of acceleration due to gravity produced from these results. 2

MARKING GUIDELINES Criteria Marks  Obtains a formula suitable for calculating the value of gravity AND uses 2 an average value (runs 2 and 3) by discarding unreliable data (run 1)  Obtains a formula suitable for calculating the value of gravity 1

Sample answer:

A 100 kg satellite is in orbit at an altitude of 400 km above the surface of a planet. If the radius of the planet is 4880 km and the mass of the planet is 4.2 X 1020 kg,

(a) Calculate the value of acceleration due to gravity at the altitude of the satellite. 2

MARKING GUIDELINES Criteria Marks  Manipulates a correct equation to obtain the correct answer. 2  Identifies a correct equation AND substitutes values in correctly. 1

Sample answer: Gm m 6.67 X1011 X100 X 4.2 X10 20 F F  1 2  g    2.06 X104 ms2 d 2 (400000  4880000) 2 m 100

(b) If another satellite at an altitude of 100 km has a period of 847 minutes,  calculate the period of the 100 kg satellite (in minutes). 2

MARKING GUIDELINES Criteria Marks  Obtains correct result. 2  Correctly applies equations to solve the problem. 1

Sample answer: 2 2 3 2 3 2 T 1 T 2 R 2 .T 1 (1 0 0  4 8 8 0 ) .(8 4 7 ) 3  3 T 2  3  3  R 1 R 2 R1 (4 0 0  4 8 8 0 )

(c) Explain why a wrench left inside the 100 kg satellite floats. 2  MARKING GUIDELINES Criteria Marks  Resolves the forces acting on the satellite to justify their answer. 2  States that the satellite is weightless due to its falling. 1

Sample answer: While in orbit, the satellite is actually falling towards the planet. Due to this free fall, there is no net force acting on the wrench hence it is weightless. This is because everything around the wrench is also in free fall thus it cannot exert a reaction force on it.

3- - (d) Discuss the stability of this orbit relative to a geostationary orbit. 2

MARKING GUIDELINES Criteria Marks  Explains how the orbit is affected by atmospheric drag, gravitational 2 perturbations, electromagnetic interactions.  States some points about geostationary orbits. 1

Sample answer: A geostationary orbit parks a satellite above the same position of the planet. Being far above the atmosphere, it is not subjected to atmospheric drag. As seen in part (c), there is still a weight force acting on the satellite and the influence of other bodies, eg a moon and the Sun, may have a slight affect on the stability of the orbit.

Discuss the implications of mass increase, time dilation and length contraction for space travel 8

MARKING GUIDELINES Criteria Marks  Gives an in-depth explanation of the relativistic issues AND energetic 7-8 issues in space travel.  Gives an in-depth explanation of the relativistic issues OR energetic 5-6 issues in space travel.  Identifies relativity and discusses some issues related to relativity 4  Use energy transformations to explain the relationships between mass increase OR Identifies relativity and discusses some issues related to 3 relativity  Identifies some issues related to journey times in space travel 2  Defines / Uses the terms correctly: mass increase, time dilation, length 1 contraction

Sample answer: The interstellar distances in space are vast. This means that journeys between stars take years. As spacecraft move faster relative to an observer, relativistic effects come into play. At speeds approaching that of the speed of light, additional energy supplied in terms of an energy input is converted to kinetic energy. However, this increase in kinetic energy is not necessarily an increase in speed; it can also increase the relativistic mass of the object. Other relativistic effects are also apparent. Time on the spacecraft will run slower compared to a “stationary” observer (eg a planet) and the length of the spacecraft will appear to decrease relative to the observer on the said planet.

A motor has 3000 turns of wire in its armature with a total resistance of 40Ω. The wires form the equivalent of a square loop 15 cm on a side. It uses four magnets with a net magnetic field of 0.2T. If the supply voltage is 12V,

(a) Explain how the motor effect works. 2

MARKING GUIDELINES Criteria Marks  Gives the cause and effect between the relative motion of a magnetic 2 field and a generated current.  Describes the principle behind the motor effect 1

Sample answer: The motor effect is a discovery of Faraday where current in a conductor a magnetic field and an electric conductor creates a generated electric current.

(b) Calculate the maximum torque generated by the motor. 1

MARKING GUIDELINES Criteria Marks 

Sample answer:

(c) Sketch a graph of how the torque changes over 360°. 2

MARKING GUIDELINES Criteria Marks  

Sample answer:

(d) Explain the relationship between the supply emf and back emf . 2

MARKING GUIDELINES Criteria Marks 

Sample answer:

Describe the application of the motor effect in a loudspeaker. 3 MARKING GUIDELINES Criteria Marks   

Sample answer:

5- - 6- - Question 21 (6 marks) Marks

(a) Discuss the advantages and disadvantages of AC and DC generators and relate these to their use. In your discussion, you should address the competition between Westinghouse and Edison to supply electricity to cities. 6

MARKING GUIDELINES Criteria Marks  Provides a historical context of the use of AC and DC generators using 5-6 the competition between Westinghouse and Edison as examples.  Compares the advantages and disadvantages of AC and DC generators. 3-4  States some features of AC and DC generators. 1-2

Sample answer: AC and DC generators have some similiarities and many differences. DC generators can produce constant low voltages at high currents generally while AC generators produce a sinusoidally changing voltage. While a DC power output is constant, AC power output varies according to the frequency of the cycle. AC voltages can be transmitted over longer distances than DC, which require repeater stations. In the 1880s Edison set up a DC power grid in Chicago while Westinghouse set up an AC grid in the same city. Edison had to place his power stations within the city every few blocks whereas Westinghouse placed his power stations outside the city and transmitted the power into the city. Much disinformation about the safety of AC and DC was spread by Edison and Westinghouse in their competition to supply electricity. Eventually Westinghouse’s AC network won over Edison’s DC network. This was mainly due to economic reasons – few power stations to set up, more efficient transmission of power and hence less electrical energy loss, etc.

Assess the need for transformers in the transfer of electrical energy from a power station to its point of use. 5 MARKING GUIDELINES Criteria Marks  Gives an informed opinion about the need for transformers on the basis 4-5 of defined criteria in terms of the features mentioned.  Provides detailed features of transformers as used between power 3 stations and point of use.  Provides some features of transformers as used between power stations 1-2 and point of use.

Sample answer: Transformer allow AC voltages to be transported more efficiently and converted to appropriate voltages at the point of use. In order to minimise the loss of electrical energy as heat as it is transported over long distances, voltages are stepped up by transformers at the power station to 330 kV so that the currents required are minimised. This is because heating effects are due to power dissipitation, and P=I2R, hence a doubling of current would produce a fourfold loss of energy as heat. At the substation, the high AC voltage is stepped down to a lower 10 kV for distribution to a smaller grid. Within domestic situations, small transformers adapt the AC voltage to the specific needs of particular pieces of equipment. Hence the need for transformers to efficient transport electrical energy and convert AC voltages to useful values is desirable and thus is needed.

Describe the main features of an AC induction motor using a sketch. 2

MARKING GUIDELINES Criteria Marks  Provides features and characteristics of an AC induction motor. 2  Provides a labelled diagram of an AC induction motor. 1

Sample answer:

A space technology that was trialled in the 1990’s for power generation was the space tether. In 1997, the space shuttle lowered a 20 km copper cable out of its shuttle bay. Unfortunately, the cable broke, cutting the experiment short. If the average strength of Earth’s magnetic field at this altitude is 2.3 X 10-5 T and the shuttle is moving at 27,000 km/hr relative to the ground,

(a) Explain how this technology can used be for electrical power generation. 2

MARKING GUIDELINES Criteria Marks  Provides the causes (motion through the Earth’s magnetic field) to the effect (push on electrons in the tether) in terms of energy conservation 2 (electrical energy gained = kinetic energy lost  gravitational potential energy lost)  Describes how a voltage could be generated in the tether. 1

Sample answer: df Motion through the Earth’s magnetic field pushes on electrons in the tether according to Faraday’s law V = - n . The dt electrical energy gained is equalled by the kinetic energy lost which in turn causes a loss in gravitational potential energy.

(b) Identify why a geostationary orbit does not produce electricity. 1

MARKING GUIDELINES Criteria Marks  No relative motion between satellite and earth 1

Sample answer: No relative motion between satellite and earth hence no induced voltage.

8- - (c) Calculate the theoretical voltage produce by this tether. 1

MARKING GUIDELINES Criteria Marks  Obtains correct result. 1

Sample answer: 27000000m v = 27000 km/hr = =7500 m/s 3600s V=vlB = 7 500 m/s X 20 000 m X 2.3 X 10-5 T = 3.45 X 103 V

(d) Calculate the magnetic flux covered in one minute. 2

MARKING GUIDELINES Criteria Marks  Calculate the magnetic flux in one minute. 2  Calculates area covered in one minute. 1

Sample answer: Area covered in one minute = 7500 m/s X 60s X 20 000 m = 9 X 109 m2 Thus  = BA = 2.3 X 10-5 X 9 X 109 = 207000 Wb

(e) Describe the effect on the orbit of the shuttle as the space tether generates an electrical current. 3

MARKING GUIDELINES Criteria Marks  Identifies that the orbit would lower due to energy transformations AND 3 speed loss due to Lenz’s law.  Describes energy transformation that occur in this situation OR Applies 2 Lenz’ law to identify how eddy currents oppose their production.  Applies Lenz’ law to state that eddy currents are produced. 1

Sample answer: Eddy currents would be produced in the tether as it generated a voltage due to the resistance of the cable. This is produced in accordance with Lenz’s law, which states that you can’t get something for nothing (really it is a statement of conservation of energy). The electrical energy would come from the kinetic energy of the spacecraft which in turn would borrow the energy from its orbit, hence lowering its gravitational potential energy. This would cause a speed loss and lower orbit.

(f) Describe one way in which heating effects in the tether be overcome. 1

MARKING GUIDELINES Criteria Marks  Provide one feature that would reduce heating effects. 1

Sample answer: Heating effects could be overcome by using:  Lots of small wires instead of a single thick wire (lamination)  A cooling jacket filled with coolant.