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2005 Half – Yearly HSC EXAM Weighting: 10% Physics Theme: “Jane’s Birthday Exam”. General Instructions Reading time – 5 minutes Working time – 2 hours Board-approved calculators may be used Write using blue or black pen Draw diagrams using pencil A Data Sheet and Periodic Table, and Formulae Sheets are provided at the back of this paper. Total marks (70) Part I This section has three parts, Part A, Part B and Part C Part A Total marks (15) Attempt Questions 1 – 15 Allow about 30 minutes for this part Part B Total marks (45) Attempt Questions 16-21 Allow about 1 hour and 10 minutes for this part Section II – Elective Style Part C Total marks (10) Attempt Question 22 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 A (B) 6 B (C) 8 C (D) 9 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: A B correct C D Outcomes Assessed H1 H2 H3 H5 H6 H7 H8 H9 H10 H11 H12 H14 evaluates how major advances in scientific understanding and technology have changed the direction or nature of scientific thinking analyses the ways in which models, theories and laws in physics have been tested and validated assesses the impact of particular advances in physics on the development of technologies identifies possible future directions of physics research explains events in terms of Newton’s Laws, Law of Conservation of Momentum and relativity explains the effect of energy transfers and transformation analyses wave interactions and explains the effects of those interactions explains the effects of electric, magnetic and gravitational fields describes the nature of electromagnetic radiation and matter in terms of the particles justifies the appropriateness of a particular investigation plan evaluates ways in which accuracy and reliability could be improved in investigations assesses the validity of conclusions from gathered data and information 2- - It was Jane's birthday, and all the fizzix students were sitting around the Souberon room drinking stuff, relaxing from their exams. Question 1 'I wish I could go into space' said Lucy. 'It would be fun to be weightless in orbit'. This is because (a) (b) (c) (d) all gravity forces are balanced out. objects in orbit are falling. there is no gravity in space. the centripetal force is cancelled out by the centrifugal force. Question 2 'Yeah, this guy I studied was the first to launch a liquid fuel-based rocket that could get you into space' said Lei. The guy's name is (a) (b) (c) (d) Oberth Esnault-Pelterie Goddard von Braun [N.B. I couldn't spell Tsiolkovsky so I didn't include him in the question - Mr. N.] Question 3 Georgia then said 'When we were at the Powerhouse museum, I played this game about launching a rocket - I crashed it many times on purpose, heh, heh.' What Georgia should have done to get the rocket into orbit was to (a) (b) (c) (d) balance the thrust force against the weight force of the rocket. calculate the total energy needed to achieve a particular orbit. calculate the impulse given to the rocket by the fuel and (Lucy, you’ll love this) created a differential equation showing how to maintain a constant thrust as the rate mass of the rocket decreases. not used the simulation in the first place because it was too childish. Question 4 'Well then, what orbital speed should I use to keep the spacecraft at 200 km altitude if the radius of the Earth is 6380 km?' demanded Georgia, trying to avoid doing maths, but also amazed that she remembered the radius of the earth. Lucy immediately pulled her calculator and obtained the correct value of (a) (b) (c) (d) 2.07 km/sec 8.03 km/sec 11.4 km/sec 27.3 km/sec 3- - Question 5 'But what do you need to get into space?' asked Lei. Jane correctly answered: “To save fuel and get the fastest speed quickly, you need to move (a) (b) (c) (d) east to west along the equator.” west to east along the equator.” south from the North pole.” north from the South pole.” Question 6 “Hey, but it’s more fun seeing the spaceship burn up on re-entry” said __________ (Come on, who else would want to see spaceships burning up…?). A spaceship would generate large amounts of heat on reentry due to (a) (b) (c) (d) a steep entry angle and friction with the air. a steep entry angle and a compression of the air column below it. a shallow entry angle and friction with the air. a shallow entry angle and a compression of the air column below it. Question 7 'But I want to go faster than a chemical rocket. I want to feel the rush of aether on my face; I want to meet my identical twin when she is 100 years older than me; I want to feel the shockwave from a supernova explosion before the star blows up!' Jane said. The concepts Jane had in mind were, in order (a) (b) (c) (d) simultaneity, the twin paradox and a nineteenth century idea about the medium for light. a nineteenth century idea about the medium for light, the twin paradox and simultaneity. the twin paradox, a nineteenth century idea about the medium for light and simultaneity. the twin paradox, simultaneity and a nineteenth century idea about the medium for light. Question 8 'I can't watch my favourite movies in space'' Georgia exclaimed. 'Not so,' said Lucy 'there are many cathode ray tubes on the older Russian spacecraft, but they all have the same basic design:” D B A C The parts labelled A, B, C, D are respectively (a) (b) (c) (d) anode accelerator, electrostatic deflector, electromagnetic deflector, heating filament. anode accelerator, electromagnetic deflector, electrostatic deflector, electron gun. heating filament, anode accelerator, electrostatic deflector, electromagnetic deflector. heating filament, anode accelerator, electromagnetic deflector, electron gun. 4- - Question 9 'Here, let me show you a calculation...' Lucy said. 'If the voltage on the electrostatic deflector is 28000V and it is separated by 6 cm, and the magnetic field is 0.23 T as shown, then the speed of the undeflected electrons is...' V = 28 000 V X X X X X Magnetic Field 0.23T into the page electron X X X X X d = 6 cm X X X X X (a) (b) (c) (d) 1.03 X 102 m/s 5.08 X 104 m/s 1.02 X 105 m/s 2.03 X 106 m/s Question 10 'But the spacecraft will also need solar cells.' said Lei. “Without these, you won’t get a picture on the screen. Hey, didn’t Albert (Einstein) in lab 1 do something in making solar cells?” What did Einstein contribute? (a) (b) (c) (d) He produced and measured the speed of radio waves. He suggested that radiation in a black body was quantised. He created the idea of a photon to explain black body radiation. He discovered how to coat a metal surface with silicon to produce a voltage. Question 11 “But how much energy will I need to run a 100W TV?” exclaimed Georgia. ”Mr. N said that the wavelength of yellow light was 590 nm and I don’t know the work function of whatever metal they are using in the solar cell but if we assume that all the energy of this light is converted into electrical energy, then the number of photons we need every second is.. well, come on, Lucy, calculate it… (N.B. Everyone doing this exam should perform the correct calculation as well – Mr. N.) (a) (b) (c) (d) 2.95 X 1020 photons 4.5 X 1023 photons. 9.82 X 1024 photons 5.6 X 1035 photons. Question 12 “I just realised something!” yelled Jane. “A related concept to the work function is the (a) (b) (c) (d) band gap”. positive hole”. conduction band.” depolarisation layer.” 5- - Question 13 Suddenly an argument broke out. “No, no, I didn’t call you a dope!” said Lucy. “I said, doping, you know, when… (a) (b) (c) (d) a small amount of another element replaces the atoms of another element in a crystal.” a large amount of another element replaces the atoms of another element in a crystal.” a small amount of another element contaminates another element in a crystal.” a large amount of another element contaminates another element in a crystal.” Question 14 But no one was listening. The confusion over dope and doping continued. Georgia ripped out an electrical cable. Jane yelled “Wait! The liquid nitrogen in the cable will spill out and freeze us all to death! Not to mention it will cut power to all of Mentie building.” The type of cable Jane was describing consists of (a) (b) (c) (d) a superconducting core surrounded by a liquid nitrogen jacket. a liquid nitrogen core surrounded by a conductive metal jacket. a conductive metal core surrounded by a liquid nitrogen superconductor. a liquid nitrogen core surrounded by a superconducting jacket. Question 15 Georgia waved the cable like a snake. “I don’t care if we all freeze, I’m not a dope, dopant or even a superconductor, for that matter” she exclaimed. As she said this, Mr. N. came into the room, dragging behind him a really, really powerful electromagnet he had borrowed from some alien friends. He switched it on and Georgia started levitating, letting go of the cable. Georgia was levitated due to (a) (b) (c) (d) the Meissner effect. Cooper pairs in her body moving through without resistance creating an opposing magnetic field. unpaired electrons in her body creating an opposing magnetic field. an antigravity field created by the strong magnetic field. 6- - Part B Total marks (45) Attempt Questions 16 – 24 Allow about 1 hour and 10 minutes for this part Answer Questions 16 – 24 in this Booklet. Show all relevant working in questions involving calculations. Part B – Answer this section in the booklet provided. Question 16 (7 marks) Marks The cable twisted away from Georgia. Mr. N. aimed the electromagnet at the 3 kg cable, switched on another button and the cable was instantly teleported to Xenos, about 52 light years away. On this planet the cable has a weight of 24.5N (a) Calculate the value of gravity on Xenos. 1 (b) On the return stroke of the teleportation, a birthday cake materialised. However, the cake still had a lot of momentum from its journey. It appeared in the air at a height of 2 metres at an angle of 30 to the horizontal and landed 3 metres from its starting point, as shown below: initial speed trajectory of cake height of ceiling 3 m 30 2m 3m (i) Calculate the initial speed of the cake, 2 7- - (ii) Calculate whether the cake would have hit the ceiling if the height of the ceiling was 3 metres. 1 (iii) Describe qualitatively how the motion of the cake would have been different on Xenos. 2 Question 17 (9 marks) Marks The cake landed at Jane’s feet, who was so stunned by the entire incident that she failed to notice that the cake did not go ‘splat’ but rather went into an orbit around her. A spoon that had followed the cake through the teleporter also started orbiting Jane at a different radius. (a) Identify a law that relates the periods of these two orbits. 1 (b) Describe the action of the cake and spoon if Jane were to suddenly disappear, say, as if she was teleported accidentally. 1 8- - (c) Jane suddenly found herself on Xenos, looking at some very bemused aliens holding a snaking electrical cable. The Xenosians were in the process of duplicating the way Earthlings measure the metre. Describe the way Earthlings measure the metre currently. (d) Explain why Earthlings cannot check if the speed of light changes. 9- - 2 2 (e) The Xenosians thought it was not a good idea for a student who did not have the proper clearance from Earth channels to remain on Xenos and so Jane was instantly transported back to the Souberon room, just in time to catch the cake and spoon before they fell to the ground. Explain how a few minutes could have passed on Xenos while only one second passed on Earth. 3 Question 18 (6 marks) With all the moving about, Jane was feeling queasy, a similar feeling to what astronauts experience during launch. (a) Describe the forces that act on astronauts during launch. 10 - - 2 (b) Explain some methods used to help astronauts overcome these forces. 2 (c) Outline how would Jane know that she is in a non-inertial frame of reference in a launching rocket. 2 Question 19 (10 marks) Mr. N. said “Sorry about that, but Georgia looked a bit dangerous; well, more dangerous than normal.” He put the electromagnet down and locked it before Lucy had a chance to examine it. “Neat, isn’t it? It’s a superconducting electromagnet using a high-temperature ceramic that has yet to be invented here on Earth. It can reflect about 462 T and concentrate that field in a small volume to levitate almost anything. (a) Explain why an external magnetic field cannot penetrate the superconducting electromagnet. 11 - - 3 (b) Discuss the BCS theory, detailing why it does not apply to this electromagnet. 5 (c) Explain why Georgia could hover above the electromagnet even though she is not ferromagnetic. 2 12 - - Question 20 (7 marks) Lucy asked “But how does the electromagnet work?” Mr. N. brought out a portable electron microscope about the size and shape of a hard disk and placed it on the circuitry of the electromagnet. ”Here, let me show you” he said. After speaking some instructions to the device, a hologram appeared displaying a silicon lattice with a few large atoms randomly placed in the matrix. Lei exclaimed “Oh, I see. There’s a p-doped layer in between two n-doped layers. It’s made of transistors! But really smaller than the ones we have seen in class.” (a) Describe how doping a semiconductor can change its electrical properties to make a transistor. 2 (b) Assess the impact of the invention of transistors on society with particular reference to their use in microchips and microprocessors. 5 13 - - Question 21 (6 marks) Lucy was still holding her cake and spoon. “Are we going to have this cake or what!” she said. Georgia had completely forgotten the events of the last few minutes and asked one of her “normally tangential” questions: “But what would happen if I fired an ion beam at the superconducting electromagnet? How could I figure out what ions are in the beam?” (a) Outline Thomson’s experiment to measure the charge to mass ratio of an electron, using equations where appropriate. 3 (b) Mr. N. demonstrated Thomson’s experiment using a proton beam from the electromagnet (it also doubled as a portable cyclotron). Another section of the electromagnet contained antiproton beams. Of course, being fizzix students, what do you do with a proton and anti-proton beam – you smash them together to annihilate them! The collisions produced pairs of gamma rays. Calculate the frequency of the gamma rays from each protonantiproton collision. 14 - - 3 Part C Total marks (10) Attempt Question 22 Allow about 20 minutes for this part Start this question on a new sheet of paper. Show all relevant working in questions involving calculations. 22. The Rail Gun. Jane asked Mr. N. “Why do you have a superconducting electromagnet in the first place? And when are we going to eat this cake?” “Well, this is a component from an experimental rail gun system to launch satellites into geosynchronous orbit. The Xenosians loaned it to us but I thought we’d have a bit of fun with it before bringing it to the rail gun project.” Mr. N. said. (a) Describe how superconductors can be used in the development of a maglev system for the rail gun. 2 (b) Describe qualitatively the differences between a low Earth and geosynchronous orbit. 2 (c) Given that the mass of the earth is 5.98 X 1024 kg, calculate the radius of a geosynchronous orbit. 2 (d) Explain why thermionic valves are not a good idea for satellites launched by the rail gun. 3 (e) Discuss the importance of Newton’s Law of Universal Gravitation in understanding and calculating the motion of satellites. 3 End of Exam – Check your answers. Epilogue Everyone finally sang “Happy Birthday” to Jane and she cut the cake (with the spoon). Something didn’t taste right about the cake (it had made a journey of 52 light-years, after all) and everyone politely excused themselves from the party. Mr. N. brought the electromagnet back to the secret rail gun project. Georgia spent the rest of the day repairing electrical cables. Lucy went back and solved that differential equation for the motion of the rocket. Lei wrote another ancient history essay on Tiberius and nepotism. Jane had an uneventful, but unexplosive, rest of her birthday. 15 - - Kambala Year 12 Half-Yearly Examinations 2005 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 1 A B C D 2 A B C D 3 A B C D 4 A B C D 5 A B C D 6 A B C D 7 A B C D 8 A B C D 9 A B C D 10 A B C D 11 A B C D 12 A B C D 13 A B C D 14 A B C D 15 A B C D 16 - - HSC Physics Half Yearly Exams 2005 Mapping Grid Question Mark Content Syllabus Outcomes Targeted Performance Band 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16(a) 16(b)(i) 16(b)(ii) 16(b)(iii) 16(b)(iv) 17(a) 17(b) 17(c) 17(d) 17(e) 18(a) 18(b) 18(c) 19(a) 19(b) 19(c) 20(a) 20(b) 21(a) 21(b) 22(a) 22(b) 22(c) 22(d) 22(e) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 2 1 1 2 2 3 2 2 2 3 5 2 2 5 3 3 2 2 2 3 3 9.2.1.1(2) 9.2.2.3(3) 9.2.2.7(2) 9.2.2.4(3) 9.2.2.6(2) 9.2.2.8(2) 9.2.4.4(2) 9.4.1.6(2) 9.4.1.3(3) 9.4.2.5(2) 9.4.2.4(3) 9.4.3.3(2) 9.4.3.4(2) 9.4.4.5(2) 9.4.4.4(3) 9.2.1.2(3) 9.2.2.3(3) 9.2.2.3(3) 9.2.2.3(3) 9.2.2.3(3) 9.2.2.5(3) 9.2.2.10(2) 9.2.4.4(2) 9.2.4.5(2) 9.2.4.6(2) 9.2.2.4(2) 9.2.2.5(2) 9.2.4.1(2) 9.4.4.4(3) 9.4.4.5(2) 9.4.4.4(3) 9.4.3.5(2) 9.4.3.4(3) 9.4.2.6(2) 9.4.3.4(3) 9.4.4.5(3) 9.2.2.4(2) 9.2.2.10(2) 9.4.3.8(2) 9.2.3.5(2) H6 H1 H4 H4 H3 H4 H1,H3 H3 H4 H1 H10 H2 H4 H4 H2 H6 H6 H6 H6 H6 H1 H6 H3 H2 H7 H3 H3 H9 H2 H2 H2 H3 H4 H2 H5 H4 H7 H3 H4 H2 2 2 3 5 2 2 4 2 5 2 5 4 2 3 4 4 5 4 5 4 2 4 3 3 4 3 2 4 3 2-6 4-6 3 2-6 3 4-6 3 2 5 4 4 1- - Correct Answer Question 16 (3 marks) Marks During your course you have gathered and analysed information on the contribution of one scientist to the development of space exploration. Explain how this scientist’s ideas contributed to our understanding of space science. (b) MARKING GUIDELINES Criteria Relates how the ideas of the scientist had the effect of increasing our understanding of space science. Describes some findings of the scientist. 3 Marks 3 1-2 Sample answer: Goddard is considered the “father of space flight”. He performed many experiments in the 1920’s and 30’s on rocketry and was the first to develop a liquid fuel-based rocket. This allowed for higher altitudes and ranges for rockets that eventually led to rockets capable of reaching space. Question 17 (7 marks) Marks A 100 kg satellite is in orbit at an altitude of 38400 km above the surface of the Earth. If the radius of the Earth is 6380 km and the mass of the Earth is 6.2 X 1021 kg, (a) State the specific name of this orbit. 1 MARKING GUIDELINES Criteria Correct answer. Marks 1 Sample answer: Geostationary orbit. (b) Calculate the value of gravity at this altitude. 2 MARKING GUIDELINES Criteria Obtains correct result. Correctly applies equations to solve the problem. Marks 2 1 Sample answer: F (c) Gm1m2 6.67 X 10 11 X 100 X 6.2 X 10 21 F .0206 0.0206 g 2.06 X 10 4 ms 2 2 2 m 100 d (38400000 6380000) Calculate the orbital velocity of the satellite relative to the surface of the Earth. MARKING GUIDELINES Criteria Obtains correct result. Correctly applies equations to solve the problem. Marks 2 1 Sample answer: F 2 mv 2 mg v gr 2.06 X 10 4 X (38400000 6380000) 9230m / s r 2- - (d) Discuss the stability of this orbit. 2 MARKING GUIDELINES Criteria Marks Explains how the orbit is affected by atmospheric drag, gravitational perturbations, electromagnetic interactions. 2 States some points about geostationary orbits. 1 Sample answer: A geostationary orbit parks a satellite above the same position of the earth. 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 the Moon and the Sun, may have a slight affect on the stability of the orbit. Question 18 (3 marks) Marks Outline the features of the aether model for the transmission of light. MARKING GUIDELINES Criteria Gives an in-depth description of the main characteristics of the aether model. Describes two points of the aether model. 3 Marks 2-3 1 Sample answer: The aether model for the transmission of light assumes that there is a medium called aether that is responsible for transmitting light. This medium is required because at the time that the aether model was proposed, all waves required a medium. Scientists of the time knew that space was effectively a vacuum therefore another medium was required for starlight to reach the earth. The properties of this aether medium allowed light to pass through it. Question 19 (4 marks) Marks Discuss the role of the Michelson-Morley experiments in science in making determinations about competing theories. MARKING GUIDELINES Criteria 4 Marks Explains how the Michelson-Morley experiment changed the theories of light that led to the current ideas about the nature of light. 4 Gives a brief historical account of the development of the particle and wave models of light. 3 Accounts for the results of the Michelson-Morley experiment and states how it changed the way scientists viewed the nature of light. 2 Provides a brief description of the Michelson-Morley experiment. 1 Sample answer: The Michelson-Morley experiment was set up to determine the speed of the earth through a light-transmitting medium called the aether. The experiment was designed to test the prevailing idea of the time that light must travel through such an aether. This idea had its roots in earlier experiments. People had long debated whether light is a particle or a wave. In a definitive experiment done by Young in 1803, light was shown to be a wave when it was passed through a double slit, causing an interference pattern. Thus since light was a wave it required a medium – this was called the aether. The Michelson-Morley experiment attempted to establish the speed of the earth through this aether in space. The results turned the ideas of the day on their head as a null result was obtained after many measurements. This forced scientists to either question the methodology of the experiment or the accepted theory of light. Once the methodology of the experiment was accepted, then the theory of light was replaced. This led to our current understanding of light as both a particle and a wave – a photon. 3- - Question 20 (6 marks) Marks Discuss the relationship between theory and the evidence supporting it, using Einstein’s predictions based on relativity that were made many years before evidence was available to support it. MARKING GUIDELINES Criteria 6 Marks Provides further points and generalisations about the nature of scientific research and the use of the scientific method. 5-6 Explains the predictive power of a good theory such as relativity and how it can provide experiments that can be used to test it. 3-4 States some of the predictions of relativity theory. 1-2 Sample answer: All theories proposed by scientists require some form of experimentation to strengthen or disprove the theory. The theory of general relativity was proposed at a time when many of its predictions could not be tested. The general theory of relativity related the strength of a gravitational field to its ability to warp space-time. In 1916 was the general theory of relativity was published this could not be tested. However, in 1919 there was a total eclipse of the Sun that allowed scientists to look at stars close to, and according to general relativity, directly behind the Sun. This is because the Moon blocks out most the sunlight except for the coronal discharge during an eclipse. According to general relativity, stars directly behind the sun should be visible at the edge of the Sun because the gravity Question 21 (10 marks) Marks During the course you have planned, chose equipment or resources for, and performed a firsthand investigation to demonstrate the production of an alternating current. (a) Describe briefly your investigation. 2 MARKING GUIDELINES Criteria States some of the equipment used and rationalises their use. Provides a correct method for the production of an alternating current. Marks 2 1 Sample answer: An alternating current can be produced by turning an AC generator at high speed. The higher the kinetic energy given to the armature, the higher the current. The AC generator consists of an armature with many turns of coil immersed in a strong magnetic field generated by a permanent magnet. As the armature is turned in the magnetic field, an induced emf is created that is sinusoidal in nature. (b) Explain the differences between this AC generator and DC generators. MARKING GUIDELINES Criteria Relates the differences between AC and DC generators to their effect on a generated current. Sample answer: An AC generator creates a sinusoidal current that becomes positive and negative at the same frequency as the rate of turn of the armature. A DC generator creates a current that builds up to a value and drops to zero at twice the rate of the armature spin rate. 4- - 2 Marks 1-2 (c) 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. MARKING GUIDELINES Criteria 6 Marks Provides a historical context of the use of AC and DC generators using the competition between Westinghouse and Edison as examples. 5-6 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. Question 22 (3 marks) Marks Explain how induction is used in cooktops in electric ranges. MARKING GUIDELINES Criteria Relates the application of Lenz’s law to its use in induction cooking. States some features of induction cooking. 3 Marks 2-3 1 Sample answer: Induction cooking involves placing a solenoid under a non-conductive surface such as glass. A high AC current is run through the solenoid causing an intense changing magnetic field in the volume above the non-conductive surface. A metal pot placed on the glass will be immersed in the changing magnetic field. According to Faraday’s law, an emf will be induced in the metal pot. Since the metal has a resistance, an induced current will result. Lenz’s law states that the induced current will be formed in such a way as to oppose its production. This means that the electrical energy created by the magnetic induction will be attempted to be destroyed by the induced current, causing the electrical energy to transform into heat. It is this heat that is used for cooking. Question 23 (4 marks) Marks Discuss how difficulties of heating caused by eddy currents in transformers may be overcome. MARKING GUIDELINES Criteria Provides points in terms of energy changes / transformations Describes some methods for reducing eddy currents or reducing heating effects. States how eddy currents are produced in transformers. 4 Marks 4 2-3 1 Sample answer: Eddy currents are produced as a result of Lenz’s law. When a changing magnetic field induces an emf in a conductor according to Faraday’s law, the resulting emf causes a current in any material that has resistance. These induced currents are referred to as eddy currents because they go against the main current that is causing the changing magnetic field. By reducing the size of the eddy currents, the transformation of electrical to magnetic energy is made more efficient and loss of energy due to heat is minimised. This can be done by lamination, which is splitting a single large conductor into many smaller plates. This does not allow a large induced current to build hence minimising energy loss to heat. Other methods of reducing these heat losses include 5- - running the transformer at higher voltages, hence producing lower currents and selecting the type of material with a reasonable resistance to reduce the current. Question 24 (5 marks) Marks Discuss the impact of the development of transformers on society. MARKING GUIDELINES Criteria 5 Marks Gives a historical account of the use of transformers and outlines how transformers have changed society. 4-5 Describes how transformers have allowed various technologies to develop. 2-3 States some of the uses of transformers. 1 Sample answer: Transformers have transformed our society (sorry I couldn’t help the pun!). Since transformers can change one value of voltage to another, they find uses in all type of AC devices. Electrical power is supplied to homes at a voltage of 240V AC. Many devices such as computers, phones, etc. operate at far lower voltages, typically 5-12V. A transformer is used to step down the 240V supply voltage to required voltage for the device. Other devices require high voltages up to 50,000 V such as TV, computer monitors and microwave ovens. In this case a step up transformer is used. The use of these transformers has allowed the development of many technologies based on electrical energy, to the extent that electrical energy dominates our energy usage today. At the turn of the twentieth century, the primary energy sources in the home were coal, wood and gas. These have been phased out by electrical energy predominantly. The use of transformers in electrical devices allowed a single voltage to be supplied to homes and industry that was changed on-site, making electrical energy very convenient and easy to use. This has allowed many industries based on electronics to flourish in the twentieth century such as microproccesors, consumer electronics, computer programming, etc. This has resulted in millions of jobs being created. People in the twenty-first century would find it difficult not to use electrical devices, most of which employ a transformer, hence transformers are part of our everyday lives. 6- - Question 25 (20 marks) Marks (a) Outline Newton’s analysis of escape velocity. 3 MARKING GUIDELINES Criteria Marks 3 Has a complete description of Newton’s analysis of escape velocity. Gives a brief description of Newton’s analysis of escape velocity. 2 Defines / Uses the concept of escape velocity. 1 Sample answer: (b) Derive an expression for escape velocity in terms of the centripetal and gravitational forces acting on a projectile. MARKING GUIDELINES Criteria Correctly rearranges and derives an expression for velocity. States the centripetal and gravitational forces acting on a projectile. 2 Marks 2 1 Sample answer: mv 2 mv 2 Gm1m2 Fg mg mg r r r2 v2 Gm gv rg r r Fc (c) Explain how Tsiolkovsky’s tower could launch a projectile into a stable orbit. MARKING GUIDELINES Criteria 2 Marks Relates the causes of projectile motion to its effect of setting a satellite into orbit. 2 Briefly states some features of Tsiolkovsky’s tower. 1 Sample answer: (d) Discuss some factors that affect the strength of the gravitational force at the bottom and top of the tower. MARKING GUIDELINES Criteria 3 Marks Provides points for difference in gravitational acceleration between the top and bottom of the tower in terms of distance from the centre of the earth. 3 Differentiates between the value of gravity at the top and bottom of the tower. 2 States some factors that affect gravitational field. 1 Sample answer: 7- - (e) Describe an experiment that could be performed to measure the value of the acceleration due to gravity at the top of the tower. MARKING GUIDELINES Criteria 3 Marks 3 Provides points as to how the experiment is reliable and valid. Identifies variables and control in the experiment. 2 States an experimental method that is correct. 1 Sample answer: (f) Contrast qualitatively the value of gravitational acceleration obtained at the top and bottom of the tower. MARKING GUIDELINES Criteria Provides reasons for why the value of gravity at the top is lower. States that the value of gravity at the top of the tower is lower than at the bottom of the tower (surface of the earth) 2 Marks 2 1 Sample answer: (g) Calculate the work done in moving a 100 kg satellite up a 300 km tower. MARKING GUIDELINES Criteria Obtains correct answer. Sample answer: Assuming g to be constant at 9.8 m/s2, Marks 1 W F.d mgd 100X9.8X300,000 28400000J (h) Discuss the effect of the Earth’s orbital and rotational motions on a satellite launched from the top of this tower. MARKING GUIDELINES Criteria 1 4 Marks Provides points for the motion of the satellite as a relative velocity to the earth and how this relative velocity is affected by the earth’s orbital and rotational motions. 4 Relates the motion of the satellite to the orbital and rotational motion of the earth. 2-3 States some effects of the Earth’s orbital and rotational motions on a satellite. Sample answer: 8- - 1 Question 26 – Motors and Generators (20 marks) Marks The national electricity grid requires many components: electrical power stations, transformers, cabling from cross-country to home, sub-stations and other components as well. This grid has been developed over the last 130 years. (a) Outline the discovery of the generation of an electric current by a moving magnet by Michael Faraday. MARKING GUIDELINES Criteria Give a chronological or logical order to the discoveries made by Faraday Provides some points about the discovery of electrical generation by Faraday. 3 Marks 3 1-2 Sample answer: (b) Derive/Define and explain an expression for the generation of emf in terms of the change in magnetic flux in an electrical generator. MARKING GUIDELINES Criteria Relates Faraday’s law to how it generates electricity. States Faraday’s law either in language or mathematically. 2 Marks 2 1 Sample answer: (c) Explain the role of the transformers in electricity sub-stations. MARKING GUIDELINES Criteria Relates the reasons for the use of transformers in sub-stations (causes) to the production of electricity (effects) 2 Marks 1-2 Sample answer: (d) Discuss why some electrical appliances used in the home that are connected to the mains domestic power supply use a transformer. MARKING GUIDELINES Criteria 3 Marks Provides points about how transformers allow AC voltages to be converted. 3 Provides points about the need for different appliances to run on different voltages. 2 Defines/Uses the definition of transformer and mains domestic power supply. 1 Sample answer: 9- - (e) Describe an experiment to demonstrate the production of an alternating current. MARKING GUIDELINES Criteria Identifies some variables and controls in the experiment. States an experiment that can produce A.C. 3 Marks 3 1-2 Sample answer: (f) Contrast the use of step-up and step-down transformers in the national electricity grid. MARKING GUIDELINES Criteria 2 Marks Explains the difference between the uses of step-up and step-down transformers and their applications in the national grid. 2 Defines/Uses the definition of step-up and step-down transformers. 1 Sample answer: (g) Calculate the secondary voltage produced when a transformer with a winding ratio of 33:1 has an input voltage of 330kV MARKING GUIDELINES Criteria Provides correct answer. 1 Marks 1 Sample answer: n p Vp n 1 Vs V p . s 330000X 10kV n s Vs np 33 (h) Discuss the energy losses that occur as energy is fed through transmission lines from the generator to the consumer. MARKING GUIDELINES Criteria 4 Marks For each stage in the transmission of electricity, provides points for how energy is lost and in what forms. 3-4 Briefly provides points for the transmission of electricity from generator to consumer. 1-2 Sample answer: 10 - -