hscphysics.wikispaces.comhscphysics.wikispaces.com/file/view/12T203xm.doc · Web view... spinning a needle attached to loops of wire in an external permanent magnetic field. (c) applying

Physics

General Instructions Reading time – 5 minutes Working time – 3 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.

2003 Half – Yearly HSC

EXAMWeighting: 10%

Total marks (100)Part IThis section has two parts, Part A and Part B

Part ATotal marks (15) Attempt Questions 1 – 15 Allow about 30 minutes for this part

Part BTotal marks (45) Attempt Questions 16-24 Allow about 1 hour and 20 minutes for

this part

Part II – Elective StylePart CTotal marks (40) Attempt Questions 25-26Allow about 1 hour and 10 minutes for this part

Part ATotal 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) 9A 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:

correctA 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 technologiesH5 identifies possible future directions of physics researchH6 explains events in terms of Newton’s Laws, Law of Conservation of Momentum and

relativityH7 explains the effect of energy transfers and transformationH8 analyses wave interactions and explains the effects of those interactionsH9 explains the effects of electric, magnetic and gravitational fieldsH10 describes the nature of electromagnetic radiation and matter in terms of the particles H11 justifies the appropriateness of a particular investigation planH12 evaluates ways in which accuracy and reliability could be improved in investigationsH14 assesses the validity of conclusions from gathered data and information

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Question 1

When a change in the gravitational potential energy of an object occurs,

(a) work is done.(b) the object follows a gravitational equipotential line.(c) the value of gravitational acceleration on the object remains constant.(d) none of the above.

Question 2

Satellites in low Earth orbit

(a) experience orbital decay due to gravitational drag.(b) are weightless.(c) maintain their orbit due to their interactions with the atmosphere.(d) accelerate along a line parallel to their linear velocity.

Question 3

If the re-entry angle of an unpowered spacecraft into Earth’s atmosphere is too shallow, the craft may

(a) burn up on re-entry.(b) bounce off the atmosphere.(c) compress a column of air underneath it to slow it down too quickly.(d) miss the Earth and move into deep space.

Question 4

During a slingshot manoeuvre,

(a) some kinetic energy of the planet is used to increase the kinetic energy of the space probe.(b) some kinetic energy of the space probe is used to increase the kinetic energy of the planet.(c) some potential energy of the planet is used to increase the kinetic energy of the space probe.(d) some kinetic energy of the planet is used to increase the potential energy of the space probe.

Question 5

A rock falling off a cliff can be considered

(a) an inertial frame relative to a person standing at the base of the cliff.(b) a non-inertial frame relative to a person standing at the base of the cliff.(c) an inertial frame to all observers.(d) a non-inertial frame to all observers.

Question 6

The current definition of the metre is

(a) the length of a certain number of wavelengths of a krypton-86 laser.(b) one-millionth the distance from the North pole to the equator going through Paris.(c) the distance light travels in 1/299,975 of a second.(d) a particular length of stick kept near Paris.

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Question 7

A spaceship with a rest mass of 1000 kg accelerates to 2.8 X 108 m/s. Its apparent mass at this speed relative to an observer moving with the same velocity is

(a) 720 kg(b) 1000 kg(c) 1320 kg(d) 2030 kg

Question 8

The function of a commutator in a motor is to

(a) convert DC to AC.(b) convert AC to DC.(c) allow the motor to move.(d) provide a strong magnetic field.

Question 9

A galvanometer works by

(a) producing a torque in a small coil of wire against a larger current.(b) spinning a needle attached to loops of wire in an external permanent magnetic field.(c) applying a voltage to a loop of wire that causes a current to push against a permanent

magnetic field.(d) none of the above.

Question 10

During the course you have performed an experiment to predict and verify the effect on a generated electric current when the distance between coil and magnet is varied; the strength of the magnet is varied; and the relative motion between the coil and the magnet is varied. Accepted results for this experiment are

Response Distance increased Magnetic field increased Relative motion fasterA Current increases Current increases Current increasesB Current decreases Current decreases Current increasesC Current increases Current decreases Current decreasesD Current decreases Current increases Current increases

Question 11

In motors,

(a) the supply emf opposes the back emf(b) the supply emf enhances the back emf(c) the back emf opposes the supply emf(d) the back emf enhances the supply emf

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Question 12

A transformer has an input voltage of 240V AC and needs to produce 60V AC at 2A. The input current and ratio of primary to secondary turns respectively is

(a) 0.5A, 4:1(b) 0.5A, 1:4(c) 8A, 4:1(d) 8A, 1:4

Question 13

A motor must be designed supply a torque of 200 Nm. The largest area that can be accommodated by the rotor is a square 10 cm on a side. If the maximum field strength of its permanent magnets is 3.0 X 10-2 T and the maximum current allowable is 2A, then the number of turns needs in this motor is

(a) 66 turns.(b) 3 333 turns.(c) 66 666 turns.(d) 333 333 turns.

Question 14

Transformers

(a) convert electrical energy into magnetic energy.(b) use soft iron cores to enhance the back emf.(c) can increase the power output of a device while keeping energy conserved.(d) are used to reduce losses due to heating effects.

Question 15

A wire carrying 5A to the right of the page is immersed for 3.0 metres in a magnetic field of 0.20 T going into the page, according to the diagram below:

X X X X X X X 0.20 T3.0 metres

X X X X X X X

X X X X X X XI = 5 A

X X X X X X X

X X X X X X X

The force acting on the wire is

(a) 3N up.(b) 3N to the left.(c) 15N down.(d) 15N to the left.

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Part BTotal marks (45)Attempt Questions 16 – 24Allow about 1 hour and 20 minutes for this part

Answer Questions 16 – 20 in the Part B1 Answer Booklet.Answer Questions 21 – 24 in the Part B2 Answer Booklet.

Show all relevant working in questions involving calculations.

Part B1 – Answer this section in the booklet provided.

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.

(a) Name the scientist that you have studied.

(b) Explain how this scientist’s ideas contributed to our understanding of space science. 3

Question 17 (7 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

(b) Calculate the value of gravity at this altitude. 2

(c) Calculate the orbital velocity of the satellite relative to the surface of the Earth. 2

(d) Discuss the stability of this orbit. 2


Outline the features of the aether model for the transmission of light. 3

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Discuss the role of the Michelson-Morley experiments in science in making determinations about competing theories. 4


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. 6

Part B2 – Answer this section in the booklet provided.


During the course you have planned, chose equipment or resources for, and performed a first-hand investigation to demonstrate the production of an alternating current.

(a) Describe briefly your investigation. 2

(b) Explain the differences between this AC generator and DC generators. 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. 6


Explain how induction is used in cooktops in electric ranges. 3


Discuss how difficulties of heating caused by eddy currents in transformers may be overcome. 4


Discuss the impact of the development of transformers on society. 5

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Part CTotal marks (40)Attempt Questions 25-26Allow about 1 hour and 10 minutes for this partStart each question on a new sheet of paper.

Show all relevant working in questions involving calculations.

26. Space

Newton proposed a model for projectile motion that was further developed by Tsiolkovsky and his “launching tower”.

(a) Outline Newton’s analysis of escape velocity. 3

(b) Derive an expression for escape velocity in terms of the centripetal and gravitational forces acting on a projectile. 2

(c) Explain how Tsiolkovsky’s tower could launch a projectile into a stable orbit. 2

(d) Discuss some factors that affect the strength of the gravitational force at the bottom and top of the tower. 3

(e) Describe an experiment that could be performed to measure the value of the acceleration due to gravity at the top of the tower. 3

(f) Contrast qualitatively the value of gravitational acceleration obtained at the top and bottom of the tower. 2

(g) Calculate the work done in moving a 100 kg satellite up a 300 km tower. 1

(h) Discuss the effect of the Earth’s orbital and rotational motions on a satellite launched from the top of this tower. 4

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26. Motors and Generators

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. 3

(b) Derive/Define and explain an expression for the generation of emf in terms of the change in magnetic flux in an electrical generator. 2

(c) Explain the role of the transformers in electricity sub-stations. 2

(d) Discuss why some electrical appliances used in the home that are connected to the mains domestic power supply use a transformer. 3

(e) Describe an experiment to demonstrate the production of an alternating current. 3

(f) Contrast the use of step-up and step-down transformers in the national electricity grid. 2

(g) Calculate the secondary voltage produced when a transformer with a winding ratio of 33:1 has an input voltage of 330kV 1

(h) Discuss the energy losses that occur as energy is fed through transmission lines from the generator to the consumer. 4

End of Exam – Check your answers.

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Patrician Brothers College Fairfield

Year 12 Half-Yearly Examinations 2003

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

A B C DIf 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:

correctA 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

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Physics

Part B1 Answer Booklet

Name / Number: _________________________________

Answer Questions 16 – 21 in this Answer Booklet.

16. (a) ________________________________________________________________________________

(b) ________________________________________________________________________________

17. (a) ________________________________________________________________________________

(b) (c)

(d) ________________________________________________________________________________

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18. ___________________________________________________________________________________

19. ___________________________________________________________________________________

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Name / Number: __________________________

20. ___________________________________________________________________________________

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Additional Writing Space is available here.

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Physics

Part B2 Answer Booklet

Name / Number: _________________________________

Answer Questions 21 – 24 in this Answer Booklet.

21. (a) ________________________________________________________________________________

(b) ________________________________________________________________________________

(c) ________________________________________________________________________________

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Name/Number:__________________

22. ___________________________________________________________________________________

23. ___________________________________________________________________________________

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24. ___________________________________________________________________________________

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HSC Physics Half Yearly Exams 2003 Mapping GridQuestion Mark Content Syllabus

OutcomesTargeted

Performance BandCorrect Answer

1 1 9.2.1.2(2) H9 2-3 A2 1 9.2.2.11(2) H9 2-3 B3 1 9.2.2.13(2) H7 3 B4 1 9.2.3.4(2) H6 2 A5 1 9.2.4.4(2) H6 4 D6 1 9.2.4.8(2) H3 2 C7 1 9.2.4.9(2) H6 4 B8 1 9.3.1.6(2) H3 2 A9 1 9.3.1.5(3) H7 3 A10 1 9.3.2.2(3) H2 3 D11 1 9.3.2.6(2) H7 2 C12 1 9.3.4.2(3) H9 5 A13 1 9.3.1.4(3) H3 5 D14 1 9.3.4.1(2) H3 2 A15 1 9.3.1.3(3) H9 5 A

16(a) 0 - - -16(b) 3 9.2.2.3(3) H1 2-317(a) 1 9.2.2.11(2) H9 217(b) 2 9.2.2.4(3) H6 517(c) 2 9.2.3.2(3) H9 517(d) 2 9.2.2.11(2),

9.2.3.1(3)H3 4

18 3 9.2.4.1(2) H2 319 4 9.2.4.3(2) H2 520 6 9.2.4.4(3) H2 6

21(a) 2 9.3.3.1(3) H11 321(b) 2 9.3.3.3(2) H3 221(c) 6 9.3.3.3(3)

9.3.3.4(3)H4 6

22 3 9.3.2.3(3) H4 323 4 9.3.4.3(3) H3 424 5 9.3.4.7(2) H4 6

25(a) 3 9.2.2.4(2) H6 225(b) 2 9.2.2.6(2) H9 625(c) 2 9.2.2.3(3) H1 325(d) 3 9.2.3.1(3) H9 325(e) 3 9.2.1.1(3) H11 425(f) 2 9.2.1.2(3) H6 325(g) 1 9.2.1.3(2) H7 525(h) 4 9.2.2.6(2) H4 5-626(a) 3 9.3.2.1(2) H2 326(b) 2 9.3.2.4(2) H5 626(c) 2 9.3.4.5(2) H4 426(d) 3 9.3.4.6(2) H4 426(e) 3 9.3.3.1(3) H11 3-426(f) 2 9.3.4.2(2) H4 426(g) 1 9.3.4.2(3) H6 526(h) 4 9.3.3.4(2) H4 5-6

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During your course you have gathered and analysed information on the contribution of one scientist to the development of space exploration.

(b) Explain how this scientist’s ideas contributed to our understanding of space science. 3

MARKING GUIDELINESCriteria Marks

Relates how the ideas of the scientist had the effect of increasing our understanding of space science. 3

Describes some findings of the scientist. 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.


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


Correct answer. 1

Sample answer:Geostationary orbit.

(b) Calculate the value of gravity at this altitude. 2


Obtains correct result. 2

Correctly applies equations to solve the problem. 1

Sample answer:

(c) Calculate the orbital velocity of the satellite relative to the surface of the Earth. 2

MARKING GUIDELINES

Criteria Marks Obtains correct result. 2

Correctly applies equations to solve the problem. 1

Sample answer:

(d) Discuss the stability of this orbit. 2- -6

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.


Outline the features of the aether model for the transmission of light. 3


Gives an in-depth description of the main characteristics of the aether model. 2-3

Describes two points of the aether model. 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.


Discuss the role of the Michelson-Morley experiments in science in making determinations about competing theories. 4


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.

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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. 6


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


During the course you have planned, chose equipment or resources for, and performed a first-hand investigation to demonstrate the production of an alternating current.

(a) Describe briefly your investigation. 2


States some of the equipment used and rationalises their use. 2

Provides a correct method for the production of an alternating current. 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. 2


Relates the differences between AC and DC generators to their effect on a generated current. 1-2

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.

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(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. 6


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.


Explain how induction is used in cooktops in electric ranges. 3MARKING GUIDELINES

Criteria Marks Relates the application of Lenz’s law to its use in induction cooking. 2-3

States some features of induction cooking. 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.


Discuss how difficulties of heating caused by eddy currents in transformers may be overcome. 4


Provides points in terms of energy changes / transformations 4

Describes some methods for reducing eddy currents or reducing heating effects. 2-3

States how eddy currents are produced in transformers. 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 running the transformer at higher voltages, hence producing lower currents and selecting the type of material with a reasonable resistance to reduce the current.

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Discuss the impact of the development of transformers on society. 5


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.

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(a) Outline Newton’s analysis of escape velocity. 3


Has a complete description of Newton’s analysis of escape velocity. 3

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. 2


Correctly rearranges and derives an expression for velocity. 2

States the centripetal and gravitational forces acting on a projectile. 1

Sample answer:

(c) Explain how Tsiolkovsky’s tower could launch a projectile into a stable orbit. 2


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. 3


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:

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(e) Describe an experiment that could be performed to measure the value of the acceleration due to gravity at the top of the tower. 3


Provides points as to how the experiment is reliable and valid. 3

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. 2


Provides reasons for why the value of gravity at the top is lower. 2

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) 1

Sample answer:

(g) Calculate the work done in moving a 100 kg satellite up a 300 km tower. 1


Obtains correct answer. 1

Sample answer:Assuming g to be constant at 9.8 m/s2,

(h) Discuss the effect of the Earth’s orbital and rotational motions on a satellite launched from the top of this tower. 4


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. 1

Sample answer:

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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. 3


Give a chronological or logical order to the discoveries made by Faraday 3

Provides some points about the discovery of electrical generation by Faraday. 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. 2


Relates Faraday’s law to how it generates electricity. 2

States Faraday’s law either in language or mathematically. 1

Sample answer:

(c) Explain the role of the transformers in electricity sub-stations. 2


Relates the reasons for the use of transformers in sub-stations (causes) to the production of electricity (effects) 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. 3


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:

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(e) Describe an experiment to demonstrate the production of an alternating current. 3


Identifies some variables and controls in the experiment. 3

States an experiment that can produce A.C. 1-2

Sample answer:

(f) Contrast the use of step-up and step-down transformers in the national electricity grid. 2


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 1


Provides correct answer. 1

Sample answer:

(h) Discuss the energy losses that occur as energy is fed through transmission lines from the generator to the consumer. 4


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:

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hscphysics.wikispaces.comhscphysics.wikispaces.com/file/view/12T203xm.doc · Web view... spinning a needle attached to loops of wire in an external permanent magnetic field. (c) applying