In 2 Physics

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Stephen Bosi

John O’Byrne

Peter Fletcher

Joe Khachan

Jeff Stanger

Sandra Woodward

PHYSICS

_{@ HSC}

Sydney, Melbourne, Brisbane, Perth, Adelaide and associated companies around the world

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Series features vi

How to use this book viii

Stage 6 Physics syllabus grid x

Module 1 Space

Module 1 Introduction 2

Chapter 1 Cannonballs, apples, planets and gravity 4

1.1 Projectile motion 4

1.2 Gravity 10

1.3 Gravitational potential energy 16

Practical experiences 20

Chapter summary 22

Review questions 22

Chapter 2 Explaining and exploring the solar system 26

2.1 Launching spacecraft 26

2.2 Orbits and gravity 35

2.3 Beyond Kepler’s orbits 41

2.4 Momentum bandits: the slingshot effect 44

2.5 I’m back! Re-entry 46

Chapter summary 53

Review questions 54

Chapter 3 Seeing in a weird light: relativity 58 3.1 Frames of reference and classical relativity 58 3.2 Light in the Victorian era 61 3.3 Special relativity, light and time 64

3.4 Length, mass and energy 69

Chapter summary 76

Review questions 76

Module 1 Review 80

Module 2 Motors and Generators

Module 2 Introduction 82

Chapter 4 Electrodynamics: moving charges and

magnetic fields 84

4.1 Review of essential concepts 84 4.2 Forces on charged particles in magnetic fields 89

4.3 The motor effect 90

4.4 Forces between parallel wires 93

Chapter summary 98

Review questions 98

Chapter 5 Induction: the influence of changing

magnetism 100

5.1 Michael Faraday discovers electromagnetic

induction 100 5.2 Lenz’s law 104 5.3 Eddy currents 106 Practical experiences 109 Chapter summary 110 Review questions 110

Chapter 6 Motors: magnetic fields make the world

go around 114

6.1 Direct current electric motors 114 6.2 Back emf and DC electric motors 120 6.3 Alternating current electric motors 121

Chapter summary 127

Review questions 127

Chapter 7 Generators and electricity supply: power

for the people 130

7.1 AC and DC generators 130

7.2 Transformers 136

7.3 Electricity generation and transmission 141

Chapter summary 149

Module 2 Review 152

Module 3 From Ideas to Implementation

Module 3 Introduction 154

Chapter 8 From cathode rays to television 156

8.1 Cathode ray tubes 156

8.2 Charges in electric fields 160 8.3 Charges moving in a magnetic field 164

8.4 Thomson’s experiment 165

8.5 Applications of cathode rays 167

Chapter summary 171

Chapter 9 Electromagnetic radiation: particles

or waves? 174

9.1 Hertz’s experiments on radio waves 174 9.2 Black body radiation and Planck’s hypothesis 178

9.3 The photoelectric effect 182

9.4 Applications of the photoelectric effect 184

Chapter summary 186

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10.1 Conduction and energy bands 189

10.2 Semiconductors 190

10.3 Semiconductor devices 193 10.4 The control of electrical current 197

Chapter summary 202

Chapter 11 Superconductivity 204

11.1 The crystal structure of matter 204

11.2 Wave interference 205

11.3 X-ray diffraction 207

11.4 Crystal structure 208

11.5 Electrical conductivity and the crystal

structure of metals 209

11.6 The discovery of superconductors 211 11.7 The Meissner effect 212 11.8 Type-I and type-II superconductors 212 11.9 Why is a levitated magnet stable? 213 11.10 BCS theory and Cooper pairs 215 11.11 Applications of superconductors 217

Chapter summary 221

Module 4 Quanta to Quarks

Chapter 12 From Rutherford to Bohr 228

12.1 Atomic timeline 228

12.2 Rutherford’s model of the atom 229 12.3 Planck’s quantised energy 231

12.4 Spectral analysis 232

12.5 Bohr’s model of the atom 235 12.6 Bohr’s explanation of the Balmer series 236 12.7 Limitations of the Rutherford–Bohr model 239

Chapter summary 242

Chapter 13 Birth of quantum mechanics 247

13.1 The birth 247

13.2 Louis de Broglie’s proposal 248

13.3 Diffraction 250

13.4 Confirming de Broglie’s hypothesis 251 13.5 Electron orbits revisited 252 13.6 Further developments of atomic theory

1924–1930 253

Chapter summary 256

14.2 The need for the strong force 261 14.3 Atoms and isotopes 262

14.4 Transmutation 263

14.5 The neutrino 265

14.6 Was Einstein right? 266

14.7 Binding energy 268 14.8 Nuclear fission 269 14.9 Chain reactions 270 14.10 Neutron scattering 272 Practical experiences 273 Chapter summary 274 Review questions 275

Chapter 15 The particle zoo 279

15.1 The Manhattan Project 279 15.2 Nuclear fission reactors 280

15.3 Radioisotopes 282

15.4 Particle accelerators 286 15.5 The Standard Model 292

Chapter summary 296

Module 5 Medical Physics

Chapter 16 Imaging with ultrasound 304

16.1 What is ultrasound? 304 16.2 Principles of ultrasound imaging 305 16.3 Piezoelectric transducers 308 16.4 Acoustic impedance 310 16.5 Types of scans 312 16.6 Ultrasound at work 315 Practical experiences 317 Chapter summary 318 Review questions 318

Chapter 17 Imaging with X-rays 320

17.1 Overview and history: types of X-ray images 320

17.2 The X-ray tube 321

17.3 Types of X-rays 322

17.4 Production of X-ray images 324 17.5 X-ray detector technology 326 17.6 Production of CAT X-ray images 326 17.7 Benefits of CAT scans over conventional

radiographs and ultrasound 329

Chapter summary 331

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Chapter 18 Imaging with light 333

18.1 Endoscopy 333

18.2 Medical uses of endoscopes 336

Chapter summary 339

Chapter 19 Imaging with gamma rays 340 19.1 Isotopes and radioactive decay 340

19.2 Half-life 343

19.3 Radiopharmaceuticals: targeting tissues

and organs 344

19.4 The gamma camera 346

19.5 Positron emission tomography 347

Chapter summary 351

Chapter 20 Imaging with radio waves 354

20.1 Spin and magnetism 354

20.2 Hydrogen in a magnetic field 355

20.3 Tuning in to hydrogen 357

20.4 It depends on how and where you look 359

20.5 The MRI scanner 360

20.6 Applications of MRI 362 Practical experiences 363 Chapter summary 364 Review questions 364 Module 5 Review 366

Module 6 Astrophysics

Chapter 21 Eyes on the sky 370

21.1 The first telescopes 370

21.2 Looking up 373

21.3 The telescopic view 374

21.4 Sharpening the image 377

21.5 Interferometry 380

21.6 Future telescopes 382

Chapter summary 384

Chapter 22 Measuring the stars 388

22.1 How far? 388

22.2 Light is the key 389

22.3 The stellar alphabet 394

22.4 Measuring magnitudes 397

22.5 Colour matters 400

Chapter summary 405

Chapter 23 Stellar companions and variables 407

23.1 Binary stars 407 23.2 Doubly different 411 23.3 Variable stars 413 23.4 Cepheid variables 415 Practical experiences 418 Chapter summary 418 Review questions 419

Chapter 24 Birth, life and death 422

24.1 The ISM 422

24.2 Star birth 423

24.3 Stars in the prime of life 425

24.4 Where to for the Sun? 428

24.5 The fate of massive stars 430

24.6 How do we know? 433 Practical experiences 435 Chapter summary 436 Review questions 436 Module 6 Review 438

Module 7 Skills

Chapter 25 Skills stage 2 442

25.1 Metric prefixes 442

25.2 Numerical calculations 443

25.3 Sourcing experimental errors 445 25.4 Presenting research for an exam 446

25.5 Australian scientist 447

25.6 Linearising a formula 447

Chapter 26 Revisiting the BOS key terms 448 26.1 Steps to answering questions 449

Numerical answers 452

Glossary 454

Index 465

Acknowledgements 471

Formulae and data sheets 473

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@

HSC

in2 Physics is the most up-to-date physics package written for the NSW Stage 6 Physics syllabus. The materials comprehensively address the syllabus outcomes and thoroughly prepare students for the HSC exam.

Physics is presented as an exciting, relevant and fascinating discipline. The student materials provide clear and easy access to the content and theory, regular review questions, a full range of exam-style questions and features to develop an interest in the subject.

in2 Physics @ HSC student book

• The student book closely follows the NSW Stage 6 Physics syllabus and its modular structure.

• It clearly addresses both the contexts and the prescribed focus areas (PFAs).

• Modules consist of chapters that are broken up into manageable sections.

• Checkpoint questions review key content at regular intervals throughout each chapter. • Physics Philes present short, interesting

snippets of relevant information about physics or physics applications.

• Physics Features highlight important real-life examples of physics.

• Physics For Fun—Try This! provide hands-on activities that are easy to do.

• Physics Focus brings together physics concepts in the context of one or more PFAs and provides students with a graded set of questions to develop their skills in this vital area.

Each student book includes an interactive student CD containing: • an electronic version of the student book.

• all of the student materials on the companion website with live links to the website.

From cathode rays to television 8 168 169 From ideas to implementation

The vertical deflection plates cause the beam to move up or down in synchronisation with an input voltage. For example, a sinusoidal voltage will display a sinusoidal waveform (known as a trace) on the screen.

Television

Cathode ray tube (CRT) television sets used the principles of the cathode ray tube for most of the 20th century. These are now being superseded by plasma and liquid crystal display television sets, which use different operating principles and allow a larger display area with a sharper image. However, the CRT television holds quite a significant historical place in this form of communication.

A schematic diagram of a colour CRT television set is shown in Figure 8.5.5. Its basic elements are similar to those of the CRO. The main difference is the method of deflecting the electrons. Magnetic field coils placed outside the tube produce horizontal and vertical magnetic fields inside it. The magnitude and direction of the current determine the degree and direction of electron beam deflection. Recall your right-hand palm rule for the force on charged particles in a magnetic field. The vertical magnetic field will deflect the electrons horizontally; the horizontal field will deflect them vertically.

The picture on the screen is formed by scanning the beam from left to right and top to bottom. The electronics in the television switches the beam on and off at the appropriate spots on the screen in order to reproduce the transmitted picture. However, to reproduce colour images, colour television sets need to control the intensity of red, blue and green phosphors on the screen. Three separate electron guns are used, each one aimed at one particular colour. The coloured dots on the screen are clustered in groups of red, blue and green dots that are very close to each other and generally cannot be distinguished by eye without the aid of a magnifying glass. For this reason a method of guiding the different electron beams to their respective coloured dots was devised. A metal sheet, known as a shadow mask (Figure 8.5.6) and consisting of an array of holes, is placed behind the phosphor screen. Each hole guides the three beams to their respective coloured phosphor as the beams move horizontally and vertically. Black and white television sets did not need the shadow mask since they had only one beam.

heater cathode (negative) electrons 'boil' off the heated cathode anode (positive) electron beam electrons attracted to the positive anode collimator

Figure 8.5.3 The components of an electron gun used in both cathode ray oscilloscopes and CRT televisions

V Time V Time

sawtooth voltage for timebase sinusoidal vertical voltage

Figure 8.5.4 A sawtooth voltage waveform on the horizontal deflection plates of a CRO sweeps the electron beam across the screen to display the sinusoidal waveform on the vertical deflection plates.

electron gun magnetic coils electron beam fluorescent screen

Figure 8.5.5 A television picture tube showing the electron gun, deflection coils and fluorescent screen electron guns deflecting coils focusing coils glass fluorescent screen vacuum mask phosphor dots on screen fluorescent screen mask holes inmask blue beam red beam green beam R G B electron beams Figure 8.5.6

A colour CRT television set has three electron guns that will only strike their respective coloured phosphor dots with the aid of a shadow mask.

try this!

Do not aDjust your horizontal!

If you have access to an old black and white TV set or an old style monochrome computer monitor, try holding a bar magnet near the front of the screen and watch how the image distorts. This occurs because the magnetic field deflects the electrons that strike the screen. DO NOT do this with a colour TV set. This can magnetise the shadow mask and cause permanent distortion of the image and its colour. You can move a bar magnet near the back of a colour TV set to deflect the electrons from the electron gun and therefore distort or shift the image without causing permanent damage to the TV set.

Can an osCillosCope be used as a television set?

The similarity between the cathode ray oscilloscope (CRO) and CRT television suggests that a CRO can be used as a television set. In fact, there have been some devices that have made use of the CRO as you would a computer monitor. So, in principle, it can be used as a television. One is then forced to ask ‘why did they need to deflect the beam in a television set with magnetic fields rather than with electric fields as in the CRO?’

In principle all television sets could be made in the same design as a CRO; however, it is much easier and cheaper to deflect the beam with a magnetic field on the outside of the tube rather than embed electrodes in the glass and inside the vacuum—this is a little trickier. So now another question arises: ‘why not deflect the beam of the CRO using magnetic fields, wouldn’t it result in cheaper CROs?’.

Cathode ray oscilloscopes are precision instruments. The horizontal sweep rate must be able to be increased to very high frequencies in order to detect signals that change very quickly. Electric fields can be made to change very quickly without significant extra power requirements. However, a magnetically deflected system requires higher and higher voltages with increasing horizontal and vertical deflection frequencies in order to maintain the same current in the coils, and therefore, the same angle of beam deflection – thus having a significantly greater power requirement. Cathode ray tube television sets, however, only operate at fixed and relatively low scanning horizontal and vertical frequencies. Thus it is simpler and cheaper for the mass market to deflect with a magnetic field.

CheCkpoint 8.5

1 Outline the purpose of a CRO. 2 List the main parts of a CRO.

3 Describe the role of each of these parts in the CRO. 4 State the similarities and differences between the cathode ray tube CRO and CRT TV.

THE COMPLETE PHYSICS PACKAGE FOR NSW STUDENTS

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that provides a structured approach to the mandatory practical experiences, both first-hand and secondary-source investigations. • Dot point and skills

focused.

in2 Physics @ HSC Teacher Resource

• Editable teaching materials, including teaching

programs, so that teachers can tailor lessons to suit their classroom.

• Answers to student book and activity manual questions, with fully worked solutions and extended answers and support notes. • Risk assessments for all first-hand

investigations.

in2 Physics @ HSC companion website

Visit the companion website

in the student lounge

and teacher lounge

of Pearson Places

• Review questions—

auto-correcting multiple-choice questions for each chapter. • Web destinations—a list

of reviewed websites that support further investigation. 68

3

MODULE from ideas to implementation 69 Method

1 Set up the equipment as shown in Figure 8.1.1.

2 Observe the patterns and note the pressure in the tube.

3 Replace the tube with the next in the series. 4 Repeat the process of observing the patterns and

noting the pressure for each of the tubes in your set.

HAZARD

High voltages are produced by induction coils and may produce unwanted X-rays. The voltages necessar y to operate the tubes depend upon the dimensions of the tube and the pressure of the gas in the tube. Generally, the higher the voltage used, the greater the danger of the production of unwanted X-rays.

Use the lowest possible voltage and stand a minimum of 1 m away from the equipment.

Chapter 8

from Cathode rays to television

Changing pressure of discharge tubes

Perorm an investigation and gather first-hand information to observe the occurrence of different striation patterns for different pressures in discharge tubes.

Physics skills

The skills outcomes to be practised in this activity include: 12.1 perform first-hand investigations 12.2 gather first-hand information 14.1 analyse information

The complete statement of these skills outcomes can be found in the syllabus grid on pages vi–viii.

Aim

To observe the striation patterns for different pressures in discharge tubes. Hypothesis

Theory

Ever since Heinrich Geissler and Julius Plücker collaborated to create a tube in which the pressure could be reduced substantially, our understanding of the atom and developing uses for the cathode ray tube have adv

anced tremendously.

Normally air is considered to be an insulator, but it can be made to conduct by ionising the air molecules. the very small fraction of free electrons that are always in air are accelerated (with an electric field). At high pressures these electrons collide frequently with the air, losing their energy and, as a result, do not gain sufficient energy to ionise the air atoms. As pressure is reduced, these electrons travel further before colliding with air molecules, thereby acquiring enough energy to ionise the air molecules. This will produce more free electrons that, in turn, can ionise other atoms.

When they are able to travel far enough to gain the energy to be absorbed by atoms, we see a light show (known as a discharge).

The lower the pressure, the further the electrons can travel before colliding with gas molecules and producing a discharge.

The light that is emitted is a result of the electrons around the gas atom becoming excited (increasing in energy) and re-emitting the photon of light as they return to the ground state (the lowest energy they can have in an atom). Light will also be produced when free electrons recombine with ions and the electrons return to the ground state, emitting photons. As every element has a distinct set of energy levels, the colour of light seen will vary with the element with which the electron collides. Equipment

If you have the apparatus at school, you can carry out the experiment first hand. The patterns ar e hard to see unless the room is very dark.

• induction coil • discharge tubes at different pressures

• connecting wires • DC power supply Alternatively, you can use the simulations in Part B and make observations from them. Risk assessment

aCtivity 8.1

first-hand investigation

DC power supply

Figure 8.1.1 Induction coil and discharge tube

For more information on the

in2 Physics series,

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in2 Physics @ HSC is structured to enhance student

learning and their enjoyment of learning. It contains many outstanding and unique features that will assist students succeed in Stage 6 Physics. These include:

• Module opening pages introduce a range of contexts for study, as well as an inquiry activity that provides immediate activities for exploration and discussion.

2

Motors and

Generators

83

Figure 4.0.1 A generator produces electricity in each of these wind turbines.

82

The first recorded observations of the relationship between electricity and magnetism date back more than 400 years. Many unimagined discoveries followed, but progress never waits. Before we understood their nature, inventions utilising electricity and magnetism had changed our world forever.

Today our lives revolve around these forms of energy. The lights you use to read this book rely on them and the CD inside it would be nothing but a shiny coaster for your cup. We use magnetism to generate the electricity that drives industry, discovery and invention. Electricity and magnetism are a foundation for modern technology, deeply seated in the global economy, and our use impacts heavily on the environment.

The greatest challenge that faces future generations is the supply of energy. As fossil fuels dry up, electricity and magnetism will become even more important. New and improved technologies will be needed. Whether it’s a hybrid car, a wind turbine or a nuclear fusion power plant, they all rely on applications of electricity and magnetism.

Context

InQUIRY ACtIVItY BUIld YoUR own eleCtRIC motoR Many of the devices you use every day have electric motors. They spin your DVDs, wash your clothes and even help cook your food. Could you live without them, and how much do you know about how they work?

The essential ingredients for a motor are a power source, a magnetic field and things to connect these together in the right way. It’s not as hard as you think. All you need is a battery, a wood screw, a piece of wire and a cylindrical or spherical magnet. Put these things together as shown in Figure 4.0.2 and see if you can get your motor to spin. Be patient and keep trying. Then try the following activities.

1 Test the effects of changing the voltage you use. You could add another

battery in series or try a battery with a higher voltage.

2 Try changing the strength of the magnet by using a different magnet or

adding another. What does this affect?

3 Try changing the length of the screw, how sharp its point is or the material

it is made from. Does it have to be made of iron?

Figure 4.0.2 A simple homopolar motor

11

204 Superconductivity 205 from ideaS to implementation

crystal, constructive interference, destructive interference, path length, diffraction grating, Bragg law, phonons, critical temperature, type-I superconductors, type-II superconductors, critical field strength, vortices, flux pinning, BCS theory, Cooper pair, coherence length, energy gap, spin

Surprising discovery

Just as an improved understanding of the conducting properties of semiconductors led to the wide variety of electronic devices, research into the conductivity of metals produced quite a surprising discovery called superconductivity. This is the total disappearance of electrical resistance below a certain temperature, which has great potential applications ranging from energy transmission and storage to public transport. An understanding of this phenomenon required a detailed understanding of the crystal structure of conductors and the motion of electrons through them.

of interference of electromagnetic radiation, and examine how this was applied to crystals using X-rays. Then we will see how the BCS theory of superconductivity made use of the crystal structure of matter.

11.1 The crystal structure of matter

A crystal is a three-dimensional regular arrangement of atoms. Figure 11.1.1 shows a sodium chloride crystal (ordinary salt also called rock salt when it comes as a large crystal). The crystal is made from simple cubes repeated many times, with sodium and chlorine atoms at the corners of the cubes. Crystals of other materials may have different regular arrangements of their atoms. There are 14 types of crystal arrangements that solids can have.

The regular arrangement of atoms in crystals was a hypothesis before Max Von Laue and his colleagues confirmed it by X-ray diffraction experiments. William and Lawrence Bragg took this method one step further by measuring the spacing between the atoms in the crystal. Let us first look at the phenomenon

Figure 11.1.1 Crystal structure of sodium chloride. The red spheres represent positive sodium ions, and the green spheres represent negative chlorine ions.

try thiS!

Crystals in the kitChen

Look at salt grains through a magnifying lens. Each grain is a single crystal that is made from the basic arrangement of sodium and chlorine atoms shown in Figure 11.1.1. Although the grains mostly look irregular due to breaking and chipping during the manufacturing process, occasionally you will see an untouched cubic or rectangular prism that reflects the underlying crystal lattice structure.

CheCkpoInT 11.1

Explain what is meant by the crystal structure of matter.

11.2 Wave interference

The wave nature of light can be used to measure the size of very small spaces. Recall that two identical waves combine to produce a wave of greater amplitude when their crests overlap, as shown in Figure 11.2.1a (seein2 Physics @ Preliminarysections 6.4 and 7.4). The overlapping waves will cancel to produce a resulting wave of zero amplitude when the crest of one wave coincides with the trough of the other (Figure 11.2.1b). This addition and subtraction is called constructive and destructive interference respectively and is a property of all wave phenomena.

As an example, two identical circular water waves in a ripple tank overlap (see Figure 11.2.2). The regions of constructive and destructive interference radiate outwards along the lines as shown. Increasing the spacing between the sources causes the radiating lines to come closer together (Figure 11.2.2b).

Figure 11.2.1 Two identical waves (red, green) travelling in opposite directions can add (blue) (a) constructively or (b) destructively.

Figure 11.2.2 Interference of water waves for two sources that are (a) close together and (b) further apart t = 0 s t = 1 s t = 3 s t = 4 s t = 5 s t = 6 s t = 7 s t = 0 s t = 1 s t = 3 s t = 4 s t = 5 s t = 6 s t = 7 s a b lines of constructive interference lines of destructive interference b a

The interference of identical waves from two sources can also be represented by outwardly radiating transverse waves (see Figure 11.2.3). The distance that a wave travels is known as its path length. Constructive interference occurs when the difference in the path length of the two waves is equal to 0, λ, 2λ, 3λ, 4λ or any other integer multiple of the wavelength λ. Destructive interference occurs when the two waves are half a wavelength out of step. This corresponds to a path length difference of λ/2, 3λ/2, 5λ/2 etc.

constructive interference constructive interference destructive interference waves in phase

Figure 11.2.3 Constructive and destructive interference between identical transverse waves from two sources

3 72 Seeing in a weird light: relativity 73 Space PHYSICS FEATURE TwISTIng SPACETImE ... And YoUR mInd

There are two more invariants in special relativity. Maxwell’s equations (and hence relativity) requires that electrical charge is invariant in all frames. Another quantity invariant in all inertial frames is called the spacetime interval.

You may have heard of spacetime but not know what it is. One of Einstein’s mathematics lecturers Hermann Minkowski (1864–1909) showed that the equations of relativity and Maxwell’s equations become simplified if you assume that the three dimensions of space (x, y, z) and time t taken together form a four‑dimensional coordinate system called spacetime. Each location in spacetime is not a position, but rather an event—a position and a time.

Using a 4D version of Pythagoras’ theorem, Minkowski then defined a kind of 4D ‘distance’ between events called the spacetime interval s given by:

s 2 = (c × time period)2 – path length2

= c 2t 2 – ((∆x)2 + (∆y)2 + (∆z)2) Observers in different frames don’t agree on the 3D path length between events, or the time period between events, but all observers in inertial frames agree on the spacetime interval s between events.

In general relativity, Einstein showed that gravity occurs because objects with mass or energy cause this 4D spacetime to become distorted. The paths of objects through this distorted 4D spacetime appear to our 3D eyes to follow the sort of astronomical trajectories you learned about in Chapter 2 ‘Explaining and exploring the solar system’. However, unlike Newton’s gravitation, general relativity is able to handle situations of high gravitational fields, such as Mercury’s precessing orbit around the Sun and black holes. General relativity also predicts another wave that doesn’t require a medium: the ripples in spacetime called ‘gravity waves’. Figure 3.4.6 One of the four ultra-precise superconducting spherical

gyroscopes on NASA’s Gravity Probe B, which orbited Earth in 2004/05 to measure two predictions of general relativity: the bending of spacetime by the Earth’s mass and the slight twisting of spacetime by the Earth’s rotation (frame-dragging)

1. The history of physics

Mass, energy and the world’s most famous equation

The kinetic energy formula K = 12mv 2 doesn’t apply at relativistic speeds, even if you substitute relativistic mass mv into the formula. Classically, if you apply a net force to accelerate an object, the work done equals the increase in kinetic energy. An increase in speed means an increase in kinetic energy. But in relativity it also means an increase in relativistic mass, so relativistic mass and energy seem to be associated. Superficially, if you multiply relativistic mass by c 2 you get mv c 2, which has the same dimensions and units as energy. But let’s look more closely at it.

Solve problems and analyse information using: E = mc2 ll v c v=0− 2 2 1 t t v c v= − 0 2 2 1 m m v c v= − 0 2 2 1

How does this formula behave at low speeds (when v 2/c 2 is small)?

m c m c v c m c v c v2 0 2 2 2 02 2 2 1 2 1 1 = − = −      −

Using a well-known approximation formula that you might learn at university, (1 – x )n ≈ 1 – nx for small x: m c v c 02 2 2 1 2 1−     − ≈ m c v c 02 2 2 11 2 + ×     = m0c 2 + 12m0v 2 Rearrange: mvc 2 – m0c 2 = (mv – m0)c 2 ≈ 1 2m0v 2

In other words, at low speeds, the gain in relativistic mass (mv – m0) multiplied by c 2 equals the kinetic energy—a tantalising hint that at low speed mass and energy are equivalent. It can also be shown to be true at all speeds, using more sophisticated mathematics. In general, mass and energy are equivalent in relativity and c 2 is the conversion factor between the energy unit (joules) and the mass unit (kg). In other words:

E = mc 2

where m is any kind of mass. In relativity, mass and energy are regarded as the same thing, apart from the change of units. Sometimes the term mass-energy is used for both. m0 c 2 is called the rest energy, so even a stationary object contains energy due to its rest mass. Relativistic kinetic energy therefore:

m cm c m c v c m c v202 02 2 2 02 1 − = − − Whenever energy increases, so does mass. Any release of energy is accompanied by a decrease in mass. A book sitting on the top shelf has a slightly higher mass than one on the bottom shelf because of the difference in gravitational potential energy. An object’s mass increases slightly when it is hot because the kinetic energy of the vibrating atoms is higher.

Because c 2 is such a large number, a very tiny mass is equivalent to a large amount of energy. In the early days of nuclear physics, E = mc 2 revealed the enormous energy locked up inside an atom’s nucleus by the strong nuclear force that holds the protons and neutrons together. It was this that alerted nuclear physicists just before World War II to the possibility of a nuclear bomb. The energy released by the nuclear bomb dropped on Hiroshima at the end of that war (smallish by modern standards) resulted from a reduction in relativistic mass of about 0.7 g (slightly less than the mass of a standard wire paperclip).

Worked example

qUESTIon

When free protons and neutrons become bound together to form a nucleus, the reduction in nuclear potential energy (binding energy) is released, normally in the form of gamma rays. Relativity says this loss in energy is reflected in a decrease in mass of the resulting atom.

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

evil tWinS

The most extreme mass–energy conversion involves antimatter. For every kind of matter particle there is an equivalent antimatter particle, an ‘evil twin’, bearing properties (such as charge) of opposite sign. Particles and their antiparticles have the same rest mass. When a particle meets its antiparticle, they mutually annihilate—all their opposing properties cancel, leaving only their mass‑energy, which is usually released in the form of two gamma‑ray photons. Matter– antimatter annihilation has been suggested (speculatively) as a possible propellant for powering future interstellar spacecraft.

PRACTICAL EXPERIENCES

350

19Imaging with gamma rays

351

Chapter summary mEdICAL PhySICS

Activity 19.2: HeAltHy or diseAsed? Typical images of healthy bone and cancerous bone are shown. The tumours show up as hot-spots. Use the template in the activity manual to research and compare images of healthy and diseased parts of the body. Discussion questions

1 Examine Figure 19.4.2. There is a hot-spot that is not cancerous near the

left elbow. Explain.

2 In the normal scan (Figure 19.6.2a), the lower pelvis has a region of high

intensity. Why is this? (Hint: It may be soft tissue, not bone. Looking at Figure 19.6.2b might help you with this question.)

3 State the differences that can be observed by comparing an image of

a healthy part of the body with that of a diseased part of the body.

Gather and process secondary information to compare a scanned image of at least one healthy body part or organ with a scanned image of its diseased counterpart.

Review questions ChAPTER 19

This is a starting point to get you thinking about the mandatory practical experiences outlined in the syllabus. For detailed instructions and advice, use

in2 Physics @ HSC Activity Manual. Activity 19.1: Bone scAns A bone scan is performed to obtain a functional image of the bones and so can be used to detect abnormal metabolism in the bones, which may be an indication of cancer or other abnormality. Because cancer mostly involves a higher than normal

Perform an investigation to compare a bone scan with an X-ray image.

Figure 19.6.1 Comparison of an X-ray and bone scan of a hand

Figure 19.6.2 Bones scans of (a) a healthy person and (b) a patient with a tumour in the skeleton

• The number of protons in a nucleus is given by the atomic number, while the total number of nucleons is given by the mass number. • Atoms of the same element with different numbers of

neutrons are called isotopes of that element. • Many elements have naturally occurring unstable

radioisotopes. • In alpha decay an unstable nucleus decays by emitting

an alpha particle (α-particle). • In beta decay, a neutron changes into a proton and

a high-energy electron that is emitted as a beta particle (β-particle). • In positron decay, a positron—the antiparticle of the

electron—is emitted.

• When a positron and an electron collide, their total mass is converted into energy in the form of two gamma-ray photons. • In gamma decay a gamma ray (g) is emitted from a

radioactive isotope. • The time it takes for half the mass of a radioactive

parent isotope to decay into its daughter nuclei is the half-life of the isotope. • Artificial radioisotopes are produced in two main ways:

in a nuclear reactor or in a cyclotron. • A gamma camera detects gamma rays emitted by

a radiopharmaceutical in the patient’s body. • PET imaging uses positron-emitting

radiopharmaceuticals to obtain images using gamma rays emitted from electron–positron annihilation.

PHysicAlly sPeAking

Below is a list of topics that have been discussed throughout this chapter. Create a visual summary of the concepts in this chapter by constructing a mind map linking the terms. Add diagrams where useful.

Radioactive decay Radiation Radioisotope Nucleon

Neutron Proton Isotope Alpha decay

Beta decayGamma decay AntimatterPET

Half-life Bone scan Positron decay Scintillator

reviewing

1 Recall how the bone scan produced by a radioisotope compares with that from a conventional X-ray.

2 Analyse the relationship between the half-life of a radiopharmaceutical and its potential use in the human body.

3 Explain how it is possible to emit an electron from the nucleus when the electron is not a nucleon.

4 Assess the statement that ‘Positrons are radioactive particles produced when a proton decays’.

5 Discuss the impact that the production and use of radioisotopes has on society.

6 Describe how isotopes such as Tc-99m and F-18 can be used to target specific organs to be imaged.

7 Use the data in Table 19.6.1 to answer the questions: a Which radioactive isotope would most likely be

used in a bone scan? Justify your choice. b Propose two reasons why cesium-137 would not

be a suitable isotope to use in medical imaging. Table 19.6.1 Properties of some radioisotopes

Radioactive souRce Radiation emitted Half-life

C-11 β+, g 20.30 minutes Tc-99m g 6.02 hours TI-201 g 3.05 days I-131 β, g 8.04 days Cs-137 α 30.17 years U-238 α 4.47 × 109 years rate of cell division (thus producing a tumour), chemicals

involved in metabolic processes in bone tend to accumulate in higher concentrations in cancerous tissue. This produces areas of concentration of gamma emission, indicating a tumour.

Compare the data obtained from the image of a bone scan with that provided by an X-ray image. Discussion questions

1 Identify the best part of the body for each of these

diagnostic tools to image.

2 Compare and contrast the two images in terms of

the information they provide.

a b

• Chapter openings list the key words of each chapter and introduce the chapter topic in a concise and engaging way.

• Key ideas are clearly highlighted with a and Syllabus flags indicate where domain dot points appear in the student book. The flags are placed as closely as possible to where the relevant content is covered. Flags may be repeated if the dot point has multiple parts, is complex or where students are required to solve problems.

• Each chapter concludes with: – a chapter summary

– review questions, including literacy-based questions (Physically Speaking), chapter review questions (Reviewing) and physics problems (Solving Problems). Syllabus verbs are clearly highlighted as and where appropriate

– Physics Focus—a unique feature that places key chapter concepts in the context of one or more prescribed focus areas.

• Chapters are divided into short, accessible sections— the text itself is presented in short, easy-to-understand chunks of information. Each section concludes with a Checkpoint—a set of review questions to check understanding of key content and concepts.

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• Module reviews provide a full range of exam-style questions, including multiple-choice, short-response and extended-response questions.

224 225

from ideas to implementation

3

The review contains questions in a similar style and proportion to the HSC Physics examination. Marks are allocated to each question up to a total of 25 marks. It should take you approximately 45 minutes to complete this review.

multiple choice

(1 mark each)

1 Predict the direction of the electron in Figure 11.13.1 as it enters the magnetic field.

A Straight up

B Left

C Right

D Down

2 The diagrams in Figure 11.13.2 represent semiconductors, conductors and insulators. The diagrams show the conduction and valence bands, and the energy gaps. Which answer correctly labels each of the diagrams?

I II III

AConductor Insulator Semiconductor

BInsulator Conductor Semiconductor

CInsulator SemiconductorConductor

DSemiconductorConductor Insulator

3 The graph in Figure 11.13.3 shows how the resistance of a material varies with temperature. Identify each of the parts labelled on the graph.

I II III

ACritical temperature Superconductor material Normal material

BSuperconductor material Critical temperature Normal material

CCritical temperature Normal materialSuperconductor material

DNormal materialSuperconductor material Critical temperature

Figure 11.13.1 An electron in a magnetic field

Figure 11.13.2 Energy bands

Figure 11.13.3 Resistance varies with temperature – I II III Temperature (K) Resistance ( Ω ) I IIIII

4 Experimental data from black body radiation during Planck’s time showed that predicted radiation levels were not achieved in reality. Planck best described this anomaly by saying that:

A classical physics was wrong.

B radiation that is emitted and absorbed is quantised.

C he had no explanation for it.

D quantum mechanics needed to be developed.

5 Figure 11.13.4 shows a cathode ray tube that has been evacuated. Which answer correctly names each of the labelled features?

I II III

AStriations Cathode Anode

BFaraday’s dark space Striations Cathode

CCrooke’s dark space Anode Faraday’s dark space

DCathode Faraday’s dark space Striations

extended response

6 Explain, with reference to atomic models, why cathode rays can travel through metals. (2 marks)

7 Outline how the cathode ray tube in a TV works in order to produce the viewing picture. (2 marks)

8 Give reasons why CRT TVs use magnetic coils and CROs use electric plates in order to deflect the beams, given that both methods work. (2 marks).

9 In your studies you were required to gather information to describe how the photoelectric effect is used in photocells.

a Explain how you determined which material was relevant and reliable.

b Outline how the photoelectric effect is used in photocells. (3 marks)

10 Justify the introduction of semiconductors to replace thermionic devices. (4 marks)

11 Magnetic levitation trains are used in Germany and Japan. The trains in Germany use conventional electromagnets, whereas the one in Japan uses superconductors. Compare and contrast the two systems. (3 marks)

12 a Determine the frequency of red light, which has a wavelength λ = 660 nm. (Speed of light

c = 3.00 × 108 m s–1)

b Calculate the energy of a photon that is emitted with this wavelength. (Planck’s constant

h = 6.63 × 10–34 J s) (4 marks) Figure 11.13.4 An evacuated cathode ray tube

II III I 48 MODULE motors and generators 2 49 Chapter 6 motors: magnetic fields make the world go around

Risk assessment Method

1 Cut a length of cotton-covered wire so that the wire is long enough to wrap around the exterior of a matchbox three times (as shown in Figure 6.2.2).

2 Leave a straight piece (approx. 10 cm long) hanging out and then wind the remainder of the wire around the box 2½ times. Leave another straight piece the same length as at the start, on the opposite side. 3 Wrap the straight pieces around the loops so that they tie both ends. 4 Fan out the loops so that you get equally spaced loops and that it

looks like a bird cage (see Figure 6.2.3). 5 Push out the middle of the paper clip as shown and Blu-Tack to

the bench.

6 Slip the straight pieces of wire through the paper clip supports. Unwrap the cotton from these parts. 7 Connect an AC power supply to the paper clips. 8 Place two magnets so that a north pole and a south pole face on

opposing sides of the cage. 9 Turn on. You may need to give the cage a tap to get it spinning.

Results

1 Record your observations of the motor.

2 How did adding more magnets affect how the motor ran?

3 When the current is increased, what changes occurred?

Motors and torque

Solve problems and analyse information about simple motors using: τ = nBIA cos θ

Physics skills

The skills outcomes to be practised in this activity include:

12.4 process information 14.1 analyse information

The complete statement of these skills outcomes can be found in the syllabus grid on pages vii–viii.

Aim Hypothesis Theory

The motor effect means that a current-carrying wire experiences a force when placed in a magnetic field. This is the basis for the workings of a motor.

For a motor to work as needed, the motion resulting from the motor effect needs to be circular and the force needs to be adjusted so the direction of rotation does not change.

Question

Figure 6.2.1 shows the simplified workings of a motor that you will be making. Label all the parts of the motor.

Equipment • insulated wire from which insulation can be removed easily • Blu-Tack • magnets • connecting wires with alligator clips • magnetic field sensor and data logger (if available) • power supply • paperclips matchbox wire loop wire through a b alligator clip wires paper clip cage fanned out

power source Figure 6.2.2 Equipment set-up 1

Figure 6.2.3 Equipment set-up 2

First-hand investigation aCtIVItY 6.2 A: C: D: B: N S Figure 6.2.1 Simplified motor

Other features

• Physics Philes present short, interesting items to support or extend the text.

• Physics for Fun—Try This! activities are short, hands-on activities to be dPhysics for Fun—Try This! activities are short, hands-one quickly, designed to provoke discussion.

• Physics Features are a key feature as they highlight contextual material, case studies or prescribed focus areas of the syllabus.

• A complete glossary of all the key words is included at the end of the student book.

• The final two chapters provide essential reference material: ‘Skills stage 2’ and ‘Revisiting the BOS key terms’.

• In all questions and activities, except module review questions, the BOS key terms are highlighted.

in2 Physics @ HSC Student CD

This is included with the student book and contains: • an electronic version of the student book

• interactive modules demonstrating key concepts

Practical experiences

The accompanying activity manual covers all of the mandatory practical experiences outlined in the syllabus.

in2 Physics @ HSC Activity Manual is a write-in

workbook that outlines a clear, foolproof approach to success in all the required practical experiences.

Within the student book, there are clear cross-references to the activity manual: Practical Experiences icons refer to the activity number and page in the activity manual. In each chapter, a summary of possible investigations is provided as a starting point to get

students thinking. These include the aim, a list of equipment and

discussion questions. Activity 10.2

PRACTICAL EXPERIENCES

Activity Manual, Page 94

• the companion website on CD

• a link to the live companion website (Internet access required) to provide access to the latest information and web links related to the student book.

The complete in2 Physics @ HSC package

Remember the other components of the complete package: • in2 Physics @ HSC companion website at Pearson Places • in2 Physics @ HSC Teacher Resource.

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Prescribed focus areas

1. The history of physics H1. evaluates how major advances in scientific understanding and

technology have changed the direction or nature of scientific thinking Feature: pp. 12, 29, 72

Focus: pp. 25, 246, 299

2. The nature and practice of physics H2. analyses the ways in which models, theories and laws in physics

have been tested and validated Focus: p. 79

3. Applications and uses of physics H3. assesses the impact of particular advances in physics on the

development of technologies Feature: pp. 12, 29, 307, 334, 346

Focus: pp. 57, 79, 129, 173, 223, 246, 259, 278 4. Implications for society and the

Environment H4. assesses the impacts of applications of physics on society and the environment Feature: pp. 29, 307, 344

Focus: pp. 113, 173, 353 5. Current issues, research and

developments in physics H5. identifies possible future directions of physics research Feature: pp. 391, 410

Focus: pp. 79, 113, 173, 223, 353, 386

Module 1 Space

1. The Earth has a gravitational field that exerts a force on objects both on it and around it

STuDEnTS lEARn TO: PAGE STuDEnTS: PAGE

define weight as the force on an object

due to a gravitational field 13 perform an investigation and gather information to determine a value for acceleration due to gravity using pendulum motion or computer-assisted

technology and identify reason(s) for possible variations from the value 9.8 m s–2

Act. 1.2 explain that a change in gravitational

potential energy is related to work done 16 gather secondary information to predict the value of acceleration due to gravity on other planets Act. 1.3

define gravitational potential energy as the work done to move an object from a very large distance away to a point in a gravitational field: m m r = 1 2 P E G

16 analyse information using the expression:

F = mg

to determine the weight force for a body on Earth and for the same body on other planets

Act. 1.3

2. Many factors have to be taken into account to achieve a successful rocket launch, maintain a stable orbit and return to Earth

describe the trajectory of an object undergoing projectile motion within the Earth’s gravitational field in terms of horizontal and vertical components

5 solve problems and analyse information to calculate the actual velocity of

a projectile from its horizontal and vertical components using: vx2= ux2 v=u+at vy2= uy2+2ay ∆y ∆x=u_xt ∆y=u_yt +1 2ay t 2 7, 9, 23, 24

describe Galileo’s analysis of projectile

motion 5 perform a first-hand investigation, gather information and analyse data to calculate initial and final velocity, maximum height reached, range and time of

flight of a projectile for a range of situations by using simulations, data loggers and computer analysis

Act. 1.1

explain the concept of escape velocity in terms of the:

– gravitational constant – mass and radius of the planet

18 identify data sources, gather, analyse and present information on the contribution

of one of the following to the development of space exploration: Tsiolkovsky, Oberth, Goddard, Esnault-Pelterie, O’Neill or von Braun

29 Act. 2.1

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outline Newton’s concept of escape

velocity 18

identify why the term ‘g forces’ is used to explain the forces acting on an astronaut during launch

31 discuss the effect of the Earth‘s orbital motion and its rotational motion on the launch of a rocket

34

analyse the changing acceleration of a rocket during launch in terms of the: – Law of Conservation of Momentum – forces experienced by astronauts

30, 33

analyse the forces involved in uniform circular motion for a range of objects, including satellites orbiting the Earth

25, 32, 34, 37, 54, 55

solve problems and analyse information to calculate the centripetal force acting on a satellite undergoing uniform circular motion about the Earth using:

F= mv_r 2

37, 54, 55 Act. 2.2 compare qualitatively low Earth and

geo-stationary orbits 43

define the term orbital velocity and the quantitative and qualitative relationship between orbital velocity, the

gravitational constant, mass of the central body, mass of the satellite and the radius of the orbit using Kepler’s Law of Periods

36, 40,

56 solve problems and analyse information using:_r

T GM 3 2=₄_π2 39, 43, 56

account for the orbital decay of

satellites in low Earth orbit 46

discuss issues associated with safe re-entry into the Earth’s atmosphere and landing on the Earth’s surface

47 identify that there is an optimum angle for safe re-entry for a manned spacecraft into the Earth’s atmosphere and the consequences of failing to achieve this angle

47

3. The solar system is held together by gravity

describe a gravitational field in the region surrounding a massive object in terms of its effects on other masses in it

13 present information and use available evidence to discuss the factors affecting

the strength of the gravitational force Act. 1.3

define Newton’s Law of Universal Gravitation: m m d = 1 2 2 F G

11 solve problems and analyse information using:

m m d = 1 2 2 F G 23, 24, 25, 37, 54, 55 discuss the importance of Newton’s

Law of Universal Gravitation in understanding and calculating the motion of satellites

35, 38

identify that a slingshot effect can be

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outline the features of the aether model

for the transmission of light 61

describe and evaluate the Michelson-Morley attempt to measure the relative velocity of the Earth through the aether

62 gather and process information to interpret the results of the Michelson-Morley

experiment 62 Act. 3.2

discuss the role of the Michelson-Morley experiments in making determinations about competing theories

62

outline the nature of inertial frames of

reference 58 perform an investigation to help distinguish between non-inertial and inertial frames of reference 60 Act. 3.1

discuss the principle of relativity 58 analyse and interpret some of Einstein’s thought experiments involving mirrors

and trains and discuss the relationship between thought and reality 66

describe the significance of Einstein’s assumption of the constancy of the speed of light

65 analyse information to 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

78 identify that if c is constant then space

and time become relative 65

discuss the concept that length standards are defined in terms of time in contrast to the original metre standard

79

explain qualitatively and quantitatively the consequence of special relativity in relation to:

– the relativity of simultaneity – the equivalence between mass and

energy

– length contraction – time dilation – mass dilation

64, 69 solve problems and analyse information using: E = mc 2 l l v c v= 0 − 2 2 1 t v c v t0 = 1− 2₂ m v c v m₀ = − 2 2 1 66, 69, 72, 77, 78

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

70, 73

Module 2 Motors and Generators

1. Motors use the effect of forces on current-carrying conductors in magnetic fields

discuss the effect on the magnitude of the force on a current-carrying conductor of variations in:

– the strength of the magnetic field in which it is located

– the magnitude of the current in the conductor

– the length of the conductor in the external magnetic field

– the angle between the direction of the external magnetic field and the direction of the length of the conductor

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describe qualitatively and quantitatively the force between long parallel current-carrying conductors: F l k I I d = 1 2

94 solve problems using:

F l k I I d = 1 2 94

define torque as the turning moment of a force using:

t= Fd

115 solve problems and analyse information about the force on current-carrying

conductors in magnetic fields using: F = BIl sin θ

92 Act. 4.1 identify that the motor effect is due to

the force acting on a current-carrying conductor in a magnetic field

90,

116 solve problems and analyse information about simple motors using: t = nBIA cos θ 117 Act. 6.2

describe the forces experienced by a current-carrying loop in a magnetic field and describe the net result of the forces

117 identify data sources, gather and process information to qualitatively describe the

application of the motor effect in: – the galvanometer

– the loudspeaker

91, 119 Act. 6.1 describe the main features of a DC

electric motor and the role of each feature

115 identify that the required magnetic

fields in DC motors can be produced either by current-carrying coils or permanent magnets

115

2. The relative motion between a conductor and magnetic field is used to generate an electrical voltage

outline Michael Faraday’s discovery of the generation of an electric current by a moving magnet

100 perform an investigation to model the generation of an electric current by moving

a magnet in a coil or a coil near a magnet 101 Act. 5.1

define magnetic field strength B as

magnetic flux density 101 plan, choose equipment or resources for, and perform a first-hand investigation to predict and verify the effect on a generated electric current when: – the distance between the coil and magnet is varied

– the strength of the magnet is varied

– the relative motion between the coil and the magnet is varied

Act. 5.1

describe the concept of magnetic flux in terms of magnetic flux density and surface area

101 gather, analyse and present information to explain how induction is used in

cooktops in electric ranges

108 Act. 5.2 describe generated potential difference

as the rate of change of magnetic flux through a circuit

103 gather secondary information to identify how eddy currents have been utilised in

electromagnetic braking Act. 5.2 113

account for Lenz’s Law in terms of conservation of energy and relate it to the production of back emf in motors

105, 120 explain that, in electric motors, back emf opposes the supply emf

120 explain the production of eddy currents

in terms of Lenz’s Law 106

3. Generators are used to provide large scale power production

describe the main components of a

generator 131 plan, choose equipment or resources for, and perform a first-hand investigation to demonstrate the production of an alternating current Act. 5.1

compare the structure and function of

a generator to an electric motor 135 gather secondary information to discuss advantages/disadvantages of AC and DC generators and relate these to their use 135 Act. 7.1

describe the differences between AC

and DC generators 135 analyse secondary information on the competition between Westinghouse and Edison to supply electricity to cities 141 Act. 7.2

discuss the energy losses that occur as energy is fed through transmission lines from the generator to the consumer

144 gather and analyse information to identify how transmission lines are:

– insulated from supporting structures – protected from lightning strikes

146 Act. 7.3 assess the effects of the development

of AC generators on society and the environment

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describe the purpose of transformers in

electrical circuits 136 perform an investigation to model the structure of a transformer to demonstrate how secondary voltage is produced Act. 7.3

compare step-up and step-down

transformers 137 solve problems and analyse information about transformers using:V

V n n p s p s = 137 Act. 7.3

identify the relationship between the ratio of the number of turns in the primary and secondary coils and the ratio of primary to secondary voltage

137 gather, analyse and use available evidence to discuss how difficulties of heating

caused by eddy currents in transformers may be overcome 139 Act. 7.3

explain why voltage transformations are

related to conservation of energy 139 gather and analyse secondary information to discuss the need for transformers in the transfer of electrical energy from a power station to its point of use 145 Act. 7.3 explain the role of transformers in

electricity substations 142

discuss why some electrical appliances in the home that are connected to the mains domestic power supply use a transformer

136, 144 discuss the impact of the development

of transformers on society 147

5. Motors are used in industries and the home usually to convert electrical energy into more useful forms of energy

STuDEnTS lEARn TO: PAGE STuDEnTS: PAGE

describe the main features of an AC electric motor

124 perform an investigation to demonstrate the principle of an AC induction motor Act. 6.3

gather, process and analyse information to identify some of the energy transfers and transformations involving the conversion of electrical energy into more useful forms in the home and industry

124, 153 Act. 7.3

Module 3 From Ideas to Implementation

1. Increased understandings of cathode rays led to the development of television

explain why the apparent inconsistent behaviour of cathode rays caused debate as to whether they were charged particles or electromagnetic waves

157 perform an investigation and gather first-hand information to observe the

occurrence of different striation patterns for different pressures in discharge tubes

Act. 8.1

explain that cathode ray tubes allowed the manipulation of a stream of charged particles

157 perform an investigation to demonstrate and identify properties of cathode rays

using discharge tubes: – containing a Maltese cross – containing electric plates – with a fluorescent display screen – containing a glass wheel

analyse the information gathered to determine the sign of the charge on cathode rays

Act. 8.2

Act. 8.2 identify that moving charged particles

in a magnetic field experience a force 164 solve problem and analyse information using:F = qvB sinθ

F = qE and E V d = 162, 164

identify that charged plates produce an

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describe quantitatively the force acting on a charge moving through a magnetic field:

F = qvB sinθ

164

discuss qualitatively the electric field strength due to a point charge, positive and negative charges and oppositely charged parallel plates

160

describe quantitatively the electric field

due to oppositely charged parallel plates 161

outline Thomson’s experiment to measure the charge/mass ratio of an electron

165 outline the role of:

– electrodes in the electron gun – the deflection plates or coils – the fluorescent screen – in the cathode ray tube of

conventional TV displays and oscilloscopes

167

2. The reconceptualisation of the model of light led to an understanding of the photoelectric effect and black body radiation

describe Hertz’s observation of the effect of a radio wave on a receiver and the photoelectric effect he produced but failed to investigate

182 perform an investigation to demonstrate the production and reception of

radio waves Act. 9.1

outline qualitatively Hertz’s experiments in measuring the speed of radio waves and how they relate to light waves

175 identify data sources, gather, process and analyse information and use available

evidence to assess Einstein’s contribution to quantum theory and its relation to black body radiation

Act. 9.2

identify Planck’s hypothesis that radiation emitted and absorbed by the walls of a black body cavity is quantised

179 identify data sources, gather, process and present information to summarise the

use of the photoelectric effect in photocells 184 Act. 9.3

identify Einstein’s contribution to quantum theory and its relation to black body radiation

179 solve problems and analyse information using:

E = hf and c = f λ

181 Act. 9.3

explain the particle model of light in terms of photons with particular energy and frequency

179 process information to discuss Einstein and Planck’s differing views about

whether science research is removed from social and political forces Act. 9.4

identify the relationships between photon energy, frequency, speed of light and wavelength:

E = hf and c = f λ