p r e l i m i n a r y c o u r s e

Xiao L. Wu Robert FaRR

physicsin focus

First published 2009Text 2009 Xiao L. Wu and Robert FarrIllustrations and design 2009 McGraw-Hill Australia Pty LtdAdditional owners of copyright are acknowledged on the acknowledgments page

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National Library of Australia Cataloguing-in-Publication Data

Author: Wu, Xiao L. Title: Physics in focus : preliminary course / Xiao L. Wu, Robert Farr. ISBN: 9780070138919 (pbk.) Notes: Includes index. Bibliography. Target Audience: For secondary school age. Subjects: PhysicsTextbooks. Other Authors/Contributors: Farr, Robert. Dewey Number: 530

Published in Australia byMcGraw-Hill Australia Pty LtdLevel 2, 82 Waterloo Road, North Ryde NSW 2113Publisher: Eiko BronEditorial Assistant: Ivy ChungManaging Editor: Kathryn FairfaxSenior Production Editor: Yani SilvanaCopy Editor: Rosemary MoorePermissions Editor: Wendy MorrisArt Director: Astred Hicks Cover Design: Astred Hicks Internal Design: Jenny Pace Walter and Astred Hicks Illustrator: Chris WelchProofreader: Terry TownsendIndexer: Tricia WatersTypesetter: Midland TypesettersCD-ROM design: Hurix Systems Pvt LtdCD-ROM preparation: Emma Mullenger and Yani SilvanaCD-ROM cover: Astred HicksPrinted in China on 80 gsm matt art by 1010 Printing International Ltd

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Contents

About the authors ixTo the student ixAcknowledgments xList of Board of Studies verbs xiPhysics skillsan introduction xii

THE WORLD COMMUNICATES 1Chapter 1 The transfer of information using waves 2

The wave model can be used to explain how current technologies transfer information 21.1 Energy transformations are necessary for communication to occur 31.2 Mechanical waves require a medium 41.3 Waves can occur in one, two or three dimensions 5First-hand investigation: Observing waves 61.4 The characteristics of waves 71.5 Motion of the medium determines the type of wave 81.6 Transverse motion and longitudinal motion 9First-hand investigation: The frequency and amplitude of waves 91.7 Displacementtime graphs of wave motion 10Present and analyse information from displacementtime graphs for transverse wave motion 10First-hand investigation: The relationship between frequency and wavelength for a wave 111.8 The wave equation 12Solve problems and analyse information by applying the mathematical model of v = f to a range of situations 12Chapter revision questions 14

Chapter 2 Sound is a wave 15

Features of a wave model can be used to account for the properties of sound 152.1 Sound consists of vibrations travelling through a medium 152.2 Sound waves may be graphically represented as transverse waves because longitudinal waves

such as sound are difficult to draw 162.3 The physics of pitch and volume 17First-hand investigation: Analysing sound waves 172.4 Echoes have practical applications 182.5 How the CRO has helped to advance understanding in physics 192.6 Waves can add to form a resultant wave 20First-hand investigation: Demonstrating the principle of superposition 222.7 Applications of the principle of superposition 23Present graphical information, solve problems and analyse information involving superposition of sound waves 232.8 Acoustics and the principle of superposition 24Chapter revision questions 24

Chapter 3 Using the electromagnetic spectrum 26

Recent technological developments have allowed greater use of the electromagnetic spectrum 263.1 Electromagnetic waves do not require a medium 273.2 The Earths atmosphere filters most dangerous radiation 303.3 Identifying the electromagnetic wavebands 323.4 Intensity of radiation and the inverse square law 33First-hand investigation: Modelling the inverse square law 36

Contents

CONTENTS

iv

CONTENTS

3.5 Modulation 363.6 The energy transfers in modern communication technologies 38Analyse information to identify the waves involved in the transfer of energy that occurs during the use of one of the following: mobile telephone television radar 383.7 Making use of the electromagnetic spectrum for communications 40Analyse information to identify the electromagnetic spectrum range utilised in modern communication technologies 403.8 The many uses for the available electromagnetic spectrum can lead to overcrowding 40Chapter revision questions 41

Chapter 4 The applications of the reflection and refraction of electromagnetic waves 43

Many communication technologies use applications of reflection and refraction of electromagnetic waves 434.1 The law and effect of reflection 434.2 Transferring information through reflection and applications of reflection 47First-hand/secondary source investigation: Path and direction of travel of rays and waves 494.3 Refraction and waves 504.4 Refractive index 51First-hand investigation: Graphing the angles of incidence and refraction of light 55Solve problems and analyse information using Snells law 554.5 Refraction and the critical angle 56First-hand investigation: The refractive index of glass or perspex 574.6 Internal reflection and optical fibres 59Chapter revision questions 60

Chapter 5 Communication technology for now and for the future 61

Electromagnetic waves have potential for future communication technologies and data storage technologies 615.1 Digital communication data 62Secondary source investigation: Some underlying physical principles related to wave technologies 62Chapter revision questions 66The world communicates: review questions 67

ELECTRICAL ENERGY IN THE HOME 69Chatper 6 Electricity 70

Society has become increasingly dependent on electricity over the last 200 years 706.1 Changes in the main sources of domestic energy in history 716.2 The impacts of changes in energy sources and the development of technologies 726.3 The electricity distribution system 73Secondary source investigation: The work of Luigi Galvani and Alessandro Volta 76Chapter revision questions 78

Chapter 7 Electric charges, voltage, current and resistance 79

One of the main advantages of electricity is that it can be moved with comparative ease from one place to another through electric circuits 797.1 Electric charges 797.2 Methods of charging 807.3 Electric fields 83Secondary source investigation: Present diagrammatic information to describe electric field strength and direction 83Solve problems and analyse information using E =

F

q 83

CONTENTS CONTENTS

v

7.4 Voltage 887.5 Current 917.6 Resistance and Ohms law 94

Solve problems and analyse information applying R = V

I 94

7.7 More about resistance 967.8 Ohmic versus non-ohmic conductors 967.9 Conductors and insulators 98Secondary source investigation: Materials that are commonly used as conductors to provide household electricity 987.10 Basic electric circuits and circuit diagrams 997.11 DC circuits 101First-hand investigation: The relationship between voltage across and current through a resistor in a DC circuit 101First-hand investigation: Measuring voltage across different points around a DC circuit 102Chapter revision questions 104

Chapter 8 Series and parallel circuits 106

Series and parallel circuits serve different purposes in households 1068.1 Electric circuitsseries versus parallel 1068.2 Series circuits 1068.3 The ammeter 1098.4 Parallel circuits 1118.5 Voltmeter 1148.6 More complex circuits 1158.7 Household circuits 118First-hand investigation: Measuring voltage and current for series and parallel circuits 119First-hand investigation: Modelling the household circuit 121Chapter revision questions 122

Chapter 9 Electric power and energy 126

The amount of power is related to the rate at which energy is transformed 1269.1 Power 126Solve problems and analyse information using: P = VI and Energy = VIt 1269.2 Total energy consumption 128Solve problems and analyse information using: P = VI and Energy = VIt 1289.3 Power and energy dissipation in series and parallel circuits 130Solve problems and analyse information using: P = VI and Energy = VIt 1309.4 The kilowatt-hour 134Solve problems and analyse information using: P = VI and Energy = VIt 134First-hand investigation: Demonstrating the relationship between current, voltage and power using a heating coil 136Chapter revision questions 138

Chapter 10 Magnetic field 140

Electric currents also produce magnetic fields and these fields are used in different devices in the home 14010.1 Magnetic field 14010.2 Magnetic fields of ferromagnets 14110.3 The Earths magnetic field 14310.4 The magnetic field of a straight current-carrying conductor 144Secondary source investigation: Representing magnetic field and current direction using dots and crosses 14510.5 The magnetic field of a solenoid 146

CONTENTS

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CONTENTS

10.6 The magnetic field of an electromagnet 148Secondary source investigation: Applications of magnetism 149First-hand investigation: Building an electromagnet 150First-hand investigation: Observing magnetic fields 151Chapter revision questions 153

Chatper 11 Electric shock and safety devices 155

Safety devices are important in household circuits 15511.1 Electric shocks 15511.2 Safety devices 156Chapter revision questions 160Electrical energy in the home: review questions 161

MOvING AbOUT 163Chapter 12 Basic concepts in motion 164

Vehicles do not typically travel at a constant speed 16412.1 Scalar quantities and vector quantities 16512.2 Distance and displacement 16612.3 Speed 16612.4 Velocity 168

Solve problems and analyse information using the formula vav = rt where r = displacement 168

12.5 Addition and subtraction of scalar quantities 170Secondary source investigation: Motion graphs 171First-hand investigation: Measuring average speed 177Chapter revision questions 178

Chapter 13 The laws of motion 182

An analysis of the external forces on vehicles helps to understand the effects of acceleration and deceleration 18213.1 Force 18213.2 Vector addition and subtraction 182Solve problems using vector diagrams to determine resultant velocity, acceleration and force 18213.3 Relative motion 18813.4 Resolving vectors 19013.5 Newtons laws of motion 19113.6 Newtons first law of motion 19113.7 Newtons second law of motion 19313.8 Acceleration 19413.9 Mass and weight 19613.10 Newtons third law of motion 19813.11 Uniform circular motion 199

Solve problems and analyse information involving F = mv2

r for vehicles travelling around curves

13.12 A closer look at the forces acting on a vehicle in different scenarios 201Analyse the effects of external forces operating on a vehicle 20113.13 Further examples involving Newtons second law 203Solve problems using vector diagrams to determine resultant velocity, acceleration and force 203Solve problems and analyse information using: F = ma for a range of situations involving modes of transport 20313.14 Acceleration, velocity and displacement 20613.15 Using ticker tape 207

CONTENTS CONTENTS

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13.16 Accelerationtime graph 207First-hand investigation: Positive and negative accelerations 208First-hand investigation: Demonstrating vector addition and subtraction 209First-hand investigation: The relationship between force, mass and acceleration 210Chapter revision questions 212

Chapter 14 Energy 215

Moving vehicles have kinetic energy and energy transformations are an important aspect in understanding motion 21514.1 Energy and work 21514.2 The law of conservation of energy 21714.3 More about work 21914.4 A closer look at kinetic energy 220Solve problems and analyse information to determine the kinetic energy of a vehicle and the

work done using the formulae: Ek = 12

mv2 and W = Fs 221

14.5 Collisions 22314.6 Energy involved in car collisions 225Analyse information to trace the energy transfers and transformation in collisions leading to irreversible distortions 225Chapter revision questions 228

Chapter 15 Momentum and impulse 230

Change of momentum relates to the forces acting on the vehicle or the driver 23015.1 Momentum 230Solve problems and analyse secondary data using: p = mv and Impulse = Ft 23115.2 Defining Newtons second law using momentum 23115.3 Impulse and momentum 233Solve problems and analyse secondary data using: p = mv and Impulse = Ft 23315.4 Momentum and impulse: further examples 235Solve problems and analyse secondary data using: p = mv and Impulse = Ft 23515.5 The law of conservation of momentum 24015.6 Using the law of conservation of momentum 241Solve problems that apply the principle of conservation of momentum to qualitatively and quantitatively describe the collision of a moving vehicle with: a stationary vehicle an immoveable object another vehicle moving in the opposite direction another vehicle moving in the same direction 241First-hand investigation: Change in momentum during collisions 247First-hand investigation: Conservation of momentum in two dimensions 249Chapter revision questions 250

Chapter 16 Safety devices in vehicles 253

Safety devices are utilised to reduce the effects of changing momentum 25316.1 Newtons first law revisited 25316.2 Impulse and momentum revisited 25416.3 Driving safely 25616.4 Benefits of technologies for avoiding or reducing the effects of a collision 259Secondary source investigation: Technology to reduce collision effects 259First-hand investigation: Loose objects in a vehicle 261Chapter revision questions 263Moving about: review questions 264

CONTENTS

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THE COSMIC ENGINE 265Chapter 17 Models of the Universe 266

Our Sun is just one star in the galaxy and ours is just one galaxy in the Universe 26617.1 Models of the Universe 266Secondary source investigation: Historical limitations to developing a model 266Chapter revision questions 271

Chapter 18 The Universe begins 272

The first minutes of the Universe released energy which changed to matter, forming stars and galaxies 27218.1 The Big Bang 272Secondary source investigation: Describing the origins of the Universe 27218.2 The equivalence of mass and energy 27518.3 After the Big Bang 27618.4 The formation of stars and galaxies 278Chapter revision questions 279

Chapter 19 Stars eventually die 280

Stars have a limited life span and may explode to form supernovas 28019.1 The temperature and colour of hot bodies 28019.2 The colour of stars 28219.3 The HertzsprungRussell diagram 28219.4 Energy sources and star groups 283Process and analyse information using the HertzsprungRussell diagram to examine the variety of star groups, including Main Sequence, red giants, and white dwarfs 283Secondary source investigation: Brightness, luminosity and distance 284Solve problems to apply the inverse square law of intensity of light to relate the brightness of a star to its luminosity and distance from the observer 284Chapter revision questions 287

Chapter 20 The Sun affects the Earth in many ways 288

The Sun is a typical star, emitting electromagnetic radiation and particles that influence the Earth 28820.1 Energy release from nuclei 28820.2 Alpha (), beta () and gamma () rays 289First-hand investigation: Comparing the penetrating power of alpha, beta and gamma radiation 29120.3 The solar wind 29220.4 Sunspots 293Explaining sunspots using scientific principles 294Secondary source investigation: Assessing the effects of sunspot activity 295Chapter revision questions 296The cosmic engine: review questions 297

Glossary 299Answers to chapter revision questions 302Appendix 349Picture credits 352Index 353

CONTENTS

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About the authors

Dr Xiao L. (William) Wu graduated from Sydney Boys High School with first place in physics, and received the Premiers All Rounder Award for his Higher School Certificate. He completed Bachelor of Medicine and Surgery degrees (Honours) at the University of New South Wales (UNSW) while simultaneously studying chemistry, physics and biology as a part of his Bachelor of Science (Honours) degree.

Dr Wu is passionate about teaching. He has taught at UNSW and in eight years of high school tutoring has produced many outstanding students, some of whom were among the top 10 in Higher School Certificate science subjects, with perfect UAI scores. Many of his students have gone on to study Medicine and Law. Besides pursuing a career in orthopaedic surgery, Dr Wu continues to dedicate his time to teaching high school sciences.

Rob Farr has been teaching physics for 25 years in New South Wales schools. He has been on review panels for the current physics syllabus and has extensive experience as a marker, senior marker and supervisor in physics and chemistry. Rob graduated with a Bachelor of Science (Honours) degree from the University of Sydney in 1982 and completed his Diploma of Education the next year. He has a Master of Arts, specialising in science education and school leadership, from Macquarie University. Robs passion for science and science teaching have led him to become a consultant and contributor to the Biology in Focus series, especially in developing the approach to the Prescribed Focus Areas. He is currently Science Coordinator at Brigidine College St Ives, Sydney.

To the student

Physics is rich in its history, its accidental discoveries, its geniuses and in the way theories, models and laws have been developed or discarded. Importantly, physics has many varied and profound impacts on society and the environment, both positive and negative. The teaching and learning of physics without reference to these impacts is akin to teaching words with no sentences. Ultimately, it is to science that we turn to find solutions to the wide variety of problems arising from overpopulation, pollution and threats from outer space in an effort to ensure our survival. Learning physics within these contexts gives it relevance; hopefully this will encourage students to pursue the subject at tertiary levels.

Physics in Focus is a succinct and easy-to-follow book for the New South Wales Stage 6 Physics Syllabus. As in the syllabus, the text is divided into modules. Each module is made up of chapters based on the divisions in the syllabus. Chapters are divided into sections to specifically cover the syllabus dot points.

The Preliminary volume covers all four core modules; the HSC volume covers three core modules and three optional modules: From quanta to quarks, Medical physics and Astrophysics.

Physics in Focus is a valuable guide, not only to the syllabus content but also to practical procedures. The NSW Board of Studies intends, as with all science courses, that physics is taught in the contexts formed by the five Prescribed Focus Areas (PFAs). The PFAs have been a misunderstood concept for too long. This book attempts to address this shortfall by giving specific examples and information that relates to these broader issues.

Physics in Focus clearly indicates where the skills, PFAs and first-hand investigations are being addressed within the text. It also provides risk assessments, animations, exercises and worked examples, all marked with icons and colour coding.

The dot points in the students learn to columns are marked in blue and the third column investigations are marked in green. Exceptions are for made for dot points that start with either solve or analyse; these are marked in red, emphasising that students may need some guidance to learn this material, rather than learning by themselves through investigations.

xOther features within the text include the use of notes to highlight tips and hints or to clarify confusing and difficult concepts. Analogies are used to help to explain difficult concepts. There are extensive practice questions as well as examination-style questions to help students to consolidate the concepts and to prepare for their HSC exams.

The authors would like to emphasise that the studying of any science subject can be considered as a four-step process: reading, understanding, memorising and applying. Understanding is the most important step, and for this students need their teachers help. Applying comes after understanding and memorising and can be perfected by completing the practice questions in this book.

Finally, the authors hope that this book will help students to enjoy learning physics.

Acknowledgments

From Xiao L. WuI would like to thank my parents and friends for their understanding, support and encouragement during the creation of this book.

I would also like to thank my students for transcribing a part of this text and drafting parts of the solutions to the exercise questions.

I encourage students to understand and enjoy science and have tried to make it interesting and easy by providing study strategies.

From Rob Farr I would like to offer my heartfelt thanks to my wife, Elisa, who has assisted me in many ways in the construction of this text, including the proofing of my manuscript. She has given me much support and encouragement, allowing her dining room table to be converted into a workspace and keeping our young children happy and content when my mind has been elsewhere.

I would also like to thank my colleagues at Brigidine College St Ives for their understanding during the writing of this text. Glenda Chidrawi deserves a special mention for suggesting that I get involved with this project.

Thanks also to my students over the years who have helped me maintain my enthusiasm and love of teaching, so that now, 25 years after graduating, I still enjoy what I do.

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List of Board of Studies verbs

Account Account for: state reasons for, report onGive an account of: narrate a series of events or transactions

Analyse Identify components and the relationship among them; draw out and relate implications

Apply Use, utilise, employ to a particular situation

Appreciate Make a judgement about the value ofAssess Make a judgement of value, quality, outcomes, results or sizeCalculate Ascertain/determine from given facts, figures or information

Clarify Make clear or plain

Classify Arrange or include in classes/categories

Compare Show how things are similar or different

Construct Make; build, put together items or arguments

Contrast Show how things are different or opposite

Critically (analyse/evaluate)

Add a degree or level of accuracy depth, knowledge and understanding, logic, questioning, reflection and quality to (analysis/evaluation)

Deduce Draw conclusions

Define State meaning and identify essential qualities

Demonstrate Show by example

Describe Provide characteristics and features

Discuss Identify issues and provide points for and/or against

Distinguish Recognise or note/indicate as being distinct or different from; to note differences between

Evaluate Make a judgement based on criteria; determine the value ofExamine Inquire into

Explain Relate cause and effect; make the relationships between things evident; provide why and/or how

Extract Choose relevant and/or appropriate details

Extrapolate Infer what is known

Identify Recognise and name

Interpret Draw meaning from

Investigate Plan, inquire into and draw conclusions about

Justify Support an argument or conclusion

Outline Sketch in general terms; indicate the main features of

Predict Suggest what may happen based on available information

Propose Put forward (for example a point of view, idea, argument, suggestion) for consideration and actionRecall Present remembered ideas, facts or experiences

Recommend Provide reasons in favour

Recount Retell a series of events

Summarise Express concisely the relevant details

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pHYSICS SkILLSAN INTRODUCTION

Physics skillsan introduction

During the Preliminary course, it is expected that students will further develop skills in planning and conducting investigations, communicating information and understanding, scientific thinking and problemsolving and working individually and in teams. Each module specifies content through which skill outcomes can be achieved. Teachers should develop activities based on that content to provide students with opportunities to develop the full range of skills.

preliminary course outcomes Content

A student: Students:

P11. identifies and implements improvements to investigation plans

11.1 identify data sources to:a) analyse complex problems to determine appropriate ways in which

each aspect may be researchedb) determine the type of data that needs to be collected and explain

the qualitative or quantitative analysis that will be required for this data to be useful

c) identify the orders of magnitude that will be appropriate and the uncertainty that may be present in the measurement of data

d) identify and use correct units for data that will be collectede) recommend the use of an appropriate technology or strategy for

data collection or information gathering that will assist efficient future analysis

11.2 plan first-hand investigations to:a) demonstrate the use of the terms dependent and independent

to describe variables involved in the investigationb) identify variables that need to be kept constant, develop

strategies to ensure that these variables are kept constant, and demonstrate the use of a control

c) design investigations that allow valid and reliable data and information to be collected

d) describe and trial procedures to undertake investigations and explain why a procedure, a sequence of procedures or the repetition of procedures is appropriate

e) predict possible issues that may arise during the course of an investigation and identify strategies to address these issues if necessary

a) identifying and/or setting up the most appropriate equipment or combination of equipment needed to undertake the investigation

b) carrying out a risk assessment of intended experimental procedures and identifying and addressing potential hazards

c) identifying technology that could be used during investigations and determining its suitability and effectiveness for its potential role in the procedure or investigation

d) recognising the difference between destructive and non-destructive testing of material and analysing potentially different results from these two procedures

pHYSICS SkILLSAN INTRODUCTION

xiii

preliminary course outcomes Content

A student: Students:

P12. discusses the validity and reliability of data gathered from first-hand investigations and secondary sources

12.1 perform first-hand investigations by:a) carrying out the planned procedure, recognising where and

when modifications are needed and analysing the effect of these adjustments

b) efficiently undertaking the planned procedure to minimise hazards and wastage of resources

c) disposing carefully and safely of any waste materials produced during the investigation

d) identifying and using safe work practices during investigations

12.2 gather first-hand information by:a) using appropriate data collection techniques, employing

appropriate technologies, including data loggers and sensorsb) measuring, observing and recording results in accessible and

recognisable forms, carrying out repeat trials as appropriate

12.3 gather information from secondary sources by:a) accessing information from a range of resources, including

popular scientific journals, digital technologies and the Internetb) practising efficient data collection techniques to identify useful

information in secondary sourcesc) extracting information from numerical data in graphs and tables

as well as from written and spoken material in all its formsd) summarising and collating information from a range of

resourcese) identifying practising male and female Australian scientists, the

areas in which they are currently working and information about their research

12.4 process information to:a) assess the accuracy of any measurements and calculations and

the relative importance of the data and information gatheredb) identify and apply appropriate mathematical formulae and

conceptsc) best illustrate trends and patterns by selecting and using

appropriate methods, including computer assisted analysisd) evaluate the validity of first-hand and secondary information and

data in relation to the area of investigatione) assess the reliability of first-hand and secondary information and

data by considering information from various sourcesf) assess the accuracy of scientific information presented in mass

media by comparison with similar information presented in scientific journals

P13. identifies appropriate terminology and reporting styles to communicate information and understanding in physics

13.1 present information by:a) selecting and using appropriate text types or combinations

thereof, for oral and written presentationsb) selecting and using appropriate media to present data and

informationc) selecting and using appropriate methods to acknowledge sources

of informationd) using symbols and formulae to express relationships and using

appropriate units for physical quantitiese) using a variety of pictorial representations to show relationships

and present information clearly and succinctlyf) selecting and drawing appropriate graphs to convey information

and relationships clearly and accuratelyg) identifying situations where use of a curve of best fit is appropriate

to present graphical information

pHYSICS SkILLSAN INTRODUCTION

xiv

preliminary course outcomes Content

A student: Students:

P14. draws valid conclusions from gathered data and information

14.1 analyse information to:a) identify trends, patterns and relationships as well as

contradictions in data and informationb) justify inferences and conclusionsc) identify and explain how data supports or refutes an hypothesis, a

prediction or a proposed solution to a problemd) predict outcomes and generate plausible explanations related to

the observationse) make and justify generalisationsf) use models, including mathematical ones, to explain phenomena

and/or make predictionsg) use cause and effect relationships to explain phenomenah) identify examples of the interconnectedness of ideas or scientific

principles

14.2 solve problems by:a) identifying and explaining the nature of a problemb) describing and selecting from different strategies, those which

could be used to solve a problemc) using identified strategies to develop a range of possible solutions

to a particular problemd) evaluating the appropriateness of different strategies for solving

an identified problem

a) design and produce creative solutions to problemsb) propose ideas that demonstrate coherence and logical

progression and include correct use of scientific principles and ideas

c) apply critical thinking in the consideration of predictions, hypotheses and the results of investigations

d) formulate cause and effect relationships

ContentsAbout the authorsTo the studentAcknowledgmentsList of Board of Studies verbsPhysics skillsan introduction