A Student’s Guide to Waves

229 Pages·2015·9.037 MB·English

by  Daniel Fleisch, Laura Kinnaman

AStudent’sGuidetoWaves
Wavesareanimportanttopicinthefieldsofmechanics,electromagnetism,and
quantumtheory,butmanystudentsstrugglewiththemathematicalaspects.Writtento
complementcoursetextbooks,thisbookfocusesonthetopicsthatstudentsfindmost
difficult.
RetainingthehighlypopularapproachusedinFleisch’sotherStudent’sGuides,the
bookusesplainlanguagetoexplainfundamentalideasinasimpleandclearway.
Exercisesandfullyworkedexampleshelpreaderstesttheirunderstandingofthe
concepts,makingthisanidealbookforundergraduatesinphysicsandengineering
tryingtogettogripswiththischallengingsubject.
Thebookissupportedbyasuiteofonlineresourcesavailableat
www.cambridge.org/wavesguide.Theseincludeinteractivesolutionsforevery
exerciseandprobleminthetextandaseriesofpodcastsinwhichtheauthorsexplain
theimportantconceptsofeverysectionofthebook.
danielfleischisaProfessorintheDepartmentofPhysicsatWittenberg
University,wherehespecializesinelectromagneticsandspacephysics.Heisthe
authorofseveralStudent’sGuidebooks,includingmostrecentlyAStudent’sGuideto
theMathematicsofAstronomy(CambridgeUniversityPress,2013).
laurakinnamanisanAssistantProfessorofPhysicsatMorningsideCollege,
where she carries out computational research in chemical physics and organizes the
PhysicsClub.

A Student’s Guide to Waves
DANIEL FLEISCH
WittenbergUniversity
LAURA KINNAMAN
MorningsideCollege
UniversityPrintingHouse,CambridgeCB28BS,UnitedKingdom
CambridgeUniversityPressispartoftheUniversityofCambridge.
ItfurtherstheUniversity’smissionbydisseminatingknowledgeinthepursuitof
education,learningandresearchatthehighestinternationallevelsofexcellence.
www.cambridge.org
Informationonthistitle:www.cambridge.org/9781107643260
(cid:2)c D.FleischandL.Kinnaman2015
Thispublicationisincopyright.Subjecttostatutoryexception
andtotheprovisionsofrelevantcollectivelicensingagreements,
noreproductionofanypartmaytakeplacewithoutthewritten
permissionofCambridgeUniversityPress.
Firstpublished2015
PrintedintheUnitedKingdombyTJInternationalLtd.PadstowCornwall
AcatalogrecordforthispublicationisavailablefromtheBritishLibrary
LibraryofCongressCataloginginPublicationdata
Fleisch,DanielA.,author.
Astudent’sguidetowaves/DanielFleisch,WittenbergUniversity,LauraKinnaman,
MorningsideCollege.
pages cm
Includesbibliographicalreferencesandindex.
ISBN978-1-107-05486-8(Hardback)–ISBN978-1-107-64326-0(Paperback)
1. Waves–Textbooks. I. Kinnaman,Laura,author. II. Title.
QC157.F542015
530.12(cid:3)4–dc23 2014032243
ISBN978-1-107-05486-8Hardback
ISBN978-1-107-64326-0Hardback
Additionalresourcesforthispublicationatwww.cambridge.org/9781107643260
CambridgeUniversityPresshasnoresponsibilityforthepersistenceoraccuracyof
URLsforexternalorthird-partyinternetwebsitesreferredtointhispublication,
anddoesnotguaranteethatanycontentonsuchwebsitesis,orwillremain,
accurateorappropriate.
Contents
Preface pagevii
Acknowledgements ix
1 Wavefundamentals 1
1.1 Definitions 1
1.2 Basicrelationships 6
1.3 Vectorconcepts 9
1.4 Complexnumbers 14
1.5 Eulerrelations 23
1.6 Wavefunctions 26
1.7 Phasorrepresentationofwavefunctions 33
1.8 Problems 43
2 Thewaveequation 44
2.1 Partialderivatives 44
2.2 Theclassicalwaveequation 53
2.3 Propertiesofthewaveequation 59
2.4 PDEsrelatedtothewaveequation 69
2.5 Problems 74
3 Wavecomponents 75
3.1 Generalsolutionstothewaveequation 75
3.2 Boundaryconditions 80
3.3 Fouriertheory 94
3.4 Wavepacketsanddispersion 116
3.5 Problems 123
4 Themechanicalwaveequation 124
4.1 Propertiesofmechanicalwaves 124
v
vi Contents
4.2 Wavesonastring 126
4.3 Pressurewaves 134
4.4 Energyandpowerofmechanicalwaves 141
4.5 Waveimpedance,reflection,andtransmission 149
4.6 Problems 161
5 Theelectromagneticwaveequation 162
5.1 Propertiesofelectromagneticwaves 162
5.2 Maxwell’sequations 165
5.3 Electromagneticwaveequation 168
5.4 Plane-wavesolutionstotheelectromagneticwaveequation 171
5.5 Energy,power,andimpedanceofelectromagneticwaves 178
5.6 Problems 184
6 Thequantumwaveequation 185
6.1 Waveandparticlecharacteristics 185
6.2 Wave–particleduality 189
6.3 TheSchrödingerequation 194
6.4 Probabilitywavefunctions 199
6.5 Quantumwavepackets 200
6.6 Problems 213
References 214
Index 215
Preface
Thisbookhasonepurpose:tohelpyouunderstandthefoundationalconcepts
of waves and the mathematics of the wave equation. The authors have
attempted to fill the book with clear, plain-language explanations, using just
enough mathematical rigor to help you understand the important principles
without obscuring the underlying physics. Armed with that understanding,
you’ll be ready to tackle the many excellent texts that deal with mechanical,
electromagnetic,andquantumwaves.
Youshouldunderstandthatthisbookismeanttobeusedasasupplemental
textandisnotintendedtobeacomprehensivetreatmentofwavephenomena.
Thatmeansthatwehaven’tattemptedtocovereveryaspectofwaves;instead,
we’veincludedthetopicsthatourstudentshavefoundmosttroubling.
Asyou’llsee,thedesignofthebooksupportsitsuseasasupplementaltext.
Whenever possible, we’ve made the chapters modular, allowing you to skip
material you’ve already mastered so you can proceed directly to the topics
with which you need help. As a Student’s Guide, this book is accompanied
by a website that provides a variety of freely available material that we
think you’ll find very helpful. That includes complete, interactive solutions
to every problem in the book, as well as a series of podcasts in which we
explain the most important concepts, equations, and graphs in every section
of every chapter. By “interactive" we mean that you can see the full solution
immediately, or you can request one or more hints that will guide you to
thefinalsolution.Theicon appearsthroughoutthebookandhighlights
wherethereisaccompanyingmaterialavailableonline.Ifyouchoosetoread
theebookonadevicethatsupportsinteractivity,theseadditionalfeatureswill
appear directly within the text. If your device doesn’t support interactivity,
clickingon willtakeyoustraighttothebookswebsite.
vii
viii Preface
Isthisbookrightforyou?Itisifyou’relookingforhelpinunderstanding
waves, whether you need that help to supplement your work in a physics or
engineering class, in preparing for the physical science portion of a standard
exam, or as a part of a program of self-study. Whatever your reason, we
commendyourinitiative.
Acknowledgements
Primaryresponsibilityforthegoodbitsinthisbookbelongstothestudentsin
our classes, whose curiosity, intelligence, and persistence have inspired us to
pursue(andoccasionallyfind)deeperunderstandingandbetterexplanationsof
thephysicsofwaves.Wethankthosestudents.
We also thank Dr. Nick Gibbons, Dr. Simon Capelin, and the world-class
production team of Cambridge University Press, whose support has been
essential during the two-year process that has resulted in this book. The e-
bookversionofthistextwouldnothavebeenpossiblewithoutthethoughtful
guidanceofClaireEudallandCatherineFlack.
Laura also thanks her sister, Dr. Carrie Miller, for all of the feedback,
support,andencouragementthatshe’sgiven.IcanalwayscountonCarrieto
helpmeseemywayoutofatrickyspot.IalsothankBennettforhispatience
and support when I hole myself up, writing. My parents, sisters, brothers-
in-law, nieces, and nephews who all provided encouragement and diversion,
thankyou!
And as always, Dan thanks Jill for her unwavering support and acknowl-
edges the foresight and intuition of Dr. John Fowler, who made possible my
contributionstotheCambridgelineofStudent’sGuides.
ix