Electricity and Magnetism - Sicyon

200 Pages·2012·2.77 MB·English

Electricity and Magnetism
For50years,EdwardM.Purcell’sclassictextbookhasintroducedstudentstotheworld
ofelectricityandmagnetism.Thisthirdeditionhasbeenbroughtuptodateandisnow
inSIunits.Itfeatureshundredsofnewexamples,problems,andfigures,andcontains
discussionsofreal-lifeapplications.
Thetextbookcoversallthestandardintroductorytopics,suchaselectrostatics,mag-
netism,circuits,electromagneticwaves,andelectricandmagneticfieldsinmatter.Tak-
inganontraditionalapproach,magnetismisderivedasarelativisticeffect.Mathemat-
ical concepts are introduced in parallel with the physical topics at hand, making the
motivationsclear.Macroscopicphenomenaarederivedrigorouslyfromtheunderlying
microscopicphysics.
Withworkedexamples,hundredsofillustrations,andnearly600end-of-chapterprob-
lemsandexercises,thistextbookisidealforelectricityandmagnetismcourses.Solu-
tionstotheexercisesareavailableforinstructorsatwww.cambridge.org/Purcell-Morin.
EDWARDM. PURCELL(1912–1997)wastherecipientofmanyawardsforhisscientific,
educational,andcivicwork.In1952hesharedtheNobelPrizeforPhysicsforthedis-
covery of nuclear magnetic resonance in liquids and solids, an elegant and precise
methodofdeterminingthechemicalstructureofmaterialsthatservesasthebasisfor
numerousapplications,includingmagneticresonanceimaging(MRI).Duringhiscareer
heservedasscienceadvisertoPresidentsDwightD.Eisenhower,JohnF.Kennedy,
andLyndonB.Johnson.
DAVIDJ.MORINisaLecturerandtheAssociateDirectorofUndergraduateStudiesinthe
DepartmentofPhysics,HarvardUniversity.HeistheauthorofthetextbookIntroduction
toClassicalMechanics(CambridgeUniversityPress,2008).

THIRD EDITION
ELECTRICITY
AND MAGNETISM
EDWARD M. PURCELL
DAVID J. MORIN
HarvardUniversity,Massachusetts
CAMBRIDGE UNIVERSITY PRESS
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Singapore,SãoPaulo,Delhi,MexicoCity
CambridgeUniversityPress
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©D.Purcell,F.Purcell,andD.Morin2013
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andtotheprovisionsofrelevantcollectivelicensingagreements,
noreproductionofanypartmaytakeplacewithoutthewritten
permissionofCambridgeUniversityPress.
PreviouslypublishedbyMc-GrawHill,Inc.,1985
FirsteditionpublishedbyEducationDevelopmentCenter,Inc.,1963,1964,1965
FirstpublishedbyCambridgeUniversityPress2013
PrintedintheUnitedStatesbySheridanInc.
AcatalogrecordforthispublicationisavailablefromtheBritishLibrary
LibraryofCongresscataloging-in-publicationdata
Purcell,EdwardM.
Electricityandmagnetism/EdwardM.Purcell,DavidJ.Morin,HarvardUniversity,
Massachusetts.–Thirdedition.
pagescm
ISBN978-1-107-01402-2(Hardback)
1. Electricity. 2. Magnetism. I. Title.
QC522.P852012
537–dc23
2012034622
ISBN978-1-107-01402-2Hardback
Additionalresourcesforthispublicationatwww.cambridge.org/Purcell-Morin
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PrefacetothethirdeditionofVolume2 xiii CONTENTS
PrefacetothesecondeditionofVolume2 xvii
PrefacetothefirsteditionofVolume2 xxi
CHAPTER1
ELECTROSTATICS:CHARGESANDFIELDS 1
1.1 Electriccharge 1
1.2 Conservationofcharge 4
1.3 Quantizationofcharge 5
1.4 Coulomb’slaw 7
1.5 Energyofasystemofcharges 11
1.6 Electricalenergyinacrystallattice 14
1.7 Theelectricfield 16
1.8 Chargedistributions 20
1.9 Flux 22
1.10 Gauss’slaw 23
1.11 Fieldofasphericalchargedistribution 26
1.12 Fieldofalinecharge 28
1.13 Fieldofaninfiniteflatsheetofcharge 29
1.14 Theforceonalayerofcharge 30
1.15 Energyassociatedwiththeelectricfield 33
1.16 Applications 35
vi CONTENTS
Chaptersummary 38
Problems 39
Exercises 47
CHAPTER2
THEELECTRICPOTENTIAL 58
2.1 Lineintegraloftheelectricfield 59
2.2 Potentialdifferenceandthepotentialfunction 61
2.3 Gradientofascalarfunction 63
2.4 Derivationofthefieldfromthepotential 65
2.5 Potentialofachargedistribution 65
2.6 Uniformlychargeddisk 68
2.7 Dipoles 73
2.8 Divergenceofavectorfunction 78
2.9 Gauss’s theorem and the differential form of
Gauss’slaw 79
2.10 ThedivergenceinCartesiancoordinates 81
2.11 TheLaplacian 85
2.12 Laplace’sequation 86
2.13 Distinguishingthephysicsfromthemathematics 88
2.14 Thecurlofavectorfunction 90
2.15 Stokes’theorem 92
2.16 ThecurlinCartesiancoordinates 93
2.17 Thephysicalmeaningofthecurl 95
2.18 Applications 100
Chaptersummary 103
Problems 105
Exercises 112
CHAPTER3
ELECTRICFIELDSAROUNDCONDUCTORS 124
3.1 Conductorsandinsulators 125
3.2 Conductorsintheelectrostaticfield 126
3.3 Thegeneralelectrostaticproblemandthe
uniquenesstheorem 132
3.4 Imagecharges 136
3.5 Capacitanceandcapacitors 141
3.6 Potentialsandchargesonseveralconductors 147
3.7 Energystoredinacapacitor 149
3.8 Otherviewsoftheboundary-valueproblem 151
3.9 Applications 153
Chaptersummary 155
CONTENTS vii
Problems 155
Exercises 163
CHAPTER4
ELECTRICCURRENTS 177
4.1 Electriccurrentandcurrentdensity 177
4.2 Steadycurrentsandchargeconservation 180
4.3 ElectricalconductivityandOhm’slaw 181
4.4 Thephysicsofelectricalconduction 189
4.5 Conductioninmetals 198
4.6 Semiconductors 200
4.7 Circuitsandcircuitelements 204
4.8 Energydissipationincurrentflow 207
4.9 Electromotiveforceandthevoltaiccell 209
4.10 Networkswithvoltagesources 212
4.11 Variablecurrentsincapacitorsandresistors 215
4.12 Applications 217
Chaptersummary 221
Problems 222
Exercises 226
CHAPTER5
THEFIELDSOFMOVINGCHARGES 235
5.1 FromOerstedtoEinstein 236
5.2 Magneticforces 237
5.3 Measurementofchargeinmotion 239
5.4 Invarianceofcharge 241
5.5 Electricfieldmeasuredindifferentframes
ofreference 243
5.6 Fieldofapointchargemovingwithconstantvelocity 247
5.7 Fieldofachargethatstartsorstops 251
5.8 Forceonamovingcharge 255
5.9 Interactionbetweenamovingchargeandother
movingcharges 259
Chaptersummary 267
Problems 268
Exercises 270
CHAPTER6
THEMAGNETICFIELD 277
6.1 Definitionofthemagneticfield 278
6.2 Somepropertiesofthemagneticfield 286
viii CONTENTS
6.3 Vectorpotential 293
6.4 Fieldofanycurrent-carryingwire 296
6.5 Fieldsofringsandcoils 299
6.6 ChangeinBatacurrentsheet 303
6.7 Howthefieldstransform 306
6.8 Rowland’sexperiment 314
6.9 Electricalconductioninamagneticfield:
theHalleffect 314
6.10 Applications 317
Chaptersummary 322
Problems 323
Exercises 331
CHAPTER7
ELECTROMAGNETICINDUCTION 342
7.1 Faraday’sdiscovery 343
7.2 Conductingrodmovingthroughauniform
magneticfield 345
7.3 Loopmovingthroughanonuniformmagneticfield 346
7.4 Stationaryloopwiththefieldsourcemoving 352
7.5 Universallawofinduction 355
7.6 Mutualinductance 359
7.7 Areciprocitytheorem 362
7.8 Self-inductance 364
7.9 Circuitcontainingself-inductance 366
7.10 Energystoredinthemagneticfield 368
7.11 Applications 369
Chaptersummary 373
Problems 374
Exercises 380
CHAPTER8
ALTERNATING-CURRENTCIRCUITS 388
8.1 Aresonantcircuit 388
8.2 Alternatingcurrent 394
8.3 Complexexponentialsolutions 402
8.4 Alternating-currentnetworks 405
8.5 Admittanceandimpedance 408
8.6 Powerandenergyinalternating-currentcircuits 415
8.7 Applications 418
Chaptersummary 420
Problems 421
Exercises 424