Solutions Manual for Physics for Scientists & Engineers with Modern Physics, Volume 2, 5th Global Edition by Douglas C. Giancoli

SolutionsManualForPhysicsfor S
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cientists&EngineerswithModern
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Physics (Volume 2)5e (Global Edit
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ion)By DouglasC. Giancoli
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,CHAPTER 21: Electric Charge and Electric Field
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Responses to Questions
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1. Suspendoaoplasticorulerobyoaothreadoandothenoruboitowithoaocloth.oAsoshownoinoFig.o21–
2a,otheoruleroisonegativelyocharged.oNowobringotheochargedocombocloseotootheoruler.oIfotheoruleroisorep
elledobyotheocomb,othenotheocomboisonegativelyocharged.oIfotheoruleroisoattractedobyotheocomb,othenoth
eocomboisopositivelyocharged.

2. Theoshirtooroblouseobecomesochargedoasoaoresultoofobeingotossedoaboutoinotheodryeroandorubbingo
againstotheodryerosidesoandootheroclothes.oWhenoyouoputoonotheochargedoobjecto(shirt),oitocauseso
chargeoseparationowithinotheomoleculesoofoyouroskino(seeoFig.o21–
9),owhichoresultsoinoattractionobetweenotheoshirtoandoyouroskin.

3. Fogoororainodropletsotendotooformoaroundoionsobecauseowateroisoaopolaromolecule,owithoaopositiveoregi
onoandoaonegativeoregion.oTheochargeocentersoonotheowateromoleculeowillobeoattractedotootheoionsooroel
ectrons,osinceooppositeochargesoattract.

4. SeeoalsooFig.o21–
9oinotheotext.oTheonegativelyochargedoelectronso
inotheopaperoareoattractedotootheopositivelyochar
gedorodoandomoveotowardso itowithinotheiromole
cules.oTheoattractionooccursobecauseotheonegati
veochargesoinotheopaperoareocloserotootheopositiv
eorodothanoareotheopositiveochargesoinotheopaper
,oandothereforeotheoattractionobetweenotheounlik
eochargesois
greaterothanotheorepulsionobetweenotheolikeocharges.

5. Aoplasticorulerothatohasobeenorubbedowithoaoclothoisocharged.oWhenobroughtonearosmallopiecesoofopape
r,oitowillocauseoseparationoofochargeo(polarization)oinotheobitsoofopaper,owhichowillocauseotheopaperotoo
beoattractedotootheoruler.oAosmalloamountoofochargeoisoableotoocreateoenoughoelectricoforceotoobeostrong
erothanogravity.o Thusotheopaperocanobeolifted.
Onoaohumidodayothisoisomoreodifficultobecauseotheowateromoleculesoinotheoairoareopolar.o Thoseopolarowa
teromoleculesowillobeoattractedotootheoruleroandotootheoseparatedochargeoonotheobitsoofopaper,opartiallyone
utralizingotheochargesoandothusoreducingotheoattraction.

6. Theonetochargeoonoaoconductoroisotheosumoofoalloofotheopositiveoandonegativeochargesoinotheoconductor.oI
foaoneutraloconductorohasoextraoelectronsoaddedotooit,othenotheonetochargeoisonegative.oIfoaoneutralocondu
ctorohasoelectronsoremovedofromoit,othenotheonetochargeoisopositive.oIfoaoneutraloconductorohasotheosame
oamountoofopositiveoandonegativeocharge,othenotheonetochargeoisozero.


Theo“freeocharges”oinoaoconductoroareoelectronsothatocanomoveoaboutofreelyowithinotheomaterialo
becauseotheyoareoonlyolooselyoboundotootheiroatoms.oTheo“freeoelectrons”oareoalsooreferredotooaso
“conductionoelectrons.”oAoconductoromayohaveoaozeroonetochargeobutostillohaveosubstantialofreeo
charges.

,Chaptero21 ElectricoChargeoandoElectricoField


7. Mostoofotheoelectronsoareostronglyoboundotoonucleioinotheometaloions.oOnlyoaofewoelectronsoperoatomo(u
suallyooneoorotwo)oareofreeotoomoveoaboutothroughoutotheometal.oTheseoareocalledotheo“conductionoele
ctrons.”oTheorestoareoboundomoreotightlyotootheonucleusoandoareonotofreeotoomove.oFurthermore,oinotheo
casesoshownoinoFigs.o21–7oando21–8,onotoalloofotheoconductionoelectronsowillomove.oInoFig.o21–
7,oelectronsowillomoveountilotheoattractiveoforceoonotheoremainingoconductionoelectronsodueotootheoinco
mingochargedorodoisobalancedobyotheorepulsiveoforceofromoelectronsothatohaveoalreadyogatheredoatotheol
eftoendoofotheoneutralorod.oInoFig.o21–
8,oconductionoelectronsowillobeorepelledobyotheoincomingorodoandowilloleaveotheostationaryorodothroug
hotheogroundoconnectionountilotheorepulsiveoforceoonotheoremainingoconductionoelectronsodueotootheoin
comingochargedorodoisobalancedobyotheoattractiveoforceofromotheonetopositiveochargeoonotheostationaryo
rod.

8. Theoelectroscopeoleavesoareoconnectedotogetheroatotheotop.oThatoconnectionocanobeo
modeledoasoaotensionoforce.oTheohorizontalocomponentoofothisotensionoforceobalanc
esotheoelectricoforceooforepulsion.oTheoverticalocomponentoofotheotensionoforceobala
ncesotheoweightoofotheoleaves.


9. Theoballoonohasobeenocharged.oTheoexcessochargeoonotheoballoonoisoableotoopolarizeotheowateromolecu
lesoinotheostreamoofowater,osimilarotooFig.o21–
9.oThisopolarizationoresultsoinoaonetoattractionoofotheowaterotowardsotheoballoon,osootheowaterostreamoc
urvesotowardsotheoballoon.

10. (a)oWhenotheoleavesoareochargedobyoinduction,onooadditionalochargeoisoaddedotootheoleaves.oIfotheoch
argedorodoisonearotheotopoofotheoelectroscopeoitorepelsochargeoontootheoleavesocausingothemotoose
parateoasoinoFig.o21–
11(a).oWhenotheorodoisoremovedotheochargeoreturnsotooitsoinitialoequilibriumopositionoandotheole
avesocomeobackotogether.
(b) Whenotheoleavesoareochargedobyoconduction,opositiveochargeoisoplacedoontootheoelectroscopeofro
motheorodocausingotheoleavesotooseparate.oWhenotheorodoisoremoved,otheochargeoremainsoonotheoel
ectroscopeoandotheoleavesoremainoseparated.o Ifonotoalloofotheoexcessochargeoleavesotheorod,otheno
whenotheorodoisoremoved,otheoleavesomightocomeobackotogetheroslightlyofromotheiromaximumode
flection.
(c) Yes.o Theoelectroscopeohasoaonegativeochargeoonotheotoposphereoandoonotheoleaves.o Thereforeotheo
electroscopeohasoaototalonetonegativeocharge,osooitomustohaveobeenochargedobyoconduction.

11. Coulomb’solawoandoNewton’solawoareoveryosimilaroinoform.oWhenoexpressedoinoSIounits,otheomagnitu
deoofotheoconstantoinoNewton’solawoisoveryosmall,owhileotheomagnitudeoofotheoconstantoinoCoulomb’sol
awoisoquiteolarge.oNewton’solawosaysotheogravitationaloforceoisoproportionalotootheoproductoofotheotwoo
masses,owhileoCoulomb’solawosaysotheoelectricaloforceoisoproportionalotootheoproductoofotheotwoocharg
es.oNewton’solawoonlyoproducesoattractiveoforces,osinceothereoisoonlyooneokindoofogravitationalomass.o
Coulomb’solawoproducesobothoattractiveoandorepulsiveoforces,osinceothereoareotwookindsoofoelectricaloc
harge.

12. TheogravitationaloforceobetweenoeverydayoobjectsoonotheosurfaceoofotheoEarthoisoextremelyosmall.
11o
(Recallotheo valueoofo G:o 6.67o10 N m2 kg .o)oConsiderotwooobjectsosittingoonotheoflooronearoeach
2o


other.oTheyoareoattractedotooeachoother,obutotheomaximumoforceoofostaticofrictionoforoeachoisomuchogrea
terothanotheogravitationaloforceoeachoexperiencesofromotheoother,oandosootheyodon’tomove.oEvenoinoanoa
bsolutelyofrictionlessoenvironment,otheoaccelerationoresultingofromotheogravitationaloforceowouldobeoso
osmallothatoitowouldonotobeonoticeableoinoaoshortotimeoframe. oWeoareoawareoofotheogravitationaloforceobe

tweenoobjectsoifoatoleastooneoofothemoisoveryomassive,oasoinotheocaseoofotheoEarthoandosatellitesoorotheoEa

, PhysicsoforoScientistso&oEngineersowithoModernoPhysics,o5e,oGlobaloEdition InstructoroSolutionsoManual

rthoandoyou.