# 11 electricity & magnetism...• the van der graaf electrostatic generator • the coulomb...
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RegentsPhysicsUnitReviewMr.Buchman
Unit11:Electricity&Magnetism
Sub-UnitI:Electrostatics
• ElectricCharge
• TheAtom&TheElectricalNeutralityofBulkMatter
• TheElementaryCharge
• PointCharges&TestCharges
• TheQuantizationofElectricCharge
• TheLawofConservationofElectricCharge
• ElectricalMaterials
• ElectrostaticConduction,Induction&Grounding
• TheElectroscope
• TheVanderGraafElectrostaticGenerator
• TheCoulomb(Electrostatic)Force
• TheElectrostaticConstant
• TheInverseSquareNatureoftheCoulombForce
• ThePrincipleofSuperposition
• TheElectricField(E)
• E-FieldDiagrams
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• ElectricPotentialDifference(Voltage)
• ElectricalPotentialEnergy
• TheElectron�volt(eV)
• ChargedParallelPlates
• TheMillikanOilDropExperiment
Sub-UnitII:ElectricCurrent&ElectricCircuits
• ElectricalCurrent&ElectronFlow
• ElectricalResistance&Ohm’sLaw
• ElectricalResistivity
• CircuitSymbols
• TheSimpleCircuit
• ElectricMetersinaCircuit
• ElectricalPower&Energy
• TheKilowatt�hour(KWH)&TheElectricBill
• Kirchoff’sRulesforCircuits
• TheSeriesCircuit
• TheParallelCircuit&CombinationCircuits
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Sub-UnitIII:Magnetism
• Magnets&TheMagneticCompass
• MagneticPoles,Forces&Flux
• TheMagneticField(FluxDensity)&B-FieldDiagrams
• SourcesofMagneticFields&Oersted’sDiscovery
• MagneticSymbols&TheLeftHandRules
• TheSolenoid&TheElectromagnet
• MagneticDomains&TheTheoryofPermanentMagnetism
• Earth’sMagneticField
• TheMagneticForceonaMovingChargedParticle
• ThePathofaChargedParticleinaMagneticField
• TheAuroras
• ElectromagneticInduction&TheGeneratorPrinciple
• TheElectricGenerator&TheElectricMotor
• TheElectricTransformer
• TheProduction&PropagationofElectromagneticWaves
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VocabularyTerms
Sub-UnitI:Electrostatics
• Electrostatics• ElectricCharge• Electron• Proton• TheElementaryCharge• TheCoulomb• NetCharge• BulkMatter• ElectricalNeutrality• PointCharge• ChargeQuantization• LawofConservationofElectricCharge• ElectricalConductor• Insulator• Semi-conductor• Conduction• Induction• Grounding• TheElectroscope• Knob• Leaves• TheVanderGraafElectrostaticGenerator• TheCoulomb(Electrostatic)Force• TheElectrostaticConstant• PrincipleofSuperpositon• Action-at-a-Distance• FieldTheory• TheElectricField• FaradayLinesofForce• TheNewton/Coulomb• TestCharge• ElectricPotential(Voltage)• TheVolt
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• ElectricalPotentialEnergy• ChargedParallelPlates• MillikanOilDropExperiment• TheElectron-volt(eV)
Sub-UnitII:ElectricCurrent&ElectricCircuits
• ElectricCurrent• TheAmpere• ElectronFlow• ElectricCircuit• CircuitSymbols• TheCell• Battery• Terminals• Resistance• Resistor• TheOhm• Ohm’sLaw• Ammeter• Voltmeter• Kirchoff’sJunctionRule• VoltageGain• VoltageDrop• Kirchoff’sLoopRule• TheSeriesCircuit• TheParallelCircuit• CircuitBreaker• TheCombinationCircuit• EquivalentResistance• TheKilowatt-hour(KWH)• ElectricMeter• Resistivity• Cross-SectionalArea
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Sub-UnitIII:Magnetism
• Magnetism• Lodestone• MagneticCompass• BarMagnet• MagneticPole• Ironfilings• MagneticField• TheTesla• MagneticFlux• TheWeber• TheGauss• Oersted’sDiscovery• DirectionalSymbols• 1stLeftHandRule• 2ndLeftHandRule• 3rdLeftHandRule• TheSolenoid• Electromagnet• PermanentMagnet• AtomicMagneticMoment• MagneticDomain• Ferromagnetism• ElectromagneticInduction(GeneratorPrinciple)• AlternatingCurrent• ElectricGeneratororDynamo• ElectricTurbine• ElectricMotor• Transformer• Lenz’Law• ElectromagneticWaves
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ReferenceTableChartsListofPhysicalConstantsPrefixesforPowersof10CircuitSymbolsResistivitiesat20°C
PhysicalConstantsk=8.99x109Nm2/C2ElectrostaticConstant1e=1.60x10-19CTheElementaryCharge1C=6.25x1018eTheCoulomb1eV=1.60x10-19JTheElectronvolt
ReferenceTableFormulas
Electricity&MagnetismFe=kq1q2/r2TheCoulomb(ElectrostaticForce)E=Fe/qElectricFieldStrengthV=W/qElectricPotential(Voltage)I=Δq/tElectricCurrentR=V/IOhm’sLawR=ρL/AElectricalResistanceofaWireSegmentP=VI=I2R=V2/RElectricalPowerW=Pt=VIt=I2Rt=V2t/RElectricalEnergy
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SeriesCircuitsI=I1=I2=I3=...RelationshipamongstCurrentsV+V1+V2+V3+...RelationshipamongstVoltagesReq=R1+R2+R3+...RelationshipamongstResistancesParallelCircuitsI=I1+I2+I3+...RelationshipamongstCurrentsV=V1=V2=V3=...RelationshipamongstVoltages1/R=1/R1+1/R2+1/R3+..RelationshipamongstResistances
AdditionalFormulasΣQBefore=ΣQAfterLawofConservationofElectricChargeQ=NeChargeQuantizationΣIIn=ΣIOutKirchoff’sJunctionRuleΣVGain=ΣVDropKirchoff’sLoopRuleE=kQ/r2ElectricFieldStrengthnearaPointChargeE=V/dElectricFieldbetweenChargedParallelPlatesV=kQ/rElectricPotentialnearaPointChargeB=Φ/AMagneticFieldStrengthasFluxDensity
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IllustrativeDiagrams
AtomicChargeofAtoms
TheElectroscope
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ElectricFields
MonopoleField
ElectricDipoleField
BetweenChargedParallelPlates
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MillikanOilDropExperiment
ConventionalCurrentvs.ElectronFlow
Resistivity
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Kirchoff’sJunctionRule
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Lodestone&Compass
MagneticFieldsMagneticDipole
Earth’sMagneticField
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MagneticFlux
1stLeft-HandRule
2ndLeft-HandRule
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3rdLeft-HandRule
ForceonaCurrent-CarryingWire(Note:TheElectronFlowistowardtheFRONToftheDiagram)
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ForceonaMovingChargeinaMagneticField
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KeyIdeas
Sub-UnitI:Electrostatics
• ElectricChargecomesintwovarieties,Positive&Negative.Theyexertforcesononeanotherasfollows:
1)LikeChargesRepeloneanother.
2)UnlikeChargesAttractoneanother.
• ElectricChargeisQuantized.
1)ItcomesinasmallestunitcalledtheElementaryCharge(e).2)TheElectronhasonenegativeElementaryChargeonit.
3)TheProtonhasonepositiveElementaryChargeonit.4)AllchargesareWholeNumberMultiplesoftheElementaryCharge.
Q=Ne,whereN=0,1,2,3,...,etc.
• MostatomsareElectricallyNeutral(QNet=0),sincetheycontainequalnumbersofprotons&electrons.BulkMatter,madeupofmanyatoms,isalsoelectricallyneutral.Ionsareatomswitheithertoofew,ortoomany,electrons,andcarryanetelectricalcharge.
• APointChargeisanelectricchargedistributedoveranextremelysmallobjectsothat,forallintentsandpurposes,itcanbeconsideredtobeanearperfectpointinspacewithnodimensionsofsize.
• ATestChargeisasmallimaginaryPositivecharge,whichwepretendwecanplacewithinanelectrostaticsproblemandnoteitsdirectionofmotion.
• Electricalchargeisconserved,andobeystheLawofConservationofElectricCharge:Inaclosedsystem,thetotalnetelectricchargeisconstant.
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• TheElectrostatic(Coulomb)Forcehasthefollowingproperties:
1)Itcanberepulsiveorattractive.2)ItobeysanInverse-Squarerelationship,likegravity.3)ItobeysthePrincipalofSuperposition:Thetotalelectricforceactingonachargeisthevectorsumofalltheforcesactingonitduetoallothercharges.
• ElectricField(E):ElectricForceperUnitChargepresentatapointinspace.ItisaForceFieldproducedbycharge.Itisstrongernearthechargeandisweakerfarfromthecharge.
• ElectricFieldLines,alsoknownasFaradayLinesofElectricForce,always:
1)PointinthedirectionaTestChargewouldmoveifplacedatthatpositionwithintheField.
2)Pointawayfrompositivecharges(ElectricFieldSources),and
towardnegativecharges(ElectricFieldSinks).
• ElectricMonopoleField:Thefieldofeitherasinglepositiveorasinglenegative,charge.LiketheCoulombforce,itvariesinaninverse-squarewayfromthesourcecharge.
• ElectricDipoleField:Fieldbetweentwopointchargesoftheoppositesign.
• ElectricPotentialDifference(Voltage):WorkPerUnitChargeittakestomoveachargebetweentwopointsinanelectricfield.Thinkofitastheamountofenergycarriedbyeachcoulombofcharge.Ex:12voltsmeansthateachcoulombofchargehas12Joulesofenergyinmovingbetweenthetwopointsofthatpotentialdifference(voltage).
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• Theelectron-volt(eV)isaunitofenergy,notvoltage.
1)Itistheamountofenergyittakestomove1elementarychargeacrossapotentialdifferenceof1volt.
2)Itisausefulunitusedtodescribetheenergyofindividualparticles.
• ElectricPotentialEnergy(W):Istheenergycontainedwithinagroupofindividualelectriccharges.Iftheyareallofthesamesignthentheirpotentialenergyincreasesastheyareforcedclosertogether.Sinceittakesworktogetsuchchargestocometogether,theclosertogethertheyare,thegreatertheworkdonetoaccomplishthis,andthehighertheirelectricpotentialenergy.
• Ittakesexternalworktogetapairofopposite-signedelectricchargestospreadfurtherapart,sothefartheraparttheyarethegreatertheirelectricpotentialenergy.
Sub-UnitII:ElectricCurrent&ElectricCircuits
• ElectricCurrent(I)istherateatwhichnetchargeflows.TheunitistheAmpereandisdefinedtobetheflowof1coulombofnetcharge/second.1)ElectronsaretheMobileChargeCarriersinsolids.2)Electrons,Protons,andIonsaremobileinAqueousSolutions.
• InanElectricCircuit,electronsflowfromasourceofhigherpotentialtolower.Theyusuallyalongclosedloopsofelectricalconductingmaterial,suchaswire,attachedtotheterminalsofabatteryorcell.
• ElectricalResistance(R):AmeasureofhowdifficultitisforCurrenttoflow.ItsunitiscalledtheOhm(Ω),where1Ohm(Ω)=1Volt/Coulomb.
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• Anelectricalresistanceof1Ωmeansittakes1voltofpotentialdifferenceto“push”1coulombofchargethroughawireordevice.Aresistanceof10Ωmeansitwouldtake10timesasmuchpotentialdifferencetogetthatsamecoulombofchargetomove.
• Kirchoff’sRulesforCircuits:
1)JunctionRule:Thetotalcurrententeringajunctionisequaltothetotalcurrentleavingthatjunction.(ConservationofChargeinacircuit)ΣIin=ΣIout
2)LoopRule:Thetotalvoltagegainaroundaloopisequaltothe
totalvoltagedroparoundthatloop.(ConservationofEnergyinacircuit)ΣVGain=ΣVDrop
• ASeriesCircuitisoneinwhichthereisasingleloopthroughwhichcurrentcanflow.Itobeysthefollowing:
1)Thecurrentisthesameeverywhere.
2)ThetotalVoltageGain(voltagethataddsenergytoacircuit,likefromaBattery,Cell,Generator,SolarCell,etc.)isequaltothesumoftheVoltageDrops(voltagethattakesenergyawayfromacircuit,likefromaresistor).3)ThetotalorEquivalentResistanceisequaltothesumoftheindividualresistorsandisthereforegreaterthenanyofthem.
• AParallelCircuitisoneinwhicheachresistorisonitsownloopbacktothepowersource.Itobeysthefollowing:
1)Thetotalcurrentisthesumofallthecurrentsgoingintothejunctions.
2)TheVoltageGainsandDropsareallequaltooneanother,andisthesameasthevoltageofthesource
3)ThetotalorEquivalentResistanceisalwayslessthanthesumoftheindividualresistors.Theextraloopsgivethecurrentmoreroomtomove,makingiteasiertoflow.
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• ElectricalMetersareplacedinacircuitasfollows:1)Ammeter(MeasuresCurrent):PlacedinSerieswiththedevicewhosecurrentisbeingmeasured.
2)Voltmeter(MeasuresVoltage):PlacedinParallelacrossthedevicewhosevoltageisbeingmeasured.
• ElectricalResistivitydependsonlyonthechemicalmakeupofasubstanceandnotonitssizeorshape.
Sub-UnitIII:Magnetism
• Lodestone,adark,dense,metallicrock,attracts,andisattractedto,iron.
• Sliversoflodestone,allowedtofreelyrotate,willalignthemselvesinaroughlyNorth-Southorientation,formingasimpleMagneticCompass.
• AllMagnetshaveaNorthPoleaswellasaSouthPole.Thesearetheendsofthemagnetthattendtolineupinthosedirections.
• TheMagneticField(B),alsoknownasMagneticFluxDensity,isameasureofhowcloselypackedtogetherlinesofMagneticFlux(FieldLines)areinaregionofspace.
• MagneticFieldsobeysthefollowing:
1)Theyalwaysformedclosedloopswithnobeginningorend.
2)FieldLinesflowfromthemagnet’sNorthPoletoitsSouthPoleoutsideofthemagnet.3)FieldLinesnevertouchorintersect.
• LinesofMagneticFluxcomeinunitscalledWebers(Wb).MagneticFieldstrengthisameasureofhowcloselypackedtogethertheseFieldLinesareinagivenareaofspace.
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1)1Tesla(T)=1Weber/meter2=1Wb/m22)IGauss(G)=10-4Tesla3)Earth’smagneticfieldstrengthatthesurfaceisapproximately0.50Gauss,or5x10-5Tesla.
• TheSimplestmagneticfieldistheMagneticDipoleField.
• TherearenoMagneticMonopoleFields.CuttingamagnetintotwopiecesresultsintwopieceswithDipoleFields.
• Magneticfieldsareproducedbyelectricalcurrents,orchargesthatareinmotion.Magnetismisanelectricalphenomenon.
• Themagneticfieldaroundastraightcurrent-carryingwireconsistsofconcentricringscirclingaroundthewirewhosedirectionisgivenbythe1stLeftHandRule.
• 1stLeftHandRule:
1)Thumb:DirectionofElectronFlow2)CurledFingers:DirectionofMagneticFieldLoops
• Themagneticfieldthroughacircularloopofcurrent-carryingwireresemblesthatofabarmagnet.Itsdirectionisgivenbythe2ndLeftHandRule.
• 2ndLeftHandRule:
1)CurledFingers:DirectionofElectronFlow2)Thumb:DirectionofNorthMagneticPole
• Thedirectionofthemagneticforceactingonachargemovingwithinamagneticfieldisgivenbythe3rdLeftHandRule.
• 3rdLeftHandRule:1)StraightFingers:DirectionofMagneticField(FluxLines)2)Thumb:DirectionofElectronFlow
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3)Palm:TheMagneticForce
• Themagneticforce(FB)alwayspointsinadirectionperpendiculartoboththemagneticfield(B),anddirectionofelectronflow,subjecttothefollowingconditions:
1)Iftheelectronflowisparallel(0°),orantiparallel(180°),tothemagneticfield,themagneticforceonthemiszero.2)Iftheelectronflowisperpendicular(90°)tothemagneticfield,themagneticforceonthemismaximum.3)Amagneticforceonlyexistiftheelectronflow“cutsacross”themagneticfieldlinesinsomesense.
• Achargedparticlemovingthroughamagneticfieldwilleithermoveincirclesaroundthefieldlines,ormoveonahelicaltrajectoryalongthefieldlines.ChargedparticlesfromspacethatstrikeEarth’smagneticfieldaredeflectedinthiswaytowardthepolarregionswheretheystriketheupperatmosphere,giveoffflashesoflightwhentheydoso,andthusformtheauroras.
• Anelectromagneticwaveformswhenelectricchargesaremadetoaccelerate(usuallyoscillate).
1)Theoscillatingchargesproduceseparatewavesintheirelectricandmagneticfields.2)Thesewavesoscillateinplanesthatareperpendiculartooneanother.3)Thewavespropagateatthespeedoflight,forlightisoneparticularexampleofthesewaves