# 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


• 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)


• 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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• 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


• 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.


• 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.


• 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

# 11 Electricity & Magnetism...• The Van der Graaf Electrostatic Generator • The Coulomb...

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