SP212 Lab: One  Electrostatics
Version: January 21, 2015
PHYSICS II
LAB 2A
SP212
ElectricFieldSimulations
I.
Introduction
A. Inclass,wehavestudiedtheelectricfieldproducedbychargedobjects.In
thislabwewillexperimentallyverifysomeofourtheoreticalresults,and
connecttheelectricfieldtotheconceptofelectricpotential.

B. Theelectricfield, E ,isavectorfield;itconsistsofadistributionofvectors,
representingtheforceperunitchargethatapositivetestchargewould
feelateachpointintheregionaroundachargedobject.
C. Electricfieldlinesextendawayfrompositivecharges(wherethey
originate)andtowardnegativecharges(wheretheyterminate.)
D. Theprimarypurposeofthislabistouseelectricfieldlinestovisualizethe
electricfieldproducedbyvariouschargedsources.Thisexerciseis
intendedtobemoredynamicthanstaticdrawingsintextbooks,whichare
limitedtojustafewspecificscenarios.Here,studentswillbeableto
controlandchangemultipleparametersandseetheeffectsonthe
resultingelectricfields.
II.
Procedure
A. UsingthePhETChargesandFieldSimulationapplet,predictthe
relationshipbetweenelectricfieldanddistancefromachargedobject,
E(r).
1) Goto Charges and Field simulation at
http://phet.colorado.edu/en/simulation/charges‐and‐fields.
2) Click Run Now!.
Page 1 of 4 SP212 Lab: One  Electrostatics
Version: January 21, 2015
3) Oncetheappletstarts,checktheboxesnexttoShowE‐field,grid,andShow
numbers.
4) Placeasinglepositivechargeroughlyinthemiddleofthegrid.Notethat
computerautomaticallycalculatesandillustratestheelectricfieldgenerated
bythispointcharge.
5) Takean“E‐fieldSensor”andmeasurethemagnitudeoftheelectricfieldat
severalpointsawayfromthecharge.RecordyourdatainExcel,andusethem
toplotE(r).Fitacurvetoyourdata.Whatcurvefitsbest?Why?
B. Usingtheapplet,showtheinteractionbetweentwochargedparticles.
1) Placeachargedparticleofyourchoosingatalocationwhereitistwofullblocks
fromthefarleftsidebutnearthecenterintheydirection.
2) Placeasecondchargeofthesamesignatadistanceof2metersonthehorizontal.
3) Observetheelectricfieldlines.
4) Predictwhattheelectricfieldvaluewouldbeatthe1meterpointmidway
betweenthetwochargesthenplaceanE‐fieldsensorthereandseeifthe
measuredvaluematchesyourprediction.Didtheresultsmatchyourprediction?
Ifnotresolvethereasonwhywithyourlabpartnerorifnecessary,theinstructor.
Whatdoesthissayaboutuncertaintyinthemeasuredvalue?
5) Nowpredictwhattheelectricfieldmagnitudeanddirectionwouldbeataposition
1meterverticallyabovethecenterofthetwoparticles.Showallworkincluding
thevectordiagram.
6) ThenplaceanE‐fieldsensorthereandseeifthemeasuredvaluematchesyour
prediction.Didtheresultsmatchyourprediction?Ifnotresolvethereasonwhy
withyourlabpartnerorifnecessary,theinstructor.
7) Whenyoufeelyouunderstandandarereadytomoveon,clicktheClearAllbutton.
8) Removethefieldsensorandreplacetherighthandchargewithachargeofthe
oppositepolarity. 9) Ongraphpapertohelpwithscale,drawtheelectricfielddiagramthatyousee.
Insteadofusingintensity,usearrowlengthstorepresentthemagnitudeofthe
field.UseE‐fieldsensorstohelpdeterminethelengthofyourvectors.
10) Predictwhattheelectricfieldvaluewouldbemidwaybetweenthetwocharges.
PlaceanE‐fieldsensorthereandseeifthemeasuredvaluematchesyour
prediction.Didtheresultsmatchyourprediction?Ifnotresolvethereasonwhy
withyourlabpartnerorifnecessary,theinstructor.Whydoesthisvalueno
longerequalzero?Isthisvaluethemaximumorminimumvalueoftheelectric
fieldbetweenthetwoparticles?
Page 2 of 4 SP212 Lab: One  Electrostatics
Version: January 21, 2015
11) Whenyouhavecompletedansweringtheabovequestions,removeallE‐field
sensors.
C. Electricfieldstrengthversusdistancerelationshipforadipole:
1) Nowbringyourtwooppositechargesveryclosetogether.Youhavecreateda
dipole.Moveyourdipoletooneextremesideofyourgraph.Note,youcanget
betterresultsifyoustackmultiplepositivechargesontopofoneanother,andan
equalnumberofnegativechargesontopofeachother.
2) MoveanE‐fieldsensortomeasuretheelectricfieldvalueatvariouslocations
horizontallytotherightbetween0.5metersandupto4metersawayfromthe
centerofthedipole.Recordthepositionandtheelectricfieldvalueforeach
position.Itisbesttogetatleast5values.
3) EnterthevaluesintoExcel(orequivalentprogram),createagraphofE(r),and
determinethebestfitcurve.
4) Doesthisbestfitequationmatchtheoryinproportionality?Ifnot,whatare
possiblereasonswhy?
5) Whenyoufeelyouunderstandandarereadytomoveon,clicktheClearAll
button.
D. ElectricFieldStrengthvs.distancerelationshipforalonglineofcharge:
1) Alongoneedgeofthegraph,createalonglineofcharges,allthesamesign.You
needtousealotofcharges,probably30‐40.
2) UseanE‐fieldsensortomeasurethestrengthoftheelectricfieldasafunctionof
distancefromthecenteroftheline.YoushouldbemovingyourEsensoraway
fromtheline,notalongtheline.
3) AgainuseExceltodiscoverafunctionforE(r).
E. Discussionpoints:
1) Whatdidyoulearnabouttheelectricfieldversusdistancerelationshipsfora
pointcharge,averylonglineofcharge,andforadipole?
F. (Timepermitting)UsingthePhETElectricFieldHockeySimulationapplet
usingelectricfieldtheorytomoveachargedparticleintoaspecificgoal
location.
1) StartingtheAppletandsetup.
2) GotoChargesandFieldsimulationat
http://phet.colorado.edu/en/simulation/electric‐hockey.
3) ClickRunNow!(ItmighttakesometimetoloadevenaftertheJavasymbolleaves
thescreen,bepatient.)
Page 3 of 4 SP212 Lab: One  Electrostatics
Version: January 21, 2015
4) ChecktheTraceandFieldboxes,andpractice.Moveachargedparticlefromitsbin
toanywhereonthescreen.Thenhitstartandseewhathappens.Feelfreeto
experiment.Onceyouthinkyouunderstandthepremiseandarereadyfora
challengethenselectdifficulty1.
5) Yourobjectiveistocauseyourpositivelychargedpucktogetintothegoalby
placingadditionalparticlesofeitherpositiveornegativechargeontotheplaying
fieldatstrategiclocations.Youshouldstrivetodothisusinglessthan12charged
particles,andultimatelyuseasfewaspossible.
6) Onceyouachieveagoal,drawonapieceofgraphpaperyourwinningsolution.
7) (Evenmoretimepermitting)Attempttoachieveanothergoalwithevenfewer
charges.
III.
Clean‐Up
A. GoldenRule:“Dountoothersasyouexpectthemtodountoyou.”
ThisappliesasmuchhereinthelabasitdoesintheFleet.AsfutureNavalOfficers,
howcanyouexpectyourenlistedsailorstomaintainacleanworkareaifyour
stateroom,workareas,messarea,etcisa“pigsty?”Soasofficersitisimperativethat
wecleanupafterourselvesnotonlytofollowtheGoldenRule,butalsotoleadby
examplefortheenlistedpersonnelunderourcharge.
1. EndofLabCheckout:Beforeleavingthelaboratory,tidyuptheequipmentatthe
workstationandquitallrunningsoftware.
2. Thelabstationshouldbeinbetterconditionthanwhenyouarrivedandmore
importantly,shouldbeofanappearancethatyouwouldbePROUDtoshowto
yourlegalguardiansduringa“ParentsWeekend.”
3. Haveyourinstructorinspectyourlabstationandreceivetheirpermissionto
leavetheLabRoom.
4. YouSHALLfollowthisprocedureduringeverylabforSP212!
Many thanks to Dr. Katz, LCDRs Grant Miller, Tim Barry, Dave Riebel , and Mr. Gary Bishop for their assistance in producing this Laboratory procedure; specific references can be supplied on request. LCDR Timothy Shivok Page 4 of 4