p2 topic 1 & 2 · component resistance filament lamp. as they get hot the resistance decreases....
TRANSCRIPT
Proton
Neutron Electron
Charge
+1 0 -1
Mass 1 1 0.0005 (almost zero)
The charge and mass of electrons, protons and neutrons P2.1Sta)cElectricity
Protons=posi0velychargedElectrons=nega0velycharged.Electronsareintheshellsofatoms.Chargeofanatom=neutralasthe+andthe–areequal.
Sta)celectricityIninsulatorcanbecomechargedbyfric0onthroughthetransferofelectrons.Asubstancethatgainselectronsbecomesnega)velycharged,whileasubstancethatloseselectronsbecomesposi)velycharged.WhenachargedobjectcomesneartoanotherobjecttheywilleitheraIractorrepeleachother.Ifthechargesarethesame-theyrepelIfthechargesareopposite-theya9ract
P2.1Electrosta0cPhenomenaThenega0velychargedballoonrepelstheelectronsinthewallandtheymoveaway.Theposi0vechargeleKbehindaIractstheballoon.
Thenega0velychargedcombrepelstheelectronsinthepaper.Theposi0vechargeleKbehindisaIractedtothecombwhichiswhyitpicksupthepaper.
P2.2UsesandDangersofsta)cHowlightningiscaused:
• Sta0celectricitycanbuildupinclouds.Thiscancauseahugesparktoformbetweenthegroundandthecloud.
• Aflowofchargethroughtheatmosphere.Sta0cisdangerouswhen:• Thereareinflammablegasesorvapoursorahighconcentra0onofoxygen.Aspark
couldignitethegasesandcauseanexplosion.• Youtouchsomethingwithalargeelectricchargeonit.Thechargewillflowthrough
yourbodycausinganelectricshock.Sta0celectricitybuildsuponeverydayobjects.Itcanbedangerousifitcancreateaspark.Aconduc0ngpathcanbeusedtopreventsparking.
Earthingremovesexcesschargebymovementofelectrons.Theelectronsflowthroughtheearthingcabletoearthratherthantherebeingadischargeandspark.
PaintSpraying1)Thecarisnega0velycharged.2)Thepaintisposi0velycharged.Theposi0velychargedpaintspreadsoutastherepeleachother.3)Thenega0veaIractedtotheposi0veands0ck.4)Themetalspraynozzleisconnectedtotheposi0veterminalofthepowerpackandthepaintpicksupaposi0vecharge.
AircraKcanbuildupasta0cchargewhenflyingthroughtheairandrefuellingcanalsobuildacharge.TostopexplosionstheaircraKhasabondinglinewhichisusedtoconnecttheaircraKtotheearthbeforeithasbeenrefuelled.
Insec)cidespraysInsec0cideusesta0celectricity.SprayedfromaircraKsothattheycoveralargearea.Riskthatsomeofthespraywillblowawayorfallunevenly.Topreventthis,theinsec0cideisgivenasta0cchargeasitleavestheaircraK.Thesta0cdropsspreadevenlyastheyallhavethesamechargeandareaIractedtotheearth.
P2.2UsesandDangersofsta)c
P2.3ElectricCurrentsMaterialscontainelectrons.Insula0ngmaterialstheelectronscannotmovebutinametaltheymoveandthiscanandthiscreatesacurrent.
Beabletousetheequa0on:charge(coulomb,C)=current(ampere,A)x)me(second,s)
Q=Ixt
Keyterms• Currentistheflowofcharge• Currentinmetalsistheflowofelectrons• CellsandbaIeriessupplydirectcurrent
(d.c.)• Directcurrentisthemovementofchargein
onedirec0on.
Voltmeter Ammeter
MeasuresvoltageinVolts
MeasurescurrentinAmps
Measurestheenergydifferencebetweentheelectronsgoingintothecomponentandback.
Electronsnotusedupouttheoutputisthesameastheinputbacktothecell.
Parallel Series
Nojunc0ons Currentsplitsupatajunc0on
Poten0aldifferencemeasured.
Currentsizemeasured.
P2.4CurrentandVoltage.
Poten0aldifferenceistheenergytransferredperunitcharge.1Voltis1JouleperCoulomb
P2.6Changingresistances• Resistancemeasureshowharditisfortheelectricitytoflowthrougha
circuit.• MeasuredinOhms• Dependantonhowmanycomponentsareinthecircuit.• Thehighertheresistancethelowerthecurrent.• Variableresistor=canchangetheresistanceofawire.
Component Resistance
Filamentlamp. Astheygethottheresistancedecreases.Theygethotastheyhaveahigherpoten0aldifference.
Diodes Electricityflowsinonedirec0on.Ifapoten0aldifferenceisappliedintheotherdirectnocurrentwillflow.
Lightdependantresistor Resistanceishighinthedarkandlowintheday0me
Thermistor Highresistancewhencold,lowresistancewhenhot.
Beabletousetheequa0on:poten)aldifference(volt,V)=current(ampere,A)xresistance(ohm,Ω)
V=IxR
P2.7Transferringenergy Equa0onsyoumustbeabletouseCalcula0ngElectricalPower
electricalpower(waI,W)=current(ampere,A)xpoten)aldifference(volt,V)P=IxV
Energytransferred(joule,J)=current(ampere,A)xpoten)aldifference(volt,V)x)me(second,s)E=IxVxt
Dis0nguishbetweentheadvantagesanddisadvantagesofthehea0ngeffectofanelectriccurrent
Advantages Disadvantages
UsefulHea0ngakeIle
Wastedenergy
UsefulinFires Causeburns
Acurrentinawireisaflowofelectrons.Astheelectronsmoveinametaltheycollidewiththeionsinthelagceandtransfersomeenergytothem.Thisiswhyaresistorheatsupwhenacurrentflowsthrough.
VectorsandVelocityQuan00eswhichhaveadirec0onandsizeareknownasVECTORQUANTITIES.4Examples• Displacement–distancetravelledinapar0culardirec0on.• Velocity–speedinapar0culardirec0on.• Force–alwayshasasizeanddirec0on.• Accelera0on–ithassizeanddirec0on
Speed(m/s)=distance(m)÷0me(s)
Accelera0on(m/s2)=changeinvelocity(m/s)÷0me(s)
Keyequa0onsyouneedtobeabletouse:
Distance/TimeGraphs• Horizontallinesmeanthe
objectissta0onary.• Straightslopinglinesmean
theobjectistravellingataconstantspeed.
• Thesteepertheslope,thefastertheobjectistravelling.
• Acurvedlinemeansaccelera0on.
• Toworkouttheaccelera0on,youneedtocalculatethegradient.
Velocity/TimeGraph• Horizontallinesmeanthe
objectistravellingataconstantvelocity.
• Straightslopinglinesmeantheobjectisaccelera0ngordecelera0ng.
• Thesteepertheslope,thefastertheaccelera0on.
• Acurvedlinemeansaccelera0on.
• Theareaunderthegraphisthedistancetravelled.
ForcesAforceisapushorapull.Whentwobodiesinteract,theforcestheyexertoneachotherareequalinsizeandoppositeindirec0on.TheseareknownasREACTIONFORCES.
Youneedtobeabletointerpretthesediagramsandworkouttheresultantforceineachdirec0on.
Iftheresultantforceiszero,itwillremainatrestorcon0nuetotravelataconstantspeed.Iftheresultantforceisnotzero,itwillaccelerateinthedirec0onoftheresultantforce.
ForcesandAccelera0onThesizeofaccelera0ondependson:• Sizeoftheforce
• Massoftheobject
Keyequa0onyouneedtobeabletouse:
Force(N)=Mass(kg)xaccelera0on(m/s2)
Inavacuum• allfallingbodiesaccelerateatthesamerate.
Intheatmosphere• Airresistanceincreaseswithincreasingspeed.• Airresistancewillincreaseun0litisequalinsizetotheweightofafalling
object.• Whenthetwoforcesarebalanced,accelera0oniszeroandTERMINAL
VELOCITYisachieved.
TerminalVelocity
Keyequa0onyouneedtobeabletouse:
Weight(N)=Mass(kg)xgravity(N/kg)
StoppingDistancesStoppingdistance=thinkingdistance+breakingdistance
6Factorsaffec0ngstoppingdistance:1. Massofvehicle2. Speedofvehicle3. Driversreac0on0me4. Stateofthebreaks5. Stateoftheroad6. Amountoffric0onbetween
thetyreandtheroadsurface.
5Factorsaffec0ngreac0on0me:1. Ageofdriver2. Drugse.g.alcohol3. Visibility4. Tiredness5. Distrac0ons
Inves0ga0ngfric0on.Howmuchforceisneededtomoveweightsondifferentsurfaces?
MomentumAmeasureofmo0on.Massmul0pliedbyvelocity.Whenamovingobjectcollideswithanotherobject,themomentumisthesamebeforethecollisionasitisaKerthecollision.
MomentumandSafetyWhenyouaretravellinginacar(oronabike,skis,trainetc.)youaretravellingatthesamespeedasthecar.Ifthecarstopssuddenly,yourmomentumcon0nuestocarryyouforward.Ifyouarestoppedsuddenly,byhigngthedashboard(orground)youexperiencealargeforce,andthereforealargeamountofdamage.
Carsafetyfeatures:1. Seatbelts–stretchtoincreasethe0metakentostop,thusreducingtherateof
changeofmomentumandreducinginjury2. Airbags–inflatetoincreasethe0metakentostop,thusreducingtherateof
changeofmomentumandreducinginjury3. CrumpleZones–crumpleandfoldinaspecificwaytoincreasethe0metakento
stop,thusreducingtherateofchangeofmomentumandreducinginjury
Usethisformula:Force(N)=changeinmomentum÷0me
Ifyouincreasethe0meyoureducetheforce.
WorkandPowerKeydefini0ons• Work–theamountofenergytransferred.MeasuredinJoules(J)• Power–Therateofdoingwork.MeasuredinWaIs(W).1jouleper
secondis1waI.
Usethisformula:WorkDone(J)=Force(N)xdistancemoved(m)Example–ifa1kgmass(10N)ismovedthroughadistanceof2metrestheworkdoneis20J.
Usethisformula:Power(W)=WorkDone(J)÷Timetaken(s)Example–ifa24Jofworkisdoneovera30secondperiod,thePowerwouldbe24÷30=0.8W
Poten0alandKine0cEnergy
Youneedtobeabletousetheseequa0ons:GPE=mghKE=½mv2
KeyDefini0ons• Kine0cEnergy–movementenergy• Gravita0onalPoten0alEnergy–theenergysomethinghasduetoitsposi0onrela0ve
toEarth–i.e.itsheight.
Conserva0onofEnergyWhenenergyistransferred,thetotalamountalwaysremainsthesame.
P2.23Isotopes
Keywords• Sub-atomicpar)cles–apar0clethatissmallerthananatom• Nucleons–Thesubatomicpar0clesinthenucleusofanatome.g.protonsandneutrons• Isotopes–Atomsofanelementwiththesamenumberofprotonsandelectronsbutwitha
differentnumberofneutrons.
Remember• TheMassnumberisMorethat
theatomicnumber
Atoms• Atomscontainelectrons,protonsandneutrons=subatomicpar)cles• ProtonsandNeutronsinthenucleus=theyarecallednucleons• Allatomsononeelementhavesamenumberofprotons=atomicnumber• Massnumber=numberofprotonsandneutronsinthenucleusIsotopes• Atomswithdifferentnumberofneutron(samenumberofprotons)• Differentmassnumbers• Examples
– Lithium–6andLithium-7– Carbon-12andCarbon-14
• AnatomwithanumberaIachedreferredtotheisotope(asabove)
Ionisingradia)on
Keywords• Unstable–anunstablenucleusisonethatwilldecayandgiveoutionisingradia0on• Radioac)veDecay–whenanunstablenucleuschangesbygivingoutionisingradia0on
tobecomemorestable• Ion-Anatomwithanelectricalcharge(throughlossorgainofelectrons)
P2.24Ionisingradia0on
Alpha Beta Gamma
• Par0clescontaining2protonsand2neutrons(Heliumatomnucleus)
• Noelectrons=2+charge• EmiIedfromnucleusathigh
speed• Loseenergyastheyionisean
atom• Producemanyionsquicklyso
haveshortpenetra)ondistance
• Stoppedbyafewcmofairofmmofpaper
• ElectronsthatareemiIedfromanunstablenucleus
• Muchlessionisingthatalpha
• CanpenetratemuchfurtherintomaIer
• Stoppedbyafewmmoraluminiumoreventhinnerlead.
• High-frequencyelectromagne)cwavesemmitedbyunstablenuclei
• Travelatthespeedoflight
• Ten)meslessionisingthatbeta
• PenetratemaIereasily• Stoppedbyafewcmof
leadormanymetresofconcrete.
P2.25Nuclearreac0ons
Keywords• Nuclearfission–thespligngonalargenucleus.• Nuclearfusion–thejoiningoftwosmallnuclei
NuclearFission• Nucleussplitsintotwosmallernuclei• Twoormoreneutronsalsoreleased• NOTthesameasradioac0vedecay• Ifneutronareabsorbedbyothernucleiitcanmakethemunstable–theythen
splitreleasingmorenuclei=chainreac)on(likeanatomicbomb.• Canbecontrolledwithmaterialstoabsorbneutrons(likeinanuclearreactor)
Radioac)veDecay• Releasesenergy• AlphaandBeta=kine)cenergy• Gamma=energyinformofelectromagne)c
radia)on
NuclearFusion• Smallnucleicancombineto
formlargerones• Alsoreleasesalotofenergy
P2.26Nuclearpower
NuclearReactors• Transformenergycontainedinnucleiofuraniumandplutoniumintothermalenergy• Nuclearfission• Pelletsofuraniuminsertedintohollowrods• Rodsplaceinreactorcore• Rateiskeptconstantbutcontrollingthechainreac0on• Numberoffreeneutronswillnotincreaseofdecrease• Extraneutronsabsorbedbycontrolrods• Controlrodsplacedinbetweenfuelrodsinreactorcore• Controlrodscanbemovedinandouttochangetherateoffission• Fullyloweredtheyshutdownthereactor.
Keywords• Moderator–asubstancein
anuclearreactorwhichslowsdownneutronssothattheycanbeabsorbedbythenuclearfuelmoreeasily.
• Radioac)vewaste–MaterialleKoveraKerthefissionofuraniumthatisradioac0ve
Genera)ngelectricity• Thermalenergyfromcoreistransferredtocoolant
(usuallywater)• Coolantpumpedthroughreactor• Coolantathighpressurepumpedtoheatexchangerto
producesteam• Steamdrivesturbinewhichturnsgenerator• Generatortransferskine0cenergytoelectricalenergy.
P2.27Fusion–ourfuture?
KeywordsPeerreviewed–workcheckedbydifferentscien0stsworkinginthesamefieldValidate–toconfirmscien0fictheoryistrue
• Scien0stsinves0ga0ngfusiontogenerateelectricity• Theheliumproducedisnotradioac)ve• Materialsusedtocontainfusiondobecomeradioac0veGe_ngnewideasaccepted• Scien0fictheorieshavetobevalidated• Bythescien)ficcommunity• Reportandresultsarepeer-reviewed• Otherscien0stsmustcarryouttheexperimentandgetthesameresultsFusionandtemperature• Thenucleithatfusearebothposi)velychargedsorepel=electrosta)crepulsion• Nucleineedtobeextremelyclose• Highdensitynucleiaremorelikelytocollidee.g.intheSunthehighgravita0onalfieldcreateshigh
densitynuclei.• Difficultcondi0ontocreateonearth• Fusionreactorstrytoproducehighpressuresandhightemperature• Hightemperatures=morekine)cenergytoovercomerepulsionandcollide.• Thesecondi0onsrequirealotofenergy(morethanthereactorcanmakesocurrentlynotvery
efficient)
P2.28Changingideas
HenriBecquerelandMarieCurie• AccidentaldiscoverywasmadethatUraniumexposedphotographicplates=
discoveryofradioac)vity• Showedhowradia0oncouldionisegases• SkinburnsvisiblefromhandlingRadium• By1920slinksmadewithcancer(MarieCuriediedoflukaemia)• Largeamountofionisingradia)on=0ssuedamage(radia0onburns)• Smalleramountsregularly=DNAdamage(muta0ons)• Somemuta0onsleadtocancer
KeywordsHazards–causesofharmRisk–likelihoodofharmMuta)on–achangeinthebasesequenceofDNA.
Handlingradioac0vesources• Riskofharmdecreaseswithdistancefromthesource• Sourcesalwayshandledwithtongs• Riskreducedbynotpoin)ngsourcesatpeople• Keepsourcesinleadlinedcontainers
P2.29NuclearWaste
Highlevelwaste• ThefissionproductsfromUraniumfuelareveryradioac)ve• Produceslargeamountsofionisingradia)onforabout50
years• Remainsmoderatelyradioac0veforthousandsofyearsas
intermediatelevelwaste• Transportedinthickconcreteandsteelcontainers• Sealedinglasstopreventescape• Storedincanistersun0litbecomesILW
Intermediatelevelwaste• Remainsmoderatelyradioac)vefor
thousandsofyears• Includesthemetalcylindersthatcontained
uraniumfuelwhichbecomeradioac0ve• Storedinconcreteandsteelcontainers• Nonedisposedofyet
LowlevelWaste-• Onlyslightlyradioac0ve• Remainssofortensofthousandsofyears• Clothingandcleaningmaterialsfromnuclearpower
sta0ons• HospitalsalsoasourceofLLWfromradiotherapy
cancertreatments• Compactedandburiedinspeciallandfill
Advantagesofnuclearpower Disadvantagesofnuclearpower
• Sta0ondoesnotproduceCO2• Lessimpactonglobalwarming
• Makingthefuelrodsrequiresenergy(CO2released)• Wastehastobestoredfortensofthousandsofyearswithout
leaks• PeopleperceiveitasunsafeaKertheChernobylaccident
Disposalmethods1. Firingintospace
– Riskofitfallingback
2. Dumpinginbarrelsatsea– Barrelscancorrode– Entersfoodchain
3. Storageunderground– Needgeologicallystablesite– Lowearthquakerisk
P2.30Half-life
Radioac)vedecay• Unstablenucleusundergoesradioac)ve
decaytobecomemorestable• Ac0vityofasubstanceisthenumberof
nucleardecayspersecond• Measureinbecquerel(Bq)• 1Bqisonenucleardecayeachsecond• Radioac0vedecayisarandomprocess
(cannotpredictit)• Halflife=the0metakenforhalfthe
unstablenucleiinasampleofaradioac0veisotopetodecay.
• Halflifedoesnotchangeasthesamplegetssmaller
• AKerdecaying=morestablenucleus• Morestablenucleus=lowerac)vity• Halflifefoundbyrecordingac0vityovera
periodof0me.
Geiger-Mullertube• Usedtomeasureradioac0vity• Canbeconnectedtoacounterormay
giveaclickwhenradia0ondetected• Countrate=numberofclicksper
secondorminute
P2.32Backgroundradia0onKeywords• Backgroundradia)on–ionisingradia0onthatisaroundusallthe0mefromanumberofsources.
Someisnaturallyoccurring.• Backgroundcount–theaveragenumberofcountsrecordedbyaGMtubeinacertain0mefrom
backgroundradia0on• Radongas–naturallyoccurringradioac0vegasthatisemiIedfromrocksasaresultofthedecayof
radioac0veuranium
BackgroundRadia)on• Mainsource=radongas• Releasedfromdecayinguraniuminrocks• Diffusesintotheairfromrocksandsoil• Medicalsources=x-rays;gammarays(scans)andcancertreatments• Somefoodarenaturallyradioac0ve• Cosmicrays=highenergychargedpar0clesfromthestars(liketheSun)andsupernovae,
neutronstarsandblackholes.• ManycosmicraysarestoppedbytheatmospherebutsomereachEarth.
• Weareconstantlyexposedtoionisingradia)on–fromspaceandnaturallyoccurring=backgroundradia)on
• Needstobeconsideredwhenmeasuringasource• Backgroundcountissubtractedfromthesourcecount
P2.33andP2.34Usesofradia0on
TreatmentofCancer• Radiotherapy=ionisingradia0ontotreat
cancer.• Gammaraysusedasbeamstotargetandkill
cancercells.
DiagnosisofCancer• Gammaraysused• Atracersolu0oninjectedintobodythatcollects
incancers• Gammacamerausedtodetectrays• Passthroughthebodysoeasilydetected
Sterilisa)onofequipment• Tokillmicroorganismssurgical
instrumentsneedtobesterilised• Heatusuallyusedbutcannotbeused
onsomethingse.g.plas0cs• TheyareirradiatedwithGammarays
instead.
Irradia)ngfood• Bacteriawillcausefoodtodecayormakeusill• Gammarayskillbacteria• Makesfoodsaferandlongerlas0ng• Doesnotmakefoodradioac0ve• FoodslikeFruit,cerealsandshellfishare
irradiated.
SmokeAlarms• Containsasourceofalphapar)cles• Thereisanelectricalcircuitwithagap
between2chargedplates.• Airingapisconstantlyionisedtherefore
constantelectriccurrent.• Whensmokegetinthealphapar0cles
areabsorbedandstopsthecurrentdrops=alarmsounds
Checkingthickness• Useadetectortomeasuretherate
Betapassesthroughpaper• Thinnerpaper=higherbetacount.
Tracersintheenvironment• Addedtowatertomonitorpollu)onor
leakingpipesunderground• GMtubefollowsthepipetodetectleaks.