2010+experifest physics
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HANDBOOK
Physics
2010
EXPERIMENTFEST
www.newcastle.edu.au
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INTRODUCTION
ExperimentFestisanexperimentprogramdesignedtoprovideenrichingeducationalexperiencesforseniorhighschoolstudentswhoarestudyingPhysics,ChemistryandBiology.ExperimentFestissupportedbytheUniversityofNewcastlesFacultyofScienceandInformationTechnologyandtakesplaceatboththeCallaghanandOurimbah(CentralCoast)campusesoftheUniversityofNewcastle.ItisrunoverfourdaysattheCallaghanCampus
(21-25June2010-PhysicsandChemistry;18-25June2010-Biology)andfourdaysattheOurimbahCampus(28June1July2010).Studentsmayattendeithermorningsessions(9am-12pm)orafternoonsessions(12:45pm-3:45pm).PhysicsExperimentfestisalsorunningatTuncurry(June262010).
Theactivitiesallowstudentstoengageinarangeofhands-onexperimentsthataredifficulttoorganisewithinaschoolsetting,allunderthesupervisionofUniversityStaffandPostgraduatestudents.EachexperimentischosentocomplementtheNSWHSCsyllabusforPhysics,cementingclassroomtheoryandprovidingagoodbasisforexaminationpreparation.
Experimentsinclude: WilsonCloudChamber Michelson-MorleyExperiment ThePhotoelectricEffect Electric&MagneticFields WorldinMotion Superconductivity FramesofReference
Allexperimentsarecomplementedbynotes,follow-updiscussionsand
questionstoenhanceyourlearningexperience.
Forbookinginformationcontact:Larry Miltonon49469159or0404460470;orDavid Rushtonon43336965or0414238464
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WELCOME
WelcometotheFacultyofScienceandInformationTechnologyattheUniver-sityofNewcastle.ExperimentFestisawonderfulchancetogiveyoupracticalexperiencewhichcomplementsyourclassroomlearningwhilegivingyouafirsthandlookatUniversitylifeandfacilities.Scienceisanexcitingfieldofstudy,allowingyoutomovewiththetimesandcontributeactivelyandrespon-siblytosociety.Therearemanyeducationopportunitiesinscienceafterhigh
school.HereintheFacultyweprovidestudyandresearchprogramsinfast-movingmodernfieldsthatmakeourworldwork.
TheFacultystaffandstudentswhowillbetakingyouthroughtheexperimentstodayareinvolvedincontemporaryscienceresearch.Pleaseaskquestionsandutiliseyourtimewiththem.
Takethisdaytoenjoybeingoutoftheclassroom,exploringsciencewithfel-lowstudentsandparticipatinginvaluableexperimentsanddiscussionswhichwillhelpyouinyourHSCandbeyond.
Iwishyouwellinyourstudies.IhopeyouapplyyourselvestothelearningprocesswithenthusiasmandyouenjoyyourtimeattheUniversity.Wehopetoseeyoustudyingwithusinthefuture!
Bestwishes,
Prof.BillHogarthProVice-ChancellorFacultyofScienceandInformationTechnologyUniversityofNewcastle
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PHYSICS
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STUDYING PHYSICS
Why study physics?Physicsiscrucialtounderstandingtheworldaroundus,theworldinsideus,andtheworldbeyondus.Itisthemostbasicandfundamentalscience.Physicschallengesourimaginationswithconceptslikerelativityandstringtheory,anditleadstogreatdiscoveries,likecomputersandlasers,thatchangeourlives.Physicsencompassesthestudyoftheuniversefromthelargestgalaxiestothesmallestsubatomicparticles.
Moreover,itsthebasisofmanyothersciences,includingchemistry,oceanography,seismology,andastronomy.Allareeasilyaccessiblewithabachelorsdegreeinphysics.
Theimportanceofphysicsisntlimitedtothehardsciences.Increasingly,physicistsareturningtheirtalentstomolecularbiology,biochemistry,andbiologyitself.Evenmedicinehasanicheforphysicists,andsincemedicalphysicistsarehardtocomeby,theyaremuchindemand.
Physicsalsosupportsmanynewtechnologies.Cellphones,theInternet,andMRIsareonlyafewexamplesofthephysics-basedtechnologicaldevelopmentsthathaverevolutionizedourworld.Aphysicseducationequipsapersontoworkinmanydifferentandinterestingplacesin
industrialandgovernmentlabs,oncollegecampuses,andintheastronautcorps.Manytheoreticalandexperimentalphysicistsworkasengineers,andmanyengineershavephysicsdegrees.Inaddition,manyphysicsgradsleavethelabbehindandworkatnewspapersandmagazines,ingovernmentaldepartmentsplaceswheretheirproblem-solvingabilitiesandanalyticalskillsaregreatassets.
Physicsisinteresting,relevant,anditcanprepareyouforgreatjobsinawidevarietyofplaces.
Opportunities for further studies in Physics:TheBachelorofSciencedegreeprogramattheUniversityofNewcastleprovidesafoundationofknowledge,skillsand
attributesthatallowsgraduatestobeemployablenotjusttodaybutintothefutureandtocontributeactivelyandresponsiblytosociety.MajoringinPhysics,youhavetheopportunitytosampleand/orspecialiseinanyoneofthefollowing: Biophysics(doublemajor) ComputationalPhysics(doublemajor) Geophysics(doublemajor) MedicalPhysics Nanotechnology OpticalPhysics(doublemajor) ResearchPhysics SpacePhysics/Radar/Surveillance
MajoringinPhotonicsyoucanstudy: OpticalPhysics(doublemajor) OpticalPhysics/LaserEngineering/PhotonicsEngineering
Equipped with his five senses,
man explores the universe
around him and calls the
adventure science
E.PHubble.
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Research in Physics at the University of Newcastle:TherearevariousgroupshereattheUniversitywhicharecommittedtoresearchinphysics.Groupsinclude:
CentreforSpacePhysics MedicalPhysicsGroup SurfaceandNanoscienceGroup ResearchCentreforOrganicElectronics
Careers in Physics:
TheFacultyofScienceandITcareaboutourstudentsandareinterestedingivingasmuchdirectionaspossibletothosemakingcareerchoicesandbeyond.Thepossiblecareerpathslistedbelowincludearangeofopportunitiesforgraduatesatdegree,honours,andpostgraduatestudylevels.
AcousticalPhysicist Astronomer/Astrophysicist Biophysicist Cosmologist FluidDynamicsAnalyst Geophysicist GraduateTrainee(GraduateProgram) HealthPhysicist LaboratoryAnalyst Laboratory/ResearchAssistant Nanotechnologist NuclearPhysicist
OpticalPhysicist
PlasmaPhysicist ResearchScientist RiskAnalyst ScienceInformation/EducationOfficer Science/PhysicsTeacher SciencesTechnician ScientificPatentAttorney/TechnicalAdvisor ScientificPolicyOfficer ScientificWriter SoftwareEngineer/Tester UniversityLecturer/Academic
Possible careers in Photonics:
GraduateTrainee(GraduatePrograms) LaserEngineer ManufacturingEngineer Nanotechnologist NetworkCablingTechnician
NetworkSupportEngineer OpticalResearchScientist PhotonicsEngineer ProjectManager ResearchScientist
SciencesTechnician ScientificPatentAttorney ScientificPolicyOfficer ScientificWriter SystemsEngineer TechnicalSalesRepresentative TechnologyInfrastructureManager TelecommunicationsServiceDelivery TestEngineer UniversityLecturer/Academic
Formoreinformationonthesecareerpaths,pleasevisittheUniversityscareerswebsite:www.newcastle.edu.au/service/careers/majors/
FormoreinformationontheFacultyofScienceandITcheckoutourwebsite:http://www.newcastle.edu.au/faculty/science-it/
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CHARGED PARTICLES INELECTRIC AND MAGNETIC FIELDS
Extract from HSC Syllabus 9.4.1describe quantitatively the force acting on a charge moving through a
magnetic field; F=qvBsin
Solve problems and analyse information using F=qvBsin , F=qE, E=V/d.
Outline Thomsons experiment to measure the charge/mass ratio of an electron
Key WordsMagneticandelectriceldsHelmholtzcoilsElectrongunDeectionplatesCircularMotion
Electriccharge
IntroductionDuringthe1800sitwasbelievedthattheatom(Greekwordmeaningindivisible)wasthefundamentalparticleofallmatter.Inthemid1800sW.Crookes(UK,1832-1919)inventedtheequipmentthatallowedscientiststoinvestigatecathoderays.TheCrookestubeordischargetubeconsistsofaglasstubecontainingapairofseparatedmetalplatesorelectrodes.Theelectrodeswerenamedtheanodeandthecathode.Theexperimentsinvolvedapplyingalargevoltagetotheplatesandinvestigatingthepropertiesoftheraysinthetubeasafunctionofgaspressureetc.
What are Cathode rays ?ThisquestionwasinvestigatedbyJ.JThomson(UK,1856-1940)in1897.Thereare3famousphysicistsnamedThomson.1.WilliamThomson(1824-1907);AlsoknownasLordKelvin,knownfortheabsolutetemperaturescale.2.JosephJ.Thomson(1856-1940);ourguy,discoveryoftheelectron,proposedaplumpuddingatomicmodel3.GeorgeP.Thomson(1892-1975);SonofJ.JThomson,diffractionofelectronstoprovewavenature
Usingtheobservedeffectsofelectricandmagneticeldsonthecathoderays,J.J.Thomsonestimatedthecharge/massratio.FromtheresultsofFaradays(UK,1791-1867)LawofElectrolysis,Thomsonwasabletoestimatethatcathoderaysconsistedofnegativelychargedparticlesthatwereabout1800timeslighterthanhydrogen.Robert
Millikanmorepreciselymeasuredtheelectronchargein1909.
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Effect of the Electric FieldAvoltageisappliedacrossthedeflectionplatesinthetube.Iftheelectricfieldisassumedtobeuniform,thentheexpressionfortheelectricfield,Eis
E =
andtheelectronsexperienceaforcegivenby
F =
Theelectronbeamismadevisiblebycollisionsofgasatomsinthetubeandwiththemicascreen.
a) Draw a diagram showing the expected path of an electron after it enters
the electric field.
b) How can you tell if the charge on the particles is +ve or -ve?
Assumeanelectrontravelswithaninitialvelocity,v0inthehorizontal(x)directionandencountersauniformelectricfieldintheydirection.
c) In which direction is the force on the electron?
d) What is the shape of the curve traced out by the path of the electron?
electrongun
V
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Effect of the Magnetic FieldThemagneticfieldisgeneratedbyaHelmholtzcoilarrangement.
e) In what direction is the magnetic field when it intersects the electron beam?
Inthemagneticfield,theelectronsexperienceaforcegivenby
F =
f) In what direction is this magnetic force?
g) What is the shape of the curve traced out by the electron due to the force caused by the magnetic field?
Thismeansthatthemagneticforce(Bqvsin)actsasacentripetalforce:Fc=mv2
r
so,Bqvsin=mv2,andifis900thenBqv=mv2
rr
Byrearrangingtheaboveequationthecharge/massratio:q/m=
Theradiusofcurvature,risgivenbyr=(x2+y2)/(2y).Thiscanbemeasuredfromthegridscaleonthetube.Thevalueofris=............................
Charge to Mass Ratio1.EnsurethecurrentintheHelmholtzcoilsiszero(nomagneticeld).2.Switchontheelectriceld.3.IncreasethecurrenttotheHelmholtzcoilsuntilthecathoderaybeamattensout.Atthispointtheforcesfromthe
twoelds,actingonthecathoderaybeam,areequal.
ie,Felectriceld=Fmagneticeldor, Eq=Bqvsimplifyingthiswillgive E=Bvandrearrangingforv: v=E (Equation2) B
Adjustthecurrenttothecoilsuntilthetraceintersectsthecoordinate(10,0)onthegrid.Usethevalueofthecurrent,I,tocalculatethemagneticeld,B,by: B=0.00423Ih) Calculate the value of B from the given value of I.
i) Estimate the deflection plate separation from the grid scale. This is the value for d.
d=...................m.
Thepotentialdifferencebetweenthechargedplates,V,hasavalueof...........................V
j) Calculate the value of the electric field E using: E = V E = ............................Vm-1
d
k) Combine equations 1 and 2 by substituting for v in equation 1 and find the charge/mass ratio, q/m for a cathode
ray particle.
q/m =
l) What is the accepted value for q/m ?
(Equation1)
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MICHELSON-MORLEY EXPERIMENT
HSC Syllabus 9.2.4Describe and evaluate the Michelson-Morley attempt to measure the
relative velocity of the Earth through the aether
Gather and process information to interpret the results of the Michelson-
Morley experiment
What is the nature of Light?Around1800itwasthoughtthatlightwasawavebecauseitproducedinterferenceanddiffractionpatterns.Michelsons(in1879)calculatedthespeedoflight,usinganarclampandrotatingmirrors,tobe186,350milespersecond.
Like waves travelling through water it was thought that light must be similarly travelling in some mysterious material,
which was called the aether, surrounding and permeating everything even space. Since light travels so fast, the aether
must be very light and very hard to compress. It must also allow solid bodies to pass through it freely, without ether
resistance, or the planets would be slowing down.
How could the Aether be detected?Michelsonexplainedthepuzzletohischildrenasfollows:Suppose we have a river of width w (say, 100 units), and two swimmers who both swim at the same speed,(say, 5
units per second). The river is flowing at a steady rate, say 3 units per second. The swimmers race in the following
way: they both start at the same point on one bank. One (Joe) swims directly across the river to the closest point
on the opposite bank, then turns around and swims back. The other (Bob) stays on one side of the river, swimming
upstream a distance (measured along the bank) exactly equal to the width of the river, then swims back to the start.
Who wins?
Lets consider Bob who goes upstream and back. Going 100 units
upstream, the speed relative to the bank is only 2 units per second,
so that takes 50 seconds. Coming back, the speed is 8 feet per
second, so it takes 12.5 seconds, for a total time of 62.5 seconds.
Now Joe goes across the flow which is little trickier. To succeed in
going directly across, Joe must actually aim upstream at the correct
angle. If the angle is correctly chosen so that the net movement
is directly across, in one second Joe must have moved four units
across (see diagram). So, at a crossing rate of 4 units per second,
Joe gets across in 25 seconds, and back in the same time, for a total
time of 50 seconds so Joe wins. This turns out to true whatever theirswimming speed. (Of course, the race is only possible if they can
swim faster than the current!)A
CB
flow
vt
ct
Bank
river
Bank
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Michelsonthoughtthat just as the speed of sound is relative to the air, so the speed of light mustbe relative to the ether. So if you could measure the speed of light then you could measure the
speed of light travelling upwind, and compare it with the speed of light travelling downwind, and
the difference of the two measurements should be twice the windspeed.
The ExperimentLightisdirectedatanangleof45degreesatahalf-silvered,halftransparentmirror,sothathalfthelightgoesonthroughtheglass,halfisreected.Theybothgoontodistantmirrorswhichreectbacktothehalf-silveredmirror.Atthispoint,thelightisagainhalfreectedandhalftransmitted,butatelescopeisplacedbehindthehalf-silveredmirrorasshownintheguresothatthecombinedlightwillarriveinthistelescope.Now, if there is an ether wind blowing, someonelooking through the telescope should see the effect of a slightly longer time for the 2 light beams
to arrive, since one would have gone more upstream and back, one more across stream in
general.
Takingthespeedoflighttobecrelativetotheaether,andtheethertobeowingatv:
togoadistancelupstreamwilltake l/(c-v)secondsandldownstreamwilltake l/(c+v)seconds,thereforethetotalroundtriptakes2 l / (c (1- v2/c2))seconds.
We can safely assume the speed of the aether is much less than the speed of light,
otherwise it would have been noticed long ago, for example in timing of eclipses of
Jupiters satellites.
Thismeansv2/c2isasmallnumbersoweapproximatetheroundtriptimetogoupstreamanddownstreamtobe(2l/c)(1+v2/c2).FromPythagorastheorem,thecross-streamspeedis(c2-v2).Theroundtripcrossstreamtimewillbe2l/(c2-v2).Thiscanbeapproximatedas(2l/c)(1+v2/2c2).
Thetworoundtriptimesdifferbyanamount(l)(v2/c3).Now,2l/cisjustthetimethelightwouldtakeiftherewerenoaetherwindatall,say,afewmillionthsofasecond.Ifwetaketheetherwindspeedtobeequaltotheearthsspeedinorbit,thenv2/c2isabout1/100,000,000.Thismeansthetimedelaybetweenthepulsesreectedfromthedifferentmirrorsreachingthetelescopeisaboutone-hundred-millionthofafewmillionthsofasecond.Itseemscompletelyhopelessthatsuchashorttimedelaycouldbedetected.
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Michelsonwasthefirsttofigureouthowtodoitusingtheinterferencepropertiesofthelightwaves.Onesetofwavesgoesupstreamanddownstream,theothergoesacrossstreamandback.Finally,theycometogetherintothetelescopeandtheeye.Iftheonethattooklongerishalfawavelengthbehind,itstroughswillbeontopofthecrestsofthefirstwave,theywillcancel,
andnothingwillbeseen.Ifthedelayislessthanthat,therewillstillbesomedimming.However,slighterrorsintheplacementofthemirrorswouldhavethesameeffect.Tomaximizetheeffect,thewholeapparatus,includingthedistantmirrors,wasplacedonalargeturntablesoitcouldbeswungaround.
Observe how the interference pattern changes as the turntable is rotated through 90
degrees. What happens?
How does this change compare to that expected if there is an aether?
Why was the null result difcult to accept?
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WILSON CLOUD CHAMBERExtract from HSC Syllabus 9.8.3Perform a rst-hand investigation or gather secondary information to observe radiation emitted from a nucleus using Wilson
Cloud Chamber or similar detection device
Thecloudchamber,alsoknownastheWilsonchamber,isusedfordetectingparticlesofionisingradiation.Initsmostbasicform,acloudchamberisasealedenvironmentcontainingasupercooled,supersaturatedalcoholvapour.Whenanalphaparticleorbetaparticleinteractswiththemixture,itionizesit.Theresultingionsactascondensationnuclei,aroundwhichamistwillform(becausethemixtureisonthepointofcondensation).Thehighenergiesofalphaandbetaparticlesmean
thatatrailisleft,duetomanyionsbeingproducedalongthepathofthechargedparticle.Thesetrackshavedistinctiveshapes(forexample,analphaparticlestrackisbroadandstraight,whileanelectronsisthinnerandshowsmoreevidenceofdeectionbycollisions).Whenanyuniformmagneticeldisappliedacrossthecloudchamber,positivelyandnegativelychargedparticleswillcurveinoppositedirections,accordingtotheLorentzforcelawwithtwoparticlesofoppositecharge
(http://en.wikipedia.org/wiki/Cloud_chamber)
InthisdemonstrationwewilluseaDiffusionCloudChamber600(AndrewsUniversity,MI,USA)toobserveionizingradiationfromcosmicraysandalsofromaPb210source.
Pb210hastwodecaypaths.
(i) ItdecaystoHg206byemissionofa3.72MeValphaparticle.Hg206thendecaystoTl206bybetaparticleemission.
(ii) Pb210alsodecaystoBi210bybetaparticleemission.
Inbothdecaypathsgammaraysarealsoemitted.
Observe the tracks from the Pb210 source. Can alpha particle and beta particle tracks be identied?
Observe tracks when the source is removed. Where do those tracks come from?
Observe what happens to the tracks when a magnet is placed in the cloud chamber.
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THE PHOTOELECTRIC EFFECTExtract from HSC Syllabus: 9.4.2Explain the particle model of light in terms of photons with particular energy and
frequency.
Solve problems, analyse information and identify the relationship between photon
energy, frequency, speed of light and wavelength
Whenlightshinesonametalsurfaceelectronsareejected.Theenergycarriedawaybyeachelectrondependsonthefrequencybutnotontheintensityoflight.Therefore,lightcanbeconsideredtobeastreamofparticles(photons)ratherthanawave.
Theemittedelectronshavearangeofkineticenergies.Theelectronswithmaximumkineticenergyareemittedfromrightatthesurfaceafterhavingreceivedalltheenergy,E,fromthephoton.However,inleavingthesurfacetheelectronsloseanamountofenergy (calledtheworkfunctionofthesurface).
Read the above section and write down an expression for the maximum
kinetic energy of the electrons in terms of the photon energy E and workfunction .
Max kinetic energy = (1)
TheenergyofaphotonisgivenbyE=hf,wherePlancksconstanthis6.63x10-34JsandfisthefrequencyofthephotoninHzandc=f wherethespeedoflightcis3.00x108ms-1andthewavelengthofthephotonis .
Write down an expression for E in terms of . E = (2)
Combine (1) and (2) to write down a relation between maximum kinetic energy and
Maximum kinetic energy = (3)
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The Experiment Todeterminemaximumkineticenergyofemittedelectrons.
Thephototube(Fig2)istheessentialpartoftheinstrumentyouwilluse.Itisanevacuatedglasstubecontainingacoatedelectrode(cathode)shapedlikehalfofacylinder.Anotherelectrode(anode)intheformofastraightrodispo-sitionedatapproximatelythefocalpointofthecurvedsurface.Whenlightstrikesthecathodesurface,electronsareejectedandcollectedbytheanode.Thecolouredlters,placedintothelightpath,cutoffallwavelengthsaboveaparticularvalue,thereforetheminimumwavelengthoflightreachingthetubeisknown.Eqn3canthenbeusedtodeterminethemaximumkineticenergyoftheemittedelectrons.Tomeasurethehighestelectronenergyweapplyasmallreversevoltagecalledthebacking
voltage(iewithanodenegativeandcathodepositive)thatisjusthighenoughtocompletelystoptheowofelectronsreachingtheanode(absolutelyzerocurrent).
Note:Ifthebackingvoltageiscontinuedtobeincreased,thecurrentwillbegintoowbackwardsbecauseelectronsbegintoowfromtheanodetothecathode.
The Experimental Method
1. Havethedemonstratorchecktheequipment.Turnonthelight sourcelightsourcetoilluminatethephototubethroughthe
apertureintherearfaceoftheinstrument.Notethatthelight sourcewillbecomewarm. 2. Insertoneoftheltersintothewiderpairoftheslidegrooves providedinfrontofthelightsource. 3. Selecttube current onthemeter switchtomonitorthecurrent throughthephototube.Select the 0-20A range.
4. Usingthe backing voltagecontrol,adjustthevoltagefromzerovoltsuntilthecurrentthroughthetube reducesbelow 0.1 microamp.
5. Nowselectthesensitive 0-200nA range andincreasethebacking volts untiltheelectronowthroughthe tubeisreducedto0.0 nanoamps.Ifthecurrentgoesnegativereducethebacking volts until0.0 nanoamps isachieved.Atthispointthemostenergeticelectronsarepreventedfromreachingtheanode.
Fig 3
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6. Withoutdisturbinganything,selectbacking voltsonthemeter switchandobservetheexactvoltagethat isbeingappliedtothephototubeinreversetostopallelectronsfromreachingtheanode.Recordthis backingvoltageintable1.
7. Removethecolourlterandrepeattheexperimentfromsteps3to7fortheremainingcolourlters.
8. Usingthewavelengthvaluemarkedonthebluelter,calculatethefrequency(inHertz)ofthelighttransmitted bythislterandenteritintotable1.Recordyourmeasurementsofbackingvoltageintable1.
9. PlotagraphofthefrequencyinHz(Xaxis)againstthebackingvoltsinVolts(Yaxis)usingthesupplied graphpaper.
Table1
Filter Wavelength
(nm)
Frequency
f=c/ (Hz)
BackingVolts
(V)blue 450
yellow 480 6.25x1014
orange 545 5.50x1014
red 590 5.08x1014
Discussion
Thestoppingvoltageisrelatedtothemaximumkineticenergyoftheelectronssinceiftheelectronshavemoreen-ergyitwillrequirealargervoltagetostopthem.
So which colour light generates electrons with the highest kinetic energy?
Which colour light generates electrons with the lowest kinetic energy?
Is this expected from equation 3?
What can we say about the slope of the line in this graph?
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The intercept on the Y axis is related to the workfunction of the cathode. Using eqn 1, determine the work-
function of the cathode in eV.
What is the metal cathode surface most likely made from? Use the list workfunctions on the graph paper to
determine your answer.
Extension
Withtheredlterselected,placeanapertureinthelightpathtoreducetheintensityoflight.
Does this markedly change the backing volts? Is this result expected?
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REFERENCE FRAMES
Extract from HSC Syllabus 9.2.4Students perform an investigation to help distinguish between inertial and noninertial
frames of reference
Areferenceframewhichmovesatconstantvelocitywithrespecttoanotheriscalledaninertialreferenceframe.Forcesactthesamewayinthisframeasintheoriginalframe.Intheexperimentbelow,acartcarryingapendulumsitsonaninclinedplane.
Intheframeofthecartthependulumhangsdirectlydown,ifthecartisstationary.Predicthowthependulumhangsifthecartismovingdownthetrackatconstantvelocity.
Is this what happens experimentally?
Ifthecartismovingatconstantvelocitywehaveaninertialframeofreference.ThebehaviourofinertialframeswasdescribedinEinsteins
specialtheoryofrelativity.
Butwhathappensiftheframeisacceleratingi.e.ifwehaveanon-inertialframeofreference?So how should the pendulum hang if the cart is accelerating down the
track? Should it
(i) hang straight down
(ii) hang perpendicular to the incline or
(iii) in some other direction?
Is this what happens experimentally?
Wecanexplainthisbehaviourbysayingthat (i)Newtonslawsdontworkinanacceleratingframeofreferenceor (ii)thatweneedextractitiousforcestomakeNewtonslawswork.
Newtonsprincipleofequivalencesaysthatphysicscanbeexplainedinacceleratingframesbytheuseofgravitationalforces. In what direction shouldgravity point in the carts frame of reference to explain the position of the
pendulum?
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SUPERCONDUCTIVITY
Extract from HSC Syllabus 9.4.4Process information to identify some of the metals, metal alloys and compounds that have been identified as exhibiting
the property of superconductivity and their critical temperatures
Process information to discuss possible applications of superconductivity and the effects of those applications on
computers, generators and motors and transmission of electricity through power grids
Discuss the advantages of using superconductors and identify limitations to their use
Gather and process information to describe how superconductors and the effects of magnetic fields have been
applied to develop a maglev train
Process information to discuss possible applications of superconductivity and the effects of those applications oncomputers, generators and motors and transmission of electricity through power grids
Earlyinthe20thcentury,DutchphysicistHeikeKamerlinghOnnesobservedthatmercurydisplayednoelectricalresistancewhencooledtoverylowtemperatures.Superconductivitybecameascienticcuriositywithfewpracticalapplications.Theninthe1960sapracticalsuperconductingmetalwiremadeofniobiumandtinwasdeveloped.Theniobiumandtitaniumalloy,stillinusetoday,isamongthematerialscalledlow-temperaturesuperconductors.
Low-temperaturesuperconductorsmustbecooledtobelow20Kelvin(-253oCelsius)inordertobecomesuperconducting.Theyarenowwidelyusedinmagneticresonanceimaging,orMRI,machines,andintheeldsof
high-energyphysicsandnuclearfusion.Additionalcommercialusehasbeenlimitedlargelybythehighrefrigerationcostsassociatedwithliquidhelium,whichisneededtocoolthematerialstosuchlowtemperatures.
Thehopeforlow-costsuperconductivitywasignitedbytwosignicantdiscoveriesinthe1980s.In1986,twoIBMscientistsinZurich,AlexMullerandGeorgBednorz,discoveredanewclassofsuperconductors.Unlikethelow-temperaturesuperconductors,whichweremetallicorsemimetallic,thesenewcompoundswereceramicandweresuperconductingupto35K(-238oC).MullerandBednorzwonaNobelPrizefortheirdiscovery.Thenin1987,PaulChuattheUniversityofHoustontookthediscoveryonestepfurtherandannouncedacompoundthatbecamesuperconductingat94K(-179 oC).Thisdiscoverywasparticularlysignicantbecausethiscompoundcouldbecooledwithcheapandreadilyavailableliquidnitrogen.Thesenewmaterialswerecalledhigh-temperaturesuperconductors.
Bismuth-basedcompoundsarebeingfashionedintosuperconductingwiresandcoils,whicharebecomingessentialtoelectricpoweruses.Thallium-andyttriumbasedcompoundsarebeingformedintothethinlmsusedinelectronicdevices.Identify metals, alloys and compounds used as superconductors and their critical temperatures.
metals, metal alloys and compounds critical temperatures
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Some current uses of Superconductors1. Powertransmissioncablesthatcarrycurrentwithoutenergylosseswillincreasethecapacity
ofthetransmissionsystem,savingmoney,space,andenergy.PrototypepowertransmissioncableshavebeendevelopedandarebeingtestedbyteamsledbyPirelliCableCompanyand
SouthwireCompany.2. Motorsmadewithsuperconductingwirewillbesmallerandmoreefficient.A1,000-horsepowermotorhasbeenconstructedandisundergoingtestingbyanSPIteamledbyRockwellAutomation/RelianceElectricCompany.
3. Generatorswillusesuperconductingwireinplaceofironmagnets,makingthemsmallerandlighter.Newgeneratorsalsomaygetmorepowerfromlessfuel.AnSPIteamledbyGeneralElectrichasdevelopedadesignfora100-megavoltamperegenerator.
4. Currentcontrollers(i.e.,fault-currentlimiters)helputilitiesdeliverreliablepowertotheircustomers.HTSfault-currentlimitersdetectabnormallyhighcurrentintheutilitygrid(causedbylightningstrikesordownedutilitypoles,forexample).Theythenreducethefaultcurrentsothesystemequipmentcanhandleit.AnSPIteamledbyGeneralAtomicsrecentlyproducedasuccessfulHTSfault-currentlimiterthatwillsoonbereadytomarket.
5. Energystorageinflywheelsystemswillensurethequalityandreliabilityofthepowertransmittedtoutilitycustomers.Inaddition,energystorageprovidesutilitieswithcostsavingsbyallowingthemtostoreenergywhenthedemandforelectricityislowandgeneratingthepowerischeap.Thisstoredenergyisthendispensedwhendemandishighandpowerproductionismoreexpensive.
6. Magneticresonanceimaging(MRI)machinesenhancemedicaldiagnosticsbyimaginginternalorgansofteneliminatingtheneedforinvasivesurgeries.MRIs,whichcurrentlyaremadewithlow-temperaturesuperconductors,willbesmallerandlessexpensivewhenmadewithHTS.
7. Maglevtrainsseemtofloatonairasaresultofusingsuperconductingmagnets.ThesetrainshavebeenunderdevelopmentinJapanfortwodecades;thenewestprototypemayexceed
547kilometersperhour.
Discuss possible applications of superconductors and the effect of those applications as
well as advantages or limitations of superconductors
applications of
superconductivityeffects advantages or limitations
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ExperimentPerformaninvestigationtodemonstratemagneticlevitationAnalyseinformationtoexplainwhyamagnetisabletohoveraboveasuperconductingmaterial
thathasreachedthetemperatureatwhichitissuperconducting
Observe the demonstrator fill the foam container with liquid nitrogen to slightly cover the
superconductor and let the liquid nitrogen boil off until the surface is uncovered the
Yttrium Barium Copper Oxide (YBCO) sample will be near 77K and superconducting. Place
the magnet on the superconductor and observe that it is levitating. Observe what happens
when the nitrogen all boils off and the sample warms up.
What happens?
ExplanationSuperconductorsexcludemagneticelds,apropertycalledtheMeissnereffect.Thiseffectcausesasmallmagnettolevitateabovethesuperconductorsurface.Asthemagnetisbroughttowardsthesuperconductor,currentloopsaresetupinthesuperconductorwhichgeneratemagneticeldstoopposethemagneticeldcreatedbythemagnet.Theeldsetupbythesuperconductorwillpropagateoutsidethesuperconductorandcausethemagnettolevitateeventhoughthemagnethascometoastopabovethesuperconductorsurface.Thisisbecausethesuperconductorhaszeroresistanceandsothecurrentswillcontinuetoowafterthemagnethas
stopped.
Thelevitatingmagnetdoesnotslideoffthesuperconductor.ThisisamanifestationofFluxPinning,aphenomenaassociatedwithTypeIIsuperconductors,suchashightemperatureceramicsuperconductors.Herelinesofmagneticuxassociatedwithamagnetcanpenetratethebulkofthesuperconductorintheformofmagneticuxtubes.Theseuxtubesarethenpinnedtoimperfectionsorimpuritiesinthecrystallinematrixofthesuperconductortherebypinningthemagnet.
RareearthmagnetSuperconductorYBa2Cu3O7
Inducedcurrents
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PROJECTILE MOTION UNIFORMLYACCELERATED MOTION IN TWOSPATIAL DIMENSIONSExtract from HSC Syllabus: 9.2.2Describe the trajectory of an object undergoing projectile motion within the Earths gravitational field
Perform a first hand investigation, gather information and analyse data to calculate the initial and final velocity,
maximum height reached, range and time of flight of a projectile for a range of situations by using simulations,
dataloggers and computer analysis
Inphysicsweclassifydifferenttypesofmotionsothatwecanpredictwherethingswillendup.Usually,studyofmotioninphysicsbeginsbyconsideringdistanceandspeedwhere
Distance = speed x time (1)
Thiswillpredictacarsdistancetravelledprovidedthecarneitherspeedsupnorslowsdown,i.e.foraconstantspeed.Speedisascalarquantity(itonlyhasasizeormagnitude).Ifwegivethespeedadirectionaswellasamagnitudethenwemakeavectorquantitycalledvelocity.Distanceisalsoascalarquantitywhiledisplacementisavectorquantity.
Ifthecaracceleratesuniformlywithacceleration,a,thenthedistancetravelledinatime,t,is
Distance = ut + at2 (2)
Equation(2)alsoallowsforthecasewherethecarhasaninitialconstantspeed,u,andthenaccelerates.Wenowhavethemainingredientsforexaminingmotionontwodimensions.Accelerationandforcearerelatedtothemassoftheobject,i.e.itismoredifculttomoveaheavyobject.Gravityprovidesaforceintheverticaldirectionandwellcalltheverticaldirection,y.Projectilemotionisviewedintwodimensionsasthecombinationoftwocomponentmotions,oneinthehorizontal,thexdirection,andtheotherintheverticalortheydirection.
Equations1and2arethebasis(inphysics)ofprojectilemotion.Equation(1)describesmotionalongthehorizontalwhiletheainequation(2)istheaccelerationduetogravity.
Thefollowingtableshowsthequantitiesusedinthehorizontalandverticalcomponentsofprojectilemotion,asvectorsorscalars.
Vectors Scalars
DisplacementxandyInitialvelocityu
xandu
y
Finalvelocityvxandv
y
Accelerationax
anday
Time
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Thevectorcomponentsrequiretheuseofpositive(+)andnegative(-)signstoshowthedirectionoftravel.Arbitrarilywechoseapositive(+)signformotioninanupwardorverticaldirectionandaminus(-)signformotioninthedownwardsorhorizontaldirection.
Usingthesymbolsfromthetableequations1and2become:
x=uxt (3)
y=uyt+a
yt2 (4)
Typicallyforprojectilemotionay=-gwhereg=9.8ms-2.Thenequations(3)and(4)canbesolvedtodeterminethe
maximumheight,H,reachedandthemaximumhorizontaldistance,R,travelledbeforetheobjectreturnstoitsoriginalheight. H=u
y2/2g (5)
R=2uxuy/g (6)
Inthisexerciseyouwillbeabletoexamineavideoofprojectilemotion.Thecomputersoftwareallowsyoutoobtainthex,ycoordinatesofasoftballatvarioustimesduringthemotion.Fromthesedata,variousphysicalquantitiescanbestudiedastheballtracesoutprojectilemotion.Bynow,youwouldhavecompletedaunitonprojectilemotionatschool.
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Section AByaskingmembersinyourgroup,writeshortanswerstothefollowing:Asoftballisthrownfromoneplayertoanother.
What shape does the ball trace out in space? Can you show (mathematically) why?
Does the energy of the ball change during the motion? How does the friction from the air affect the energy of
the ball?
What is the relationship between the potential and kinetic energies of the ball?
Does the momentum of the ball change? In what way?
Does the acceleration of the ball change?
Would there be any difference in plots of the balls position compared with its displacement?
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Section BThevideosoftwareiscalledWorldinMotionandyoushouldseeashortcuttowimonthecomputerscreen.Thissoftwareisgreatforanalysingvideofootagebutratherpoorinpresentingthevariousoptions,navigationandinformation.Itiseasytogetlost!
Herearethestepsyouneedtogettoplayandanalysethevideo:1.Afterstartingthesoftware,thecomputerscreenshouldlooksomethinglikethis;
2.YoucanusethesymbolseithersideofHistorytonavigate
3.ClickontheProjectileMotionoptionintheleftmenu
4.ChooseVideoExperimentsSet1
5.Clickinthee1710.htmtext
6.Bynow,youshouldseethefirstframeofthevideowithoptionsontheright
7.ClickonMarkingtheVideofollowedbyClickHeretoopenthevideo
8.Youhavearrivedatthevideomarkingenvironment.ClickonPlaytoseethefootage.YoucannowuseSteptosee
theimagesoneframeatatime.
9.Movingthemouseovertheimagechangesthecursortoanarrow.Leftmouseclickandyoucandigitisethe
positionoftheball
10.Whenyouhavedigitisedthroughthewholemotion,clickonGraph>>,followedbyNext
11.ChooseObjectmovinginXandYdirections,andYisVertical,Next
12.Selectalltheplotsavailable,Next
13.Thescreenshouldnowlooklikethis:
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Onthisscreen,clickonGraph>>
Thefirstgraphispositionversustimeintermsofxandycomponentsandthevectorresultant.In the space below draw the graphs you see on the screen and explain the brown (X) and green (Y) curves.
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Thenextgraphisdisplacementwithtime.On the following axis draw the graphs shown on the screen.
What are the differences between this and the position versus time graph?
The gradient of this graph will allow you to nd what property of the motion?
Thenextgraphisvelocity.Draw the velocity/time graphs on the following axis.Notethestraightatlineforthexcomponent.
Why is the y component a straight line? Isnt the ball accelerating in this direction?
What is the numerical value of the slope of the green (vy) line?
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Thenextgraphisthemomentum.Draw the graph on the following axis. Which other graph does it look likeand why?
Finally,theaccelerationisshown. Draw the acceleration/time graph on the following axis.Notethatthexcomponentisclosetozerowhiletheycomponentisnear9.8m/s2.
Calculate values for the maximum height, H, reached (above the original starting height) and the
range, R, and compare your values to the results from equations 5 and 6.