北郵大學(xué)物理演示實(shí)驗(yàn)報(bào)告

TheReportOftheCollegePhysicsExperimentExperiment1:opticallevermirrormethodtomeasureYoung'smodulusofthemetalPurpose:1.Mastertheprincipleofmeasuringthesmalllengthchangeswithopticallevermirror.2.Learnhowtoeliminatethesystematicerrorswithsymmetricmeasurement.3.Learnhowtoestimatetheerrorstoeachmeasuredvalueinaccordancewiththeactualsituation.4.Traintodealdatawithdifferentmethodsandconstruction.Theory:Objectsshouldengenderdeformationmoreorlessbytheexternalforce.Itistheelasticdeformationwhichwilldisappearpromptlyafterwithdrawingtheexternalforcewhentheforceisnomorethanacertainlimits.Theobjectswillrestorearestitutedinternalstressafteroccurringelasticdeformation.ThereisasectionS,lengthL0oftheequablyrod-like(wire-like)material,whenitstretchedbythepullingforceF,itelongates,stressismeasuredastheforceperunitcrosssectionalareaof;andstrainistheincreaseinlengthofunitlengthof.AccordingtoHook’sLaw,thestrainrod-like(wire-like)materialburdenedisproportionaltotheburdenedstress:Fig.1theopticalleverWhereYisthecoefficientdependedonthecharacterizationofthematerials.ThemodulusisthenFig.1theopticalleverknownasYoung’smodulus(Y).andhence:(1)ThisexperimentistomeasuretheYoung’smodulusofakindofmodelsteel,inwhichFcanbedeterminedbythecalculatedweightofweight,sectionalareaScanbegetbycalculatingthediameterofthewiremeasuredwithmicrometerscrewgouge,canbemeasuredbyconventionalmeasurementapparatussuchasmeterandsoon.Butisdifficulttomeasureaccuratelyforitssmalllengthchangeusedordinaryapparatus.Sowechooseamplification——“opticallevermirror”tomeasurethissmallchange.TheopticallevermirrorphysicaldiagramisFig.1DbMΔn=n-nOFig.2theprincipleofopticallevermirrorFig.2istheprinciplechartofmeasuringthetinylengthchangebyopticallevermirror.Theleftcurledobjectistheopticallevermirror,Misareflector,bistheso-calledshort–opticallevermirrorarmlength,Oisfixed-sideofb-side,theothersidebwillriseorfallwhenthemeasuredobjectelongatingorshortening,andchangethedirectionofnormallineofM.Theoriginalwirelengthis,fromtherightadjustedtelescopewecanseethereadingofscaleimagineofMof,whilethesteeliselongated,fromthetelescopewecanseethereadingofscaleimagineofM:.Inthisway,thetinywireelongationis,thecorrespondinganglechangeoftheopticallevermirroris,andthereadingchangeofscaleimagineofMis.Bereversiblebytheopticalpaththatlightleverangleshouldbe.UsingthegeometricmethodinFig.2wecanget:(2)(3)Hence(4)Where,equivalenttothedisplacementofthelongarmofopticallevermirror.isthemagnificationofopticallevermirror,asDb,sonL,thatmeanswegetlinearamplificationofthesmallamount,andenhancethemeasurementaccuracyof.Thismeasurementisknownasamplification.Thisamplificationhasawiderangeofapplicationsindesigningallkindsoftestingequipmentforitsadvantageofstableperformance,highprecision,linearamplificationandsoon.Takingintoaccountthewirebytheexternalforcethereisalageffectofflexibility,astosaythatthesteelcan’tbedueimmediatelytotheelongatedlengthof()whenitiselongated,butonlytotheelongationof.Similarly,thesteelcan’tbereducedtothelengthofLiwhenoncethestretchingforceofthewirehasbeenreduced,butonlyreducedto.Thereforethemeasuredlengthofthewirebytheexperimentisnottheactualelongatedorcontractedlength.Inordertoeliminatethesystematicerrorsbythelageffectofflexibility,themeasurementshouldbeincludedasymmetricalmeasurementprocessofincreasingthetensilestrengthandreducingthetensilestrength.Totheexperiment,wecangetthistoincreaseorreducetheweights,wecantakeaverageamountofthestretchingofwireaslongasincreaseorreduceacorrespondingweighttoeliminatetheeffectsoflaggedvolume.Thatis:Procedure:(1)Attach2kghangerforweightstoendofthewiretoremoveanyirregularities.AdjustthethreefootscrewsundertheYoung’smoduluschassis,andobservethestandardrulerontheplatformatthesametimeuntilthemiddleoftheplatformisatthelevelofstate.(2)Regulatethelocationoftheopticallevermirror.Taketheopticallevermirrorontheplatform,thetwofrontfeetonthecross-platform,therearfootonthecylindricalcasingofthelowerendofthefixedwire(therearfootmustbeplacedontheedgeofthemetalcasing,butnotonthelocationofthegap),andletthemirrorofopticallevermirrortobebasicverticalorslightangle,asshowninFig.1.(3)Adjustthetelescope.Placethetelescopeabout2mawayfromtheopticallevermirror.Loosethefixedscrewoftelescopeandmoveupordowntoletthemirrorofopticallevermirrorandthetelescopeareonthesameheight.Takeaimatthemirrorofopticallevermirroralongthetubeaxisabovethetelescope.Shiftthefixedpositionofthetelescopeuntilwecanseethescaleimaginefromtheopticallevermirror.Andthenobservefromtheeyepiece.Adjusttheeyepiecetoseethecrosswireclearlyandfinallyrevolvethefocusinghandwheeltoflexiblethetelescopeinthetubeuntilwecanseetherulerscaleclearlyfromthetelescope.(4)Observethestretchchange.Attach2kghangerforweightstotheendofthewireasthebeginning,andtakethetelescopereadingof.Loadthemeasuredwirewithsuccessivekilogramweights,takingthetelescopereadingaftereachaddition——.Unloadkilogrambykilogram,andreadthetelescopeateachstage——.Note:Addorsubtracttheweightlightlytoavoidarelativelylargevibration.Afteraddingorsubtractingtheweight,thewirewillhaveascalablemicro-vibration,andweshouldreadafterthesteelgraduallybecomingstable.(5)Measurethedistancebfromthefrontfoottotherearfootofopticallevermirror.Rentthe3feetoftheopticallevermirrorinwhitepaper.Drawtheconnectionofthetwofrontfeetandthenmeasuretheverticaldistancefromtherearfoottothelinewiththevernierscale.(6)Measurethediameterofthewireatseveralpointsabout3-5timesalongitslengthandfindameanvalue.Thismeasurementmustbedonecarefullywithamicrometerscrew-gaugeandnotethezeroerroreachtime.(7)UsemeterrulertomeasurethedistanceDfromtheplanemirrortothescale.(8)Usemeterrulertomeasuretheoriginallengthofwire.(9)Notes①Thewiremustbeclampedtightlyatthebothside,atonehandtoreducethesystemerror,andattheotherhandtoavoidfallingdowntodamagethetestdevices.②Don’tmovethetelescopeandthetableinthemeasuringandreadingprocess,oryoumuststartmeasuringagain.③Keepthemeasuredwirestraightsoastoavoidmisusingthemeasuringprocessfortheelongation,resultinginmeasurementerror.④Keepingtheweightshouldbe1kganddon’ttouchthemirrorinthemeasuringprogress.⑤Youmustadjustthetelescopeinacertainscopetoavoiddamagingit.DataandtheresultsKG△x=0.05CM鏡尺距(hedistancefromtherulertothemirror)D=150mm;△x儀=0.05CMT