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TheLaboratory

ClosedEndAirColumnLab

Teacher'sGuide Topic: SoundandMusic

Thefollowinginformationisprovidedtothestudent:

Question: Whatisthespeedofsound?(closedendaircolumn)

Purpose: Todeterminethespeedofsoundusingaclosedendaircolumn.

AcompletelabwriteupincludesaTitle,aPurpose,aDatasection,aConclusionandaDiscussionof Results.TheDatasectionshouldincludecollecteddata;datashouldbeorganizedandlabeled(a diagrammaybemoreusefulthanatable).Calculationsofspeedshouldbeorganized,labeledand clearlyshown.Fudgefactoradjustmentsforendeffectshouldbemade;workshouldbeshownand labeled.ClassdatashouldbeincludedintheDatasection.TheConclusionshouldrespondtothe questionraisedinthePurposesection(asalways).TheDiscussionofResultsshouldincludeanerror analysis.Thereliabilityoftheresultsshouldbeevaluatedbaseduponthetheoreticalvalueforthe speedofsound.Apercenterrorcalculationshouldbeperformed;labeledworkshouldbeshown. MaterialsRequired: Tuningfork;tuningforkactivator;hollowtube(atleast30cminlength);longcylinderordeep containerofwater;meterstick;thermometer. DescriptionofProcedure: Thehollowtubeisimmersedinacylinderofwater.Atuningfork(ofknownfrequency)isstrucksoas tovibrate.Thetinesofthevibratingforkareheldabovetheopeningtothehollowtube.Thetube(and thetuningfork)areslowlyraisedabovethewaterlevelinthecylinder,creatingaclosedendcolumnof airinsidethehollowtube.Thehollowtubeisraisedtoapositionwherethevibratingtinesforcetheair columntoresonateatthesamefrequencyasthetuningfork.Oncethispositionisdetermined,the lengthoftheaircolumnismeasured.Thefrequencyofthetuningforkisrecorded.Thetemperatureof theroomismeasuredforthepurposeofcalculatingatheoreticalvalueforthespeedofsound. AlternativeMaterialsandProcedure: Onemeansofadjustingthelengthoftheaircolumninthehollowtubeinvolvestheuseofaonehole stopper,ahollowglasstube,somerubberhosingandamilkjugofwater.Aoneholestopperisinserted intotheendofthehollowtube.Theglasstubeisinsertedthroughtheholeofthestopper.(Thismustbe donewithgreatcaresoastoavoidpiercingone'shandwithbrokenglassiftheglasstubebreaks. Studentsshouldnotbeallowedtodothisstep;itshouldbedoneforthembytheteacherpriortoclass.) Thesamestopper/glasstubearrangementisaddedtothemilkjug.Thejugisfilledwithwater.The glasstubesofthehollowtubeandthemilkjugareconnectedwithrubberhosing.Themilkjugis invertedsothatitswaterflowsintothehollowglasstube.Asthemilkjugisraisedandlowered,the waterlevelinthehollowtubeisraisedandlowered.AdiagramofthisapparatuscanbefoundinThe PhysicsClassroomTutorial:http://www.physicsclassroom.com/Class/sound/u11l4b4.gif.

©ThePhysicsClassroom,2009

TheLaboratory SafetyConcern: Thereisalwaysahigherthanusuallevelofriskassociatedwithworkinginasciencelab.Teachers shouldbeawareofthisandtakethenecessaryprecautionstoinsurethattheworkingenvironmentisas safeaspossible.Studenthorseplayandofftaskbehaviorsshouldnotbetolerated. Suggestions,Precautions,Notes: 1. 2. Tuningforksshouldneverbestruckonhardsurfaces.Strikingitonorwithsoftrubberwill preservethefrequencyofthetuningfork.Alighttaponarubbershoesoleusuallysetsitinto vibration. Endeffectscausethevibrationalantinodetobelocatedjustabovetheopenendofthehollowtube. Theeffectivelengthoftheaircolumnislongerthanthemeasuredlengthbyanamountequalto 4/10thsofthetube'sdiameter.Thiscorrectionfactorshouldbeincludedinthecalculationsinorder toimprovetheresults. Poolingclassresultsforthespeedofsoundisausefulmeansofallowinglabgroupstohave feedback.Italsocanbemadeintoalessononthenatureofscienceasacooperativeventure.

3.

AuxiliaryMaterials: None ScoringRubric: S4. ClosedEndAirColumnLab Included,labeledandorganizedallpartsofthelabreport. Datasectionincludesadiagramwithorganizedandlabeleddata;unitsare shown.Workforspeedcalculationisshownandlabeled;adjustmentsfor endeffectisshownandlabeled.Classdataisorganizedinatable. Individualresultsarereasonablyaccurate(aftercorrectingfortheend effect). Conclusionstatestheexperimentallydeterminedspeedofsoundinair. DiscussionofResultsincludesawellwrittenerroranalysis;experimental valueforsoundspeediscomparedtothetheoreticalvalue.Apercenterror calculationisperformed;workisclearlyshownandlabeled. Score _____/_____

ConnectionstoThePhysicsClassroomTutorial: Thefollowingreadingisasuitableaccompanimenttothislab: http://www.physicsclassroom.com/Class/sound/u11l5d.cfm ConnectionstoMindsonPhysicsInternetModules: Sublevels10and11oftheSoundandMusicmodulearesuitableaccompanimentstothislab: http://www.physicsclassroom.com/mop/module.cfm

©ThePhysicsClassroom,2009

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