UNIT 9

Sound

APUnit9:Sound-ExamplesandTryThisProblems

Ex.1Determinethespeedofsoundinairatatemperatureof37oC.

TryThis1:Thespeedofsoundonacertaindayis343m/s.WhatisthetemperatureindegreesCelsius?

Ex.2

Ans.a)70dBb)73dBc)

TryThis2:

Ex.3

Ans.a)b)c)

TryThis3:

Ex.4

Ans.566Hz

TryThis4:

Ex.5

Ans.a)475Hzb)339Hz

TryThis5:

Ex.6

TryThis6:

Ex.7

a) b) c)

TryThis7:

Ex.8

a) b)

TryThis8:

Ex.9A certain piano string is supposed to vibrate at a frequency of 4.40 x 102 Hz. To check its frequency, a tuning fork known to vibrate at a frequency of 4.40 x 102 Hz is sounded at the same time the piano key is struck, and a beat frequency of 4 beats per second is heard. (a) Find the two possible frequencies at which the string could be vibrating. Ans. 444 Hz. and 436 Hz

TryThis9:The assistant adjusts the tension in the same piano string, and a beat frequency of 2.00 Hz is heard when the note and the tuning fork are struck at the same time. (a) Find the two possible frequencies of the string. Ans. (a) 438 Hz, 442 Hz

Unit9Problems:Sound

Video9.1-SoundasaWave,SpeedofSound,SoundIntensity,Decibels,SphericalWavesUnless otherwise stated, use 345 m/s as the speed of sound in air.

1.ThecoldestrecordedtemperatureofaironEarth,128.6°F,occurredonJuly21,1983,atVostok,aRussian

stationinAntarctica.Whatisthespeedofsoundinairatthistemperature?(Ans.272m/s)2.Agroupofhikershearsanecho3saftershouting.Ifthetemperatureis22

oC,howfarawayisthemountain

thatreflectedthesoundwave?(Ans.516m)3.Asoundwavetravelinginairat65

oChasafrequencyof845Hz.Find(a)thewavespeedand(b)the

wavelength.(Ans.a)368m/sb).436m)4.Theintensitylevelproducedbyajetairplaneatacertainlocationis150dB.Calculatetheintensityofthe

soundwavegeneratedbythejetatthislocation.(Ans.1000W/m2)5.Theareaofatypicaleardrumisabout5.0x10

-5m

2.Calculatethesoundpower(theenergypersecond)

incidentonaneardrumat(a)thethresholdofhearingand(b)thethresholdofpain.

(Ans.a)5x10-17Wb)5x10-5W)6.Anoutsideloudspeaker(consideredasmallsource)emitssoundwaveswithapoweroutputof100W.(a)

Findtheintensity10.0mfromthesource.(b)Findtheintensitylevelindecibelsatthatdistance.(c)Atwhat

distancewouldyouexperiencethesoundatthethresholdofpain,120dB?

(Ans.a).0796W/m2b)109dBc)2.82m)

Video9.2-DopplerEffect,Interference,StandingWavesonaString

7.Anairplanetravelingathalfthespeedofsound(v=172m/s)emitsasoundoffrequency5kHz.Atwhat

frequencydoesastationarylistenerhearthesound(a)astheplaneapproaches?(b)Afteritpasses?

(Ans.a)10kHzb)3.33kHz)

8.Twotrainsonseparatetracksmovetowardeachother.Train1hasaspeedof130km/h,train2aspeedof

90.0km/h.Train2blowsitshorn,emittingafrequencyof500Hz.Whatisthefrequencyheardbythe

engineerontrain1?(Ans.595Hz)9.Abatflyingat5m/sischasingainsectflyinginthesamedirection.Ifthebatemitsa40-kHzchirpand

receivesbackanechoat40.4kHz,whatisthespeedoftheinsect?(Takethespeedofsoundinairtobe340

m/s.)(NOTE:Thisisachallengingproblem!)(Ans.3.31m/s)10.Astretchedstringfixedateachendhasamassof40.0gandalengthof8m.Thetensioninthestringis

49.0N.(a)Determinethepositionsofthenodesandantinodesforthethirdharmonic.(b)Whatisthe

vibrationfrequencyforthisharmonic?(Ans.a)Nodesat0m,2.67m,5.33m;Antinodesat1.33m,4m,6.67mb)18.6Hz)11.Asteelwireinapianohasalengthof0.7mandamassof4.3x10

-3kg.Towhattensionmustthiswirebe

stretchedsothatthefundamentalvibrationcorrespondstomiddleC,frequency261.6Hz?(Ans.824N)

Video9.3-Resonance,StandingWavesinAirColumns,Beats,SoundQuality

12.Thewindpipeofatypicalwhoopingcraneisabout5.0ft.long.Whatisthelowestresonantfrequencyof

thispipe,assumingitisclosedatoneend?Assumeatemperatureof37oC.(Ans.58Hz)

13.Apipeopenatbothendshasafundamentalfrequencyof300Hzwhenthetemperatureis0

oC.(a)What

isthelengthofthepipe?(b)Whatisthefundamentalfrequencyatatemperatureof30oC?(Ans.a).552m

b)316Hz)14.Twoadjacentnaturalfrequenciesofanorganpipearefoundtobe550Hzand650Hz.Calculatethe

fundamentalfrequencyandlengthofthispipe.(Usev=340m/s.)Determinewhetherthepipeisopenatboth

endsoropenatonlyoneend.(Ans.50Hz;1.7m;Closedatoneend)

15.Twopipesofequallengthareeachopenatoneend.Eachhasafundamentalfrequencyof480Hzat300K.

Inonepipetheairtemperatureisincreasedto305K.Ifthetwopipesaresoundedtogether,whatbeat

frequencyresults?(Ans.3.98Hz)16.TheGstringonaviolinhasafundamentalfrequencyof196Hz.Itis30cmlongandhasamassof.5g.

Whilethisstringissounding,anearbyviolinistshortenstheGstringonheridenticalviolinuntilabeat

frequencyof2Hzisheardbetweenthetwostrings.Towhatlengthdidsheshortenherstring?(Ans.29.7cm)

ConceptualQuestions:Sound

1.Anautofocuscamerasendsoutapulseofsoundandmeasuresthetimetakenforthepulsetoreachan

object,reflectoffofit,andreturntobedetected.Canthetemperatureaffectthecamera’sfocus?

2.Explainhowthedistancetoalightningboltcanbedeterminedbycountingthesecondsbetweentheflash

andthesoundofthunder.

3.Asoftdrinkbottleresonatesasairisblownacrossitstop.Whathappenstotheresonantfrequencyasthe

leveloffluidinthebottledecreases?

4.Anairplanemechanicnoticesthatthesoundfromatwin-engineaircraftvariesrapidlyinloudnesswhen

bothenginesarerunning.Whatcouldbecausingthisvariationfromloudtosoft?

5.Whydoesavibratingguitarstringsoundlouderwhenplacedontheinstrumentthanitwouldifallowedto

vibrateintheairwhileofftheinstrument?

Unit9LabActivity

Inthislabactivityyourgroupwillstudyresonantfrequenciesofatubeopenatoneend.

Materials:1)PlasticTube

2)ContainerofWater

3)MeterStickorRuler

4)TuningForks

ProblemStatement:

Yourtaskistopredictthelengthoftuberequiredtocreatearesonanceforseveraldifferentfrequenciesof

tuningforks.YouwilluseagivenlengthofPVCtubingwhichmaybeimmersedinwatertovaryingdepths,

thuseffectivelycreatingatubethatisclosedatoneendwhoselengthyouareabletochange.

Using3differenttuningforks,calculatethelengthoftuberequiredtocreatearesonanceforeachone.Itmay

bepossiblethattherearetwodifferentpossiblelengthsforagiventuningfork.Inthatcase,youshouldtest

bothoftheselengths.Youwillneedtoknowthetemperatureintheroomthedayyouperformthe

experiment.

Onceyouhavemadeyourcalculations,testthembyfindingthelengthrequiredtoproducearesonancewith

eachtuningfork.Useyourmetersticktomeasurethelengthoftubeatwhichtheresonanceoccurs.Leteach

personinyourgrouptakeaturndoingthis.

AnalysisQuestions:

1)Showthecalculationsyouusedtodeterminethelengthoftuberequiredforeachofthethreetuningforks

yourgroupused.Recordthepredictedtubelengthandtheactualtubelengthinatable.

2)Discussanydiscrepanciesyounoticeinthepredictedversusactualvalues.Whyisitnecessarytoknowthe

temperaturewhenperformingthisexperiment?

PhysicsLabReportChecklistParticipantNames:____________________________________________________________Pd.______

LabTitle:_____________________________________________DueDate________________

OverallReport

Format

1.TitlePagecontainsGroupnames,Experiment

Title,DateDue,andPeriod

2.Allsectionsreportarepresent,inproperorder,

andareclearlylabeledinBoldUnderlineprint.

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Introduction 1.Thereisaclearstatementofthe

purpose/objectiveofthelab.

2.Thereisabriefdiscussionoftherelevant

backgroundinformationandtheoryinvolvedinthe

lab.

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Experimental

Procedure

1.Thereisaclearwrittendescriptionofthe

proceduresfollowedintheexperiment.

2.Thereisadiagramorpictureoftheexperiment

set-upwithcomponentslabeled.

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RawData 1.Allcollecteddatafromtheexperimentis

presentedintableformorotherappropriate

format.

2.Unitsofmeasurementsareclearlyindicated.

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Analysis 1.Asampleofeachtypeofcalculationneededin

theexperimentisprovidedandisdonecorrectly.

2.ResultsofcalculationsarepresentedforALLdata

intableform.

3.Graphsofdataareincluded,areneat,clearly

titled,anddisplayappropriateunitsandscales.

4.Sourcesofmeasurementerrorareindicatedand

discussed.

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Conclusions 1.Finalconclusionofthelabisclearlystatedand

showsunderstandingoftheobjectiveofthelab.

2.Suggestionsforhowthelabcouldbeimproved

areincluded.(Whatwouldyouhavedone

differentlyifyouweredoingthelabagain?)

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Note:Labreportsmustbetyped,nothandwritten,withthefollowingexceptions:1)Graphsmaybedonebyhandongraphpaper.2)Samplecalculationsmaybeneatlyhandwritten.

TotalScore:________/25

Comments:

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MultipleChoiceQuestions

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FreeResponseQuestions

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