A warm summer dayPBL.docx
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A warm summer dayPBL.docx
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AwarmsummerdayPBL
PBLCASEONE:
Awarmsummer’sday
EarlyonemorningyougobikingwithyourfriendsontheheathnearMaastricht.Contrarytotheweatherforecastitbecomesawarm,muggyday.Whenyoulookcarefullyyoucanseegreatquantitiesofdustparticlesrisingintheair.Towardstheendoftheafternoon,darkcloudsstartforminginthewelkin.Everybodycomplainsaboutthemuggyweather.Thereisaflashoflightninginthefardistancefollowedbyaclapofthunder.Suddenlyitstartsrainingheavily.Flashesoflightningandthunderclapscomeinrapidsuccession.Desperatelyyoulookaroundforsomesafeshelter.
Step1:
clarificationofuncleartermsorconceptsinthetextofaproblem
Chair:
haseverybodyreadtheproblem?
Okay.Areanyofthetermsorconceptsnotclear?
Jane:
whatdoeswelkinmean?
Tom:
theatmosphere,Ithink.
Sarah:
itisanarchaicwordusedmostlybypoets.Weuseitforsky,sopresumablyatmosphereiscorrect.
Chair:
okay,let’sdefinewelkintentativelyasthesky.Athomewecanlookitupinadictionarytoseeifthat’scorrect.Anyotherproblemswiththistext?
(looksaround)none?
Isthedescribedsituationcleartoeverybody?
(NOfurtherreactions)okay,shallwegoonwiththedefinitionoftheproblem?
Step2:
definetheproblem
Chair:
shallwegoonwiththedefinitionoftheproblem?
Whatphenomenaneedexplaining?
Anne:
howdoesathunderstormdevelop?
Eva:
morespecifically,whatmakeslightninghappen?
Andthethunderclap,ofcourse.
Paul:
anotherproblemseemstomehowpeoplecanprotectthemselvesfromthunderstorms.
Chair:
anybodyelse?
(Lookaround)nobody?
Okay,Isuggestwehavetwomainquestions,firstwhatmakesthunderstormand,morespecifically,thephenomenaoflightningandathunderclap?
Thesecondmainquestionis:
howcanpeopleprotectthemselvesagainstthedangersofathunderstorm?
Isuggestthatwestartbybrainstormingbrieflytopoolourideasandourexistingknowledgeofthesetopics.
Step3:
problemanalysis:
produceasmanyideasaspossible
Chair:
now,let’sstartthebrainstormingsession.First,hasanybodyanideaaboutwhatcauseslightning?
Jane:
afarasIknowithassomethingtodowithelectricity,withdifferencesincharges,electricsparksjumpingbetweenthecloudsandtheearth.
John:
Ithoughtithastodowiththefrictionbetweentheclouds.
Tom:
Ireadsomewherethatit’sallaboutstaticelectricity.Differencesinpotentialsinsideacloud.
Chair:
anyoneelse?
(silence).Noone,sofar.Let’sthinkaboutthecausesofthunder.
Sarah:
intheoldendayspeopleusedtothinkthesoundwasmadebyanangrygodoutridinghischariotandhorsesthroughtheclouds….
Anne:
Ithinkthatairgetsdisplaced.Airexpandsduetotheheatofthelightning.Thecloudsbumpintoeachotherandthatresultsinanexplosionofsound.
Chair:
otherideas?
Jane:
Ithinklightningmakesaholethroughtheclouds.Thenthecloudsrollback.Thatexplainsthunder.
Chair:
so,Annesaysitisanexplosionofclouds,whileJanestickstotheideaofimplosion,anyoneelse?
(looksaround).Nobody,thenlet’sbrainstormonthesecondproblem,howtobesagewhenthere’slightning.
Jane:
iftherearetreesaroundyoucanalwaysshelterunderthem.Youonlyhavetokeepfarenoughawayfromthetrunk.
Peter:
Ithoughtitwasbettertogooutintotheopen.
Paul:
yes,butyou’dhavetocrouchdownlow.
Jane:
yes,lightningalwaysseeksoutthehighestobject,sowhatyou’resuggestingisdangerous.
Chair:
anyoneelse?
(Looksaround,nobodyreacts).Okay,nowlet’sweexploreourideasinmoredepth.Shallwelookatwe’vegotontheblackboard?
Step4:
problemanalysis:
arrangeyourideassystematicallyandanalyzethemindepth
Chair:
shallweweewhat’sontheboard?
(readoutloudthekeywordsnoteddownbythescribe)
Lightning:
(static)electricity
Friction
Differencesinpotentiality
Thunder:
displacementofairleadstoexplosionorimplosion
Shelter:
(not)underatree,crouchingdownontheground,donotliedown,transportlightning–tree—humanbody?
Okay,letusexploreourideasinmoredepth.
Let’sgobacktothecausesoflightning.somegroupmembersthoughtithadtodowithelectricityandfriction.Jane,John,Tomyoubroughtthisup.Canyoutellusmoreaboutthis?
Tom:
thelightning,yousee,issparkswhichshort-circuitsbetweenthecloudsthemselvesandbetweenthecloudsandearth.Thereisadifferenceinpotential,ah,voltage?
Ithinkthatthecloudsgrateoneachother.Thatcausesfriction,ah,electriccharge?
Whenyourubacombthroughyourhair,youalsogetelectricity.Howdoesitgowiththateboniterod,plusorminus?
Staticelectricityistheconcept,Ithink…
Sarah:
Idon’tunderstandhowyougetthepotentials.Arecloudspositiveandnegative?
Tom:
ofcourse.That’swhycloudscollide.Theypulltogetherlikemagnets.
John:
but,thedifferencesinpotential,doesn’tthatdevelopintheclouds?
Fromabovedownwards?
Lightningusuallyhappensinsummer,whentheearthiswarm.Hotairrisesandgraduallycoolsdown.ButIdon’tunderstandhowthosecloudsgetcharged?
cloudsaremadeofraindrops,aren’tthey?
Eva:
that’sright,butthoseraindropsbecomeice.Thundercloudscangoupterrificallyhighandthismakestherainfropsfreezeandicecrystalsdevelop.Thosecrystalsoficegetsuckedupbytheupwardturbulence.Ithinkthedifferenceinpotenitaldevelopsbecauseicecrystalsareinthehigherlayersofthecloudsandwaterparticlesareinthelayersunderneath.Atthetopofthecloudsthereisapositivechargeandatthebottomanegativeone.thelightningdevelopsbetweenthesetwocharges.
Paul:
…Um,buthowdoyouexplainthelightningacrosscloudsandalsobetweenthecloudsandearth?
Eva:
Idon’tknowexactly….
Anne:
perhapsthehumidityintheairsupportstheconducticityofelectricity.Butwherearetheplusandminuschargesexactly?
Andwhatchargedoestheearthhave:
plusorminus?
Tom:
minus.Therealwaysisacurrentfromthecloudstotheearthandvisaversa.Theremustbeabalancebetweentheatmosphereandearth.Perhapslightninghassomeroleinthisprocess?
Chair:
Iamhearingmanydifferenttheories.Potentialdifferenceseitherinorbetweenclouds,apartialdescriptionoftheprocesswhichgiveselectricity,apossiblerelationbetweenlighrningandtheelectriccurrentbetweentheearthandtheatmosphere.
Scribe:
Iheardoncethattherearelotsofthunderstormsinthetropicsandthatthosestormsserveausefulinteradctionbetweentheearthandtheatmosphere.Buthentitieshavedifferencesinpotentialitywhichcannotjustgoonandonwithoutend.Nowandthentheremustbe,um.Somesortofexchange.Lightningcontributestothisprocess.Buthow?
(Silence)
Chair:
Igetthefeelingthattheseareourinitialideas?
(looksaround,nobodyreacts.Looksattheboardwherethescribehasdrawnaschemebasedontheremarks.)okay,letmetrytosummarisewhatwehavesofar.Wesupposethathotairrises.Atahighleveltheaircoolsdown.Thisresultsincondensationandfreezingwhichcreatesicecrystalsandfostersdifferencesinelectricpotentiality.Wealsomentionedsomethingaboutsvereturbulence.Andthatlightningseemstobeplayingaroleinthebalancebetweenearthandatmosphere.We’vealsohadlotsofquestions.Ourscribehaswrittendownsomeoftheimportantones,suchas,howdoesdlectricitydevelopincloudes?
Wherearethedifferencesincharge?
Istheearthplusorminus?
Whatisthespecigicrelationshipbetweentheearthandatmosphere?
Doesanybodywanttoaddmoreinformation?
(Silence)
Chair:
okay,well,let’sdiscussthethunder.Somebodythoughtthathastodowithairdisplacement.
Sarah:
thunderalwaysfollowslightning.Lightningforcestheairtodisplace.Afterthelightningtheairfallsdowntheholeathatwasdevelopedbythelightning.
Anne:
no,no!
cloudsexplodebecausethecurrentofthelightningisvery,veryhot,theyexpand.Atacertainmomentthesecloudscollidewithothercoldcloudswhichhavenotexpandedyet.Thatcausesthethunder.
Paul:
Ihadtheideathatairmustfirstgetpressedtogerher,thenitexpandslater…
(Thediscussgoon)
Chair:
(Summarisesthevarioustheoriesagain,andpresentsanoverviewofthequestionsstatedduringthediscussion.)okay,let’sdiscussthelastproblem:
howdangerousislightningandhowcanweprotectourselvesfromit?
Jane:
outside,itcanbeverydangerous.Youcanshelterunderatreeifyoukeepsomedistancefromthetrunk.
Peter:
youdobetterwalkingoutintheopen.
Anne:
yes.Butyoushouldliedownotherwiseyou’dbethehighestpointaround.
Eva:
whoa!
That’sseemsdangeroustometoo.Lyingdown,yourbodypresentsalongarea.I’veheardthatcows,forinstance,oftengethitbylightningduetothefactthatwhenthey’restretchedouttheypresentabigarea.Thecurrentgoesinthroughtheirfrontlegsandoutthroughtheirbacklegsbehind.It’sverydangeroustoliedown.
Peter:
didn’tPaulsuggestthatyoushouldmakeyuourselfsmall,andcrouchdownlow.Whyisthat?
Eva:
youshouldspreadyourlegsabitandstandontiptoesothatyouhavelesscontactwiththeground.And,pleasekeepawayfrombikesoranyothermetalobject.
Tutor:
that’sstrange.Ionceheardthatyoucanbestshelterinacarduringathunderstorm.
Eva:
that’saFaradaycage.Ithink.Inthiscasethemetalconductsthecurrenttotheearth.
Tom:
butthemetalisn’tincontactwiththeground.Cartyresaremadeofrubberwhichisabadconductorofelectricity.Sometimesyouseethoseearthingstripsunderacar,butthatisn’tis,orisit?
(Silence)
Chair:
letmebrieflysummarise.(…)Okay,Isuggestthatwestartformulatinglearninggoalsnow.variousquestionsha
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