measuring planck’s constant
TRANSCRIPT
PH315–Winter2017 Instructor:EthanMinot
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MeasuringPlanck’sConstant:Part1
1.Goals:・Characterizethewavelengthsoflightemittedfromthewavelength-selectableLED(thislab,Part1)・Findtheenergyofeachphotonemittedbythewavelength-selectableLED(Part2).・CalculatePlanck’sconstant・Writealabreportthatcombinespart1and2.Followbestpracticesforreportingtheresultsofaphysicsexperiment(seehomework5).
Equipment:Whiteboard,whiteboardpens,ruler,tape.Variableresistor9Vpowersupply4jumperwiresAdiffractiongratingwith1000slitspermillimeterGlassslidewithaslitAnLEDthatcanswitchbetweenred,greenandcyan.AprototypingbreadboardCautions:Preservethebattery
–don’tshort-circuittheredwiretotheblackwire!–unplugthebatterywhennolightisneeded
PreservetheLED–payattentiontopolarityoftheLED(+and-)–don’tput9VoltsdirectlyontotheLED,thevariableresistoristheretoprotecttheLED.
Preservethediffractiongrating–Themicroscopiclinesonthediffractiongratinggetruinedbyfingers
PH315–Winter2017 Instructor:EthanMinot
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Buildingthecircuit:Thisisthecircuityouneedtobuild:
Theprototypingbreadboardisaconvenientwaytoconnectelectronicswithoutusingcrimps,twists,ormoltenmetal.Eachholeinthebreadboardiselectricallyconnectedtoaseveralotherholes,asshowninthewiringdiagrambelow.
Connectthelongredstripontheleftsidetothe+terminalofyourbattery.Connectthelongbluestripontherightsidetothe–terminalofyourbattery.
PH315–Winter2017 Instructor:EthanMinot
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ChangingtheLEDcolor:
Onejumperalwaysstaysinthesameplace(row18inthisphoto).Thisfixedjumpergoestothenegativeterminalofthebattery.Theotherjumperisusedtoselectthecolor.
Measuringthewavelength:UseaslittocollimatethelightcomingoutoftheLED.
Findtheangleatwhichthefirst-orderdiffractionpeakisdeflectedbythediffractiongrating.
Figureouthowtomaketheanglemeasurementreproducible.Eachmemberofyourteamshouldbeabletomeasureasimilarangle.Foreachcoloroflight,makeatleastthreemeasurementsofthefirst-orderdiffractionpeakangle.Evenifthecoloristhesame,youwillmeasureaslightlydifferentanglebecausenomeasurementis“perfect”.Thespreadinyourmeasurementswillhelpyoudetermineexperimentaluncertainty.
Keepnotesaboutyourmethodsandyourdata.Guidanceonthelabwrite-upTheHomework5linkontheclasswebsiteincludes
• Anexamplelab-writeup• Adocumentthatdescribeswaystoreportmeasurementuncertainty• Thegradingrubricforthelabreport