measuring planck’s constant

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