lab manual upes physics

PHYSICSLABMANUAL

Department of Physics

College of Engineering Studies

FOREngineering Students

(Semester1)

Name...........................................................................................

Branch.................................RollNo...........................................

Institute.......................................................................................

PROFESSIONAL

University of Petroleium and Energy Studies, Dehradun2014-1stEd.Revised

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PROFESSIONAL PUBLICATOINS, 98962-31633

INSTRUCTIONSFORLABORATORY

Theobjectiveofthelaboratoryislearning.Theexperimentsaredesignedtoillustratephenomenain

differentareasofPhysicsandtoexposeyoutomeasuringinstruments.Conducttheexperimentswith

interestandan attitudeoflearning.

Youneedtocomewellpreparedfortheexperiment

Workquietlyandcarefully(thewholepurposeofexperimentationistomakereliablemeasurements!)

andequallysharetheworkwithyourpartners.

Behonestinrecordingandrepresentingyourdata.Nevermakeupreadingsordoctorthemtogeta

betterfitforagraph.Ifaparticularreadingappearswrongrepeatthemeasurementcarefully.Inanyevent

allthedatarecordedinthetableshavetobefaithfullydisplayedonthegraph.

Allpresentationsofdata,tablesandgraphscalculationsshouldbeneatlyandcarefullydone.

Bringnecessarygraphpapersforeachofexperiment.Learntooptimizeonusageofgraph papers.

Graphsshouldbeneatlydrawnwithpencil.Alwayslabelgraphsandtheaxesanddisplay units.

Ifyoufinishearly,spendtheremainingtimetocompletethecalculationsanddrawinggraphs.Come

equippedwithcalculator,scales,pencilsetc.

No. EXPERIMENT PAGENO.

LISTOFEXPERIMENTS

5

8

12

15

20

23

26

30

33

37

41

46

51

Todeterminethewavelengthofsodiumlight(monochromaticlight)byNewtonsringsmethod.Todeterminethewavelengthsofthemercury(blue,green/yellowy

1,y

2)lightbynormalincidence

method,usingdiffractiongrating.

TodeterminethespecificrotationofcanesugarsolutionwiththehelpofPolari-meter.

TodeterminetheresistanceperunitlengthofaCareyfostersbridgewireandthentodeterminethespecificresistanceofthegivenwire.

TodeterminetheenergybandgapofPNjunctionsemiconductordiodeinreversebiased.

Todeterminetheenergybandgapofasemiconductorusingfourprobemethod.

TostudytheHallEffectandhencedeterminethehallcoefficient(Rh)andcarrierdensity(n)ofa

givensemiconductormaterials.

Todeterminethe(1)numericalaperture(NA),(2)powerlossesduetomacrobendingandadaptorofgivenopticalFiber.

TostudytheV-Icharacteristicsofpnjunctiondiodeandtocalculateresistanceofadiodeinforwardandreversebias.

LaserDiffractionmethodforsingleslitexperiment.

Studyofboththecurrentvoltagecharacteristicandthepowercurvetofindthemaximumpowerpoint(MPP)andefficiencyofasolarcell

TodeterminethewavelengthofsodiumlightwiththehelpofFresnelsbiprism

Todeterminethedispersivepowerofamaterialofprismusingspectrometer.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

Index 55-56

PROFESSIONAL PUBLICATIONSAMBALA CANTT.

PROFESSIONALS Physics Lab Manual - I 5

AIM:Todeterminethewavelengthofsodiumlight(MonochromativLight)byNewtonsringsmethod.

APPARATUS:OpticalarrangementforNewtonsrings,travelingmicroscope,sodiumlamp,shortfocusconvexlens,readinglensandspherometer.

PRINCIPLE&FORMULA:ConsideraPlano-convexlensoflargeradiusofcurvatureplacedonacircularplaneglassplate.Athinfilmofairisformedbetweentheglassplateandthelensasshown.AtthepointOwherethelensisincontactwiththeglassplate,thethicknessoftheairfilmiszeroandasweproceedawayfromO,thethicknessofthefilmgraduallyincreases.AtthepointsaroundOandatequaldistancefromit,thethicknessofthefilmissamesincethebottomsurfaceofthelensisspherical.

NowsupposethatmonochromaticlightisincidentnormallyontheairfilmatXatadistanceofafromO.ThislightispartiallyreflectedatthetopsurfaceoftheairfilmatXandafterrefractioninairpartiallyatY.Thetworeflectedbeamswillhavecertainpathdifferencedependinguponthethicknessofthefilm(XY).Interferenceofthesetworeflectedbeamstakesplacewhichcanbeobservedthroughamicroscopeplacedverticallyabovethelens.ThepointXwillbebrightordark,dependinguponwhetherthepathdifferenceisoddorevennumberofhalfwavelengthofincidentlight.Similarlyinterferenceoflightoccursatallotherpointsofthefilmandasetofringswhicharealternatelybrightanddarkwillbeobservedwithadarkspotatthecentreoftherings.EachringisthelocusofallpointsinthefilmwhichareatthesamedistancefromthecentreOoftheringsystem.Ifd

mand

dnarethediametersofthemthandnthdarkringsrespectivelyandRistheradiusofcurvatureofthecurved

surfaceofthePlano-convexlens,itcanbeshownthatthewavelengthoflightisgivenby

2 2m nd d

4R m n

ThusbyformingtheseringscalledNewtonsringsandbymeasuringtheirdiameters,thewavelengthoflightcanbedetermined.

APPLICATIONS

Thicknessofathinfilm.Radiusofcurvatureofconvexsurfaceofthegivenlens.Refractiveindexofaliquid.Wavelengthofamonochromaticlight.ColorseparationscanningEquipments/Colourscanners.AntiNewtonringGlassinphotographicindustry.

Figure1.1

EXPERIMENT NO. 1


PROCEDURE:1. PlacethePlano-convexlensonthecircularplaneglassplatesuchthattheconvexsurfaceofthe

Planoconvexlensisincontactwiththeplaneglassplate.Placethiscombinationinthewoodenbox,whichcontainaplaneglassplateinclinedby45ototheincidentlightfromtheshortfocusconvexlens.Placethewoodenboxunderthetravelingmicroscopeandadjustituntilsharpringsareseen.

2. Bringthepointofthecrosswirestothecentrespotoftheringsystem.Startingfromthecentreoftheringsystemmovethemicroscopecrosswirestotheleftuptothe19thdarkring.(Thisnumberselectedarbitrarily).

3. Settheverticalcrosswiretangentialtothe19thdarkringattheleftandnotethereadingonthehorizontalscaleofthemicroscope.Repeatthesameforalternatedarkringsuntilcrosswirereaches1stdarkring.Similarlytakethereadingsofalternateringsattherightsidestartingfrom1string.

4. DeterminationofradiusofcurvatureoftheconvexsurfaceofthePlano-convexlens(R)Takeoutthelensandmarkthesurfacewhichwasincontactwithglassplate.Placethespherometerontheconvexsurfaceoftheplano-convexlensandnotethereadingofthespherometer(h

1)thenplacethe

spherometerontheplaneglassplateandnotethereading(h2).

Readingofthespherometerforconvexsurfaceofthelens(h1) =cm

Readingofthespherometerforplaneglassplate(h2) =cm

Averagedistancebetweenthelegsofthespherometer(l) =cm

Heightoftheconvexsurface(h)=(h1h

2) =cm

RadiusofcurvatureofthecurvedsurfaceofthePlano-convexlens

2 hR ...................................cm

6h 2

l

TABLE

S.No. RingNo.MicroscopeReading(cm) Diameter

d=L~R(cm)

d2(cm2)Leftside(L) Rightside(R)

1 20

2 18

3 16

4 14

5 12

6 10

7 8

8 6

9 4

10 2


GRAPH

DrawagraphwiththeringnumberonX-axisand(diameter)2onY-axis.Byjoiningthepointsastraightlinepassingthroughtheoriginisobtainedasshowninfigure1.2.Findtheslopeofthestraightline,whichis:

2 2m nd d

m n

CALCULATIONS

Radiusofcurvatureoftheplanoconvexlens(R) =cmDiametersquareofthemthringd2

m=cm2

Diametersquareofthenthringd2n

=cm2

Slopeofthestraightline =cm2

Wavelength( ) =cm

RESULT:WavelengthofSodiumlight( )isfoundtobe=cm=.AA0

PRECAUTIONS

1. Thelenssurfaceaswellascircularglassplatemustbewellcleaned.2. Thecentrespotoftheringsystemshouldbedark.

1. WhatisNewtonsRing?Howaretheseringsformed?2. Whyaretheseringscircular?Ifthefringesarenotexactlycircularwhatdoyouinfer?3. WhyareyouusingthePlano-convexlensoflargefocallength?4. Whydotheringsgetcloserastheorderofringsincreases?5. Whyisthecentreoftheseringsdark?

REFERENCES1 PracticalPhysicsGupta.Kumar2 AtextbookofPracticalPhysicsR.KGoel.GovindRam3 B.ScPracticalPhysicsC.LArora

Y

d2m

d2n

n m X

number of ring

O

Dia

me

ter

2

VIVA-VOCE

Figure1.2


EXPERIMENT NO. 2

AIM:Todeterminethewavelengthofthespectrallines(Blue,Green,Yellow,Y1,Y

2)byusingdiffraction

gratingthenormalincidencemethod.

APPARATUS:Spectrometer,diffractiongrating,spritlevel,mercuryvaporlampandmagnifyinglens.

PRINCIPLE&FORMULA

Diffractionisthephenomenonofbendingoflightaroundtheobstaclespeciallywhenpassedclosetosharpedges

orthroughaperturesornarrowopenings.Consideraplanetransmissiongratingwithalternateopaqueand

transparentlines.Letaparallelbeamoflightraysareincidentnormallyonthegrating.Mostoftheseraysare

transmittedinthedirectionoftheincidentlightthroughtransparentportionsofthegratingandifaconverginglens

isplacedintheirpath,theyarebroughttofocusatO.therewillbeaverybrightimage.Someoftheincidentlight

isdiffractedattheedgessuchasB,DandFetc.,atdifferentanglesasshowninfigure2.1.Ifweconsiderthese

rays(bendatBandDatanangle fromthedirectionoftheincidentlight)allsuchraysformaparallelbeamand

afterpassingthroughthelens,theyarebroughttofocusatI.TheintensityatIwillbemaximumorminimum

dependinguponthepathdifferencebetweenthediffractedraysfromBandD.Ifdisthegratingelement(distance

betweentwoconsecutivelinesonthegrating),pathdifferenceisequaltodsin .

B

D

F

O

I

Thusifdsinq=nl(anintegralnumberofwavelengths)thebrightimagesareformedinthefocalplaneofthelens.

Thesearecalledfirstorder,secondorder(n=1,2,3,)etc.,images.Thusonesetofimageswillbeformedonone

sideofthecentralbrightimageatO.alsothediffractionorbendingoflightraystakesplacetotheothersideof

theincidentdirectionandcorrespondingimagesofdifferentordersareformedontheothersideofthecentral

imageO.ThusinthefieldofviewofatelescopeofwhichthelensLformstheobjective,acentralbrightimage

andthediffractedimagesofdifferentorders(n=1,2,3,etc.)areobserved.Iftheincidentlightismonochromatic,

eachorderofdiffractedimagewillbeofthesamecolor,butifwhitelight(mercury)isincidentonthegrating,

eachdiffractedimageconsistsofawholespectrum.Thusspectraofdifferentordersareformedoneithersideof

thecentralwhiteimage.

APPLICATIONS

Gratingasfilters Fiberoptictelecommunication Beamsplitters

Figure2.1


Opticalcouplers Metrological Ground-basedastronomy Ramanspectroscopy Colorimetry Atomicandmolecularspectroscopy Fluorescencespectroscopy

FORMULA

a b sin n Grating equation

Or =n

b)sin(a

Where(a+b)=gratingelement

=angleofdiffraction.

n=orderofdiffraction

PROCEDURE

1. Makepreliminaryadjustmentsofthespectrometer.

2. Clampthegratingontheprismtablewiththehelpofaclamp.Adjustthegratingfornormalincidencepositionbythefollowingmethod.

I. SetthetelescopefordirectreadingpositionandnotethereadingV1andV

2.

II. Add90ototheabovereadingandrotatethetelescopetothisreadingandfixit.

III. Nowrotategratinguntiltheimageoftheslitisatcrosswiresofthetelescopeandfixtheprismtable.Nowtheincidentlightismaking45owiththegratingplane(Seefigure2.2).

IV. Releasethevernierscaleknobandrotatethevernierscalethroughanangleof45osothatthegratingmaintainsexactlynormaltotheincidentlight.Fixtheverniertableinthisposition;nowgratingisatnormalincidenceposition.

3. ReleasethetelescopeandrotateittoleftsideofthedirectreadingpositionuntiltheIorderspectrumisseen.NowcoincidetheverticalcrosswireoverthespectrallinesofdesiredcolorandnotedownthereadingsinthetwoverniersasV

1andV

2.Further,rotatethetelescopetillIIorderspectrallinesare

visible,coincidethecrosswireandnotedownthereadingsintwoverniersasV1andV

2against2nd

order.

4. Nowrotatetelescopetotherightsideofthedirectreadingpositionuntilthefirstorderspectrumisseen.ConcidethecrosswireswiththesameyellowspectrallineandnotedownthereadingsinthetwoverniersasV

1andV

2.RotatethetelescopefurtheruntiltheIIorderspectrallinesareseen,thencoincidethe

verticalcrosswireswithlinesandnotedownthereadingsasV1andV

2.Theangleofdiffractionis

givenbyhalftheanglebetweencorrespondinglines.

CALCULATIONS

No.oflinespercmonthegrating=gratingelement= 2.54

a +b = 1/N =15000

Telescope Grating

Collimator

Source

Slit

45o

45o

90o

Prism table

Figure2.2


TABLE

RESULT:Theobservedwavelengthsaregivenintable

PRECAUTIONS

1. Opticaladjustmentofthespectrometershouldbemadedirectly.

2. Theslitshouldbeasnarrowaspossible.

3. Gratingsurfaceshouldnotbetouchedwithfingersastheslitmightgetdamaged.

4. Thegratingshouldbeexactlynormaltotheincidentbeam.

5. Whiletakingobservations,telescopeandprismtableshouldbekeptfixed.

Figure2.3

Orderof

diffraction

Spectrallines

SpectrometerReadings

Left Right 1 1 2 2V V V V2

2

a b sin

n

Iorder

1V 2V 2V1V

Y1

Y2

Blue

Green

IIorderY

1

Y2

Blue

Green

Colourofspecturlline (observed) (Standard) %(Error)

BlueGreenYellow1Yellow2

........

........

........

........

........

........

........

........

........

........

........

........


1. Whatisaplanetransmissiondiffractiongrating?2. Whythegratingshouldbekeptnormaltotheplaneofgrating,thenwhichformulashouldbeapplied?3. Whatis(a+b)intheformula?4. Howmanyordersofspectradoyougethere?Whydoyounotgetthethirdorderspectrum?5. Howmanytypesofgratingareknowntoyou?6. Whatisthemaindifferencebetweenthespectrumobtainedbygratingandduetoprism?7. Whatdoyoumeanbydispersionoflight?8. Whyalightonpassingthroughtheprismdispersesintoitsconstituentcolours?9. Definedispersivepowerofanymaterial?10. Onwhatfactorsdoesthedispersivepowerdepend?11. Whatistheangleofdeviation?

REFERENCES

1 PracticalPhysicsGupta.Kumar2 AtextbookofPracticalPhysicsR.KGoel.GovindRam3 B.ScPracticalPhysicsC.LArora4 EngineeringPhysics-M.NAvadhanulu,A.ADaniandP.MPokley5 ALaboratoryManualofPhysicsD.PKhandelwal6 B.ScPracticalPhysicsHarnamSingh

VIVA-VOCE


AIM:Todeterminethespecificrotationofcanesugarwiththehelpofapolarimeter.

APPARATUS:Half-shade/Bi-quartzpolarimeter,lightsource,sugar,measuringflask,beaker,analyticalbalanceandaweightbox.

PRINCIPLE&FORMULA

IfabeamofunpolarisedlightisviewedthroughtwocrossedNicolprisms(whentheprincipalplanesof

thetwoareperpendiculartoeachother)thefieldofviewiscompletelydark.ThefirstNicoliscalledthepolariser

andthesecondiscalledtheanalyzer.IfthesugarsolutionisintroducedbetweenthetwocrossedNicols,itis

foundthatlightisrestoredinthefieldofview.Toextinguishthelight,theanalyzerhastoberotatedthrougha

finiteangledependingontheconcentrationofthesugarsolution.Thisexperimentshowsthatthesubstance

introducedbetweentheNicolshasrotatedtheplaneofpolarization.Suchsubstancesarecalledopticallyactive

substancesandthephenomenoniscalledOpticalactivity.Iftheplaneofpolarizationisrotatedclockwise,the

substanceiscalleddextro-rotatory(righthanded)andifitisrotatedanti-clockwise,thesubstanceiscalledlevo-

rotatory(lefthanded).

Theanglebywhichtheplaneofpolarizationisrotatedisdirectlyproportionaltothelengthofthepath

traveledbythelightinthesubstance(l),theconcentrationofthesubstance(c).Italsodependsonthetemperature

andwavelengthoflight.Thusforaparticularwavelengthandtemperature

vc or S c or S

c m

l l

l l

WhereS=specificrotationorspecificrotatorypowerofthesubstance=rotationproducedindegreem=massofsugaringm.dissolvedinwaterv=volumeofsugarsolutionl=lengthofthetubeindecimeter

Specificrotation,foragivenwavelengthatagiventemperature,isdefinedastherotationproducedbyonedecimeterlengthofthesolutionhavingaconcentrationof1gm/cc.

APPLICATIONS

SugarIndustry PharmaceuticalIndustryChemicalIndustry Flavours,FragrancesandEssentialOils

LAURENTSHALF-SHADEPOLARIMETER

Laurentshalfshadepolaririmeteristheinstrumentusedforfindingthespecificrotationofcertainoptically

activesolutions.TheessentialpartsofaLaurentshalf-shadepolarimeterareshowninthefigure.Sisunpolarised/

ordinarysourceoflightandLisaconvexlenswhichrenderstheincidentlightintoaparallelbeam.N1andN

2are

twoNicloprisms.N1actsaspolariserwhileN

2actsasanalyzer.N

2canberotatedaboutacommonaxisofN

1

andN2.Therotationofanalyzer(N

2)canbereadinagraduatedcircularscale(S.C.).Thevernierisalso

providedtoreadthefractionofadegree.Lightafterpassingthroughpolariserbecomesplanepolarizedwithits

EXPERIMENT NO. 3


vibrationsintheprincipalplaneoftheNicol(N1).Theplanepolarizedlightnowpassesthroughahalf-shade

device(H.S.)andthenthroughatubeTcontainingtheopticallyactivesubstance.UsuallyTisahollowglasstubehavingalargediameterinthemiddlesothatnoairbubblemaybeinthepathoflightwhenfilledwithaliquid.TheemergentlightonpassingthroughanalyzerN

2isviewedthroughatelescopeT.Thetelescopeisfocusedon

thehalfshade.

lens polariser halfshade

L N1 HS SC

circular scale tube

T

telescope

T

analyser

N2

S

PROCEDURE

1. Weightexactly4gmsofsugaranddissolveitin100c.c.ofdistilledwaterinameasuringflask;makethesolutionexactly100c.c.

2. Ifthepolarimeterisemployingahalfshadedevice,amonochromaticsourceisusedandifbiquartzdeviceisusedthanwhitelightcanbeused.Cleanthetubesuchthatitisfreefromdustandfillsitwithdistilledwaterandclosetheends.Placethetubeinpositioninsidethepolarimeter.

3. lookthroughthetelescopeandrotatetheanalyzertillthetwohalvesofthefieldofviewappearequallybright.Takethereadingofmainscaleaswellasvernierscaleandfindoutthetotalreading(

1).

4. Takeoutthetubeandfillitcompletelywiththesugarsolutionsothattherearenoairbubblesinit.(DoNot Over Tight the Cap It May Break the Tube)Closethetube,placeitinitspositioninthepolarimeterandlookthroughthetelescope.Againsetthefieldofviewasexplainedinstep-3.Notethereadingoftheanalyzeronthecircularscale(

2).

5. Repeatstep4oftheexperimentfordifferentconcentrationsofthesolutionandtabulatetheobservations.

OBSERVATIONS

Leastcountofthevernierofthecircularscale =.

Lengthofthecylindricaltube(l) =.cm

Massofthesugardissolved(x) =.gm

Volumeofthesolution(v) =.cc.

Temperatureofthesolution(T)=roomtemperature =. oC

TABLE

S.No. Concentrationofsolution(x/v)gm/cc

Readingoncircularscalewhentwohalvesareofequalintensity

xn

Angleofrotationofplaneofpolarization

n 1 = x - x

10..vS =

.xl

1.

2.

3.

4.

Air/plainwater

4/100

8/100

12/100

x1

x2

x3

x4


GRAPH

Plotagraphbetweenconcentrationofthesolution(c)ontheX-axisandangleofrotationoftheplaneofpolarizationofplanepolarizedlight()ontheY-axis.Yougetastraightlinepassingthroughtheorigin.

CALCULATIONS

c

slope Thespecificrotatorypower

S=l

10slope

Where listhelengthofthetubeincmReadingwithdistilledwater,say

1=.

RESULTS:ThespecificrotationofglucosesolutionatoCforthegivenlightis_______________degree/unitconcentration/unitlength.

PRECAUTIONS

1. Thewindowcapofthetubecontainingthesolutionshouldbegentlytight,sothattherewillbenoleakage.2. Thereshouldbenoairbubbleinthesolutioncontainedinthepolarimetertube.3. Thetemperatureofthesolutionmustberecorded(roomtemperature).4. Havingsettheanalyzerincorrectpositionw.r.tthepolarizer,turntheformerthrough180oandagainmakea

similarsetting.5. Undernocircumstancesthepolarizershouldbetouchedduringonecompletesetofobservation.6. Usesodiumlightforhalfshade,andwhitelightforbi-quartz.

1. Whatdoyoumeanbypolarizationoflight?2. Howdoespolarizedlightdifferfromordinarylight?3. Whatisangleofpolarization?4. Whataretheplaneofpolarizationandplaneofvibration?5. WhatisPolaroid?6. WhataretheusesofPolaroidsindailylife?7. WhatisBrewsterslaw?8. Whatisthepolarizinganglefortheair-glass?

REFERENCES

1 PracticalPhysicsGupta.Kumar2 AtextbookofPracticalPhysicsR.KGoel.GovindRam3 B.ScPracticalPhysicsC.LArora4 ElectronicsfundamentalsandapplicationsRyder,J.D5 PropertiesofsiliconandgermaniumConwell,E.M6 EngineeringPhysics-M.NAvadhanulu,A.ADaniandP.MPokley7 ALaboratoryManualofPhysicsD.PKhandelwal

VIVA-VOCE

X

Y

Concentration,c(ingm/cc)


AIM: TodeterminethespecificresistanceofagivenwirebyusingCarey-FostersBridge.

APPARATUSUSED:Carey-Fostersbridge,BatteryEliminator,zerocentregalvanometer,decimalresis-tancebox,thickcopperstrips,givenexperimentalresistancewire,arheostatofrange10to20,plug-key,jockey,connectionwiresandscrewgauge.

FORMULAUSED:

(i) ForResistanceperUnitlengthofbridgewire():ThestandardresistanceboxR.B.forXinG1and

thickcopperstripforshorteningsothatY=0.

Theresistanceperunitlengthofbridgewireisgivenby;

2 1

X/cm

l l

whereX=knownfractionalresistancevalueresistancebox.

l1isthebalancinglengthwithXinG1andYinG4(beforeInterchanging)

l2isthebalancinglengthwithXinG4andYinG1(afterInterchanging)

(ii) FortheunknownResistance:Theunknownresistance(Y)ofthegivenwireisgivenby;

R=Y=X-(l2 l1)

whereY(R)istheunknownresistanceofthegivenwireconnectedinG4andG

1

XisthevalueofresistanceinthedecimalresistanceboxconnectedingapG1andG

4theoutergap.

l1isthebalancinglengthwithXinG

1andYinG

4(beforeinterchanging)

l2isthebalancinglengthwithXinG

4andYinG

1(afterinterchanging)

=resistanceperunitlengthofthebridgewire.(iii) ThespecificresistanceSofthewireisgivenby:

2R A YS ohm-cm

r

l lwhere,S=specificresistance, r=radiusofwireincml=lengthofwireincm, Y= resistanceofthewireinohm.

CIRCUITDIAGRAM

EXPERIMENT NO. 4

Figure4.1:Carey Fosters bridge for determining specific resistance

E:BatteryEliminator,KKey

P,Q:StandardResistanceinG2andG3respectively.

X:VariableresistancefromResistanceBox

Y:UnknownresistanceforwhichSistobedetermined.

G:Galvanometer,J:Jockey

SR SR

G1 G2 G3 G4

E

X YP Q

K

J

GW1 W2l1

knownresistance

unknownresistance


PROCEDURE

Theexperimentisdoneinthefollowingthreesteps;

(a) MeasurementofResistanceperunitLength( )oftheBridgeWire:CalibrationoftheBridgeWire.

Forthisstep,setupthefollowingexperimentalset-up;

(i) PresstheJockeyJatthetwoendsofthewireW1andW

2.Ifthedeflectionsingalvanometerare

oppositethecircuitconnectionsarecorrect.

(ii) Plugout0.1ohmofresistanceinX(inG1).Checkfortheoppositedeflections.Thenfindthepointexactlywherethedeflectionisbecomingzerobymovingthejockey.Thispointisthebalancingpoint.

(iii) NotethedistanceofnulldeflectionpointfromthepositiveendofwireW1togetthebalancinglength

(l1)

(iv) RepeatthisprocessbychangingXvaluesfrom0.1ohmto0.5ohmandnotedownthecorrespondingvaluesofl

1.

Calculatethevalueoflinearresistanceorresistanceperunitlengthofbridgewire foreachsetof

observationsbythefollowingformulaandfindtheaveragevalueof .

2 1

R

l l

andthenfinditsmean.

(b) Measurementofunknownresistanceofthegivenwire:

(i) Connectthecircuitasshowninfigure4.1.RemovethecopperstripfromthegapG4andconnectthegivenunknownresistancewireofnearly50cmlength.

(ii) Introduceasuitableresistanceofnearly1-3ohminthedecimalresistanceboxxingapG1.

(iii) Slidethejockeyonthewiretillyougetabalancingpoint.Notebalancinglengthl1fromleftendW1ofthewire.

(iv) Interchangethepositionsofresistanceboxandunknownresistancewire.Againgetthebalancepointbyslidingthejockeyonthewireandnotethebalancinglengthl2fromW1.

(v) Repeatthisexperimentfordifferentvaluesofresistancesfromtheresistanceboxandgetothervaluesof(l2-l1).

(vi) Theunknownresistanceisgivenbytheformula:

2 1R Y X ( ' ' )l l

whereXistheresistanceintroducedintheresistanceboxand 2 1l l isthedifferenceofthetwobalancinglengthsbeforeandafterinterchangingtheR.B.andunknownresistanceineachcaseandfindthevalueofunknownresistance.

(c) Forspecificresistance:

(i) Measurethelengthoftheunknownresistancewireincm.

(ii) Measurethediameterofthegivenresistancewirebyscrewgaugeatfewplacesandthencalculatemeanvalueofdiameterandhenceradius;r=d/2


OBSERVATIONSTableforthedeterminationoflinearresistanceofBridgeWire( )

S. Resistance(ohm) BalancingLength(cm) Linear

No. X Y Before After l2l1 Resistance

Interchanging Interchanging(cm)

2 1

X/cm

l l

XinG1(l1) XinG4

(l2)

1 0.1 0

2 0.2 0

3 0.3 0

4 0.4 0

5 0.5 0

(ii)Tableforthedeterminationofunknownresistanceofagivenwire:

S. Resistance(ohm) BalancingLength(cm)

No. X Y Before After l'2l'1 2 1Y X ( )l l

(Known) (Unknown) Interchanging Interchanging (cm)

XinG1(l'1) XinG4(l'2)

1 0.5 Y

2 1.0 Y

3 1.5 Y

4 2.0 Y

5 2.5 Y

AvgY=........TheunknownresistanceofthewireisY=

(iii)Tableforthemeasurementofradiusofwirebyusingscrewguage

Error =.........Correction =.........

S.No. P.S.R. H.S.C H.S.C. L.C.TR=P.S.R+H.S.C L.C(mm) Observed Corrected (mm) (mm)

1

2

3

AverageDiameter:.mmRadiusofthewire,r=d/2=..mm=.cm


CALCULATIONS

(a) Theresistanceperunitlengthofthebridgewireisgiven:

2 1

R

l l

(Similarlycalculateforotherobservationsandtakethemean)

(b) Theunknownresistanceofthegivenwireisgivenby;

2 1Y=X l l =.......ohm.(Similarly,calculateYforotherobservationsandtakethemean)(c) Thespecificresistanceofgivenwireisgivenby;

2RS ............ohm-cm

r

l

RESULTS

1. Theresistanceperunitlengthofwire=...........ohm/cm

2. Thespecificresistanceofthematerialofthewire=...........ohm-cm

Measuredvalue(S)exp Standardvalue(S)thPercentageError

(ohm-cm) (ohm-cm) exp th

th

S - S100

S

PRECAUTIONS

1. Theendoftheconnectionwiresshouldbecottonfree,cleanandmustbetightlyconnected.

2. SeethattheresistancesinfourarmsP,Q,XandYofthebridgemustbeofthesameordersothatthebridgeremainsquitesensitive.

3. Continuouscurrentshouldnotflowinthewireotherwiseitgetsheatedupanditsresistancemayundergoachange.

4. Forthis,thejockeyshouldnotbedraggedcontinuouslyallalongthelengthofthewirebutshouldbetappedatdifferentpointsonthebridgewire.

5. Thebridgewireshouldbeuniformincross-section.

6. Thejockeyshouldbegentlyputonthewireandnotpressedhardtoavoidandchangeinthediameterofthewire.

7. Thediameterofthewiremustbemeasuredintwoperpendiculardirectionsandatmanyplacesandthenmeanvalueofitmustbeused.

8. Ahighresistanceshouldbeusedinthecircuittomeasuretheexactbalancingpoint.(conventionally)

APPLICATIONS:

1. Comparetwonearlyequalresistance

2. Determinethetemperaturecoefficientofresistance .


1. WhatistheprincipalofCareyFostersBridge?Ans. Itisbasedontheprinciplethatwhenresistanceofoutergapsareinterchanged,thereisshiftinthe

positionofbalancedpoint.Thedifferencebetweentheresistanceofbridgewirebetweenthesetwobalancepoint.

P X

Q Y

2. InwhatrespectitisanimprovementoverMeterBridge?3. Howdoestheaccuracyofresistanceperunitlengthofthewire( )dependonthedifferencebetween

theknownresistancesintheoutergaps?4. Whatcanbethemaximumvalueofthisdifferencewhichyoucantake?5. Whenwillyourapparatusbemostsensitive?6. Whatisthematerialofthebridgewire?Whyithasbeenselected?7. Whatwouldyouprefer,acopperstriporacopperwireintheoutergap?Why?8. Whatdoes represents?Willitbesameateverypointofthebridgewire?

9. WhatistheeffectofincreasingtheeffectivelengthofBridgewire?10. WhatisthebasicconstructionofaResistanceBox?11. Whyisthewiredoubledinsidethebox?12. WhatisthepercentagecompositionofthealloysconstantanandManganinofwhichresistancewiresare

made?13. Whatdoyoumeanbytheresistanceofaconductor?Ans. Theratioofthepotentialdifferencebetweenthetwoendsofaconductortothecurrentflowinginit,is

calledtheresistanceoftheconductor.14. Onwhatfactorsdoesitdepend?Ans. Resistanceofaconductorisdirectlyproportionaltoitslength(l),inverselyproportionaltotheareaofcross

section(A).Italsodependsuponthenatureofmaterialandtemperatureoftheconductor.(R=kl /A).15. Whatisitsunit?Ans. Unitofresistanceisohm.16. Whatisspecificresistance?Whatisitsunit?Ans. Specificresistanceofasubstanceisdefinedastheresistancematerialhavingunitlengthandunitareaof

crosssectionRA

Sl

ifA=1andl =1 then S=R

Itsunitisohm-cm17. Isspecificresistancesameforallmaterials?Ans. No,itisdifferentfordifferentmaterial.18. Whatiseffectoftemperatureonresistance?Ans. Itincreaseswithincreaseintemperature.19. WhatistheeffectofincreasingtheeffectivelengthofaCareyFostersbridgewire?Ans. Itwillincreasetheaccuracyoftheresultbecausethenpercentageerrorinreadingthepositionofthe

balancepointisverymuchdecreased.20. Whatistheminimumdifferenceresistancethatyoucanmeasurewithitsbridgewire?Ans. Itisequaltotheresistanceofthebridgewire.21. Whatisthemaximumdifferenceinresistancethatyoucanmeasurewiththisbridgewire?Ans. Itisequaltotheresistanceofthetotallengthofthebridgewire

VIVA-VOCE


AIM:Todeterminetheenergybandgapofasemiconductorusingajunctiondiode.

APPARATUS:Powersupply(DC-3Voltsfixed),Microammeter,electricallyheatedoven,Thermometer,Semiconductordiode(OA79).

FormulaUsed:AgraphisplottedbetweenlogsIsand(103/T)thatcomesouttobeastraightline.Itsslopeis

calculated.Bandgap,E,inelectronvolts,isgivenby

E=036.5

linetheofslopeeV

APPLICATIONS

Oneofthemostimportantapplicationsofdiodesisinthedesignofrectifiercircuits,clipper,clamper,voltagemultiplier,comparator,samplinggatesandfilters.

THEORY

Asemi-conductordopedorundopedalwayspossessesanenergygapbetweenitsconductionandvalencebands.Forconductionofelectricityacertainamountofenergyistobegiventotheelectron,sothatitgoesfromthevalencebandtotheconductionband.ThisenergysoneededisthemeasureoftheenergygapEbetweenthetwobands.

Whenap-njunctionisreversebiasedasshowninFig.thecurrentthroughthejunctionisduetominoritycarriersi.e.duetoelectronsinPsectionandholesinNsection.TheconcentrationofthesecarriersdependsupontheenergygapE.ThereversesaturatedcurrentI

svalue

isfunctionofthetemperatureofthejunctiondiode,andvariesaccordingtothefollowingrelation:

pns e n pp n

VVI A N N e E kT

P N

log log exp .(1)

WhereN

n=densityofelectronsinNmaterial

Np=densityofholesinpmaterial

Vp=velocityofholes

Vn=velocityofelectrons

A=areaofthejunctionk=BoltzmannConstantT=Absolutetemperatureofjunction

3/2nn 3

2 2 m kT eN

h

3/2

p

p 3

2 2 m kT eN

h

EXPERIMENT NO. 5

P N

Figure5.1:Reverse biasing of a PN junction


mnisthemassoftheelectronandm

pistheeffectivemassofhole.

Forsmallrangeoftemperaturerelation(1)canbeputas,

3sI constant 5.036 E 10 T log ......(2)Obviouslytherefore,ifagraphisplottedbetweenlogI

sand103/T,astraightlinewouldbeobtained.

Wheretheslopeofthisline=5.036E

HereEisinelectronvolts.

PROCEDURE

1. Plugthemainsleadtothenearestmainsocketcarrying230V 10%at50HzA.C.

2. Insertthethermometerandthediodeintheholesoftheoven(TheholeneartothemeterisfordiodeOA-79)

3. Plugthetwoleadstothediodeinthesocket,Redpluginredsocketandblackpluginblacksocket.Maketheconnectionsasperfigure5.2.

(i) Nowput thepowerON/OFFswitchtoONpositionandseethejewellightisglowing.

(ii) PuttheOVENswitchtoONpositionandallowthetemperaturetoincreaseupto90C.

Note:As soon as the temperature reaches 95C switch off the oven enabling the temperature torise further and become stable around 90CWhenthetemperaturebecomesstablestarttakingreadingsofcurrentandtemperature.Thecurrentreadingsshouldbetakeninstepsof5A.Thereadingsshouldbetakenduringfalloftemperaturefrom90Cdownwards.

(iii)Tabulatereadingsintheformshownbelow:

TABLE

(iv) Plotagraphbetweenthereadingsof103/TonX-axisandlogIsonY-axis.Thegraphshouldcome

asastraightlinecuttingboththeX-axisandY-axis.

(v) Nowdeterminetheslopeoftheline.

AfterdeterminingtheslopeofthelinecalculatestheBandGapasfollows:

E=036.5

linetheofslope=eV

Figure5.2:Circuit diagram

Reversesaturationcurrentin

Is( A )

TemperatureinoC

TemperatureT(oK)

103/T logIs


PRECAUTIONS

1. Themaximumtemperatureshouldnotexceed95C.

2. Bulbofthethermometerandthediodeshouldbeinsertedwellintheoven.

3. Silicondiodesshouldnotbeusedwiththesetupsasinthatcasethetemperatureneededis125C,andtheoventhermometerprovidedwillnotstandtothistemperature.

1. Whatdoyoumeanbyenergybandgap?

2. Howarethebandsformedinthesolids?

3. Whatdoyoumeanbyvalenceband,conductionbandandforbiddenband?

4. Howdoyoudifferentiatebetweenaconductor,aninsulatorandasemiconductorinrelationtotheenergygap?

5. Whatdoyoumeanbyintrinsicandextrinsicsemiconductors?

6. WhysemiconductorsbehaveasaninsulatoratzerodegreeKelvin?

7. WhatisaP-Njunction?

8. Whatisann-typesemiconductorandp-typesemiconductors?

9. Whatdoyoumeanbyforwardandreversebiasingofajunctiondiode?

10. What are the positions of holes and electrons in the two semiconductors (p-type and n-type)beforecontact?

11. Whatisadepletionlayer?

12. Whatistheorderofthicknessofdepletionlayer?

13. Whataretheapproximatevaluesofbandgapincaseofconductor,insulatorandsemiconductor?

Howdoestheresistivitychangeswiththechangeoftemperature?

VIVA-VOCE


AIM:Tostudytheresistivityofsemiconductorofdifferenttemperaturesandalsotodeterminetheenergybandgapofasemiconductor(germanium)usingfourprobemethod.

APPARATUS:Probearrangement,Sample(Germanium),Oven,FourProbeset-up,Thermometeretc.

FORMULAUSED:

Theresistivityofthesemiconductorcrystalwhichisgivenby:

0

0

Vwhere 2 S

W/ S If

wheref(W/S)isafractionwhichcanbeknownfortablegivenwiththesemiconductor.Sisthedistancebetweenprobes.Wisthethicknessofsemiconductorcrystal.VandIarethevoltageandcurrentacrossandthroughthecrystalchip.

TheenergybandgapEg(ineV)ofasemiconductorisgivenby:

10

2.3026E 2 log

1/ Tgk

wherekisBoltzmanconstantequalto8.6 105eV/degreeandTisthetemperatureinKelvin.

APPLICATIONS

Usedtobothcharacterizethematerialandasaprocesscontrolparameterforthesemiconductormanufacturingprocess.

Resistivityofdifferentsemiconductingmaterials.

PROCEDURE

1. Connectonepairofthedirectcurrentsourcethroughmilli-ammeter.2. Otherpairofprobesisconnectedtothemilli-voltmeter.3. Placethefourprobearrangementintheelectricovenconnectedtoapowersupply.4. Fixupathermometerinthisarrangement.5. Switchontheconstantcurrentsourceandadjustthecurrenttoaparticularsuitablevaluesay2mA.6. GoonmeasuringtheinnerprobevoltageVfordifferenttemperatures.

EXPERIMENT NO. 6

Directcurrentsource

PowerSupply

Oven

Oven

II

ProbesmV

mV

V

S

W

Figure6.1:Circuit Diagram for Four Probe Method

Sample(crystal)chip


OBSERVATIONS

Current(I) =.mA(constant)

Distancebetweenprobes(S) =.mm

Thicknessofthecrystalchip(W) =..mm

TABLE

S. Temperature Voltage Temperature 1/T 103 Log10

No. (C) (Volts) (K) (ohmcm)

1. 20 293 3.41

2. 30 303 3.30

3. 40 313

4. 50 --

5. 60 --

6. 70 --

7. 80 --

8. 90 --

9. 100 --

CALCULATIONS

FindresistancecorrespondingtotemperatureinKusing:

0

0

Vohm-cm where 2 S .........ohm cm

W/ S If

Fordifferent'V'calculate 0 andhenceinohmcm.Find(W/S)andthencorrespondingtothisvalue

choosethevalueoffunctionf(W/S)fromthefollowingtable;

TABLE:For f (W/S) function corresponding to W/S geometry of the crystal

S.No.W/S f(W/S) S.No. W/S f(W/S) S.No. W/S f(W/S)

1. 0.100 13.863 5. 0.500 2.780 9. 3.333 1.022

2. 0.141 9.704 6. 1.000 1.504 10. 5.000 1.007

3. 0.200 6.391 7. 1.414 1.223 11. 10.000 1.00045

4. 0.250 5.9 8. 2.000 1.094

GRAPH

Nowplotagraphforlog10 versus1/T 103aspresentedinfigure6.2.

Slopeofthecurveis

10logA B

1BC 1000T

0

(ohmcm)


Hencebandgap,10

T

2.3026E 2 log ( V)

Igk e

A B2 2.303 1000

BCk

A B

E 0.396 VBCg

e

RESULT

1. Resistivityofsemiconductorcrystalatdifferenttemperatureswasstudied&ispresentedinthegraphoflog10 andI/T 10

3.

2. EnergybandgapofsemiconductorcrystalEg=............eV

StandardEgofGe=0.72eVandforSi=1.1eV

Standardvalue ObservedvaluePercentageerror 100 ...........%

Standardvalue

PRECAUTIONSANDSOURCEOFERROR

1. Thesurfaceonwhichtheprobesrestshouldbeuniform.

2. Donotexceedthetemperatureoftheovenabove120Cforsafeside.

3. Semiconductorcrystalwithfourprobesisinstalledintheovenverycarefullyotherwisethecrystalmaygetdamagedbecauseitisbrittle.

4. Currentshouldremainconstantthroughouttheexperiment.

5. Minimumpressureisexertedforobtainingproperelectricalcontactstothechip.

1 Whatdoyoumeanbyenergybandgap?

2 Howarethebandsformedinthesolids?

3 Whatdoyoumeanbyvalencyband,conductionbandandforbiddenband?

4 Howdoyoudifferentiatebetweenaconductor,aninsulatorandasemiconductorinrelationtotheenergygap?

5 Whatdoyoumeanbyintrinsicandextrinsicsemiconductors?

6 WhysemiconductorsbehaveasaninsulatoratzerodegreeKelvin?

7 WhatisaP-Njunction?

8 Whatisann-typesemiconductorandp-typesemiconductors?

9 Whatdoyoumeanbyforwardandreversebiasingofajunctiondiode?

10 Whatistheadvantageoffourprobemethodoverothermethodsofmeasuringtheresistivity?

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 10 20 30 40

Slopeofthecurve=AB

BC

1

T(K)x1000

A

C B

VIVA-VOCE

Figure6.2


AIM:TostudytheHalleffectandhencedeterminetheHallcoefficient(RH)andcarrierdensity(n)of

agivensemiconductormaterial.

APPARATUS:HallProbe(GeCrystal)(thickness0.4-0.5mm);HallProbe(InAscrystal),HallEffectset-up(Digitalmillvoltmeter(0-200mV)andconstantcurrentpowersupply,Electromagnet(Fieldintensity11,0005%gauss),Constantcurrentpowersupply.

FORMULA:AsshowninFigure7.1,zisthethicknessalongZ-axisofthecrystal.HzisthemagneticfieldappliedalongZaxis.CurrentIisflowingalongX-axis.HallvoltageV

Hisdevelopedacrossthefacesnormalto

Y-axisandxisthelengthofthecrystalalongX-axis;

(i) Hallcoefficientz

HH

IH

ZVR

. voltcm Coulombcm

IH

ZVGA

z

H /10. 3811 whereV

Hisinvolts,I

i namperes,ZincmandH

zingauss.

(ii) Carrierdensity 3.

1 cmqR

nH

(whereq=electroniccharge=1.6x10-19C)

THEORY:AnE.M.F.issetuptransverselyacrossacurrentcarryingconductorwhenaperpendicularmagneticfieldisapplied.ThisiscalledtheHallEffect.

I

h

E =hVy

H

y

ZX

mV

Crystal

Polepiece

Z

S

N

Vh

Ix

Ix

Figure7.1:Sample for studying Hall effect

Figure7.2:Illustration of measurement of Hall Voltage

EXPERIMENT NO. 7


APPLICATIONS

AutomotiveIndustry:Level/tiltmeasurementsensor,Throttleanglesensorautomotivesensors,Crankshaft

positionorspeedsensor,Anti-skidsensor,DoorinterlockandignitionsensorTransmissionmountedspeed

sensor,RPMsensors,Distributormountedignitionsensoretc.

Electronicindustry:Sequencingsensors,Magneticcardreader,Proximitysensors,Officemachinesensors

Adjustablecurrentsensors,Linearfeedbacksensor,Multiplepositionsensor,Microprocessorcontrolledsensor,

BrushlessDCmotorsensorsetc.

AerospaceIndustry:Temperatureorpressuresensor,Remoteconveyorsensing,Remotereadingsensing,

Currentsensors,Flowratesensor(linearoutputPistondetectionsensor).

PROCEDURE

1. ConnectthewidthwisecontactsoftheHallProbe(withGecrystal)tothevoltageterminalandlengthwise

contactstocurrentterminalsoftheHalleffectset-up.

2. NowswitchONtheHallEffectsetupandadjustthecurrenttoafew(mA).

3. ChecktheZerofieldPotentialbychangingKnobtothevoltageside.Thisvoltageiserrorvoltageand

shouldbesubtractedfromtheHallvoltagereading.(i.e.,whenHallprobeisoutsidethemagneticfield).

4. NowplacetheHallprobeinthemagneticfield.ThisHallprobemustbefittedinthewoodenstandbefore

placing inmagneticfieldsothatHallprobebecomesperpendiculartothemagneticfield.

5. Switchontheelectromagnetpowersupplybyconnectingthepolepiecetothepowersupply.

6. NowplacetheHallprobe(InAs)attachedwithGauss-meterbetweenthepolepiecestomeasurethe

magneticfield.

7. MeasuretheHallvoltageasafunctionofcurrentkeepingthemagneticfieldconstant.

8. MeasuretheHallvoltageasafunctionofmagneticfieldkeepingasuitablevalueofcurrentasconstant

(Thisis donebyplacingtwoprobesbetweenthepolepiecesanddecreasethespacingbetweenthepole

pieceandmeasurethemagneticfieldandHallvoltage).

9. PlotthegraphbetweenVHandI(H

Z=constant);V

HandH(I=constant).

10. CalculatetheslopeVH/IandV

H/H

ZfromthetwographsandcalculateHallcoefficientintwowaysand

determinethemeanvalue.

OBSERVATIONS

ThicknessofthesemiconductorcrystalZ=0.5mm=0.05cm

Conductivity1 11 ohm cm

Table1:MagneticfieldHz=1000Gauss Table2:CurrentI=5mA

S.No. CurrentI(mA)

HallVotageV

H(mV)

1.2.3.4.5.

S.No. MagneticfieldH

Z(Gauss)

HallVotageV

H(mV)

1.2.3.4.5.


0

A

BC

AB

BCSlope=

Scalex-axis1cm=.....mAy-axis1cm=.....mV

Current,I(mA)0

A

BC

AB

BCSlope=

Scalex-axis1cm=.....Gaussy-axis1cm=.....mV

Magneticfield(H )Z

CALCULATIONS

Slope BC

AB

I

VH(FromplotV

Hvs

I), Slope BC

AB

H

V

Z

H(FromplotV

Hvs

H

Z)

(i)

z

HH

H

Z

I

VSlopeR 1 VoltcmAA-1G-1=x108cm3/coul.

I

Z

H

VSlopeR

Z

HH1 VoltcmAA-1G-1=x108cm3/coul.

Mean ./2

321 coulcmRR

R HHH

(ii) CarrierDensity )106.1(1 19 q

qRn

H

3

193/

)106.1)/(

1cm

coulcoulcmn

RESULT

ThevalueofHallCoefficient(RH)iscm3/coul.

Thecarrierdensity(n)=/cm3.

Figure7.3. Plot of VH versus I Figure7.4. Plot of V

H versus H

Z


PRECAUTIONS

1. TheHallprobe isplacedbetween thepolepieces (inmagnetic field) such thatmaximumHall

voltageisgenerated.

2. CurrentthroughtheHallprobeshouldbestrictlywithinthelimitasmentionedbythemanufacturer.

3. Hallvoltagedevelopedmustbemeasuredveryaccurately.

4. Magneticfieldisvariedgraduallyinstepstoavoiddamagetotheelectromagneticcoils.

WhatistheHallEffect?

Onwhatfactor,thesignoftheHallpotentialdifferencedevelops?

Whyisthepotentialdifferencedevelopedwhenatransversemagneticfieldisappliedtoacurrentcarrying

conductor?

Howwillyoudeterminethedirectionoftheforceexertedonthechargecarriers?

WhatistheHallcoefficient?Whatareitsunits?

REFERENCES

1 PracticalPhysicsGupta.Kumar

2 AtextbookofPracticalPhysicsR.KGoel.GovindRam

3 B.ScPracticalPhysicsC.LArora

4 ElectronicsfundamentalsandapplicationsRyder,J.D

5 PropertiesofsiliconandgermaniumConwell,E.M

6 EngineeringPhysics-M.NAvadhanulu,A.ADaniandP.MPokley

7 ALaboratoryManualofPhysicsD.PKhandelwal

8 B.ScPracticalPhysicsHarnamSingh

VIVA-VOCE


AIM:Todeterminethe(1)NumericalAperture(NA),(2)PowerLossesduetoMacrobendingandadaptorofgivemopticalfibre.

APPARATUS:LED,NAJig,D.M.M,scaledscreen,adaptor,oneandthreemeterlengthofopticalfiber,mandrel.

PRINCIPLE&FORMULA

1.TheNumericalAperture(N.A)ofanopticalfiber(stepindex)isgivenby

1

2 2 2core cladN.A. n n ......(1)

maxsin i

or 1maxi sin N.A. ......(2)

ncore

=refractiveindexofcore,n

clad=refractiveindexofcladding

imax

=acceptanceangleAsshowninfigure8.1,lightfromtheendoftheopticalfiberAfallsonthescreenBD.LetthediameteroflightfallingonthescreenBD=W,LetthedistancebetweenendofthefiberandthescreenAO=LKnowingWandL,theN.AcanbecalculatedandsubstitutingthisN.AvalueinEq(2),theacceptanceanglecanbecalculated.

2. LossesofpowerinfibreopticcablearemainlyduetoabsorptionorscatteringoflightwithOpticalfibre,macrobendingandjointsbetweencables(adaptor).ThislossofpowerPfrominput(P

o)tooutput(P

L)

atadistanceL,canbewrittenas LL 0P P e

Whereistheattenuationcoefficientindecibels(dB)perunitlength.(GenerallydB/KM)

L

P

P10.log

L

o10

L

10L 0P P 10e

APPLICATIONS

Telecommunications LocalAreaNetworks(LANs)andWideAreaNetworks(WANs) FactoryAutomation,PremisesWiring.Fiber-opticbiomedicalsensors,Endoscopicimaging,

AerospaceandMilitaryApplications,Fiberopticsensors.

EXPERIMENT NO. 8

Foled

Opticalfibre

A imax

LD

O

B

W

Screen

N.A.=W

(4L2+W2)12

Figure:8.1


PROCEDURE

1. InsertoneendofeitheroneorthreemeterlengthopticalfibercabletheLEDandNAjig..SwitchonLED,thenredlightwillappearattheendofthefiberontheN.AJig.TurnSETP0/IFknobtheintensitywillincrease.ArrangethescaledscreenatadistanceL,andthenviewtheredspotonthescreen.Measurethediameterofthespot(w).NotethemeasuredvaluesLandWinthetable.Repeattheexperimentwithdifferentdistancesandnotethereadings.

S.No L(mm) W(mm) N.A imax

1

2

3

2. InsertoneendofthethreemeterlengthplasticopticalfibrecabletotheFOLEDandconnectanotherendtothepowermetermodule.ConnectD.M.MtestleadstoPout,redleadtoredsocketandblackleadtoblacksocketrespectively.SetD.M.Mto2000mVrange.SwitchonLED,adjusttheSetPo/IFknobtosetoutputpoweroftheFOLEDtothevalue-22.0dBm(millidecibels)i.e.,DMMreadingwillbe-220mV,notethisasP

O,windthefibreonthemandrelandnotethereadingasP

Ow

1,similarlyfortwo

andthreeturns.NotethereadingsasPOw

2andP

Ow

3respectively.

xO/Ppower(dBm) Lossduetoturns(dBm)

Po0 -

POw1 - (PO0-POw1)=

POw2 - (PO0-POw2)=

POw3 - (PO0-POw3)=

3. ConnectonemeterOFcableasgivenaboveandsetD.M.Mforaconstantvalue(-120mV)andnotethereadingasP

1.SimilarlytakeP

2byreplacingonemetercablewith3metercablewithoutdisturbingSET

PO/I

fknob.Nowjointhe1and3mcableswiththeadopteronshowninthefigureandnoteDMM

readingasP3.

OBSERVATIONS

P1=

P2=

P3=

CALCULATIONS

TakeP1,P

2andP3asshowninFig.,withoutdisturbingtheSETPo/I

fknob.

Lossinonemetercable(X)=

2

PP 12

Lossduetoadopter=P3P

13X=


1m cable

PO P1

3m cable

PO P2

1m cable

PO

3m cable Adapter

P3

RESULT

1. N.AofgivenOpticalfiberis2. PowerlossduetooneturndBm,twoturnsdBmandthreeturnsdBm3. PowerlossduetoonemetercabledBmandduetoadaptordBm

PRECAUTIONS

1. GentlyinserttheopticalfibercableistoLEDbyturningclockwisedirectionofitsclinchnut.(untilyoufeelthefibertouchesthemicrolens)

2. Donotpushapplyingoverforcewhichmaydamagemicrolens3. Gentlytighttheclinchnutthatholdstheinsertedfiberfirmly.4. Beforetakingreadingcheckoutfiberisfreeofalltwistsandstrains.5. TwocablesmustmeetatthecenteroftheadopterwhiletakingP

3reading.

1. Whatdoyoumeanbynumericalaperture?2. Onwhatfactorsthenumericalaperturedepends?3. Whatdoyoumeanbyacceptanceangle?4. Onwhatfactorstheacceptanceangleofthefiberdepends?5. Afiberwithhighnumericalaperture(NA)ispreferableornot?Why?6. Whatisirradiance?7. Whatdoyoumeanbybandwidth?

REFERENCES

1 PracticalPhysicsGupta.Kumar2 AtextbookofPracticalPhysicsR.KGoel.GovindRam3 B.ScPracticalPhysicsC.LArora4 ElectronicsfundamentalsandapplicationsRyder,J.D5 PropertiesofsiliconandgermaniumConwell,E.M6 EngineeringPhysics-M.NAvadhanulu,A.ADaniandP.MPokley7 ALaboratoryManualofPhysicsD.PKhandelwal8 B.ScPracticalPhysicsHarnamSingh

Figure8.2

VIVA-VOCE


AIM:TostudythecharacteristicsofPNJunctiondiodeandtocalculateresistanceofadiodeinforwardandreversebias.

APPARATUS:Powersupply,Voltmeter,Ammeter,Diodeandconnectingwires

PRINCIPLE

WhenaPtypematerialisjoinedwithNtype,aPNJunctionisformed.Theplanedividingthetwozonesisknownasajunction.Duetodiffusion,someoftheelectronsfromNregioncrossovertoPregionwheretheyrecombinewithholes,andholesfromPregioncrossovertoNregionandrecombinewithelectrons.Thusalayerisformedwhichisknownasdepletionlayerorchargefreeregionorspacechargeregionwherethereisnofreechargesavailableforconductionofcurrent.Thediffusionoftheelectronsandholesacrossthejunctioncontinuestillapotentialbarrierisdevelopedindepletionlayerwhichpreventsfurtherdiffusionofcharges.Thepotentialbarriercanbeincreasedordecreasedbyapplyinganexternalbiasvoltage.

APPLICATIONS

Electronicindustry

Signalrectifier/Diodegates/Diodeclamps Limiter/Over-voltageprotection/Ionizingradiationdetectors Temperaturemeasuring/Computerstocellularphonestodigitalaudioplayers.

THEORY

ForwardBias:WhentheP-Njunctionisforwardbiasedi.e.,whenthe+veterminalofthebatteryisconnectedtotheP-sideandveterminalisconnectedtotheNside,theholesfromPsidearerepelledbypositivechargesofthebatterytowardsthejunction.SimilarlyatthesametimeelectronsinNsidewillberepelledbynegativechargesfromthebatterytowardsthejunction.Herebatteryvoltageshouldbehightoimpartsufficientenergytothesecarrierstoovercomethepotentialbarrieratthejunctionandenablethemtocrossthejunction.Henceacurrentstartflowingafteraminimumvoltagecalledpotentialbarriervoltage

Reverse Bias:

Revesebiasingincreasesthepotentialbarrier,therebyresultinginaverylittlecurrenttoflow.Whenthejunctionisreversebiasedi.e.,when+veterminalofthebatteryconnectedtotheNsideandveterminalisconnectedtotheP-side,theelectronsinNsideandholesinPsideareattractedawayfromthejunction.Forsufficientnegativebias,thedepletionregionbreaksdownandreversecurrentstartsflowingacrossthecircuit.

PROCEDURE

a)Forwardbias:

1. Connectthecircuitasshowninfigure9.1.

2. Vary the potential difference and note thecorrespondingcurrentvalue.

3. Drawthegraphbytakingpotentialorvoltage(V)onX-axisandcurrent(I)onY-axis.

EXPERIMENTNO.9A

+mA

V

p n RL

RheostatorPOT

+

+

Figure9.1:Forward bias


b)Reversebias:

1. Maketheconnectionsasshowninfigure9.2.2. Varythepotentialdifferenceandnotethecorrespondingcurrent

value.3. Drawthegraphbytakingpotentialorvoltage(V)onX-axis

andcurrent(I)onY-axis.

TABLE

Forwardbias

Reversebias

S.No. V(volts) I(mA) S.No. -V(volts) -I(A)

1

1

2 2

3 3

4 4

5 5

6 6

RESULT:TheVoltAmperecharacteristicsofagivenPNJunctionDiodearestudied.

PRECAUTIONS

1. Seethatalltheconnectionsgivenproperly2. Identifythepositionofthediode,whetheritisinforwardor

reversebias.3.Donotapplyvoltagebeyondcertainvaluesineitherbias.

AIM: TostudytheV-IcharacteristicsofgivenZenerDiodeandtodetermineZenerbreakdownvoltagealsofindtheforwardandreverseresistance.

APPARATUS:Zenerdiode(3Z15V),3watts,Resistor75 ,5W,Ammeter(0-500mA),Voltmeter(0-30V),RPS.

+V

pn RL

RheostatorPOT

+

+

Figure9.2:Reverse bias

mA

Forwardbias

Reversebias

V

Figure9.3

EXPERIMENTNO.9B


THEORY:Diodesaredesignedwithadequatepowersupplydissipationcapabilitiestooperateinbreakdownvoltageregionmaybeemployedasvoltagereferenceaswithoutvoltagedevices.Suchdiodesareknownasavalanchediode.

Breakdownorzenerdiode,twomechanismsofbreakdownofdiodeforincreasingreversevoltageare

found.Firstwethermallygeneratedpotentialtoproducenewcarriersinturnproduceadditionalcarrieragainthroughprocessofmiscopyingbonds.Evenifinitiallyavailablecarriersdontacquiresufficientenergytodisruptbonds.Itispossibletoinitiatebreakdownvoltagethroughadirectruptureofbondsbecauseofexistenceofstrongelectricfieldunderthesecircumstances.Breakdownisknownaszenerbreakdown.

PROCEDURE

ForwardBias:Todetermineforwardcharacteristicsbuiltupthecircuitasshowninthefigure.IncreasethesourcevaluevoltageV

cssothat

voltmeteradvancesinstepsof0.05V.NotethecorrespondingammeterreadingforincrementvalueofV

f.

ReverseBias: Todeterminereversecharacteristicsbuiltupthecircuitasshowninthefigure.IncreasesourcevoltageV

BBsothatvoltmeter

readingadvancesinstepsof0.5V.NotethatcorrespondingammeterreadingI

ZforeveryincrementatvalueofV

Z.Tabulateallreadingsand

plotforwardcharacteristics.

CALCULATIONS

Staticforwardresistance,F

FF

VR

I =.........

Staticreverseresistance,R

RR

VR

I =.........

DynamicforwardresistanceF

F

V

I

=.........

DynamicreverseresistanceZ

Z

V

I

=.........

V(0-30V)RPS

S

ZenerDiode

A+_

_

+VF+

_

+

_

V(0-30V)RPS

BBA

_

+

VZ+

_

(0-30mA) 75ohms,5W

+ _

02

3Z15V+_

Figure9.5:Reverse bias circuit

S.No. VF(Volt) IF(mA)

12345

S.No. VZ(Volt) IZ A12345

+I(mA)

I-I(mA)

Z

+V(VsHs)-VVsHs Barrier

PotentialIZMar

VZ

22mA

IF

VF

Figure9.6


RESULT

Dynamicforwardresistance =

Staticforwardresistance =

Dynamicreverseresistance =

Staticreverseresistance =

PRECAUTIONS

1. Caremustbetakenthatallthesourcesandmetersareconnectedwithcorrectpolarity.

2. Seethatthecurrentlimitofregulatedpowersupplyissetto250mA.

1. WhatisaZenerdiode?

2. Whatdoyouunderstandbybreakdownvoltage?

3. ExplainZenerandAvalanchebreakdown?

4. Whatiskneevoltage?

5. Explaintheroleofdopingfordifferentbehaviorofdiodes.

6. CanweinterchangetheVaxisandIaxisofdiodecharacteristiccurve?Ifnotwhy?

REFERENCES









VIVA-VOCE


AIM:MeasuringtheDiameterofaHumanHairbyLaserDiffraction

THEORY:Oftenitisnecessarytodeterminethediameterofafinewire,thinthreadorotherobjectthatcannotbemeasuredbyconvectionalmeans.Theseitemscanbemeasuredbyusingmethodsofdiffractionandinterfer-enceknownasYoungsDoubleSlitExperiment.WhileYoungsexperimentdealwiththepatternoflightimping-ingontwonarrowsslitsseparatedbyasmalldistance,themethodcanbyappliedtoanobjectwithasmalldiameteraswell.Wherethediameteriswithinanorderofmagnitudeofthewavelengthoflaserlightused.

PROCEDURE

1 Takea15cmby15cmpieceandmakea10cmby10cmholeinthecenterofthecardboardpiece.Thisisyourmountingbracket.

2. Selectonestrandofhairapproximately15-25cmlong.Thishairneedstobemountedonthemountingbracketfromstep1.

3 Mountthehaironthebracketusingtape.Placethehairsothatitbisectsthemountingbracket.Makesurethehairistautandstraight.

4. Setthelaserpointer(orlaser)onthelabtable.Positioningthelasersothebeamstrikesthehairinthemountingbracket.(Youmayusebinderclipsorbookstopositionthelasersourceandthemountingbracketonthetable.)

EXPERIMENT NO. 10


5. Makesurethelasersetupandmountingbracketfaceawallorscreen.6. Recordthefollowingkeyparametersonthedatasheetprovided.Recordthewavelengthofthelaser

as .Insomecaseitmaybenecessarytoaveragethewavelengthvaluesgivenonthelaserslabel.

TypicalvaluesforaredHeNeLaserare632-634nm.Redlaserpointershaveatypicalrangebetween630nm680nm.Recordthedistance(D)betweenthemountingbracketandscreenorwall.(Ifyouareusingawallforascreenitmightbeprudenttotapeapieceofwhitepaperonthewalltouseasabackground.)

7. Examinethepatternstrikingthescreen.Itshouldappearsimilartotheimagebelow.(Youmayneedtodarkentheworkareaorroomtoseethefainthigherorderbands.)

8. Carefullymeasurethebrightbandsbymeasuringfromthecenterofthebrightcentralbandtothestartingedgeoffirstbrightbandontheleft.Recordthisvalueasy1i,undertheymicolumn.(Youmayfindabringspotinthecenterofthecentralband.Thispointcanbeusedasreference.)Measurefromthecenterofthecentralbandagaintotheendofthefirstbrightbandontheleft.Recordthisasy1f,undertheymfcolumn.Theaverageofthesetwomeasurementsisthedistancebetweenthecentralbrightbandandthe1stordermaximum(m=1)ontheleftside.Recordthisonthedatatableasy1avgundertheymavgcolumnonthedatasheet.Repeatthestepsforthe2nd,3rd,4thand5thorderbands.Ifyoucanseethebandsbeyondm=5,measurethoseaswell.Makesureyoumeasurefromthemiddleofthecentralbandtothebeginningandtheendofeachofthemthorderbands.(Youmayhavetodarkentheroomtoseeallthebands.)

9. Aftermeasuringallthebandsontheleft.Proceedtomeasurethemthorderbandsontherightsideofthecentralbandusingthesametechniquesoutlinedinstep8.Thisshouldyieldatotalsetofatleasttenmeasurements.

10. Foreachymavgcalculatethediameterofthehumanhair(d)using:

mavgd m D y 11. Afterdeterminingthetenvaluesofdcalculatetheaveragediameterofahumanhairandthestandard

error d( ) inthemeasurementofd.wherethestandarderroristhestandarddeviationofddividedby

thesquarerootofthenumberofmeasurementstaken.

1/2d dS N

EXAMPLECALCULATIONS

Exampleforthe1storder(m=1)bandforaHeNelaserwavelength =633nm,andscreendistanceofD=1.5m.

9 51d 633 10 m 1 1.5 0.02m 4.75 10 m or 47 m


Exampleforthe4thorder(m=4)bandforaHeNelaserwavelength=633nm,andsecreendistanceofD=1.5m.

9 54d 633 10 m 4 1.5 0.0575m 6.61 10 m or 66 m

Thesameexperimentcanbetriedoutonaneedleorpin.

1. Whatistherangeofvaluesforhumanhair?

2. Averagetherangeofvaluesofhumanhair.Whatisthepercentdifferencebetweenyouraveragevalueandtheaverageacceptedvaluefromdifferentsourcesofinformationsuchasbooksorinternet?

3. Whatotheritemscouldyoumeasureusingthistechnique?

4. WhatisHe-Nelaser?Howitworks?

5. Whywecantmeasurehumanhairdiameterusingscrewgauge?

6. Whatisdiameterofdustparticle(floatinginair)?

DiamterofahumanhairDataSheet

Laserwavelength=

m

+7

+6

+5

+4

+3

+2

+1

0

-1

-2

-3

-4

-5

-6

-7

|m|

7

6

5

4

3

2

1

N/A

1

2

3

4

5

6

7

Ymi

Ymf Ymavg CalculatedDiameter

AverageDiameter

Error

N/A N/A

VIVA-VOCE


Someexamplesofdiameterofhumanhair

Bibliographicentry Result StandardizedResult

PiezoTechnology.Epson(UK)Ltd.

DennyR'sHomepage.Denny&GayleRossbach.Palmdale,CA

WhyChooseAWaterTreatmentSystem?Aqua-FreshDrinkingWaterSystems,Inc

Hair-ImportantFactsAboutHair.CAQTICosmetics,Inc.

"45microns,2timessmallerthanthediameterofahumanhairandclosetothelimitof

resolutionforthehumaneye"

"Diameterofahumanhairinches:0.001;centimeters:0.00254"

"Particulatecontaminantsincludingasbestos,rust,sediment,dirt,andscaleassmallas0.2microns(1/300thdiameterofahumanhair)."

"Flaxenhairisthefinest,from1/1500to1/500ofaninchindiameterandblackhairisthe

coarsest,from1/450to1/140ofaninch."

90 m

25.4 m

6 0 m

17 50 m (flaxen)

51 181 m (black)


AIM: Studyof both the current - voltage characteristic and the power curve to find themaximum power

point(MPP)andefficiencyofasolarcell.

APPARATUS:SolarPanelConsistof6solarCells,Tablelamp,Digital/AnalogD.Cammeterandvoltmeter.

THEORY:Asolarcellorphotovoltaiccellisadevicethatconvertslightenergyintoelectricalenergy.Sometimesthe

termsolar cellisreservedfordevicesintendedspecificallytocaptureenergyfromsunlight,whilethetermphotovoltaic

cellisusedwhenthelightsourceisunspecified.Fundamentally,thedeviceneedstofulfillonlytwofunctions:photo

generationofchargecarriers(electronsandholes)inalight-absorbingmaterial,andseparationofthechargecarriersto

aconductivecontactthatwilltransmittheelectricity.Thisconversioniscalledthephotovoltaic effect,andthefieldof

researchrelatedtosolarcellsisknownasphotovoltaic.

Solarcell

P n

10E/Step

RL

2V/20V

+V

+

20/200mA

mA-+

+

(A)CircuitSymbol

SiliconCoating

SunlightEnergy

MetalContact

MetalContact

Junction

(B)Cross-section

P

N

APPLICATIONS

Telecommunicationsystems:Radiotransceiversonmountaintopsortelephoneboxesinthecountrycanoftenbesolarpowered.

Remote monitoring and control: scientific research stations, seismic recording, weather stations,

etc.useverylittlepowerwhich, incombinationwithadependablebattery,isprovidedreliablybya

smallPVmodule.

Oceannavigation aids:many lighthousesarepoweredby solar cells.

WaterPumping/RuralElectrification/Domesticsupply

Health Care/Lighting Electronicindustry ElectricPowerGenerationinSpace.

EXPERIMENT NO. 11

Figure11.1

Figure11.2:Solar cell


SIMPLE EXPLANATION

1. Photonsinsunlighthitthesolarpanelandareabsorbedbysemiconductingmaterials,suchassilicon.

2. Electrons(negativelycharged)areknockedloosefromtheiratoms,allowingthemtoflowthroughthematerial

toproduceelectricity.Thecomplementarypositivechargesthatarealsocreated(likebubbles)arecalledholes

andflowinthedirectionoppositeoftheelectronsinasiliconsolarpanel.

3. Anarrayofsolarpanelsconvertssolarenergyintoausableamountofdirectcurrent(DC)electricity.

PHOTO GENERATION OF CHARGE CARRIER

Whenaphotonhitsapieceofsilicon,oneofthreethingscanhappen:

1. Thephotoncanpassstraightthroughthesiliconthis(generally)happensforlowerenergyphotons,

2. Thephotoncanreflectoffthesurface,

3. Thephotoncanbeabsorbedbythesiliconwhicheither:GeneratesheatorGenerateselectron-holepairs,ifthe

photonenergyishigherthanthesiliconbandgapvalue.

CHARGE CARRIER SEPARATION

Therearetwomainmodesforchargecarrierseparationinasolarcell:

1. Driftofcarriers,drivenbyanelectrostaticfieldestablishedacrossthedevice

2. Diffusionofcarriersfromzonesofhighcarrierconcentrationtozonesoflowcarrierconcentration(followinga

gradientofelectrochemicalpotential).

Inthewidelyusedp-n junctiondesignedsolarcells,thedominantmodeofchargecarrierseparationisbydrift.

However,innon-p-n junctiondesignedsolarcells(typicalofthethirdgenerationofsolarcellresearchsuchasdyeand

polymerthin-filmsolarcells),ageneralelectrostaticfieldhasbeenconfirmedtobeabsent,andthedominantmodeof

separationisviachargecarrierdiffusion.

PROCEDURE

1. TaketheSolarEnergyTrainerNV6005alongwithSolarPanel.

2. Placethesolarpanelinthestandandadjustthepanelatanangleofabout45withtheground.Directthesunlight

straightatthesolarpanel(angleof90).

Note: If sunlight is not properly available then any source of light like lamp can be used.

3. WiththeDB15connectorconnecttheSolarEnergyTrainerNV6005withSolarPanel.Thenwaitfor1minute

toavoiderrorsduetotemperaturefluctuations.

4. Setthepotentiometertomaximumresistancei.e.atfullyclockwisepositionandmeasureandrecorditsresistance

intotheObservationTable.

5. Connectthesolarcellasshowninthefollowingcircuitdiagramasshowninfigure11.3.

a. ConnectpositiveterminalofsolarcelltoP1terminal

ofthepotentiometer.

b. Connectotherendofpotentiometeri.e.P2topositive

terminalofammeter.

c. Connect negative terminal of ammeter to negative

terminalofsolarcell.

d. NowconnectthepositiveterminalofvoltmetertoP1

andnegativeterminalofvoltmetertoP2.

6. Recordthevaluesofcorrespondingvoltageandcurrent

intotheobservationTable.

SolarCellsPanel

V

A

+

+ -

-

P1 P2

Figure11.3


7. Nowgraduallymovethepotentiometerinanti-clockwisedirectionsothattheresistanceofthepotentiometer

decreases.Nowmeasuretheresistancesatsuccessivelysmallervaluesandrecordthecorrespondingvaluesof

voltagesandcurrentintotheObservationTablebelow.

Note: Always to measure the resistance of potentiometer at any position, first remove the patch cords from P1 and

P2 and measure resistance by multi meter. Reconnect these connections again for further measurements.

OBSERVATION TABLE

8. PlottheV-Icharacteristicsfromthemeasurementsrecordedinthetable,toshowhowthephotoelectriccurrent

dependsonthephotoelectricvoltageandtofindmaximumpowerpoint.

Fillfactor Calculation

Fill factor is the ratio of maxmium useful power to ideal power:

Maximumusefulpower isareaof largest rectangle that canbe

formed underV-I curve.Vm and I

m are values of voltage and

currentfortheseconditions.

Maximumusefulpower m mV I

And Idealpower OC SCV I

where ISC

=maximumvalueofsaturationcurrent

VOC

=emfgenratedbyphotovoltaiccellinopencircuit.

Fillfactorm m

OC SC

V I

V I

FromV-Icharacteristicsyoucaneasilyfindthemaximumpower

point (MPP).MPP occurs where the product ofvoltage and

currentisgreatest.

9. Plotthecurveofpowerasafunctionofvoltagefrom

themeasurementsrecordedinthetable.

ExpectedPower-Voltagecurveisasshowninfigure11.6.

Resistance, R Voltage,V(Volt) Current,I(mA) PowerCalculatedP=V.I(watt)

S.No.

1

2

3

4

5

6

7

8

Figure11.4: Current voltage characteristic of the solar cell

Voltage(V)

MPP

0.02

0.5 1 1.5 2.0

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Vm VOC

ISC

ISC

Im

Voltage(V)

Po

wer

(W

)

MPP

0.05

0.5 1 1.5 2.0

0.1

0.15

0.2

0.25

Figure11.6: Power curve of the solar cell as a function of voltage


Themaximumpowerpoint(MPP)isthemaximumvalueofpowerintheabovecurve.

Theresistance,RMPP,atwhichtheoutputpowerisatamaximum,canbecalculatedusingthefollowingformula:

MPPMPP

MPP

VR

I

TOCALCULATETHE EFFICIENCY () OFSOLARCELL

Theefficiencyofthesolarcellistheratioofproducedelectricalpower(Pout)andtheincidentradiantpower(Pin).

Efficiencyofsolarcell,out

in

P=

P

WherePout

istheoutputelectricalpower(maximumpowerpoint).

Piniscalculatedbymultiplyingapproximatedirradiance(irradiancemeansradiantpowerofthelightincidentperunit

area)bytheeffectiveareaofthesolarcellonthepanel.

Thismethodusedthefactthatthepracticalvalueofthecurrent(maximumphotoelectriccurrentmeasured)isproportional

tothephotons(radiation)strikingthesolarcell.Thiscurrentisthereforeproportionaltotheincidentradiantpowerofthe

light.

Theopencircuitvoltagedependsonthesemiconductormaterialofwhichsolarcellismade.Itisnotproportionaltothe

incidentradiantpowerandthereforecannotbeusedforthismeasurement.

PROCEDURE

1. Efficiencyofsolarcell,out

in

P=

P

Where

Pout

(OutputElectricalPower)=MaximumPowerPoint(MPP)

Pin(Incidentradiantpower)=ApproximatedIrradiance Areaofsolarcell=(F I

p) AA

HereA=Areaofasolarcell(LengthxBreadth)m2

Ip=Practicalvalueofcurrent(maximumphotoelectriccurrentmeasured)indicatedontheammeter,Fis

aconstantandisgivenby

Maximum solarIrradiance

F= SpecifiedbymanufacturedMaximumvalueofcurrent

Themaximumirradianceinsummerisapprox.1000W/m2.Themaximumvalueofthecurrentspecifiedbythe

manufacturerisachievedatthisvaluei.e.150mAinthegivensolarcells.(Theparametersofthesolarcell/panel

arerelatedtothestandardtestconditionsof1000W/m2andcelltemperatureof25C.)

2

W1000

mF =150mA

2

W6.67

m .mA

2. Multiplyingthepracticalvalueofcurrent(Ip)indicatedontheammeterbythefactorgivesanapproximationof

theradiantpowerperunitarea(irradiance)strikingthesolarcell.

2

WF 6.67

m -mA


Approximationoftheradiantpowerperunitarea=.

3. Nowmeasuretheareainm2andputthevaluesintheformulagivenineq.Pin=

Now,wecancalculatetheefficiencyofsolarcellwith

out

In

P=

P

WherePoutorMPP=..(Ascalculatedbeforeinexperiment)

=..

Theefficienciesofsolarcellsliebetween12to15%.Ifefficiencyisslightlylessthandeterminedvaluethenitisdueto

measuringerrorsandinaccuraciesindeterminingtheincidentradiantpower.Furthermore,theefficiencyofsolarpanel

islessthanthatoftheirseparateconstituentcells.Thisiscausedbylossesthatariseinmatchingsolarcellsthatdonotallhaveexactlythesameproperties.Ifthesolarcellsareconnectedinseriestogeneratedesiredvoltage,themaximumpowerpointmaynotbesameforallcells.Solarcelllossesariseasnotallphotonsstrikingthesolarcellcanbeconvertedintochargecarriers.Partofthelightisreflectedassoonasithitsthesurfaceandthemetalcontactscastshadows.Sincethephotonenergydoesnotcorrespondtotheenergygap,lessthanhalfoftheincidentenergyisused.Recombinationofchargecarriers(atomicrebindingofelectrons)andelectricallossescausedbyinternalresistances(ohmiclossesinthesemiconductor)ofthesolarcellanditscontactsalsoarise.

PRECAUTIONS

1. DonotmakeinterconnectionsontheboardwithmainsswitchedON.

2. Alltheconnectionsshouldbetight.

3. Switchoffaftertakingthereadings.

1. Whatissolarcell?

2. Whysolarcellisalsocalledphotovoltaiccell?

3. Whataretheusesofsolarcell?

4. Whatdoyoumeanphotoelectriceffect?

5. Onwhatfactorsdoesthephotocurrentdepend?

6. DefinetheefficiencyofSolarCell?

7. Howdoestemperatureeffectefficiencyofsolarcell/photovoltaiccell.

8. WhathappenstothecurrentwhenPhotovoltaiccellsareconnectedinseriesandinparallel.

9. Whatistheorderofcurrentinphotovoltaiccell?

10. Defineafillfactorofaphotovoltaiccell.

REFERENCES









VIVA-VOCE


AIM:Todeterminethewavelengthofsodiumlight(Monochromaticsource)withthehelpofFresnelsBi-Prism.

APPARATUS:Opticalbenchwithuprights,sodiumlamp,Bi-prism,convexlens,slitandmicrometereyepiece.Slitandmicrometereyepiecearealreadyfittedontheopticalbench.

FORMULA

ThewavelengthlofthesodiumlightisgivenbytheformulainthecaseofBi-prismexperiment.

Where b =fringewidth,2d =distancebetweenthetwovirtualsources,D =distancebetweentheslitandscreen(Eyepieceupright).

Again 1 22d d d

Where d1

= distancebetweenthetwoimagesformedbytheconvexlensinoneposition.d

2= distancebetweenthetwoimagesformedbytheconvexlensinthesecondposition.

APPLICATIONS

Tomaketwocoherentsourceforinterference.Biprismmaketwosources. Tofindwavelengthofamonochromaticlightsourceandfordeterminingthethicknessofathin

glasssheetwhenplacedbetweenbiprismandscreenoreyepiece.

DESCRIPTIONOFTHEAPPARATUS

Twocoherentsources,fromasinglesource,toproduceinterferencepatternareobtainedwiththehelpofaBi-prism.ABi-prismmayberegardedasmadeupoftwoprismsofverysmallrefractinganglesplacedbasetobase.Inactualpracticeasingleglassplateissuitablygrindedandpolishedtogiveasingleprismofobtuseangle1790leavingremainingtwoacuteanglesof30each

Theopticalbenchusedintheexperimentconsistsofaheavycastironbasesupportedonfourlevelingscrews.Thereisagraduatedscalealongitsonearm.Thebenchisprovidedwithfouruprightswhichcanbeclampedanywhereandthepositioncanbereadbymeansofvernierattachedtoit.Eachoftheuprightissubjectedtothefollowingmotions:

(i) motionalongbench,(ii) transversemotion(motionrightangletobench),(iii) rotationabouttheaxisoftheupright,(iv) withthehelpofatangentscrew,theslitandBi-prismcanberotatedintheirownverticalplanes.The

bencharrangementisshowninfigure12.1

ACTIONOFBI-PRISM

TheactionoftheBi-prismisshowninfigure12.2.MonochromaticlightfromasourceSfallsontwopointsoftheprismandisbenttowardsthebase.Duetothedivisionofwavefront,therefractedlightappearstocome

EXPERIMENT NO. 12

Slit Biprism Lens EyePieceSourceofLight

Figure12.1

d

S1

S2

S

y1 y2

E

P

F

Q

C

Figure12.2


fromS1andS

2.Thewavesfromtwosourcesuniteandgiveinterferencepattern.Thefringesarehyperbolic,but

duetohigheccentricitytheyappeartobestraightlinesinthefocalplaneofeyepiece.

PROCEDURE

ADJUSTMENTS1. Levelthebedofopticalbenchwiththehelpofspiritlevelandlevelingscrews.2. Theslit,Bi-prismandeyepieceareadjustedatthesameheight.Theslitandthecrosswireofeyepiece

aremadevertical.3. Themicrometereyepieceisfocussedoncrosswire.4. Withanopeningprovidedtothecoverofthemonochromaticsource,thelightisallowedtoincidenton

theslitandthebenchissoadjustedthatlightcomesstraightalongitslengths.Thisadjustmentismadetoavoidthelossoflightintensityfortheinterferencepattern.

5. PlacetheBi-prismuprightneartheslitandmovetheeyepiecesideway.SeethetwoimagesoftheslitthroughBi-prism;iftheyarenotseen,movetheuprightofBi-prismrightangletothebenchtilltheyareobtained.MakethetwoimagesparallelbyrotatingBi-prisminitsownplane.

6. BringtheeyepieceneartotheBi-prismandgiveitarotationatrightangleofthebenchtoobtainapatchoflight.Asamatteroffact,theinterferencefringesareobtainedinthispatchprovidedthattheedgeoftheprismisparalleltotheslit.

7. TomaketheedgeoftheBi-prismparalleltotheslit,theBi-prismisrotatedwiththehelpof tangent screw till a clearinterferencepatternisobtained.Thesefringescanbeeasilyseenevenwiththenakedeye.

ThelinejoiningthecentreoftheslitandtheedgeoftheBi-prismshouldbeparalleltothebedofthebench.Ifthisisnotso,therewillbealateralshiftandtheremovalismost important. This is shown infigure12.3.(a) Inorder toadjust thesystemfor

no lateral shift, the eyepiece ismoved away from Bi-prism. Inthiscase,thefringeswillmovetotherightorleftbutwiththehelpofbasescrewprovidedwithBi-prism,itismovedatrightangletothebenchinadirectiontobringthefringesbacktotheiroriginalposition.

(b) NowmovetheeyepiecetowardstheBi-prismandthesameadjustmentismadewiththehelpofeyepiece.Nowusingtheprocessagainandagain,thelateralshiftisremoved.

MESUREMENTS:

(A) MEASUREMENTOFFRINGEWIDTH(b)

1. Findouttheleastcountofthemicrometerscrew.2. Placethemicrometerscrewatsuchadistancewherefringesaredistinct,brightandwidelyspaced,(say100cm.)3. Thecrosswireismovedononesideofthefringestoavoi8dbacklasherror.Nowthecrosswireisfixed

atthecentreofabrightfringeanditsreadingisnotedonthemainscaleaswellasonmicrometerscrew.

S

SlitLateralShift

S1

S2

S

NoLateralShift

S1

S2

Figure12.3


4. Thecrosswireisnowmovedandfixedatthecentreofeverysecondbrightfringe.Themicrometerreadingsarenoted.Fromtheseobservationsbcanbecalculated.

(B) MEASUREMENTOFD:

Thedistancebetweenslitandeyepieceuprightsisnoted.ThisdistancegivesD.ThevalueofDiscorrectedforthebencherror.

(C) MEASUREMENTOF2d:

Thedistance2dbetweenthetwovirtualsourcescanbemeasuredwiththehelpoffig.(4).1. Toobtainthevalueof2d,thepositionsofslitandBi-prismuprightsarenotdisturbed.

2. AconvexlensisintroducedbetweenBi-prismandeye-pieceandmovedinbetweentoobtaintwosharpandfocusedimagesofthesource.Thedistancebetweentwoimagesisnoted.Inthefirstpositionfigure12.4thedistanceisdenotedbyd

1.

3. Thelensisagainmovedtowardseyepiecetoobtainthesecondpositionwhereagaintwosharpandfocusedimagesareobtained.Thedistanceinthiscaseisdenotedbyd

2.Knowingd

1andd

2.Knowing

d1andd

2,2dcanbecalculatedbyusingtheformula 1 22d d d

2d

S1

d2 d1

S2 1stpositionoflens 2ndpositionoflens

OBSERVATIONS

Pitchofthescrew =.cm.No.ofdivisionsonthemicrometerscrew =.cm.L.C.ofmicrometerscrew =..cm.

(I)TABLEFORFRINGEWIDTHb:

No.offrings

Micrometerreading(a) No.offrings

Micrometerreading(b) Deifferencefor10fringes(a b)

Meanfor10frings

Fringewidth

cms.M.S.

readingcms

V.C.reading

Totalcms.

M.S.reading

cms

V.C.reading

Totalcms.

1

3

5

7

9

11

13

15

17

19

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

......

...... ......

Figure12.4


MEASUREMENTOF2d:Positionofuprightcarryinglist =..cm.Positionofuprightcarryingtheeyepiece =..cm.ObservedvalueofD =..cm.

MEASUREMENTOF2d:

CALCULATIONS

o2d ..........AD

RESULT:

Wavelengthofsodiumlight =A0

Standardvalueof =A0

Standardvalue-ExperimentalvaluePercentage error 100

Standardvalue =.......%

PRECAUTIONS

1. Thesettingoftheuprightsatthesamelevelisessential.2. Theslitshouldbeverticalandnarrow.3. Fringeshiftshouldberemoved.4. Bencherrorshouldbetakenintoaccount.5. Crosswireshouldbefixedinthecentreofthefringewhiletakingobservationsforfringewidth.6. Themicrometerscrewshouldberotatedonlyinonedirectiontoavoidbacklasherror.7. Thefringewidthshouldbemeasuredatafairlylargedistance.8. Convexlensofshorterfocallengthshouldbeused(f=25cm.approx.).

THEORETICALERROR

Weknow2d

D

1 2d d

D

Takinglogeanddifferentiating,weget ,

2

2

1

1

2

1

2

1

d

d

d

d

D

D

Inourcase, .....21 dd

S.No.

1stpositionoflens Mean2d

Micrometerreading

2ndpositionoflens

Iimagea

IIimageb

d1=

b a Iimage

aIIimage

b

1 22d = d d

1

2

3

d2=

b a


1. Whatdoyoumeanbymonochromaticlight?WhatisBi-prism?

2. WhatisthefunctionofBi-prisminthisexperiment?

3. Whatarecoherentsources?

4. Isitpossibletoobserveinterferencefringeswithlightcomingfromtwoindependentlampsorcandles?

5. Whatdoyoumeanbyinterferenceoflight?Howmanytypesofinterferenceshaveyouread?

6. Whataretheconditionsforobtainingwelldefinedanddistinctinterference?

7. Isthereanylossofenergyininterference?Whatisfringewidth?Arethefringesequallyspaced?

8. AretheBiprismfringesperfectlystraight?

REFERENCES









VIVA-VOCE


AIM:TodeterminethedispersivepowerofamaterialofprismusingSpectrometer.

APPARATUS:Spectrometer,Prism,MercuryVaporLamp.

THEORY:Aspectrometerisusedtomeasurethenecessaryangles.Thespectrometerconsistsofthreeunits:(1)collimator,(2)telescope,and(3)prismtable.Theprismtable,itsbaseandtelescopecanbeindependentlymovedaroundtheircommonverticalaxis.Acircularangularscaleenablesonetoreadangulardisplacements(togetherwithtwovernierslocateddiametricallyoppositetoeachother).

Intheexperiment,weneedtoproduceaparallelbeamofraystobeincidentontheprism.Thisisdonewiththehelpofacollimator.Thecollimatorhasanadjustablerectangularslitatoneendandaconvexlensattheotherend.Whentheilluminatedslitislocatedatthefocusofthelens(SeeFig.1),aparallelbeamofraysemergesfromthecollimator.Wecantestthispoint,withthehelpofatelescopeadjustedtoreceiveparallelrays.Wefirstpreparethetelescopetowardsthispurposeasfollows:

SETTINGTHEEYEPIECE:Focustheeyepieceofthetelescopeonitscrosswires(forviewingthecrosswiresagainstawhitebackgroundsuchasawall)suchthatadistinctimageofthecrosswireisseenbyyou.Inthiscontext,rememberthatthehumaneyehasanaverageleastdistanceofdistinctvisionofabout25cm.Whenyouhavecompletedtheaboveeyepieceadjustment,youhaveapparentlygottheimageofthecrosswirelocatedatadistancecomfortableforyoureyes.Henceforthdonotdisturbtheeyepiece.

SETTINGTHETELESCOPE:Focusthetelescopeontoadistant(infinity!)object.Focusingisdonebychangingtheseparationbetweentheobjectiveandtheeyepieceofthetelescope.Testfortheabsenceofaparallaxbetweentheimageofthedistantobjectandtheverticalcrosswire.Parallax effect (i.e.separation oftwo things when you move your head across horizontally) exits, if the cross-wire and the image of thedistant object are not at the same distance from your eyes.Nowthetelescopeisadjustedforreceivingparallelrays.Henceforthdonotdisturbthetelescopefocusingadjustment.

SETTINGTHECOLLIMATOR:Usethetelescopeforviewingtheilluminatedslitthroughthecollimatorandadjustthecollimator(changingtheseparationbetweenitslensandslit)tilltheimageoftheslitisbroughttotheplaneofcrosswiresasjudgedbytheabsenceofparallaxbetweentheimageoftheslitandcrosswires.

OPTICALLEVELINGOFTHEPRISM:

Theprismtablewouldhavebeennearlyleveledbeforeusehasstartedtheexperiment.However,foryourexperiment,youneedtodoabitoflevelingusingreflectedrays.Forthispurpose,placethetablewithoneapexatthecenterandfacingthecollimator,withtheground(non-transparent)faceperpendiculartothecollimatoraxisandawayfromcollimator.Slightlyadjusttheprismsothatthebeamoflightfromthecollimatorfallsonthetworeflectingfacessymmetrically(Fig.2)whenyouhaveachievedthislocktheprismtableinthisposition.Turnthetelescopetoonesidesoastoreceivethereflectedimageoftheslitcentrallyintothefieldofview.Thismaybeachievedbyusingoneofthelevelingscrews.Theimagemustbecentralwhicheverfaceisusedasthereflectingface.Similarly,repeatthisprocedurefortheotherside.

FINDINGTHEANGLEOFTHEPRISM(A):Withtheslitwidthnarroweddownsufficientlyandprismtableleveled,locktheprismtableandnotetheangularpositionofthetelescopewhenoneofthereflectedimages

EXPERIMENT NO. 13

Figure13.1:Experimental setup angle of prism


coincideswiththecrosswires.Repeatthisforthereflectedimageontheotherside(withoutdisturbingtheprismandprismtable).Thedifferenceinthesetwoangularpositionsgives2a.

FINDINGANGLEOFMINIMUMDEVIATION(DM)

Unlocktheprismtableforthemeasurementoftheangleofminimumdeviation(Dm).LocatetheimageoftheslitafterrefractionthroughtheprismasshowninFig.3.Keepingtheimagealwaysinthefieldofview,rotatetheprismtabletillthepositionwherethedeviationoftheimageoftheslitissmallest.Atthisposition,theimagewillgobackward,evenwhenyoukeeprotatingtheprismtableinthesamedirection.Lockboththetelescopeandtheprismtableandtousethefineadjustmentscrewforfinersettings.Notetheangularpositionoftheprism.Inthispositiontheprismissetforminimumdeviation.Withoutdisturbingtheprismtable,removetheprismandturnthetelescope(nowunlockit)towardsthedirectraysfromthecollimator.Notethescalereadingofthisposition.Theangleoftheminimumangulardeviation,viz,D

misthedifferencebetweenthereadingsfor

theselasttwosettings.

PRINCIPLE:RefractiveIndex():

Itisdefinedas

=velocity of light invaccum

velocity of light in air

And

sinsin 2

sin sin2

mA D

i

Ar

Where AAngleofPrismDmAngleofminimumdeviation

OBSERVATIONTABLES

Forangleoftheprism:

Vernier Telescopereadingfor

reflectionfromfirstface

Telescopereadingfor

reflectionfromsecond

face

Difference

(a~b)=2A

Mean

valueof

2A

A MeanA

(Degrees)

M

S

R

V

S

R

Total(a) M

S

R

V

S

R

Total(b)

V1

V2


2.Forangleofminimumdeviation:

S.

No

Colour Vernier Dispersedimagetelescopeinminimum

deviationposition

Telescopereading

fordirectimageDifference

(a~b)

Mean

deviationDm

(Degrees)M

S

R

V

S

R

Total

(a)

M

S

R

V

S

R

Total

(b)

1.

green

V1

V2

2.

blue

V1

V2

DISPERSIVEPOWER( w):-Angularrotationforagivenwavelengthiscalleddispersivepowerofthematerialofaprism

READINGS

Directrayreading =R

Greencolourreading =R1

Bluecolourreading =R2

MinimumdeviationangleforgreenDg=RR

1

MinimumdeviationangleforblueDb

=RR2

sin2

sin2

B

b

A D

A

,

sin2

sin2

g

G

A D

A

Dispersivepowerofthematerialoftheprism,Where

SPEEDOFLIGHTINPRISM:Speedoflightinprismisgivenby


PRECAUTIONS

1. Takethereadingswithoutanyparallaxerrors

2. Thefocusshouldbeattheedgeofgreenandbluerays

RESULTS:Thedispersivepowerofamaterialofgivenprismusingspectrometeris

=Speedoflightinprism =

1. Whatdoyoumeanbydispersivepower?Defineit.

2. Onwhatfactors,thedispersivepowerdepends?

3. Whatisanormalspectrum?

4. CanyoufindoutthedispersivepowerofaPrismwithsodiumlight?

5. Howmanytypesofspectrayouknow?Whattypeofspectradoyouexpecttogetfrom(i)anincandescentfilamentlamp(ii)sunlight(iii)mercurylamp?

6. W

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