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MaximumMarks:70

TimeAllowed:3hours

GeneralInstructions:

i. Allquestionsarecompulsory.Thereare37questionsinall.

ii. Thisquestionpaperhasfoursections:SectionA,SectionB,SectionCandSectionD.

iii. SectionAcontainstwentyquestionsofonemarkeach,SectionBcontainssevenquestions

oftwomarkseach,SectionCcontainssevenquestionsofthreemarkseach,andSectionD

containsthreequestionsoffivemarkseach.

iv. Thereisnooverallchoice.However,internalchoiceshavebeenprovidedintwo

questionsofonemarkeach,twoquestionsoftwomarks,onequestionofthreemarksand

threequestionsoffivemarksweightage.Youhavetoattemptonlyoneofthechoicesin

suchquestions.

SectionA

1. AchargeQisplacedatthemouthofaconicalflask.Thefluxoftheelectricfield

throughtheflaskis

a.

b. zero

c.

d.

2. Electricfieldlinescanbesaidtobe

a. graphicalrepresentationofelectricfields

CBSE Class 12 PhysicsSample Paper - 05 (2019-20)

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b. linesofequalElectricfield

c. drawinglinesofelectricfields

d. linesofequalElectricvoltage

3. Forachargedconductorofarbitraryshape,insidetheconductor

a. V=0and

b. EandVarezero

c. E=0,butVissameasonthesurfaceandnon-zero

d. Eisnon-uniformbutViszeroeverywhere

4. Anelectrolyticcapacitorismarked8 ,220V.Itcanbeusedinacircuitwherethe

p.d.acrossthecapacitormaybe

a. 200V

b. 300V

c. 1000V

d. 500V

5. AccordingtoGauss’slawformagnetism

a.

b.

c.

d.

6. Figureshowsacapacitormadeoftwocircularplateseachofradius12cm,and

separatedby5.0cm.Thecapacitorisbeingchargedbyanexternalsource(notshown

inthefigure).Thechargingcurrentisconstantandequalto0.15A.Capacitanceand

therateofchargeofpotentialdifferencebetweentheplatesare

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a. 74.1

b. 67.1

c. 80.1

d. 70.1

7. ApproximateDopplershiftformulaforlightis

a.

b.

c.

d.

8. Alightbeamtravelsat1.94 inquartz.Thewavelengthofthelightin

quartzis355nm.Ifthissamelighttravelsthroughair,whatisitswavelengththere?

a. 549nm

b. 620nm

c. 579nm

d. 600nm

9. Agianttelescopeinanobservatoryhasanobjectiveoffocallength19mandaneye-

pieceoffocallength1.0cm.Innormaladjustment,thetelescopeisusedtoviewthe

moon.Whatisthediameteroftheimageofthemoonformedbytheobjective?The

diameterofthemoonis3.5 mandtheradiusofthelunarorbitroundtheearth

is3.8 m

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a. 18.5cm

b. 19.5cm

c. 21.5cm

d. 17.5cm

10. Foragivenfrequencyoflightandapositiveplatepotentialinthesetupbelow,Ifthe

intensityoflightisincreasedthen

a. currentislesswithmoreintensity

b. currentisinverselyproportionaltointensity

c. currentisunaffectedbymoreintensity

d. currentismorewithmoreintensity

11. Fillintheblanks:

Susceptibilityis________forparamagneticsubstances.

OR

Fillintheblanks:

Whenabarisplacednearastrongmagneticfieldanditisrepelled,thenthematerial

ofbaris________.

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12. Fillintheblanks:

Whenachargedparticlemovesperpendiculartoamagneticfield,thenspeedofthe

particlewill________.

13. Fillintheblanks:

Themagneticforceonapointchargeisgivenby________.

14. Fillintheblanks:

Densityofnucleusmatteristheratioof________ofnucleusanditsvolume.

15. Fillintheblanks:

Thecriticalangleforamaterialofrefractiveindex is________.

16. Drawagraphshowingthevariationofpotentialenergybetweenapairofnucleonsas

afunctionoftheirseparation.Indicatethefunctioninwhichthenuclearforceis(i)

attractive,(ii)repulsive.

17. Writetheequationofdecayoftheradioactivenuclei.

18. Whichtypeofbiasingisthereinthefollowingdiode?

19. Definetheintensityofradiationonthebasisofphotonpictureoflight.WriteitsSI

unit.

20. Drawablockdiagram,ofageneralizedcommunicationsystem.

OR

Istheratioofthenumberofholesandthenumberofconductionelectronsinann-

typeextrinsicsemiconductormorethan,lessthanorequaltoone?

SectionB

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21. TwocloselyspacedequipotentialsurfacesAandBwithpotentialsVandV+ V,

(where VisthechangeinV)arekept ldistanceapartasshowninthefigure.

Deducetherelationbetweentheelectricfieldandthepotentialgradientbetween

them.Writethetwoimportantconclusionsconcerningtherelationbetweenthe

electricfieldandelectricpotential.

22. Whatistheareaoftheplatesof2Fparallelplatecapacitorhavingseparationbetween

theplatesis0.5cm?

23. Usingthegraphshowninthefigureforstoppingpotentialversustheincident

frequencyofphotons,calculatePlanck'sconstant.

24. i. Writetheconditionsunderwhichlightsourcescanbesaidtobecoherent.

ii. Whyisitnecessarytohavecoherentsourcesinordertoproduceaninterference

pattern?

25. Distinguishbetweendiamagneticandferromagneticmaterialsintermsof

i. susceptibilityand

ii. theirbehaviourinanon-uniformmagneticfield.

26. A12.5eVelectronbeamisusedtoexciteagaseoushydrogenatomatroom

temperature.Determinethewavelengthsandthecorrespondingseriesofthelines

emitted.

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OR

i. Inhydrogenatom,anelectronundergoestransitionfromsecondexcitedstateto

thefirstexcitedstateandthentothegroundstate.Identifythespectralseriesto

whichthesetransitionsbelong.

ii. Findouttheratioofthewavelengthsoftheemittedradiationsinthetwocases.

27. DrawandexplaintheoutputwaveformacrosstheloadresistorR,iftheinput

waveformisasshowninthegivenfigure.

OR

DrawandexplaintheoutputwaveformacrosstheloadresistorR,iftheinput

waveformisasshowninthegivenfigure.

SectionC

28. Inacertainregionofspace,electricfieldisalongthez-directionthroughout.The

magnitudeofelectricfieldis,however,notconstantbutincreasesuniformlyalongthe

positivez-direction,attherateof105NC-1permetre.Whataretheforceandtorque

experiencedbyasystemhavingatotaldipolemomentequalto10-7cminthenegative

z-direction?

29. Threeidenticalparallelplatecapacitor(air)C1,C2,C3havecapacitanceCeach.The

spacebetweentheirplatesisnowfilledwithdielectricsasshown.Ifallthree

capacitorsstillhaveequalcapacitance,obtaintherelationbetweendielectric

constants,k,k1,k2,k3andk4.

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30. UseLenz'slawtodeterminethedirectionofinducedcurrentinthesituation

describedbyfigure:

a. Awireofirregularshapeturningintoacircularshape.

b. Acircularloopbeingdeformedintoanarrowstraightwire.

31. Whatisintensityofelectromagneticwave?GiveitsrelationintermsofelectricfieldE

andmagneticfieldB.

32. InYoung'sdoubleslitexperimentusingmonochromaticlightthefringepatternshifts

byacertaindistanceonthescreenwhenamicasheetofrefractiveindex1.6and

thickness1.964micronsisintroducedinthepathofoneoftheinterferingwaves.The

micasheetisthenremovedandthedistancebetweentheplaneoftheslitsandthe

screenisdoubled.Itisfoundthatthedistancebetweenthesuccessivemaximumnow

isthesameastheobservedfringeshiftupontheintroductionofmicasheet.Calculate

thewavelengthofthelight.

OR

Inasingleslitdiffractionexperiment,whenatinycircularobstacleisplacedinthe

pathoflightfromadistantsource,abrightspotisseenatthecentreoftheshadowof

theobstacle.Explainwhy?Statetwopointsofdifferencebetweentheinterference

patternobtainedinYoung'sdoubleslitexperimentandthediffractionpatterndueto

asingleslit?

33. Thevalueofgroundstateenergyofhydrogenatomis-13.6eV.

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i. Findtheenergyrequiredtomoveanelectronfromthegroundstatetothefirst

excitedstateoftheatom.

ii. Determine

a. thekineticenergyand

b. orbitalradiusinthefirstexcitedstateoftheatom.

(Given,thevalueofBohr'sradius=0.53A)

34. Explain,howadepletionregionisformedinajunctiondiode?

SectionD

35. DeducetheconditionforbalanceinaWheatstonebridge.Usingtheprincipleof

Wheatstonebridge,describethemethodtodeterminethespecificresistanceofawire

inthelaboratory.Drawthecircuitdiagramandwritetheformulaused.Writeany

twoimportantprecautionsyouwouldobservewhileperformingtheexperiment.

OR

a. StateGauss'slawinelectrostatics.Usethislawtoderiveanexpressionforthe

electricfieldduetoaninfinitelylongstraightwireoflinearchargedensity

.

b. Anelectricdipoleconsistsofchargesof separatedbyadistanceof2

mm.Itisplacednearalonglinechargeofdensity asshownin

thefigurebelow,suchthatthenegativechargeisatadistanceof2cmfromthe

linecharge.Calculatetheforceactingondipole.

36. i. WhatdoyouunderstandbythesharpnessofresonanceinaseriesL-C-Rcircuit?

DeriveanexpressionforQ-factorofthecircuit.

ii. ThreeelectricalcircuitshavingACsourcesofvariablefrequencyareshowninthe

figures.Initially,thecurrentflowingineachoftheseissame.Ifthefrequencyof

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theappliedACsourceisincreased,howwillthecurrentflowinginthesecircuits

beaffected?Givethereasonforyouranswer.

OR

i. UseKirchhoffsrulestoobtainthebalanceconditioninaWheatstonebridge.

ii. CalculatethevalueofRinthebalanceconditionoftheWheatstonebridge,ifthe

carbonresistorconnectedacrossthearmCDhasthecoloursequencered,redand

orange,asshowninthefigure.

iii. IfnowtheresistanceofthearmsBCandCDareinterchanged,toobtainthe

balancecondition,anothercarbonresistorisconnectedinplaceorR.Whatwould

nowbesequenceofcolourbandsofthecarbonresistor?

37. a. Drawalabelledraydiagramshowingtheformationofafinalimagebya

compoundmicroscopeatleastdistanceofdistinctvision.

b. Thetotalmagnificationproducedbyacompoundmicroscopeis20.The

magnificationproducedbytheeyepieceis5.Themicroscopeisfocusedona

certainobject.Thedistancebetweentheobjectiveandeyepieceisobservedtobe

14cm.Ifleastdistanceofdistinctvisionis20cm.Calculatethefocallengthofthe

objectiveandtheeyepiece.

OR

Anangularmagnificationof30Xisdesiredusinganobjectiveoffocallength1.25cm

andaneyepieceoffocallength5cm.Howwillyousetupthecompoundmicroscope?

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Answer

SectionA

1. (c)

Explanation:

IfQisthechargeenclosedbyconicalflaskthanthefluxis

Butthechargeisplacedatthemouthofflasksoifwedrawanotherimaginaryflask

overitthechargeissurroundedbytwoflasksnowsothechargethroughtheflask

nowhalfofthepreviousvalue(sharedbytwoflask)So

2. (a)graphicalrepresentationofelectricfields

Explanation:ElectricFieldLinescanbedefinedasacurvewhichshowsdirectionof

electricfield,whenwedrawtangentatitspoint.Theconceptofelectricfieldwas

proposedbyMichaelFaraday,inthe19thcentury.Healwaysthoughtthatelectric

fieldlinescanbeusedtodescribeandinterprettheinvisibleelectricfield.Insteadof

usingcomplexvectordiagrameverytime,Thispictorialrepresentationorformis

calledelectricfieldlines.

Electricfieldlinescanbeusedtodescribeelectricfieldaroundasystemofchargesin

abetterway.

3. (c)E=0,butVissameasonthesurfaceandnon-zero

Explanation:Theelectricfieldonthesurfaceofahollowconductorismaximumand

itdropstozeroabruptlyinsidetheconductor.

Since ,thepotentialdifferencebetweenanytwopointsinsidethehollow

conductoriszero.

Thismeansthatthepotentialatallpointsinsidethehollowchargedconductoris

CBSE Class 12 PhysicsSample Paper - 05 (2019-20)

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sameanditisequaltothevalueofthepotentialatitssurface.

4. (a)200VExplanation:Thebreakdownpotentialofthecapacitoris220V.Inorderto

preventdamagetoacapacitor,itshouldbealwaysusedinacircuitwherethep.dis

lessthanitsbreakdownpotential.Thep.ddifferencecanonlybe200V.

5. (a)

Explanation:Sincemagneticmonopolesdonotexist,fluxenteringtheclosedsurfaceisequal

tofluxleavingthesurface.Hencenetmagneticfluxthroughaclosedsurfaceiszero.

6. (c)80.1

Explanation:

Capacitance,

q=CV

Differentiatingboththesides,

or

.

7. (a)

Explanation:ThefractionalchangeinfrequencyΔV/Visgivenby–Vradial/c,whereVradialis

thecomponentofthesourcevelocityalongthelinejoiningtheobservertothesourcerelative

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totheobserver;Vradialisconsideredpositivewhenthesourcemovesawayfromthe

observer.

8. (a)549nm

Explanation:

also,

thisgives

puttingthesevalues,

so,

9. (d)17.5cm

Explanation:

Sincemoonissituatedveryfarsoitsimageisatthefocalplaneofobjectivelens.

Soanglesubtendedbydiameterofmoonisequaltoanglesubtendedbytheimage,

or

or ;whereDisdiameterofmoonandristhedistanceofmoonfromthe

earth.

10. (d)currentismorewithmoreintensity

Explanation:Withincreaseinintensityno.ofincidentphotonincreases.Sothat

moreelectronemittedfrommetalandphotocurrentincreaseswithincreasein

intensity.

11. Positive

OR

Diamagnetic

12. Remainunchanged

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13.

14. Mass

15. 45°

16. Plotofpotentialenergyofapairofnucleonsasafunctionoftheirseparationisgiven

inthefigure:

Fromtheabovegraphitcanbeeasilyconcludedthatifdistancebetweennucleonsis

greaterthanr0,forcesareattractiveinnaturewhileforseparationlessthanr0,

forcesareattractiveinnature.

17.

18. ReverseBiasing

19. Theamountoflightenergy/photonenergy,incidentpermetresquarepersecondis

calledtheintensityofradiation.

SIUnit:W/m2

20.

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OR

Inann-typeextrinsicsemiconductor,theratioofanumberofholestothenumberof

electronsislessthanone.

SectionB

21. Workdoneinmovingaunitpositivechargealonganinfinitesimaldistance l,

[sinceworkdone,w= =q×

(VB-VA)andcharge,q=1unithere]

or

i. Electricfieldisinthedirectioninwhichthechangeinelectrostaticpotential

decreasesmost.(Thisconclusioncomesduetothenegativesignoftheabove

expression)

ii. Magnitudeofelectricfieldisgivenbythechangeinthemagnitudeofelectrostatic

potentialperunitdisplacementnormaltotheequipotentialsurfaceatthepoint.

22. Accordingtothequestioncapacitance,C=2Farady

(distanceofseparationbetweenthetwoplates)

(permittivityoffreespaceorvacuum)

Asthecapacitanceofaparallelplatecapacitor,

23. AccordingtoEinsteinsphotoelectricequation

eV=hv-

Ondifferention,wegete v=h v

Inthegivengraph:

or

24. i. Coherentsources:Twosourcesaresaidtobecoherentinnatureiftheyemitlight

ofsamefrequencyandofastablepathdifference.Theessentialcondition,which

mustbesatisfiedforthesourcestobecoherentare:

a. Thetwolightwavesshouldbeofsamewavelength.

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b. Thetwosourcesmustbeveryclosetoeachother.

c. Thetwolightwavesshouldeitherbewithsamephaseorshouldhavea

constantphasedifference.

d. Thetwosourcesshouldpreferablyhavethesameamplitude.

e. Thesourcesshouldemitlightwavescontinuously.

ii. Twosourcesofemittinglightwavesofsamefrequencyorwavelengthandofa

stablephasedifferencearerequiredtoseeinterferencepattern,andwecan

obtainsuchnatureoflightwavesfromcoherentsource.

So,werequirecoherentsourcestoproducetheinterferenceoflight.

25. i. Susceptibilityfordiamagneticmaterial

Itisindependentofmagneticfieldandtemperature(exceptforbismuthatlow

temperature).

Susceptibilityforferromagneticmaterial

Thesusceptibilityofferromagneticmaterialsdecreasessteadilywithincreasein

temperature.AttheCurietemperature,theferromagneticmaterialsbecome

paramagnetic.Thevalueofmagneticsucceptibilityispositiveandmuchmore

greaterthan1forferromagneticmaterials.

ii. Behaviourinnon-uniformmagneticfield

Diamagnetsarefeeblyrepelled,whereasferromagnetsarestronglyattractedby

non-uniformfield,i.e.diamagnetsmoveinthedirectionofdecreasingfield,

whereasferromagnetfeelsforceinthedirectionofincreasingfieldintensity.

26. Thewavelengthofseriesemittedduringtransitionisgivenbytheformula:

hc/E=

E=12.5eV

hc=1240eV

Thereforewavelengthofemittedseriesis:

=1240/12.5=99.2nm

ThisbelongstotheLymanseriesofBohr'sHydrogenSpectrum.

therefore,Thewavelengthofemittedseriesis99.2nmandthisbelongstotheLyman

seriesofBohr'sHydrogenSpectrum.

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OR

i. Whenanelectronundergoestransitionfromsecondexcitedstatetothefirst

excitedstateitisknownasBalmerseriesandthentothegroundstateisknownas

Lymanseries.

ii. Thewavelengthoftheemittedradiationsinthetwocases,theyare

For

For

27. Whentheinputvoltageis+5V,thediodegetsforwardbiased,theoutputacrossRis

+5V,asshowninfigure.Whentheinputvoltageis-5V,thediodegetsreversebiased.

NooutputisobtainedacrossR.

OR

Whentheinputvoltageis+5V,thediodegetsforwardbiased,theoutputacrossRis

+5V,asshowninfigure.Whentheinputvoltageis-5V,thediodegetsreversebiased.

NooutputisobtainedacrossR.

SectionC

28. Forceactingonanelectricdipoleinthepositivez-directionwhichisplacedinanon-

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uniformelectricfield.

As,theelectricfieldchangesuniformlyinthepositivez-direciton,only,

Thus,

and

As,thesystemhasthetotaldipolemomentequalto10-7cminthenegativez-

direction.

Thus,

px=0,py=0,pz=-10-7cm

Itisindicatedbythenegativesignthattheforce10-2Nactsinthenegativez-direction.

Inanelectricfield ,thetorqueondipolemoment isgivenby

As and areactinginoppositedirection,

so,

29. AfterintroducingthedielectricsthecapacitanceofcapacitorsC1,C2andC3

respectivelyisgivenas

30. a. Whenawireofirregularshapeturnsintoacircularloop,areaofthelooptendsto

increase.Therefore,magneticfluxlinkedwiththeloopincreases.Accordingto

Lenz'slaw,thedirectionofinducedcurrentmustopposethemagneticfield,for

whichinducedcurrentshouldflowalongadcba.

b. Inthiscase,themagneticfluxtendstodecrease.Therefore,inducedcurrentmust

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supportthemagneticfieldforwhichinducedcurrentshouldflowalongadcba.

31. Intensityofelectromagneticwaveisdefinedastheenergycrossingpersecondper

unitareaperpendiculartothedirectionofpropagationofelectromagneticwaves.

Theintensityofelectromagneticwaveatapointis;

where

andcisthevelocityofelectromagneticwave,

HereE0andB0aremaximumvaluesofelectricfieldandmagneticfieldrespectively.

32. Duetointroductionofmicasheet,theshiftonthescreen

Now,whenthedistancebetweentheplaneofslitsandscreenischangedfromDto

2D,fringewidthwillbecome,

Accordingtogivenproblem,

or

OR

Wavesdiffractedfromtheedgeofcircularobstacleinterfereconstructivelyatthe

centeroftheshadowoftheobstacleresultingintheformationofabrightspot.

Characteristics Interference Diffraction

Fringewidth

Allbright

anddark

fringesareof

Thecentralbrightfringehavegotdoublewidthto

thatofwidthofsecondarymaximaorminima.

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equalwidth

Intensityof

brightfringes

Allbright

fringesareof

same

intensity

Centralfringeisthebrightestandintensityof

secondarymaxima,decreaseswiththeincreaseof

orderofsecondarymaximaoneithersideof

centralmaxima.

33. i. WeknowEnergyofelectroninnthorbitofhydrogenatomis

Forn=1 =-13.6eV

Forn=2 =-13.6/4=-3.4eV

Energyrequired=E2-E1=-3.4-(-13.6)=10.2eV

ii.

a. Kineticenergy=-(Totalenergyoftheelectroninfirstexcitedstate).=-(-3.4)=

3.4eV

b. Orbitalradiusintheexcitedstate,

r=r0n2=(0.53 10-10) (2)2=0.53 10-10 4=2.12

34. Whenpandnsemiconductorsarejoined,theholesfromp-regiondiffuseintothen-

regionandelectronsfromn-regiondiffuseintop-regionandelectron-holepair

combineandenergyisreleased.

Thisprocessdevelopslayerofpositiveionsnearthejunctiononnsideandlayerof

negativeionsonpsideofjunctionitdevelops,VBacrossthejunctionwhichopposes

thefurtherdiffusionthroughthejunction.Thus,smallregionformsinthevicinityof

thejunctionwhichisdepletedoffreechargecarrierandhasonlyimmobileionsis

calledthedepletionregion.

SectionD

35. FourresistancesP,Q,RandSareconnectedtoformquadrilateralABCD.A

galvanometerGisconnectedbetweenBandD.AbatteryisconnectedbetweenAand

C.TheresistancesaresoadjustedthatnocurrentflowsinthegalvanometerG.The

samecurrentI1willflowinarmsABandBC.Similarly,currentI2flowsinarmsAD

andDC.

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ApplyingKirchhoff'ssecondlawformeshABCD,

I1P-I2R=0

orI1P=I2R...(i)

FormeshBCDB,

I1Q-I2S=0

orI1Q=I2S...(ii)

Dividing(i)by(ii)weget

ThisisthebalancedconditionoftheWheatstonebridge.

Measurementofspecificresistance:Slidewireormeterbridgeisapracticalformof

Wheatstonebridge.

InthefigureXisunknownresistorandR.Bisresistancebox.Afterinsertingthekeyk,

jockeyismovedonwireACtillgalvanometershowsnodeflection(pointB).Ifkisthe

resistanceperunitlengthofwireAC.

P=resistanceofAB=kl

Q=resistanceofBC=k(100-l)

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or

Ifristheradiusofwireandlbeitslength,thenitsresistivitywillbe

Precautions:

i. Thenullpointshouldlieinthemiddleofthewire.

ii. Thecurrentshouldnotbeallowedtoflowinthewireforalongtime.

OR

a. Gauss'slawinelectrostatics:Itstatesthattotalelectricfluxovertheclosedsurface

Sinvacuumis timesthetotalcharge(q)containedinsideS.

Letaninfinitelylonglinechargehavinglinearchargedensity .Assumea

cylindricalGaussiansurfaceofradiusrandlengthlcoaxialwiththelinechargeto

determineitselectricfieldatdistancer.

Totalfluxthroughthecylindricalsurface,

Since isthechargeperunitlengthandlisthelengthofthewire,

Thus,thechargeenclosed

AccordingtoGaussianlaw,

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or,

b. Electricfieldintensityatadistancerfromlinechargeofdensity is

Fieldintensityonnegativecharge(r=0.02m)

Forceonnegativecharge

Itisdirectedtowardsthelinecharge.

Similarlyfieldintensityatpositivecharge(r=0.022m)

Forceonpositivecharge

Itisdirectedawayfromthelinecharge.

Netforceonthedipole,

F=F1-F2=(7.2-6.54)N=0.66N

Fistowardsthelinecharge.

36. i. ThesharpnessofresonanceinseriesL-C-Rcircuitrefershowquickfallof

alternatingcurrentincircuittakesplacewhenthefrequencyofalternating

voltageshiftsawayfromtheresonantfrequency.Itismeasuredbythequality

factor(Q-factor)ofcircuit.

TheQ-factoroftheseriesresonantcircuitisdefinedastheratioofthevoltage

developedacrossthecapacitanceorinductanceatresonancetotheimpressed

voltagewhichisthevoltageapplied.

i.e.,qualityfactor(Q)=

Q=

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[ appliedvoltage=voltageacrossR]

orQ= orQ=

Q= [using = ]

Thus,Q=

Thisisrequiredexpression.

ii. LetinitiallyIrcurrentisflowinginallthethreecircuits.Ifthefrequencyof

appliedACsourceisincreasedthen,thechangeincurrentwilloccurinthe

followingmanner:

CircuitcontainingresistanceRonly:

where,fi=initialfrequencyofACsource.

Thereisnoeffectoncurrentwiththeincreaseinfrequency.

ACcircuitcontaininginductanceonly:

WiththeincreaseoffrequencyofACsource,inductivereactanceincreaseas

I=

Forgivencircuit,

I

Currentdecreaseswiththeincreaseoffrequency.

ACcircuitscontainingcapacitoronly:

XC=

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Current,I= =

I=

Forgivencircuit,I f

Currentincreaseswiththeincreaseoffrequency.

OR

i. ThebalancedconditioninWheatstonebridge:

or

ii. LetacarbonresistorSisgiventothebridgearmCD.Then,

=1 R=S=22 103

iii. Afterinterchangingtheresistances,thebalancedbridgewouldbe

HereXistheresistanceofarmAD

X=4R=4 22 103=88k

HencecolourcodeisGreyorange.

37. a.

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whereAB=object,A'B'=imageformedbyobjective,A''B''=imageformedby

eyepiece

Listheseparationbetweentheeyepieceandtheobjective,

f0isthefocallengthoftheobjective,

feisthefocallengthoftheeyepiece,

Distheleastdistanceforclearvision

b. Fortheleastdistanceofclearvision,thetotalmagnificationisgivenby:

...(i)

Also,thegivenmagnificationfortheeyepiece:

me=5=

5=1+

fe=5cm

Substitutingthevalueofmandmeinequation(i),weget:

m=m0.me

=4

Now,wehave:

f0= =3.5cm

OR

Innormaladjustment,imageisformedatleastdistanceofdistinctvision,

d=25cm

Angularmagnificationofeyepiece

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Sincethetotalmagnificationis30,magnificationofobjectivelens,

or

As

i.e.objectshouldbeheldat1.5cminfrontofobjectivelens.

Asv0=-5u0

From

Separationbetweentheobjectivelensandeyepiece

=4.17+7.5=11.67cm