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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
