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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. Sixcharges,eachequalto+q,areplacedatthecornersofaregularhexagonofsidea.
Theelectricfieldatthepointofintersectionofdiagonalsis
a.
b. Zero
c.
d.
2. Twoequalnegativecharges-qarefixedatpoints(0,a)and(0,-a).ApositivechargeQ
isreleasedfromrestatthepoint(2a,0)onthex-axis.ThechargeQwill:
a. Movetooriginandremainatrest
CBSE Class 12 PhysicsSample Paper - 06 (2019-20)
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b. ExecuteoscillationbutnotSHM
c. ExecuteSHMabouttheorigin
d. Movetoinfinity
3. Tomakeacondenserof16 ,1000volts,howmanycondensersareneededwhich
havewrittenonthem“8 ,,250volts”?
a. 8.0
b. 32.0
c. 40.0
d. 2.0
4. Avariablecapacitorandanelectroscopeareconnectedinparalleltoabattery.The
readingoftheelectroscopewouldbedecreasedby
a. Decreasingthebatterypotential
b. Increasingtheareaofoverlappingoftheplates
c. Decreasingthedistancebetweentheplates
d. Placingadielectricbetweentheplates
5. Anironbarmagnetoflength10cmandcrosssection1cm2hasamagnetizationof
102A/m.Magnet'spolestrengthis
a. 0.0025Am
b. 0.0015Am
c. 0.01Am
d. 0.002Am
6. If, and representthewavelengthsofvisiblelight,x-raysandmicrowaves
respectivelyinthefreespacethen________________
a.
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b.
c.
d.
7. InYoung’sdouble-slitexperimentusingmonochromaticlightofwavelengthl,the
intensityoflightatapointonthescreenwherepathdifferenceis ,isKunits.What
istheintensityoflightatapointwherepathdifferenceis ?
a.
b.
c. K
d.
8. Thecriticalanglefortotalinternalreflectionataliquid–airinterfaceis42.5°Ifaray
oflighttravelingintheliquidhasanangleofincidenceattheinterfaceof35°what
angledoestherefractedrayintheairmakewiththenormal?
a. 59.1°
b. 58.1°
c. 61.1°
d. 60.1°
9. Aconvexlensisdippedinaliquidwhoserefractiveindexisequaltotherefractive
indexofthelens.Thenitsfocallengthwill:
a. Becomeinfinite
b. Becomezero
c. Reduce
d. Remainsameasinair
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10. Themaximumkineticenergyofphotoelectronsemittedfromasurfacewhenphotons
ofenergy6eVfallonitis4eV.Thestoppingpotentialis
a. 2V
b. 10V
c. 4V
d. 6V
11. Fillintheblanks:
Thespacearoundamagnetwithinwhichitsinfluencecanbeexperiencediscalledits
________.
OR
Fillintheblanks:
Horizontalandverticalcomponentsofearth'smagneticfieldareequal,thenangleof
dipis________.
12. Fillintheblanks:
Iftwoelectronbeamstravelinthesamedirection,theywill________eachother.
13. Fillintheblanks:
Teslaistheunitof________.
14. Fillintheblanks:
Theactivityofaradioactivesourceismeasuredbytherateof________ofthesource.
15. Fillintheblanks:
Theunitofsolidangleis________.
16. Writetheequationofdecayoftheradioactivenuclei.
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17. Nametheabsorbingmaterialusedtocontrolthereactionrateofneutronsina
nuclearreactor.
18. Aradarhasapowerof1kWandisoperatingatafrequencyof10GHz.Itislocatedon
asteepmountaintopof600m.Whatisthemaximumdistanceuptowhichitcan
detectanobjectlocatedonthesurroundingearth'ssurface?(useradiusofearthR=
6400km)
19. Writetherelationshipofde-Brogliewavelength associatedwithaparticleofmass
mintermsofitskineticenergyE.
20. Thegraphshowninthefigurerepresentsaplotofcurrentversusvoltageforagiven
semiconductor.Identifytheregion,ifanyoverwhichthesemiconductorhasa
negativeresistance.
OR
Whatisthemostcommonuseofphotodiode?
SectionB
21. Whatistheworkdonebythefieldofanucleusinacompletecircularorbitofthe
electron?Whatiftheorbitiselliptical?
22. Twouniformlylargeparallelthinplateshavingchargedensities and arekept
intheXZ-planeatadistancedapart.Sketchanequipotentialsurfaceduetoelectric
fieldbetweentheplates.Ifaparticleofmassmandchargeqremainsstationary
betweentheplates.Whatisthemagnitudeanddirectionofthisfield?
23. Whyarealkalimetalsmostsuitedforphotoelectricemission?
24. UnpolarisedlightispassedthroughapolaroidP1.Whenthispolarisedbeampasses
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throughanotherpolaroidP2andifthepassaxisofP2makesanangle withthepass
axisofP1,thenwritetheexpressionforthepolarisedbeampassingthroughP2.Draw
aplotshowingthevariationofintensity,when variesfrom to .
25. Writetherelationbetweenrelativepermeability andsusceptibility .
26. A12.5eVelectronbeamisusedtoexciteagaseoushydrogenatomatroom
temperature.Determinethewavelengthsandthecorrespondingseriesofthelines
emitted.
OR
Findoutthewavelengthoftheelectronorbitinginthegroundstateofhydrogen
atom.
27. Usingtheconceptofelectronandholecurrent,writeanexpressionforthe
conductivityofasemiconductor.
OR
Statethefactor,whichcontrols:
i. Wavelengthoflightand
ii. intensityoflightemittedbyanLED.
SectionC
28. Supposethattheparticleinanelectronprojectedwithvelocity
.IfEbetweentheplatesseparatedby0.5cmis
,wherewilltheelectronstriketheupperplate?
.
29. Amagneticfieldof100G(1G=10-4T)isrequiredwhichisuniforminaregionof
lineardimensionabout10cmandareaofcrosssectionabout10-3m2.Themaximum
currentcarryingcapacityofagivencoilofwireis15Aandthenumberofturnsper
unitlengththatcanbewoundroundacoreisatmost1000turnsm-1.Suggestsome
appropriatedesignparticularsofasolenoidfortherequiredpurpose.Assumethe
coreisnotferromagnetic.
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30. WriteFaraday'slawofelectromagneticinduction.Expressitmathematically.A
conductingrodoflength'l',withoneendpivoted,isrotatedwithauniformangular
speed'ofinaverticalplane,normaltoauniformmagneticfield'B'.Deducean
expressionfortheemfinducedinthisrod.
31. Answerthefollowingquestions.
i. Namethewaveswhichareproducedduringradioactivedecayofanucleus.Write
theirfrequencyrange.
ii. Welderswearspecialglassgoggleswhileworking.Why?Explain.
iii. Whyareinfraredwavesoftencalledasheatwaves?Givetheironeapplication
32. ThemaximumintensityinYoung'sdouble-slitexperimentisI0.Distancebetweenthe
slitsisd=5 ,where isthewavelengthofmonochromaticlightusedinthe
experiment.Whatwillbetheintensityoflightinfrontofoneoftheslitsonascreenat
adistanceD=10d?
OR
Showusingaproperdiagramshowhowunpolarisedlightcanbelinearlypolarised
byreflectionfromatransparentglasssurface.
33. StateanytwopostulatesofBohr'stheoryofhydrogenatom.Whatisthemaximum
possiblenumberofspectrallinesobservedwhenthehydrogenatomisinitssecond
excitedstate?Justifyyouranswer.
Calculatetheratioofthemaximumandminimumwavelengthsoftheradiations
emittedinthisprocess.
34. Thecharacteristicscurveofadiodeisshownintheabovefigure.Determinethed.c.
anda.c.resistancearoundpoint.
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SectionD
35. a. Statetheworkingprincipleofapotentiometerwiththehelpofacircuitdiagram.
Describeamethodtofindtheinternalresistanceofaprimarycell.
b. Inapotentiometerarrangement,acellofemf1.20voltgivesabalancepointat30
cmlengthofthewire.Thiscellisnowreplacedbyanothercellofunknownemf.If
theratioofthelengthofthetwocellsis1.5.Calculatethedifferenceinthe
balancinglengthofthepotentiometerwireinthetwocases.
OR
a. UsingGauss'theorem,obtainanexpressionfortheelectricfieldintensityata
pointatadistancerfromaninfinitelylonguniformlychargedstraightwire.
b. AnelectricdipoleABconsistsofcharges±5nCandseparatedbyadistanceof2
10-3m[Fig].
Thedipoleisplacednearalonglinechargehavinglinearchargedensity4.5 10-4
Cm-1,suchthatthenegativechargeisatadistanceOA=2 5cmfromtheline
charge.Findtheforceactingonthedipole.
36. a. DeriveanexpressionfortheimpedanceofaseriesL-C-Rcircuitconnectedtoan
ACsupplyofvariablefrequency.
b. Explainbrieflyhowthephenomenonofresonanceinthecircuitcanbeusedinthe
tuningmechanismofaradiooraTVset?
OR
Anetworkofresistorsisconnectedtoa16Vbatterywithinternalresistanceof as
showninfigure
a. Computetheequivalentresistanceofthenetwork.
b. Obtainthecurrentineachresistor
c. AlsoobtainthevoltagedropsVAB,VBCandVCD.
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37. Howistheworkingofatelescopedifferentfromthatofamicroscope?
Thefocallengthsoftheobjectiveandeyepieceofamicroscopeare1.25cmand5cm
respectively.Findthepositionoftheobjectrelativetotheobjectiveinordertoobtain
anangularmagnificationof30innormaladjustment.
OR
i. Drawalabelledraydiagramtoobtaintherealimageformedbyanastronomical
telescopeinnormaladjustmentposition.Defineitsmagnifyingpower.
ii. Youaregiventhreelensesofpower0.5D,4Dand10Dtodesignatelescope.
a. Whichlensesshouldbeusedasobjectiveandeyepiece?Justifyyouranswer.
b. Whyistheapertureoftheobjectivepreferredtobelarge?
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Answer
SectionA
1. (b)Zero
Explanation:Thefieldofoppositechargescancelseachothersonetelectricfieldat
centre=0
2. (b)ExecuteoscillationbutnotSHM
Explanation:Directionofnetelectricfielddueboththechargesatanypointon+X
axiswillbealong-Xaxis,hencethepositivechargewillexperienceforceinnegativeX
axisdirection.
Whenitreachesorigin,netelectricfieldwillbecomezero,butduetoitskinetic
energypositivechargewillcontinuemovinginthe-Xdirection,butnowthedirection
ofelectricfieldandhenceforceonpoitivechargewllbeinthe+Xaxisdirection,
whichwilltendtobringitbacktowardsorigin.Sothechargewilloscillateabout
origin.Sinceforceandhenceaccelerationisnotproportionaltodisplacement,itsnot
SHM.
3. (b)32.0
Explanation:
Eachcapacitorofcapacitance canwithstandamaximumpotentialof250V.
Whenequalcapacitorsareconnectedinseries,thepotentialdifferenceacrossthemis
equal.
Iftherearemcapacitorsinseriessuchthatthepotentialacrosseachis250V,then,
.
Theequivalentcapacitanceof4capacitorsconnectedinseriesis
.
Toachieveacapacitanceof16,nsuchrowsofcapacitorsneedtobeconnectedin
parallel.
.
Tomakeacondenserof16 ,8rowsofcapacitorswitheachrowcontaining4
CBSE Class 12 PhysicsSample Paper - 06 (2019-20)
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capacitorsaretobeconnected.
Thetotalnumberofcapacitors=n×m=4×8=32.
4. (a)DecreasingthebatterypotentialExplanation:Anelectroscopeisadevicewhich
measuresthepotentialdifference.Ifitisconnectedinparalleltothecapacitor,the
potentialacrossitwillbeequaltothepotentialacrossthecapacitor,whichisequalto
thepotentialacrossthebattery.Ondecreasingthebatterypotential,thepotential
differenceacrosstheelectroscopereducesandhencethereadingreduces.Whilethe
capacitorisconnectedtothebattery,Placingadielectricbetweentheplates,or
decreasingthedistancebetweentheplatesorincreasingtheareaoftheplateswillnot
changethepotentialdifferenceacrossit;sinceitwillalwaysremainequaltothe
potentialdifferencemaintainedbythebattery.InthecasesB,CandD,The
capacitanceofthecapacitor,howeverincreases;butthisincreasehappensdueto
increaseinthechargestoredinthecapacitorwhilethepotentialremainsconstant.
5. (c)0.01Am
Explanation:
Hencepolestrength,qm=M×A=100A/m×10-4m2=10-2Am
6. (a)
Explanation:Sinceofthegivenregions,wavelengthofmicrowaveishighestandthat
ofx-rayisminimum.
7. (d)
Explanation:
use
Whenphasedifferenceis pathdifferenceis
=
8. (b)58.1°
Explanation:fortotalinternalreflection,
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internalreflection,existatthispoint
where
usingsnell'slaw:
thesegivesratiosofrefractiveindex
againapplyingsnell'slaw
so,
9. (a)Becomeinfinite
Explanation:
since,
10. (c)4V
Explanation:
eV0=kmax
eV0=4eV
V0=4V
11. Magneticfield
OR
45°
12. Attract
13. Magneticinduction
14. Disintegration
15. Steradian
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16.
17. Heavywater
18. Here,R=6400km=6.4 106m,h=600mFromtherelation
d=
=
=87.6km
Distancedisindependentofthepowerandfrequencyofthesignal.
19. RelationbetweenKineticenergyandlinearmomentumis,
wherep=momentum,k=kineticenergy,m=mass
So,
de-Brogliewavelength,where,p=
20. TheslopeoftheV-Igraphgivestheresistance.Negativeslopeofcurvemeans
negativeresistance.Inthegivengraph,partBCofthecurveshowsthenegative
resistanceasinthisregionslopeisnegativeandcurrentdecreasesbyincreasingthe
voltage.
OR
Thephotodiodecanbeusedaslightdetector.
SectionB
21. Whatsoeverbetheshapeoftheorbitworkdoneisalwayszerobecauseelectronwill
beinthesameenergystateafteritcompletesanorbit.
22.
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Theequipotentialsurfaceisatadistanced/2fromeitherplateinXZ-plane.-qcharge
experiencesaforceinadirectionoppositetothedirectionofelectricfieldi.e.along
thedirectionoftheplatehavingchargedensity .
Theforceonthe'-q'chargebalanceswhen,theelectrostaticforcebecomesequalto
theweightofthechargeitselfi.e.
Thedirectionofelectricfieldalongverticallydownwarddirection.TheXZ-planeisso
chosenthatthedirectionofelectricfieldduetotwoplatesisalongvertically
downwarddirection,otherwiseweight(mg)ofthechargedparticlecouldnotbe
balanced.Theequipotentialsurfaceliesinbetweenthetwogivenplatesandonthe
XZ-plane,asshownbelow.
23. Thisisbecausealkalimetalshaslowworkfunction.Itiseasytoremoveelectrons
fromalkalithanfromothermetals.
24. Thefigurewhenunpolarisedlightbeamispassedthroughpolaroidisshownbelow.
BythelawofMalus,
intensityreceivedafterpassingthroughthePolaroid, .
Variationofintensitywithrotationangle from0toπi.e.from0°to180°ofthe
Polaroidisshownbelow.
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25.
26. Thewavelengthofseriesemittedduringtransitionisgivenbytheformula:
hc/E=
E=12.5eV
hc=1240eV
Thereforewavelengthofemittedseriesis:
=1240/12.5=99.2nm
ThisbelongstotheLymanseriesofBohr'sHydrogenSpectrum.
therefore,Thewavelengthofemittedseriesis99.2nmandthisbelongstotheLyman
seriesofBohr'sHydrogenSpectrum.
OR
Radiusofgroundstateofhydrogenatom .
AccordingtodeBroglierelation2πr=nλ
Forgroundstaten=1
therefore,
27. InaSemi-Conductoroflength(ℓ)andareaofCross-Section.Letneandnhbetheno.
ofelectronsandholeswithdriftvelocitiesVeandVhrespectively.So,thetotalcurrent
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inthesemi-conductorwillbethesumofcurrentduetoelectronsaswellasholes,i.e.I
=Ie+Ih.....(i)
AsweknowthatI=neAVd
Ie=neeAVeAndIh=nheAVh
I=neeAVe+nheAVh
I=eA[neVe+nhvh]
......(ii)
AsweknowthatE= (inmagnitude)
Also, or
WhereρisresistivityandRisresistance
or
or
or ...(iii)
Put(3)in(2)weget,
Here,mobility(m)=
Thisisthederivationandexpressionfortheconductivityofasemiconductor.
OR
i. Energy,hencethewavelengthofphotonsemitteddependsuponthebandgap.
ii. Theforwardcurrentincreasesastheintensityoflightincreasesandreachesa
maximum.Further,increaseintheforwardcurrentresultsindecreaseoflight
intensity.LEDsarebiasedsuchthatthelightemittingefficiencyismaximum.
SectionC
28. Acceleration,
Usingformula
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Weget,
Simplifyingforvalueoft,weget
Theelectroncoversverticaldistanceisshownas
y=vxt
=1.6cm
29. Given,B=100G=10-2T
I=15A,n=1000m-1
Magneticfieldinsideasolenoidis
WemayhaveI=10Aandn=800
Thesolenoidmayhavelength50cmandcrosssection (fivetimesgiven
values)soastoavoidedgeeffectsetc.
30. AccordingtoFaraday'slawofelectromagneticinduction,themagnitudeofinduced
emfisequaltotherateofchangeofmagneticfluxlinkedwiththeclosedcircuit(or
coil).Mathematically,
whereNisthenumberofturnsinthecircuitand isthemagneticfluxlinkedwith
eachturn.
SupposetheconductingrodcompletesonerevolutionintimeT.Then
Changeinflux
Inducedemf
But
31. i. -raysareproducedduringradioactivedecayofanucleus.Itsfrequencyrangeis
from3x1018Hzto5x1022Hz.
ii. Welderswearspecialglassgoggleswhileworkingtoprotecttheireyesfrom
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radiationhazardsofultravioletrays(UVrays).TherangeofUVraysis1015Hzto
1017Hz.Becausetheradiationhazardsareharmfultohumaneyes.
iii. Infraredwavesarecalledheatwavesbecausetheycausetheatomsandmolecules
tovibratewhentheyencounterasubstance.Thisincreasesthevelocityandhence
internalenergyofatomsandmolecules.Thereby,increasingthetemperatureof
thesubstance(As,heatproducedinmatterisdirectlyproportionaltotheinternal
energyofatomsandmolecules).Theyareusedinphysicaltherapyandweather
forecasting.
32. Pathdifference,
Here,y= (asd=5 )
andD=10d=50
So,
Correspondingphasedifferencewillbe
or,
I=I0cos2
I=I0cos2
OR
Whenanunpolarizedlightfallsonapolaroid,onlythoseelectricvectorsthatare
oscillatingalongadirectionprependiculartothealignedmoleculeswillpassthrough.
Thus,incidentlightgetslinearlypolarized.
Electricvectorswhicharealongthedirectionofthealignedmoleculesgetsabsorbed.
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Wheneverunpolarizedlightisincidentontheboundarybetweentwotransparent
media,thereflectedlightgetspartiallyorcompletelypolarized.Whenreflectedlight
isperpendiculartotherefractedlight,thereflectedlight,iscompletelypolarizedlight.
33. Bohr'sPostulates
i. Everyatomconsistsofsmallandmassivecentralcore,knownasnucleusaround
whichelectronrevolveandnecessarycentripetalforceprevailedbyelectrostatic
forceofattractionbetweenpositivelychargednucleusandnegativelycharged
electrons.
ii. Theelectronsarerevolvedaroundthenucleusinonlythosecircularorbitswhich
satisfythequantumconditionthattheangularmomentumofelectronsisequalto
integralmultipleof where,hisPlanck'sconstant.
where,n=1,2,3,...
Insecondexcitedstatei.e.,n=3,twospectrallinesnamelyLymanseriesand
Balmerseriescanbeobtainedcorrespondingtotransitionofelectronfromn=3to
n=1andn=3ton=2,respectively.
ForLymanseries,n=3ton=1,forminimumwavelength
...........(i)
ForBalmerseries(maximumwavelength),
..........(ii)
OndividingEq.(i)byEq.(ii),weget
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34. d.c.resistance
a.c.resistance
SectionD
35. a. Theconnectionsaremadeasshowninthefigure.Eisthecellwhoseinternal
resistanceristobedetermined.AresistanceRisconnectedacrossthecell
throughakeyk.Thekeyk'isclosedandkiskeptopen.Thebalancepointisfound
out.Letthebalancinglengthbe11.Then,
...(i)
AsuitableresistanceRisintroducedintheresistanceboxRandwiththekeyk'
closed,thebalancinglengthl2isfoundout.Whenthecircuitisclosed,the
potentialdifferenceacrossthecellfallsto .Then,
....(ii)
Dividingequation(i)by(ii)weget
or
or
b. Given,
or =20cm
Differenceinthebalancinglength,
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11-12=30-20=10cm
OR
a. Considerathininfinitelylongstraightlinechargehavingauniformlinearcharge
density placedalongYY'.Drawacylindricalsurfaceofradiusrandlengthl
aboutthelinechargeasitsaxis.
IfEisthemagnitudeofelectricfieldatpointP,thenelectricfluxthroughthe
gaussiansurfaceisgivenby
areaofthecurvedsurfaceofacylinderofcylinderradiusrandlengthl
or
AccordingtoGauss'theorem,wehave
Now,chargeenclosedbythegaussiansurface,q= l
Thus,
or
b. Electricfieldatadistancerfromthelinecharge,
Tocalculateforceoncharge-qatpointA:
Here,OA=2 5cm=2 5 10-2m
ElectricfieldatpointA,
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=3 24 108NC-1
Forceoncharge-qatpointA,F1=qE1=5 10-9 3 24 108=1 62N(towards
thelinecharge)
Tocalculateforceoncharge+qatpointB:
Here,OB=2 5 10-2+2 10-3=2 7 10-2m
ElectricfieldatpointB,
=3 108NC-1
Forceoncharge+qatpointB,
F2=qE2=5 10-9 3 10-8=1 5N(awayfromthelinecharge)
Hence,netforceonelectricdipole,
F=F1-F2=1.62-1.5=0 12N(towardsthelinecharge)
36. a. ExpressionforimpedanceinLCRseriescircuit:
SupposearesistanceR,inductanceLandcapacitanceCareconnectedtoseries
andanalternatingvoltageV= isappliedacrossit.
SinceL,CandRareconnectedinseries,currentflowingthroughthemisthesame.
ThevoltageacrossRisVR,inductanceacrossLisVLandacrosscapacitanceisVC.
ThevoltageVRandcurrentiareinthesamephase,thevoltageVLwillleadthe
currentbyangle90owhilethevoltageVCwilllagbehindthecurrentby90o.
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Thus,VRand(VC-VL)aremutuallyperpendicularandthephasedifference
betweenthemis90o.Asseeninthefig,wecansaythat,astheappliedvoltage
acrossthecircuitisV,theresultantofVRandVC-VL)willalsobeV.
So,
V=
But,VR=Ri,Vc=XciandVL=XLi
where,Xc= andXL= L
So,V= ,
Therefore,impendanceofthecircuitisgivenby,
Z= =
Z=
ThisistheimpedanceoftheLCRseriescircuit.
b. AradiooraTVsethasanLCcircuitcapacitorofvariablecapacitanceC.The
circuitremainsconnectedwithanaerialcoilthroughthephenomenonofmutual
inductance.SupposearadioorTVstationhastransmittedaprogramatfrequency
f,thenwavesproduceanalternatingvoltageoffrequencyinarea,duetowhichan
emfofthesamefrequencyisinducedinLCcircuit.WhencapacitorCisincircuit
isvariedthenforaparticularvalueofcapacitance,C,f= ,theresonance
occursandmaximumcurrentflowsinthecircuit;sotheradioorTVgetstuned.
OR
a. Equivalentresistanceoftwo resistorsinparallelis i.e. .Equivalent
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resistanceof and resistorsinparallelis i.e. or .Now
and (equivalentof and )areinseries.So,totalresistanceis
,i.e. .
b. =2A
ConsidertheresistorsbetweenAandB.Itisacaseoftwoequalresistors
connectedinparallel.So,currentineachresistoris1A.currentthrough is
clearly2A.LetusnowconsiderresistorsbetweenCandD.Itisaparallel
combinationoftworesistances.Currentwouldbedividedintheinverseratioof
resistances.IfI1isthecurrentthrough andI2isthecurrentthrough ,then
.So,currentthrough resistoris .
Similarly,currentthrough resistoris .
c. ThevoltageVABbetweenAandBistheproductoftotalcurrentbetweenAandB
andtheequivalentresistancebetweenAandB.
Similarly =2V =8V
37. WorkingDifferences:
i. Theobjectiveofatelescopeformstheimageofaveryfaroffobjectat,orwithin,
thefocusofitseyepiece.Themicroscopedoesthesameforasmallobjectkeptjust
beyondthefocusofitsobjective.
ii. Thefinalimageformedatelescopeismagnifiedrelativetoitssizeasseenbythe
unaidedeye,whilethefinalimageformedbyamicroscopeismagnifiedrelativeto
itsabsolutesize.
iii. Theobjectiveofatelescopehaslargefocallengthandlargeaperture,whilethe
correspondingforamicroscopehaveverysmallvalues.
Given:f0=1.25cm,fe=5cm
M=-30(Magnifyingpowerisnegative)
Weknow,
Where,v0=Distanceofimagefromobjective,u0=Distanceofobjectfromobjective,D
=Distanceofleastdistinctvision
Thus,
-30=
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v0=-5u0
Usinglensformula,
u0=-1.5cm
Thusthedistanceofobjectfromobjectiveis1.5cm.
OR
i. Inastronomicaltelescopefornormaladjustment,finalimageisformedatinfinity
anditisvirtual.
Thelabelledraydiagramtoobtainoneoftherealimageformedbythe
astronomicaltelescopeisshownbelow:
Magnifyingpowerisdefinedastheratiooftheanglesubtendedattheeyebythe
focalimageasseenthroughthetelescopetotheanglesubtendedattheeyebythe
objectseendirectly,whenboththeimageandtheobjectliesatinfinity.
ii.
a. Weknowtheobjectivelensofatelescopeshouldhavelargerfocallengthand
eyepiecelensshouldhavesmallerfocallength.Andfocallengthisinverseof
power,Solensofpower(P=1/f).
10Dcanbeusedaseyepieceandlensofpower0.5Dcanbeusedasobjective
lens.
b. Theobjectivelensofatelescopeshouldhavelargeraperture,inordertoform
brightimageofdistantobjects,sothatitcangathersufficientlightraysfrom
thedistantobjects.