CBSE Class12 Physics 06 (2019-20) · CBSE Class12 Physics Sample Paper - 06 (2019-20) 2 / 25 b. Execute oscillation but not SHM c. Execute SHM about the origin d. Move to infinity

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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.