exercise multiple choice questions (mcqs) · 2020. 9. 16. · electricity 1. a cell, a resistor, a...

CBSEClass10Science

NCERTExemplarSolutions

Chapter12

Electricity

1.Acell,aresistor,akeyandammeterarearrangedasshowninthecircuitdiagrams

ofFigure12.1.Thecurrentrecordedintheammeterwillbe

(a) maximumin(i)

(b) maximumin(ii)

(c) maximumin(iii)

(d) thesameinallthecases

Ans.(d)Thesameinallthecases

Exercise

Multiple Choice Questions (MCQs)

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Explanation:Noneoftheconditionschangeinanyofthecircuits.Hence,currentwouldbe

sameinallcircuits.

2. Inthefollowingcircuits(Figure12.2),heatproducedintheresistororcombination

ofresistorsconnectedtoa12Vbatterywillbe

(a) sameinallthecases

(b) minimumincase(i)

(c) maximumincase(ii)

(d) maximumincase(iii)

Ans.(c)Maximumincase(ii)

Explanation:Inthiscase,tworesistorsareinseries.Hence,theirsumwillbeequaltotheir

arithmeticsum.Infigure(iii)thetotalresistancewillbelessthanindividualresistances

becausetheyareconnectedinparallel.Ahigherresistanceproducesmoreheatsooption(c)


https://www.ncertbooks.guru/ncert-exemplar-problems-solutions-pdf/

iscorrect.

3. Electricalresistivityofagivenmetallicwiredependsupon

(a) itslength

(b) itsthickness

(c) itsshape

(d) natureofthematerial

Ans.(d)Natureofthematerial

4. Acurrentof1Aisdrawnbyafilamentofanelectricbulb.Numberofelectrons

passingthroughacrosssectionofthefilamentin16secondswouldberoughly

(a)

(b)

(c)

(d)

Ans.(a)

Explanation:WehavecurrentI=1Aandtimet=16s

Weknow;

or,

or,

Chargecontainedin1electron

So,16Cchargeiscontainedinfollowingnumberofelectrons;


5. Identifythecircuit(Figure12.3)inwhichtheelectricalcomponentshavebeen

properlyconnected.

(a) (i)

(b) (ii)

(c) (iii)


(d) (iv)

Ans.(b)(ii)

6. Whatisthemaximumresistancewhichcanbemadeusingfiveresistorseachof1/5

Ω?

(a) 1/5Ω

(b) 10Ω

(c) 5Ω

(d) 1Ω

Ans.(d)

Explanation:Whenresistorsareconnectedinseriesthenwegetthemaximumresistance

outofthecombination.

Whenthegivenresistorsareconnectedinseries,theresistanceofcombinationcanbe

calculatedasfollows:

7. Whatistheminimumresistancewhichcanbemadeusingfiveresistorseachof1/5

Ω?

(a) 1/5Ω

(b) 1/25Ω

(c) 1/10Ω

(d) 25Ω

Ans.(b)1/25Ω

Explanation:Whenresistorsareconnectedinparallelthenwegettheminimumresistance


outofthecombination.

Whengivenresistorsareconnectedinparallel,theresistanceofcombinationcanbe

calculatedasfollows:

Or

8. Theproperrepresentationofseriescombinationofcells(Figure12.4)obtaining

maximumpotentialis

(a) (i)

(b) (ii)

(c) (iii)

(d) (iv)

Ans.(a)(i)

Explanation:Inthiscombination,positiveterminalofnextcellisadjacenttonegative

terminalofpreviouscell.


9. Whichofthefollowingrepresentsvoltage?

(a)

(b

(c)

(d)

Ans.(a)

10. AcylindricalconductoroflengthlanduniformareaofcrosssectionAhas

resistanceR.Anotherconductoroflength2landresistanceRofthesamematerialhas

areaofcrosssection

(a) A/2

(b) 3A/2

(c) 2A

(d) 3A

Ans.(c)2A

Explanation:Boththeconductorsareofsamematerialhencetheirresistivityissame.

Fordoublethelength;

or,

or,

or,


11. AstudentcarriesoutanexperimentandplotstheV-Igraphofthreesamplesof

nichromewirewithresistancesR1,R2andR3respectively(Figure.12.5).Whichofthe

followingistrue?

(a) R1=R2=R3

(b) R1>R2>R3

(c) R3>R2>R1

(d) R2>R3>R1

Ans.(c)R3>R2>R1

Explanation:Currentisinverselyproportionaltoresistance.So,higherresistancewould

allowlesscurrenttopass;whichisshownbyresistanceR3.

12. IfthecurrentIthrougharesistorisincreasedby100%(assumethattemperature

remainsunchanged),theincreaseinpowerdissipatedwillbe

(a) 100%

(b) 200%

(c) 300%

(d) 400%

Ans.(c)300%


Explanation:Theheatgeneratedbyaresistorisdirectlyproportionaltosquareofcurrent.

Hence,whencurrentbecomesdouble,dissipationofheatwillmultiplyby =4.Thismeans

therewillbeanincreaseof300%.

13. Theresistivitydoesnotchangeif

(a) thematerialischanged

(b) thetemperatureischanged

(c) theshapeoftheresistorischanged

(d) bothmaterialandtemperaturearechanged

Ans.(c)theshapeoftheresistorischanged

14. InanelectricalcircuitthreeincandescentbulbsA,BandCofrating40W,60Wand

100Wrespectivelyareconnectedinparalleltoanelectricsource.Whichofthe

followingislikelytohappenregardingtheirbrightness?

(a) Brightnessofallthebulbswillbethesame

(b) BrightnessofbulbAwillbethemaximum

(c) BrightnessofbulbBwillbemorethanthatofA

(d) BrightnessofbulbCwillbelessthanthatofB

Ans.(c)BrightnessofbulbBwillbemorethanthatofA

Explanation:Sincebulbsareconnectedinparallelsoresistanceofcombinationwouldbe

lessthanarithmeticsumofresistanceofallthebulbs.So,therewillbenonegativeeffecton

flowofcurrent.Asaresult,bulbswouldglowaccordingtotheirwattage.

15. Inanelectricalcircuittworesistorsof2Ωand4Ωrespectivelyareconnectedin

seriestoa6Vbattery.Theheatdissipatedbythe4Ωresistorin5swillbe

(a) 5J


(b) 10J

(c) 20J

(d) 30J

Ans.(c)20J

Explanation:Totalresistanceofcombination=

Currentthroughthecircuitcanbecalculatedasfollows:

Heatdissipationby canbecalculatedasfollows:

16. Anelectrickettleconsumes1kWofelectricpowerwhenoperatedat220V.Afuse

wireofwhatratingmustbeusedforit?

(a) 1A

(b) 2A

(c) 4A

(d) 5A

Ans.(d)5A

Explanation:Power=1kW=1000W

Currentflowingthroughthekettlecanbecalculatedasfollows:

Or

or

So,requiredratingoffusewire=5A

17. Tworesistorsofresistance2Ωand4Ωwhenconnectedtoabatterywillhave

(a) samecurrentflowingthroughthemwhenconnectedinparallel

(b) samecurrentflowingthroughthemwhenconnectedinseries


(c) samepotentialdifferenceacrossthemwhenconnectedinseries

(d) differentpotentialdifferenceacrossthemwhenconnectedinparallel

Ans.(b)samecurrentflowingthroughthemwhenconnectedinseries.

Explanation:Inseriescombination,currentdoesnotchangebecauseeachresistorreceives

acommoncurrent.Inotherwords,currentdoesnotgetdividedintobranches.

18. Unitofelectricpowermayalsobeexpressedas

(a) voltampere

(b) kilowatthour

(c) wattsecond

(d) joulesecond

Ans.(b)kilowatthour


Short Answer Questoins

19.AchildhasdrawntheelectriccircuittostudyOhm’slawasshowninFigure12.6.His

teachertoldthatthecircuitdiagramneedscorrection.Studythecircuitdiagramand

redrawitaftermakingallcorrections.

Ans.Correctdiagramisasfollows:

20. Three2Ωresistors,A,BandC,areconnectedasshowninFigure12.7.Eachofthem

dissipatesenergyandcanwithstandamaximumpowerof18Wwithoutmelting.Find

themaximumcurrentthatcanflowthroughthethreeresistors?

Ans.Currentcanbecalculatedasfollows:



or,

or,

or,

Thisisthemaximumcurrentthatcanflowthroughthegivenresistors.

21. Shouldtheresistanceofanammeterbeloworhigh?Givereason.

Ans.Resistanceofammetershouldideallybezerosothatammetershouldnotaffectthe

flowofcurrentincircuit.Hence,resistanceofanammetershouldbeverylowbecausezero

resistanceisnotpossibleinreallife.

22. Drawacircuitdiagramofanelectriccircuitcontainingacell,akey,anammeter,a

resistorof2Ωinserieswithacombinationoftworesistors(4Ωeach)inparallelanda

voltmeteracrosstheparallelcombination.Willthepotentialdifferenceacrossthe2Ω

resistorbethesameasthatacrosstheparallelcombinationof4Ωresistors?Give

reason.

Ans.

Totalresistanceforparallelcombinationof resistorscanbecalculatedasfollows:

or,


Thus,resistanceofparallelcombinationisequaltoresistanceofresistorsinseries.So,

potentialdifferenceacross resistancewillbesameaspotentialdifferenceacrossthe

othertworesistorswhichareconnectedinparallel.

23. Howdoesuseofafusewireprotectelectricalappliances?

Ans.Fusewirehashighresistancethancurrentratingofthemainwiring.So,whenever

thereisasurgeinelectriccurrent,thefusewiremeltsandbreaksthecircuit.Thisprevents

anydamagetotheelectricalappliances.Thus,afusewireprotectselectricalappliances.

24. Whatiselectricalresistivity?Inaserieselectricalcircuitcomprisingaresistor

madeupofametallicwire,theammeterreads5A.Thereadingoftheammeter

decreasestohalfwhenthelengthofthewireisdoubled.Why?

Ans.Theinherentpropertyofaconductorbecauseofwhichitresiststheflowofelectric

currentiscalledresistivity.Resistivityforaparticularmaterialisunique.

Resistancevariesdirectlyaslengthoftheconductor.

Currentvariesinverselyasresistance.

So,whenlengthofthewireisdoubled,itsresistancebecomesdouble.Whenresistance

becomesdouble,currentbecomeshalf.

Thisexplainswhythereadingofammeterdecreasestohalfwhenthelengthofthewireis

doubled.

25. Whatisthecommercialunitofelectricalenergy?Representitintermsofjoules.

Ans.Thecommercialunitofelectricalenergyiskilowatthour.

1kWh=11000Wh

1000Wh=(1000Joule/second)×hour


=3600×1000J

=3.6×

26. Acurrentof1ampereflowsinaseriescircuitcontaininganelectriclampanda

conductorof5Ωwhenconnectedtoa10Vbattery.Calculatetheresistanceofthe

electriclamp.Nowifaresistanceof10Ωisconnectedinparallelwiththisseries

combination,whatchange(ifany)incurrentflowingthrough5Ωconductorand

potentialdifferenceacrossthelampwilltakeplace?Givereason.

Ans.Totalresistanceofcircuitcanbecalculatedasfollows:

Sincelampandconductorareinseriessoresistanceoflamp

Thenewresistanceinparalleltoearliercombinationhassamevalue,i.e. asthe

resistanceofseriescombination.Thismeansthattheamountofcurrentwouldbeequally

dividedintotwobranches.Hence,0.5Acurrentwillflowthrough conductor.

Now,resistanceremainsthesamebutcurrenthasbecomehalf.UsingOhmformula,

potentialdifferenceacrossthelampcanbecalculatedasfollows:

27. Whyisparallelarrangementusedindomesticwiring?

Ans.Inparallelarrangement,totalresistanceofthecircuitislessthanarithmeticsumof

resistorsinthewiring.Thishelpsinreducingtheloadonthewiring.Inparallel

arrangement,eachappliancecanhaveitsindependentswitch.Faultinonesectionisnot

goingtoaffectanyothersection.Theseadvantagesmakeparallelarrangementidealof

domesticwiring.


28. B1,B2andB3arethreeidenticalbulbsconnectedasshowninFigure12.8.Whenall

thethreebulbsglow,acurrentof3AisrecordedbytheammeterA.

(i)WhathappenstotheglowoftheothertwobulbswhenthebulbB1getsfused?

Ans.Inparallelcircuit,potentialdifferencedoesnotgetdivided.Hence,glowofotherbulbs

willnotbeaffectedwhenbulbB1getsfused.

(ii)WhathappenstothereadingofA1,A2,A3andAwhenthebulbB2getsfused?

Ans.AmmeterAshowsareadingof3A.ThismeanseachoftheA1,A2,andA3show1A

reading.

WhenthebulbB2getsfused,nocurrentflowsthroughthisbulb.So,allthecurrentisequally

dividedbetweenremainingtwobulbs.So,ammetersA1andA2willshow3/2=1.5Acurrent

each.AmmeterA3willshowzerocurrent.

(iii) Howmuchpowerisdissipatedinthecircuitwhenallthethreebulbsglowtogether?

Ans.Forfindingpower,weneedtofirstcalculatetheresistanceinthecircuit.

Now,


Long Answer Questions

29.Threeincandescentbulbsof100Weachareconnectedinseriesinanelectric

circuit.Inanothercircuitanothersetofthreebulbsofthesamewattageareconnected

inparalleltothesamesource.

(a)Willthebulbinthetwocircuitsglowwiththesamebrightness?Justifyyouranswer.

Ans.Voltagegetsdividedinseriescombination,Sobulbsinseriescombinationwillglow

withlessbrightness.Voltagedoesnotgetdividedinparallelcombination,sobulbsinparallel

combinationwillglowwithmorebrightness.

(b)Nowletonebulbinboththecircuitsgetfused.Willtherestofthebulbscontinuetoglow

ineachcircuit?Givereason.

Ans.Incaseofseriescombination,faultinevenasinglecomponentwillbreakthecircuit.

So,whenoneofthebulbsgetsfused;anotherbulbwouldcontinuetoglow.

30. StateOhm’slaw?Howcanitbeverifiedexperimentally?Doesitholdgoodunderall

conditions?Comment.

Ans.Ohm’sLaw:Atconstanttemperature,potentialdifferenceacrossaconductorisdirectly

proportionaltoelectriccurrentpassingthroughit.IfVisthepotentialdifferenceandIis

electriccurrent,thenasperOhm’slaw;

or,

WhereRistheconstantofproportionalityanditiscalledresistance.

VerifyingOhm’sLaw:


Takeanichromewire,someelectriccells,key,voltmeterandammeter.

Connectthecomponenttomakeacircuit;asshowningivenfigure.

Startwith1cellinthecircuit.Switchonthekeyandtakethereadingofammeter.

Increasethenumberofcellsto2.Switchonthekeyandtakethereadingofammeter.

Increasethenumberofcellsinsimilarincrementsandtakethereadingofammeter

ineachcase.

TabulateyourdataandplotaV-Igraph.

Thegraphshowsthatpotentialdifferencevariesdirectlyaselectriccurrent.Ohm’slawholds

goodundernormalconditions.But,itmaynotholdgoodunderexceptionalconditions.

31. Whatiselectricalresistivityofamaterial?Whatisitsunit?Describeanexperiment

tostudythefactorsonwhichtheresistanceofconductingwiredepends.


Ans.Theinherentpropertyofaconductorbecauseofwhichitresiststheflowofelectric

currentiscalledresistivity.Resistivityforaparticularmaterialisunique.

TheSIunitofresistivityis (Ohmmetre).

Experimenttostudythefactorsonwhichresistanceofconductingwiredepends:

Takeanammeter,electriccell,plugkey,nichromewireandwiresofdifferent

materials.

Makethecircuitasshowninfigure.

Starttheexperimentwithnichromewire.Attachitinthecircuitandtakeammeter

reading.

Changethelengthofnichromewireandtakeammeterreading.

Changethethicknessofnichromewireandtakeammeterreading.

Afterabovesteps,usecopperwirefortheexperiment.Attachacopperwireinthe

circuitandtakeammeterreading.

Changethelengthofcopperwireandtakeammeterreading.

Changethethicknessofcopperwireandtakeammeterreading.

Repeatabovestepswithwiresofdifferentmaterials.

Observations:

Itisseenthatresistancedependsonmaterialofconductor.

Resistancedependsonlengthofconductor.

Resistancedependsonareaofcross-section.

32. Howwillyouinferwiththehelpofanexperimentthatthesamecurrentflows

througheverypartofthecircuitcontainingthreeresistancesinseriesconnectedtoa

battery?

Ans.


TakethreeresistancesR1,R2andR3.

Connecttheminseriescombinationtocompleteacircuit;asshowninfigure.

Firstofall,connecttheammeterbetweenbatteryandR1andtakeitsreading.

Afterthat,connecttheammeterbetweenR1andR2andtakeitsreading.

Then,connecttheammeterbetweenR2andR3andtakeitsreading.

Observation:

Itisobservedthatammetershowssamereadinginallsituation.Thisshowsthatsame

currentflowsthrougheverypartofthecircuitcontainingthreeresistancesinseries.

33. Howwillyouconcludethatthesamepotentialdifference(voltage)existsacross

threeresistorsconnectedinaparallelarrangementtoabattery?

Ans.

TakethreeresistorsR1,R2,andR3andconnecttheminparalleltomakeacircuit;as

showninfigure.

Usevoltmetertotakereadingofpotentialdifferenceofthreeresistorsinparallel

combination.

Now,removetheresistorR1andtakethereadingofpotentialdifferenceofremaining

resistors’combination.

Then,removetheresistorR2andtakethereadingofpotentialdifferenceofremaining

resistor.

Observation:Voltmeterreadingwassameineachcase.Thisshowsthatthesamepotential

differenceexistsacrossthreeresistorsconnectedinaparallelarrangement.

34. WhatisJoule’sheatingeffect?Howcanitbedemonstratedexperimentally?Listits

fourapplicationsindailylife.

Ans.TheJoule’sLawofHeatingstatesthattheheatproducedinaresistoris:

(a) Directlyproportionaltothesquareofcurrentforagivenresistor.


(b) Directlyproportionaltoresistanceforagivencurrent,and

(c) Directlyproportionaltothetimeforwhichthecurrentflowsthroughtheresistor.

Thiscanbeexpressedbyfollowingequation:

Here;Iiselectriccurrent,Risresistance,tistimeandHisheatingeffect.

ExperimenttoDemonstrateJoule’sLawofHeating:

Inthisexperiment,wewillshowtheeffectofcurrentonheating.

Takeawaterheatingimmersionrodandconnecttoasocketwhichisconnectedto

regulator.Itisimportanttorecallthataregulatorcontrolstheamountofcurrent

flowingthroughadevice.

Keepthepointerofregulatoronminimumandcountthetimetakenbyimmersion

rodtoheatacertainamountofwater.

Increasethepointerofregulatortonextlevel.Countthetimetakenbyimmersionrod

toheatthesameamountofwater.

Repeatabovestepforhigherlevelsonregulatortocountthetime.

Observation:Itisseenthatwithincreasedamountofelectriccurrent,lesstimeisrequired

toheatthesameamountofwater.ThisshowsJoule’sLawofHeating.

Application:Electrictoaster,oven,electrickettleandelectricheateretc.workonthebasisof

heatingeffectofcurrent.

35. FindoutthefollowingintheelectriccircuitgiveninFigure12.9

(a) Effectiveresistanceoftwo8Ωresistorsinthecombination


Ans.Theseresistorsareinparallel,soeffectiveresistancecanbecalculatedasfollows:

or,

(b) Currentflowingthrough4Ωresistor

Ans.Forthis,wefirstneedtofindeffectiveresistanceinthecircuit,

or

(c) Potentialdifferenceacross4Ωresistance

Ans.Potentialdifferenceisgettingdividedintotworesistanceof each.Hence,potential

differenceacross

(d) Powerdissipatedin4Ωresistor

Ans.

(e) Differenceinammeterreadings,ifany.

Ans.Sinceresistorsareconnectedinseries,sotherewillbenodifferenceinammeter

reading.



exercise multiple choice questions (mcqs) · 2020. 9. 16. · electricity 1. a cell, a resistor, a...

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