Objective Questions on Electric Current _ Electrical4u

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ObjectiveQuestionsonElectricCurrent

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1. Theflowofcurrentinsolidsisdueto

A. electronsandions

B. electrons.

C. atoms.

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D. nucleus.

Hints

Allelectriccurrentsconsistofchargesinmotion.Thechargeiscarriedentirelybyelectrons.Electronsarefreetomovefromatomtoatomthatenablesthecurrentto

flowinasolidconductor.

2. Amperesecondcouldbetheunitof

A. power.

B. conductance.

C. charge.

D. energy.

Hints

Aunitofelectricalchargeisequaltotheamountofchargethatcanbetransferredbyancurrentof1amperein1second.

3. Thedriftvelocityofelectronsis

A. verysmallascomparedtospeedoflight.

B. equaltospeedoflight.

C. almostequaltospeedoflight.

D. greaterthanspeedoflight.



Hints

Thedriftvelocityoftheelectronsistheorderofmillimeterspersecondandthespeedofthespeedoflightistheorderofmillionmeterspersecond,whichis

approximately300millionmeterspersecond.Thatiswhythedriftvelocityoftheelectronsisverysmallcomparedtospeedofthelight.

4. Thechargeonanelectronisknowntobe1.61019coulomb.Inacircuitthecurrentflowingis1A.Howmanyelectronswillbeflowingthroughthecircuitinasecond?

A. 1.61019.

B. 1.61019.

C. 0.6251019.

D. 0.6251012.

Hints

Weknowthatthenumberofelectronsinonecoulombistheratioofonecoulombtothechargeononeelectron.

Thus,thenumberofelectronsinasecondisequalsto0.6251019.

5. Ingasestheflowofcurrentisdueto

A. electronsonly.

B. positiveionsonly.

C. negativeionsonly.



D. electrons,positiveionsandnegativeionsonly.

Hints

Basically,thecurrentingasesconsistsofaflowofpositiveionsinonedirectionandittogetherwithaflowofnegativeioninthatoppositedirection.Then,the

positivechargeshouldhavethesamemagnitudeofthenegativechargeanditmustbeincludedasacontributionofthetotalcurrent.Theflowofcurrentisreferredto

theflowofelectrons.

6. Ancurrentof5Aissameas

A. 5J/C.

B. 5C/Sec.

C. 5V/C.

D. 5W/C.

Hints

Theflowofchargepersecondoftimeissameasthecurrentwhichflowsthroughthecircuit.So,ampereandcharge/secondaresame.

7. Aninstrumentwhichdetectscurrentisknownas

A. voltmeter.

B. wattmeter.

C. galvanometer.

D. rheostat.

Hints



Voltmeterandwattmetercannotbeusedtomeasurethecurrentandrheostatwouldbeusedtoresistthecurrentinelectricalcircuits.Thegalvanometerisusedto

detecttheelectriccurrent.Because,thegalvanometerhasacoilthatenergizesbycurrentandaccordingtothatcurrent,needleisactuated.Since,itisusedtodetectsomemicroamperecurrentonly.Tomeasurethehighratingcurrents,ithastobe

modifiedasanammeter.

8. Currentflowsinacircuitwhen

A. aswitchisopened.

B. aswitchisclosed.

C. theswitchiseitheropenorclosed.

D. thereisnovoltage.

Hints

Whileaswitchisclosedinanycircuits,whichwouldmakeapathwaytoflowthecurrentintothecircuit.

9. Eighttenthscoulombpassesapointin4s.Thecurrentinamperesis

A. 1.6A.

B. 2A.

C. 16A.

D. 0.2A.

Hints

Thegiventermsare, Q=8/10CoulombandT=4Sec.WeknowthatcurrentIisgivenby,



10. Anammeterisanelectricalinstrumentusedtomeasure

A. voltage.

B. current.

C. resistance.

D. reluctance.

Hints

Ammeterisatoolthatisdesignedtomeasuretheflowofcurrentinacircuit.

11. Therateofflowanelectricchargeisknownas

A. current.

B. voltage.

C. conductance.

D. power.

Hints

Therateofflowofanelectricchargeisreferredasthemovementofelectricchargesincoulombspersecondoftime.Thiscoulomb/secisanotherunitof

current.

12. Theminimumrequirementforcausingflowofcurrentare

A. Avoltagesource,aresistorandaswitch.



B. Avoltagesourceandaconductor.

C. Apowersourceanbulb.

D. Avoltagesource,aconductor,anammeterandswitch.

Hints

Weknowthat,V=IRI=V/R.So,anyconductorwouldhavetheirownresistance,becauseofitsresistivity.Whileavoltagesourceisappliedinthis

conductor,accordingtotheaboveexpressionancurrentflowsthroughthecircuit.

13. Whichofthefollowingcurrentisconsidereddangeroustothehumanbody

A. 1mA.

B. 50mA.

C. 0.5mA.

D. 25mA.

Hints

Refertothetablebelow,Currentlevel(milliamperes)

ProbableEffectonHumanBody

1mA Perceptionlevel.Slighttinglingsensation.Stilldangerousundercertainconditions.

5mASlightshockfelt,notpainfulbutdisturbing.Averageindividualcanletgo.However,stronginvoluntaryreactionstoshocksin

thisrangemayleadtoinjuries.10mA30mA

Painfulshock,begintolosemuscularcontrol.Commonlyreferredtoasthefreezingcurrentorletgorange.

30mA99mA

Extremepain,respiratoryarrest,severemuscularcontractions.Individualcannotletgo.Deathispossible.

100mA Ventricularfibrillation(uneven,uncoordinatedpumpingofthe



2,000mA heart.)Muscularcontractionandnervedamagebeginstooccur.Deathislikely.

>2,000mA Cardiacarrest,internalorgandamage,andsevereburns.Deathisprobable.

14. Theratioofvoltageandelectricalcurrentinaclosedcircuit

A. increases.

B. varies.

C. falls.

D. remainconstant.

Hints

Theratioofvoltagetothecurrentisreferredastheresistance.Iftheresistanceremainsconstantinanelectricalcircuit,thentheratioofvoltagetothecurrent

shouldbeconstantatalltime.Theoretically,theresistanceofanyelectricalcircuitwouldbeconstant.

15. Currentvelocitythroughthecopperconductoris

A. nearly3108m/sec.

B. independentofthecurrentstrength.

C. thesameaspropagationvelocityofelectricalenergy.

D. oforderoffewmicrom/s.

Hints

Thevelocityofcurrentthroughaconductorisgivenby



Where, V=Velocityofthecurrent(m/s)

I=Current(Amps) n=Numberofelectronspercubicmeter(8.51028perm3forcopper)

A=Crosssectionalareaofconductor(m2) Q=Chargeonasingleelectron(Coulombs)

Ifweusethisaboveexpressionwithsomepracticalvalues,wewouldgetsomefractionofnanoorpicometerpersecondofcurrentvelocity.Itstooless.Althoughthedriftvelocityofelectronsissolessbutactuallycurrenttravelsata

speedofnearly3108m/secthatisthespeedoflight.

16. Whichofthefollowingstatementsistrue?

A. Agalvanometerwithlowresistanceinparallelisavoltmeter.

B. Agalvanometerwithhighresistanceinparallelisavoltmeter.

C. Agalvanometerwithlowresistanceinseriesisanammeter.

D. Agalvanometerwithhighresistanceinseriesisanammeter.

Hints

Basically,galvanometersareammetersonly.Inelectricalcircuits,ammetersareconnectedinseries.Iftheresistanceisverylow,thenitcouldallowmorecurrent

totheloadwithoutasmuchaspowerlossinthatresistance.

17. Anelectricbulbcanbeworkedfrom

A. ACsupplyonly.

B. DCsupplyonly.

C. batterysupplyonly.

D. allofthese.



Hints

Inelectricbulb,ancurrentwouldflowthroughthefilamentwireandtherebyitcanbeworked.So,wecanuseanyofthepowersupplysourcetoglowabulb,because

allthepowersupplywouldproducecurrentwhileitisconnectedwithsource.

18. Electriccurrentpassingthroughthecircuitproduces

A. magneticeffect.

B. thermaleffect.

C. luminiuseffect.

D. allofabove.

Hints

Ifancurrentpassesthroughtheinductororelectromagnet,itwouldcreatemagneticeffect.Ifancurrentpassesthroughthefurnace,itwouldcreatethermaleffectandifancurrentpassesthroughtheelectricbulbs,thenitwouldcreateluminouseffect.Thus,anelectricalenergycanbeconvertedintoanykindof

energyveryeasily.

19. Whencurrentpassesthroughametallicconductor,ittemperaturerises.Thisisdueto

A. collisionsbetweenconductionelectronsandatoms.

B. thereleaseofconductionelectronsfromparentatoms.

C. mutualcollisionsbetweenmetalatoms.

D. mutualcollisionsbetweenconductingelectrons.

Hints

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Whenanelectricfieldisappliedthroughametallicconductor,duetodriftvelocity,theelectronscanbemovedtooppositedirectionofthefield,becauseof

theirnegativecharge.Thisgivestheflowofcurrent.Thecollisionsbetweenconductionelectronsandatomsarecorrespondencetotheresistanceofthe

metallicconductor.Ifthecollisionbetweenconductionelectronsandatomsishigh,thentheresistancevalueisalsohigh.Duetothepresenceofresistance,heat

israisedinthatconductor.

20. Ifaparallelcircuitisopenedinthemainline,thecurrent

A. increasesinthebranchofthelowestresistance.

B. increasesineachbranch.

C. iszeroinallbranches.

D. iszerointhehighestresistivebranch.

Hints

Ifthemainlineofanycircuitisopened,thenthereisnowaytoflowthecurrent.Thus,thecurrentisallconnectedbrancheswiththatparallelcircuitwouldbe

zero.

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Objective Questions on Electric Current _ Electrical4u