4E Phy Prelim 2021 ans

C O N F I D E N T I A L 2021Prelim▪ 6091Physics▪ Secondary4E Paper 1(40marks) [1] ×40 1 2 3 4 5 6 7 8 9 10 C C C A B C C B C B 11 12 13 14 15 16 17 18 19 20 C D B B C B C B A D21 22 23 24 25 26 27 28 29 30 B C A B C A C D B A31 32 33 34 35 36 37 38 39 40 B A A C C C D A B B Paper 2 SectionA(50marks) 1 (a)(i) The weight of Ypullingitdownis equal to the resultant force due tothetensionsinthestringspullingit up.SinceresultantforceonYiszero,Yremainsatrest. B1 (a)(ii) scale=1cm:0.5N resultantforceof3.5Ndrawnupwards(orweightdrawndownwards)witharrowandlabeltensionsinstringsdrawnatcorrectangleswitharrowsandlabels weightofX=2.75N[accept2.65–2.85N] M1 M1 A1 (b) The moment Y starts to drop, its gravitational potential energyconvertstokineticenergyasYacceleratesdownwards.Someofitskineticenergythenconvertstoheat andsoundenergyasYdoesworkagainst air resistance. B1 B1 2 (a) Theclockwisemoment duetotheforceof thefoot onthebrakepedalaboutpivot is equal totheclockwise moment due to the force on thepistonaboutpivot.Sincemoment=Fxdandthe perpendicular distance fromforce onpiston to pivot is greater thantheperpendicular distancefromforceof foot topivot,theforceonpistonisgreaterforthesamemoment. B1 B1 B1 MdmNur Hazwah Page 1 of 6

C O N F I D E N T I A L 2021Prelim▪ 6091Physics▪ Secondary4E (b) P=F/A pressureonpistonA =pressureonpistonB 6402.0 = 𝐹15 F=4800N(shownthatforceonpistonBisgreaterthantheforceof640NonpistonA) M1 A1 3 (a) n=1/sinc1.4=1/sincc=46° A1 *angle32.9°shouldbe33° (b)(i) (b)(ii) (b)(iii) n=sini/sinr1.4=sin50/sinrr =33° OnFig.3.1,drawrefractedrayfromAtoB. OnFig.3.1,drawnormalatBandreflectedrayfromBtoC.angleofreflection=33° OnFig.3.1,drawnormalatCandrefractedrayoutatC.angleofrefraction=50° B1 B1 B1 B1 (c) Thebeadsareusedtoreflectlightfallingontheroadsignsintomotorists’eyessothattheycanseethesignsclearly. B1 4 (a) Itisthedistancebetweentheopticalcentreofthelensanditsfocalpoint. B1 MdmNur Hazwah Page 2 of 6

C O N F I D E N T I A L 2021Prelim▪ 6091Physics▪ Secondary4E (b) focallength=1.9cm M1 A1(c) P: Power=energyconverted/timeR: Sincethelensisableto converge light rays onto the solar cell,itwill increasetheamount of energyabsorbedbythecell.O:Thiswill leadtoan increase in the amount of electrcial powergeneratedbythesolarcell. B1 B1 (d) P: The light rays will converge at a further distanceafterpassingthroughthelensoflongerfocallength.R: Since less light rays converge onto the solar cell,theamountofelectricalpowergeneratedbythesolarcellwillreduce.O:Thismakesthesolarcell lessefficient. B1 B1 5 (a) V =IR240=(P/V)xR240=(48/240)xRR=1200Ω M1A1 (b) P: V=IRR: Atthestart,the resistance of the lamp increasesatadecreasingrate.O:Hence, current inthelampdecreasesatadecreasingrate.R: Theresistanceof thelampthenbecomesconstant.O:Hence, current inthelampremainsconstant. B1B1B1 (c) 1Thefilamentinthesecondlampislongerthanthefirst.2Thefilamentinthesecondlampisthinnerthanthefirst. B1B1 6 (a)(i) V=IR4.20=Ix12I=0.35A A1 (a)(ii) V=6.0–4.20=1.8V V=IR1.8=0.35xRR=5.14Ω M1 A1 (b)(i) P: Xconnectedinparallel withthe12Ωresistor resultsina lowereffectiveresistanceintheparallel partofthecircuit.R: Since,V=IR,thevoltageacrossthe12Ωresistor decreases.O:Hence,thereadingonthevoltmeter decreases. B1 B1 (b)(ii) P: Xconnectedinparallel withthe12Ωresistor resultsina lowereffectiveresistanceofthewholecircuit.R: Since,V=IR,theoverall current inthecircuit increases.O:Hence,thereadingontheammeter increases. B1 B1 MdmNur Hazwah Page 3 of 6

C O N F I D E N T I A L 2021Prelim▪ 6091Physics▪ Secondary4E 7 (a)(i) north B1 (a)(ii) upwards B1 (b)(i) increasethenumberofturnsofcoilaroundtheironcoreORincreasethevoltageofthed.c.supplytoincreasecurrentthroughthecircuitORincreasethenumberofelectronsinthebeam B1 (b)(ii) reversethedirectionofcoilaroundtheironcoreORreversethepolaritiesofthed.c.supplyORuseabeamofprotonsinstead B1 8 (a) 𝑉𝑆 𝑉𝑃 = 𝑁𝑆 𝑁𝑃 𝑉𝑆 𝑉𝑃 = 200400 VS =0.5VP P=VI Efficiency = 𝑢𝑠𝑒𝑓𝑢𝑙 𝑜𝑢𝑡𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟𝑖𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟 ×100 = 3.0 × 0.5𝑉𝑃 5.0 ×𝑉𝑃 ×100 =30% M1 M1 A1 (b) ● Therearepowerlossesduetotheresistanceofthecoils.● Thereisleakageofmagneticfluxbetweentheprimaryandsecondarycoils.● Therearepowerlossesduestoeddycurrentsinducedintheironcore.● Thereishysteresislosscausedbytheflippingofmagneticdipolesintheironcoreduetothea.c.supply. [anytworeasonableanswersfor1markeach] B2 (c)(i) Asa.c.currentflowsthroughtheprimarycoil,therateof changeofmagneticfluxinducesane.m.f.inthecoilconnectedtothelamp.ThisisgivenbyFaraday’sLawofElectromagneticInduction.Henceaninducedcurrentflowsinthecoilconnectedtothelamp,causingthelamptolightup. B1 B1 (c)(ii) Ifthedistancebetweenthetwocoilsincrease,therateof changeofmagneticfluxwill decreaseinducingasmaller e.m.f.,andhenceasmallerinducedcurrent,inthecoilconnectedtothelamp.Thissmallerinducedcurrentcausesthelamptobedimmer. B1 SectionB(30marks) 9 (a)(i) Moment=Fxd=165x(240/100÷2) M1 MdmNur Hazwah Page 4 of 6

C O N F I D E N T I A L 2021Prelim▪ 6091Physics▪ Secondary4E =198Nm A1 (a)(ii) Moment=Fxd=FH x100/100+FV x240/100=(FH +2.4FV )Nm M1A1 (b)(i) Asthemanwalksdowntheramp,theperpendicular distancebetweenthelineof actionof hisweight andendOdecreases.Sincemoment=Fxd,theclockwisemoment duetohisweight aboutendOdecreases.Hence,thetotalclockwisemomentsaboutendOdecreases. B1 B1 (b)(ii) point–Oforce–frictionORnormalreactionforce B1B1 (b)(iii) Theweight of therampproducesananticlockwisemoment about T.Ifthisotherforceisnotpresentto produceaclockwisemoment aboutT, therampwill not beableto remain in equilibriuminthepositionshowninFig.9.1. *frictioncannotbeexplainedusingmomentsaboutT B1B1 Totalmarks 10 10 (a) The relative power increases at a decreasing rate until a maximumvalue.It thendecreasesatanapproximatelyconstant rate. B1 B1 (b) Somethermal radiationemittedbythestovehavewavelengthsintheredregionof visiblelight.However, none of the radiation emitted by the rock havewavelengthswithinthevisiblelight region. B1 B1 (c) A large portion of the radiation emitted by the light bulb havewavelengthsthat fall withintheinfraredregion.Sincethelightbulbgivesoutmoreheatthanvisiblelight,itisinefficient. B1 B1 (d)(i) Ultravioletradiationisan ionising radiation.Excessamountsofitcandamage biological moleculesandleadtoabnormal patternsof celldivision.[harmfuleffects] B1 (d)(ii) v =fλ3x10 8 =fx400x10 -9 f =7.5x10 14 Hz [M1foridentifyinglongestwavelength][M1forstatingthevalueofspeed] M2A1 Totalmarks 10 11 EITHER(a)(i) Numberofpulses =(6.0x60)÷(4.62x10 -3 )=7.79x10 4 M1A1 (a)(ii) Totalenergy =7.79x10 4 x1.2x10 -4 =9.35J A1 (a)(iii) Q=mc Δθ9.35=50x4.2xΔθ M1 MdmNur Hazwah Page 5 of 6

C O N F I D E N T I A L 2021Prelim▪ 6091Physics▪ Secondary4E Δθ=0.0445°C A1 (b) Thebrainisfoundunder layersof hair andskin,whichwouldhave absorbed some of the energyfromtheradiowavesduringthephonecall.Sincetherewillbelessenergytransferredtothebrainascomparedtothewater,thetemperatureriseproducedinthebrainwillbelesser. [anyotherreasonableanswers] B1 B1 (c)(i) Thephoneconverts0.20Jofelectrcialenergytootherformsofenergyinonesecond. B1 (c)(ii) fractionofenergy = 𝑟𝑎𝑑𝑖𝑜 𝑤𝑎𝑣𝑒 𝑒𝑛𝑒𝑟𝑔𝑦𝑖𝑛𝑝𝑢𝑡 𝑒𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝑝ℎ𝑜𝑛𝑒 = 9.350.20 ×6.0×60 = 1871 440 M1 A1 Totalmarks 10 11 OR(a)(i) Pressuresabovethewaterlevelsinbotharmsofthemanometerwereequal. B1 (a)(ii) Whenthegastapwasopened,the number of gas molecules per unitvolumeofthespacebetweenthewaterandthegastapincrease.The frequency of collisions with the walls of the tube and the watersurfaceincreases.Thepressureofgasinthatspaceincreases.The water levels readjust such that atmospheric pressure, togetherwithpressureof 0.14mof water, ontheleft sideof themanometer isequal tothegaspressureontheright sideof themanometer. B1 B1 B1 (b) Pgas =Patm +Pwater =100000+ρ hg=100000+1000x0.14x10=101400Pa(or101kPain3sf) M1A1 (c) Itwouldnotbesuitable.Awaterpressureof50kPawill require a much larger height of waterandhenceamuchtallertube. [anyotherreasonableanswers] B1B1 (d)(i) Theliquidlevelsremainthesameinbotharms. B1 (d)(ii) Theliquidlevelsremainthesameinbotharms. B1 Totalmarks 10 MdmNur Hazwah Page 6 of 6