Practical Skills in

PHYSICSSUPPLEMENTARY

MATERIAL (AS PER THE REVISED CBSE SYLLABUS 2019-20)

(Progressive Educational Publishers)

Full Marks Pvt LtdNew Delhi-110002

11CBSE

As per the Circular – Curriculum dt. 29/3/2019 The following changes have been

made in Practical Skills in Physics by the CBSE

EXPERIMENTS ADDED

1. Elasticity 1.2 Tofindtheforceconstantofahelicalspringbyplottingagraphbetweenload

andextension 2. Atmospheric Pressure 2.1 Tostudythevariationinvolume(V)withpressure(P)forasampleofairatcon-

stanttemperaturebyplottinggraphsbetweenPandVandbetweenPand1/V

5. Thermal Radiation and Heat 5.1 Tostudytherelationshipbetweenthe temperatureofhotbodyandtimeby

plottingacoolingcurve

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1.2 TO FIND THE FORCE CONSTANT OF A HELICAL SPRING BY PLOTTING A GRAPH BETWEEN LOAD AND EXTENSIONThe force constant of a spring is also known as the spring constant. It is the ratio ofrestoringforceandextension.AspringworksontheprincipleofHooke’slaw.

Aim

Tofindtheforceconstantofahelicalspringbyplottingagraphbetweenloadandextension.Materials Required Helicalspring Slottedweights Weightpan Pointer Verticalmetrescale AstandwithrigidsupportTheoryIfaloadFissuspendedfromahelicalspringitincreasesthelengthofthespring.Ifchangeinlengthis∆l,then F ∝ ∆lor, F = k∆lwhere,kisthespringconstant.

Springconstant, k = ( ), ( )

ExtensionRestoring force F

l∆ Ifmisthemassoftheload,then mg = k∆l ∆l = k

mg

If ∆l = 1Then, k = mg=FSo,springconstantcanbedefinedastheforcerequiredtoproduceaunitextensioninthespring.

ProcedureSetting up the Apparatus

● Suspendahelicalspringfromarigidsupport. ● Attachapointerandahangertofreeendofthehelicalspring. ● Checkforfreemovementofpointeroverdivisionsoftheverticalscale. ● Ensurethatthetipofthepointerdoesnottouchtheverticalscale.

Measurement of Extension in Length ● Notedowntheinitialpositionofthepointer. ● Addasuitableweight(e.g.50g) to thehanger.Thetipofpointermovesdown.

● Allowthetipofthepointertocometorest. ● Notedownthepositionofthepointer. ● Addweightsinincrementalstepsandrepeattheabovesteps.

● Similarly remove weights in incremental stepsand note the position of the tip of the pointereachtime.

ObservationsLeastcountofverticalscale=____cm.Massofhanger=____g.

Elasticity of Helical Spring

A

B

A

Restoringforce = F

C

l

Applied force = F

Extension of Spring

4

Massofeachslottedweight=____g.Meanextensioninlength,Dl=____cm.

CalculationThespringconstantkcanbecalculatedbyusingfollowingformula: k =

l

mg

∆ Example:Supposeaweightof200gwt.producesanextensionof2mminthespring.Then

k= 2200 9.8

2 100.2 9.8

mmg ms kg N×

××2

3

–

–= =980N/m

Plotting of GraphPlotagraphbetweenload,mg(orrestoringforce,F)andextension,Dl.TakeloadonX-axisandextensionalongY-axis.Thegraphisastraightline.

Slopeofstraightline = k = Fl∆

tanq = GCAC

EFBD

=

So, k = tanq=____Nm–1

Reults ● Theforceconstantof thegivenspring=____Nm–1(fromgraph)

=____Nm–1(fromformula)

● The graph between load and extension is astraightline.

Precautions ● Allowthepointertocometorestbeforetakingreading. ● Weightshouldbeincreasedinsmallincrements. ● Loadingshouldnotbedonebeyondelasticlimitsofthespring. ● Motionintheloadedspringshouldnotbejerky. ● Begentlewhileaddingorremovingweights. ● Tipofpointershouldnottouchtheverticalscale. ● Verticalscaleshouldbeparalleltoverticalspring.

Sources of Error ● Slottedweightsmaynotshowcorrectweight. ● Pointermaynotbehorizontal. ● Thesupportmaynotberigid. ● Toomuchloadmayendupstretchingthespringpermanently.

Suggested Experiments 1. Repeatthisexperimentwithastiffspring. 2. Repeatthisexperimentwithaleaststiffspring.

VIVA VOCE

Q1. Defineforceconstantorspringconstantofaspring.

Load-extension graph for helical spring

5

Ans. Theforcerequiredtoproduceunitextensioninaspringiscalledtheforceconstantorspringconstantofthatspring.

Q2.WhatistheSIunitofforceconstant? Ans. Newtonpermetre(Nm–1) Q3.Whatistheeffectofthicknessofwireonspringconstant? Ans. Thevalueofspringconstantincreaseswiththicknessofwire. Q4. Itisensuredthatthetipofpointershouldnottouchtheverticalscale.Why? Ans. Thisisdonetonullifytheeffectoffrictionbetweenpointerandverticalscale.If

frictionisthere,itwillgiveerrorsinreading. Q5. DefineSpringconstant. Ans. Springconstantisdefinedastheforcerequiredtoproduceaunitextension. Q6.WhichdevicesuseHelicalspring? Ans. Springbalance.

NCERT LAB MANUAL QUESTIONS

Q1. Ifthelengthofthewireusedisreducedwhatwillbeitseffecton (a)extensiononthewireand(b)stressonthewire Ans. (a) Ifthelengthofthewireusedisreducedthentheextensiononthewireisreduced. (b) Ifthelengthofthewireusedisreducedthentherewillbenochangeinthestress

onthewire. Q2. Usewireofdifferentradii(r1, r2, r3)butofsamematerialintheaboveexperimental

set up. Is there any change in the value ofYoung’smodulus of elasticity of thematerial?Discussyourresult.

Ans. No,sinceYoung’smodulusofelasticityofamaterialisconstantanditdoesn’tchangewithradiusofthewireofthesamematerial.

qqq

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2.1 TO STUDY THE VARIATION IN VOLUME (V) WITH PRESSURE (P) FOR A SAMPLE OF AIR AT CONSTANT TEMPERATURE BY PLOTTING GRAPHS BETWEEN P AND V AND BETWEEN P AND 1/V

Boyle’slawgivestherelationshipbetweenpressureandvolume,atconstanttemperature.AccordingtoBoyle’s lawpressure is inverselyproportional to thevolumeof thegasatconstantpressure.

Aim

To study the variation in volume (V) with pressure (P) for a sample of air at constanttemperaturebyplottinggraphsbetweenPandVandbetweenPand1/V.

Materials Required Boyle’slawapparatus Plumbline Fortin’sBarometer Thermometer Apairofset-squares

TheoryBoyle’s lawForanenclosedgas,atconstanttemperature(T)

Pµ 1V

or PV = constantAgraphbetweenPand1/Visastraightline.PressureandvolumecanbedeterminedusingBoyle’slawapparatus.Procedure

● Settheapparatuswithwoodenboardverticallywiththehelpoflevellingscrews.

Measurement of Pressure ● Thepressureofenclosedair intubeABismeasuredbynotingthedifference(h)inmercurylevelsintwotubes.

● Thisisdonebyusingasetsquare;asshowninfigure.

h= Y–X⇒ P(pressureofenclosedair)= Z±h(where,Zisatmosphericpressure)

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Measurement of Volume of Trapped Air ● Whentheclosedtubeisnotgraduatedthevolumecanbefoundasfollows:

Volumeof air in tube=Volumeof air inLengthPR–Volumeof air in curvedportionPQ.

● Theradius(r)ofthetubecanbefoundwiththehelpofaVerniercalliper. Volumeofcurvedportion= Volumeofhemisphereofradiusr.

= 21× 34

32

r r3 3π π=

VolumeofPQ= pr2 × r=pr3

Errorinvolume= VolumeofPQ–Volumeofcurvedportion

= – 32

31

r r r3 3 3π π π=

Correctioninlength= – 31

31PQr =

Requiredcorrectioninlengthneedstobesubtractedfrommeasuredlength.

Measurement of Volume of Air at Given Pressure ● SetuptheplankofBoyle'slawapparatusverticallybyadjustinglevellingscrewsandspiritlevel.

● Usingathermometer,notedownroomtemperature. ● UsingFortin’sBarometernotedownatmosphericpressure. ● AdjusttheheightoftubeCDsothatmercurylevelinboththetubesbecomesame. ● Afterthat,notedownthevolumeofairintubeAB.

Raising the tube CD ● RaisethetubeCDbyabout2cm. ● NotedownthehigherlevelofmercuryintubeAB. ● NotedownthereducedvolumeofairinAB. ● NotedownthemercurylevelinCD. ● FurtherraisethetubeCDbyabout2cmandrepeatabovesteps. ● Repeatthepreviousstepsafewmoretimes.

Lowering the tube CD ● NowlowerthetubeCDbyabout2cm. ● NotedowntheincreasedvolumeofairinAB. ● NotedownthemercurylevelinCD. ● LowerdownCDfurtherbyabout2cmandrepeatabovesteps. ● Repeatthepreviousstepsafewmoretimes.

ObservationsMean of Atmospheric PressureAtmosphericpressureatthebeginningofexperiment,Z1=_____cmofHgAtmosphericpressureattheendofexperiment,Z2=_____cmofHg

MeanAtmosphericPressure,Z= 2Z Z1 2+

=_____cmofHg

8

Room TemperatureRoomtemperatureatthebeginningofexperiment,t1=_____°C

Roomtemperatureattheendofexperiment,t2= 2t t1 2+ =_____°C

Meantemperature,T=t1 + t2/2=_____°C

Correction in Level of Mercury due to curved portion of tube AB

Readingatthetopendoftube,AB=x1=_____cmReadingatthebeginningofcurvedportionoftubeAB=x2=____cm

Correction= 31( – )x x1 2 =____cm

Alternately,correctioncanalsobecalculatedbyusing

l= 31

r where,r=radiusoftube

Position of Hg level Pressure Difference (p)

(cm)Tube AB – Tube CD

Pressure of Air

P = Z0 + p(cm of Hg)

Volume of air V

(cm3)V1

(cm–3 )PVIn Tube

AB (cm)In Tube CD (cm)

20 20 0 75.0 20 0.050 150019.5 15.6 +3.9 78.9 19 0.053 1499.118.5 5.3 + 13.2 88.2 17 0.059 1499.5420.5 24.1 – 3.6 71.4 21 0.048 1499.421.5 27.8 –6.8 68.2 22 0.045 1500.421.5 31.3 –9.8 65.2 23 0.043 1499.6

Plotting of graph ● DrawagraphbetweenP(ony-axis)andV(onx-axis).Thegraphisahyperbola. ● DrawagraphbetweenP(y-axis)and1/V(x-axis).Thegraphisastraightline.

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Results ● The graph of P vs 1/V shows an upward slanting line. This means that as perBoyle’slawvolumeofagivenmassofgasisinverselyproportionaltopressureatconstanttemperature.

● The graph of P vsV shows a downward sloping curve.Thismeans that as perBoyle’slawvolumeofagivenmassofgasisinverselyproportionaltopressureatconstanttemperature.

Precautions ● Theapparatusshouldbesetinperfectlyverticalandhorizontalposition. ● Theopentubeshouldbemovedgradually. ● Setsquareshouldbepositionedattheuppermeniscuslevelwhiletakingthereading. ● Calculate the correction for curved portion of closed tube and use this whilemeasuringthevolumeofair.

● Plugtheopentubewithcotton;whenitisnotinuse. ● Mercuryshouldbeclean,withouttracesofglass.

Sources of Error ● Possiblechargesinatmosphericpressureandroomtemperatureduringtheexperiment. ● Presenceofmoistureinairinclosedtube. ● Errorwhiletakingthereading. ● Chancesofoxidizationofmercuryduringexposuretoair.

Suggested Experiments 1.Determinethevaluesof1/Vfordifferentvaluesofh. 2.Analysethesignificanceofatmosphericpressureinthisexperiment.

VIVA VOCE

Q1.WhatisBoyle’sLaw? Ans. Boyle’sLawexplains the relationbetweenpressureandvolumeofagivenmass

ofgasatconstanttemperature.Itstatesthatatconstanttemperature,thevolumeofgivenmassofgasvariesinindirectproportiontothepressure.

P∝ V1

Where,PispressureandVisvolumeofthegivenmassofgas. Q2.Whathappenstothevolumeofairwhenitisreleasedfromaninflatedtube? Ans. Thevolumeofairreleasedfromaninflatedtubeexperienceslesspressureonceit

isoutsidethetube.So,byfollowingBoyle’slawitsvolumeincreases. Q3.Whatisanidealgas? Ans. ThegaswhichobeysCharles’law,Boyle’slawandAvogadro’slawofgasesiscalled

anidealgas. Q4.WhatdoyouunderstandbyLPGorLiquefiedPetroleumGas?

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Ans. ThecookinggassuppliedincylindersiscalledLPGorLiquefiedPetroleumGas.This isbecause thegas isfilled in cylindersbyapplyingveryhighpressure andthehighpressureturnsthegasintoliquidform.

Q5.Whydotubesofvehiclesburstduringsummers?

Ans. According to Charles’ Law, the volume of a given mass of gas varies directlywithtemperature.Duringsummerstheairintheinflatedtubeincreasesinvolumebecause of rise in temperature. The pressure on tube increases because of this,whichfinallyleadstoburstingofthetube.

Q6.Whatdoyouunderstandbyatmosphericpressure?

Ans. Amountofforceperunitareaexertedbytheatmosphereiscalledatmosphericpressure.

Q7.WhatistheSIunitofatmosphericpressure?

Ans. SIunitofatmosphericpressureisbar.

1bar = 105Nm–2

Anotherunitforatmosphericpressureisonestandardatmosphere.Itisabbreviatedas‘atm’.1atmisthepressureexertedbyamercurycolumnofheight76cm.

Q8.Whichinstrumentisusedformeasuringatmosphericpressure?

Ans. Barometer.

Q9.Whatisthereasonformercurybeingusedinbarometer?

Ans. Anyliquidcanbeusedformakingabarometer.Mercuryhas thehighestdensityamong liquids.As a result the height of barometer can be conveniently small.Hence,mercuryisusedinbarometer.

Q10.WhatisAneroidbarometer?

Ans. Aneroidbarometerisusedinaeroplanestomeasuretheattainedheight.Itdoesnotcontainaliquid.

Q11. Howwouldyouuseabarometertoforecastastorm?

Ans. A sudden fall in the level ofmercury shows reduced air pressure,which is anindicationofanupcomingstorm.

Q12.Which lawgives the relationshipbetweenpressureandvolumeofagas?DefineBoyle’slaw?

Ans. According to Boyle’s law; pressure varies inversely as volume of a gas; iftemperatureandmassareconstant.

Q13.Whichdeviceisusedformeasuringpressureofgas?

Ans. Barometerisadevicetomeasurepressureofgas.

Q14.What happens to the volume of gas inside a bicycle tube when temperatureincreases?

Ans. Bicycletube’sburstduetoincreaseinvolume.ThisisinaccordancetoCharles’law.

Q15.Whichtwolawsgivetheidealgasequation?

Ans. CombinationofBoyle’slaw,pressurelawandCharles’lawgivesidealgasequation.

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NCERT LAB MANUAL QUESTIONS

Q1. Plot1V versus‘h’graphanddeterminethevalueof

1V whenh=0.Comparethis

tothevalueofatmosphericpressure.Giveasuitableexplanationforyourresult.

Ans. Weknowthatpressurep=H±h.Wealsoknowthatgraphbetween1V andpisa

straightline.Hence,thegraphbetween1V andhwouldalsobeastraightline.This

showsthatpressureofagivenmassofgasisinverselyproportionaltoitsvolume.

Q2. Comment on the twomethods used for estimation of the volume of the curvedportionoftheclosedtube.Whataretheassumptionsmadeforthetwomethods?

Ans. One of themethods assumes the curved portion as a hemisphere,while anothermethodassumesthecurvedportiontobeacylinderwithsameradiusandheight.Boththemethodsshowsomedifferenceinfinalcalculation.

Q3. IfthediameteroftubeABislarge,whywouldtheestimationofthecurvedportionbeunreliable?

Ans. IfdiameterofthetubeABislargethenradiuswillnotbeequaltoheight.Hence,therewillbeunreliableestimationofthecurvedportion.

Q4. Theapparatuswhennotinuseshouldbekeptcoveredtoavoidcontaminationofmercuryintheopentube.Howwilloxidationofmercuryaffecttheexperiment?

Ans. Oxidationofmercurywillreducetheamountofmercuryinthetubeandwillthusleadtoincorrectmeasurementofpressure.

qqq

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5.1 TO STUDY THE RELATIONSHIP BETWEEN THE TEMPERATURE OF HOT BODY AND TIME BY PLOTTING A COOLING CURVE

AccordingtotheNewton’slawofcooling,therateofcoolingisdirectlyproportionaltothetemperatureoftheobjectaboveitssurroundings,providedthatthedifferencebetweenthetemperatureoftheobjectanditssurroundingisnotverylarge.

Aim

To study the relationship between the temperature of hot body and time by plotting acoolingcurve.

Materials Required Twothermometers Clampandstand Newton’slawofcoolingapparatus Beaker Burner Wiregauge Tripodstand Stopwatch Tworubberstopperswithholes Thread

TheoryThe Newton’s law of cooling apparatushas a double walled enclosure which isclosedbyaninsulatinglid.Thecalorimeteris suspended inside the double walledenclosure. In between the double walls,water is filled to keep the temperature ofsurroundingconstant.Throughtheholesoflidthermometersareinserted.AccordingtoNewton’slawofcooling

Qdtd

= –k (T–T¢) ...(i)

Rateofcooling,Qdtd

= msTdtd

or –k (T–T¢) = msTdtd

[fromeq.(i)]

Tdtd

= –k ¢ (T–T¢)Onintegrating

T TTd– l# = – k ¢ dt#

    ln(T–T¢) = –k¢t + Cor 2.303log(T–T¢) = –k¢t + Cwhere,Cisintegrationconstant.Agraphbetweenlog(T–T¢)andtwillbeastraightline.

Newton’s law of cooling apparatus

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ProcedureCalibrate the Thermometer

● CleantheNewton’slawofcoolingapparatusandkeepitontable. ● Determinetheleastcountsofboththethermometers(T1andT2). ● PutthethermometerT1inabeakerbyusingaclampstandandmeasureitstemperature. ● PutthethermometerT2 inthedouble-walledcontainerbyusingtheclampstandandmeasureitstemperature.

● Thedifferencebetweenthetworeadingsgivesthevalueofrequiredcorrection.

Measuring the Falling Temperature of Hot liquid ● Findtheleastcountofstopwatch. ● Putwater(atroomtemperature)indouble-walledcontainer. ● Withthehelpofaclampstand,fixthethermometerT2inthewaterindoublewalledcontainer.

● Note the initial readingof thermometerT2 (i.e.,valueofQ1) at thebeginningofexperiment.

● Heatsomewatertoatemperatureofabout40°Cabovetheroomtemperature.Pourthehotwaterincalorimeteruptothetop.

● Keepthecalorimeteralongwithhotwater;intheenclosureandcoverthelid. ● FixthethermometerT1andstirrerinthecalorimeterthroughtheholesinthelid. ● Putrubberstoppersinthelidtomaketheapparatusairtight. ● Waitforsometimeandnotetheinitialtemperatureofthewaterbetweenthedoublewalls,withthethermometerT2.

● Whenthedifferencebetweenreadingsoftwothermometersisabout30°C,startthestopwatch.

● NotethereadingofthermometerT1aftereveryminute.ThisisT°C. ● Keeponstirringgentlyandconstantly. ● Whenthetemperaturedropstoabout5°Cabovethatofenclosure,recordthereadingofthermometerT2aftereverytwominutes.ThisisT'°C.

● Once the fall in temperaturebecomesvery low, stopnoting the temperature andstopthestopwatch.

ObservationsCalibration in ThermometerInitial reading of thermometerT1, a=____°C.Initial reading of thermometerT2, b=____°C.CorrectionneededonthermometerT2,(a – b)=____°C.

Cooling curveLeast count of stopwatch =____S.

Table for Measuring Change in the Temperature of Water with Time

S. No.

Time for

cooling, t(s)

Temperature of water in calorimeter,

T (°C)

Difference of water

temperature, T – T' (°C)

log10

(T – T')

123

20

14

Leastcountofthermometers=____°C.Initialtemperatureofwaterinenclosure,Q1=____°C.Finaltemperatureofwaterinenclosure,Q2=____°C.

Meantemperature,T¢= 2Q Q–1 2 =____°C.

Plotting of Graph ● Plotagraphbetweentemperature(T–T¢)andtime. ● Plotagraphbetweenlog(T–T¢)alongy-axisandtimealongx-axis.

Results ● Fromgraphitisconcludedthatthetemperturedecreasesquicklyinthebeginningandthenslowly.

● Thegraphbetweenchangeintemperatureandtimeisacurvedline.

Precautions ● Stirringshouldbegentleandcontinuous. ● Holesinthelidshouldbemadeairtight. ● Initialtemperatureofwaterincalorimetermustbeabout30°Caboveroomtemperature. ● Alwayscarryoutcalibrationofthermometerbeforestartingthisexperiment. ● Thermometershouldnottouchthewallofcalorimeter.

Sources of Error ● Possiblechangeintemperatureofsurrounding. ● Failuretocontinuouslystirthewater. ● Faultyoperationofstopwatch. ● Holesinlidmaynotbeairtight.

Suggested Experiments 1. PlotthegraphoftemperaturedifferenceandtimetodeterminethevalueofC. 2.VerityStefan’slawwiththisexperiment.

ResultThedownwardslopeofthecurvemeansthatathightemperaturetherateofcoolingisfastercomparedtotherateofcoolingatlowtemperature.

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VIVA VOCE

Q1.WhatisNewton’slawofcooling? Ans. It states that the rate of heat loss of a body is proportional to the difference in

temperaturesbetweenthebodyanditssurroundings.

Q2.Whiteclothesorbrighterclothesaremorecomfortableinsummers.Bywhichmodeofconductionofheatbrighterclothesreflectoffheatenergy?

Ans. Radiation.

Q3. Howisphenomenonofradiationusedincookingutensils? Ans. Bottomsofsomecookingutensilsareblackcolouredtoabsorbheatduetoradiation.

Q4.Whichtypeofheattransferismainlyresponsibleforheatingupofcookingutensil? Ans. Conduction.

Q5.Whichtypeofheattransfermechanismexplainstheflowofairfromcoasttoseaduringdaytime?

Ans. Convection.

Q6.Whichtypeofheattransfermechanismexplainstheflowofairfromseatocoastduringnight?

Ans. Convection.

Q7.Whatdoyouunderstandbyconductionofheat? Ans. Transferofheatthroughsolidstakesplacebyconduction.

Q8.Whatdoyouunderstandbyconvection? Ans. Convectionisresponsiblefortransferofheatthroughfluids.

Q9.Whatdoyouunderstandbyradiation? Ans.Withthehelpofradiationheatcanbetransferredevenintheabsenceofamedium.

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