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### Calorimetry & Heat transfer(QB).pdf

1. QUESTION FOR SHORT ANSWER Q.1 Can one object be hotter thananother if theyare at thesame temperature? Explain. Q.2 What qualities makeaparticularthermometricpropertysuitableforuseinapractical thermometer? Q.3 Youputtwouncovered pails ofwater, one containing hot waterand onecontainingcold water,outside inbelow-freezingweather.Thepailwiththehotwaterwillusuallybegintofreezefirst.Why?Whatwould happen if youcovered the pails? Q.4 Can atemperature be assigned to a vacuum? Q.5 Whatarethedimensionsof,thecoefficientoflinearexpansion?Doesthevalueofdepend ontheunit oflengthused? When Fahrenheit degreesare used insteadofCelsius degrees as theunit oftemperature change, does the numerical value of  change? If so, how? If not, prove it. Q.6 Ametal ball can pass through a metal ring. When the ball is heated, however, it gets stuck in the ring. What wouldhappen if the ring, rather than the ball, were heated? Q.7 Twostrips,oneofironandoneofzinc,arerivetedtogethersidebysideto form astraightbarthat curves when heated.Whyis the ironon the inside ofthe curve? Q.8 Explainhowtheperiodofapendulumclockcan bekept constantwith temperaturebyattachingvertical tubes ofmercuryto the bottom ofthe pendulum. Q.9 What causes water pipes to burst in the winter? Q.10 Dothepressureandvolumeofairinahousechangewhenthefurnaceraisesthetemperaturesignificantly? If not,is the ideal gas lawviolated? Q.11 Iftwosystemsareinthermal equilibrium,theyhavethesametemperature. Istheconversetrue? Thatis, iftwosystemshavethesametemperature,aretheyinthermalequilibrium? What can yousayabout two systems thathavedifferent temperatures? Q.12 As a practical matter, there is always a temperature difference between a system and some part of its environment,howeverremote.Must therealways besomeheat transferred becauseofthat temperature difference?Explain.
2. Q.9 Asteel tapegives correct measurement at20°C.Apiece of wood is being measured with the steel tape at 0°C. The readingis 25 cm on the tape, the real length ofthe given piece of wood must be: (A) 25 cm (B) <25 cm (C) >25 cm (D) can not say Q.10 A rod of length 20 cm is made of metal. It expands by0.075 cm when its temperature is raised from 0°C to 100°C.Another rod of a different metal B having the same length expands by0.045 cm for the same change in temperature, a third rod of the same length is composed of two parts one of metalAand the other of metal B. Thus rod expand by 0.06 cm.for the same change in temperature. The portion made of metalAhas the length : (A) 20 cm (B) 10 cm (C) 15 cm (D) 18 cm Q.11 Asphere ofdiameter7 cm and mass 266.5 gm floats in a bath ofa liquid.As the temperature is raised, thespherejustbegins tosinkatatemperature35°C.Ifthedensityofaliquid at 0°C is1.527 gm/cc,then neglectingtheexpansionofthesphere,thecoefficient ofcubical expansion oftheliquidisf: (A) 8.486 × 104 per 0 C (B) 8.486 × 105 per 0 C (C) 8.486 × 106 per 0 C (D) 8.486 × 103 per 0 C Q.12 The volume of the bulb ofa mercurythermometerat 0°C isV0 and cross section of thecapillaryisA0 . Thecoefficient oflinearexpansion ofglass is ag per°C andthecubical expansionof mercurym per°C. If themercuryjust fills thebulb at 0°C, what is thelength ofmercurycolumn incapillaryat T°C. (A)     T 2 1 A 3 T V g 0 g m 0 a a    (B)     T 2 1 A 3 T V g g m a a 0 0    (C)     T 3 1 A 2 T V g g m a a 0 0    (D)     T 3 1 A 2 T V g g m a a 0 0    Q.13 Ametallic rod l cm long with a square cross-section is heated through 1°C. IfYoung’s modulus of elasticityofthemetal is Eandthe meancoefficient oflinearexpansion is perdegreeCelsius,then the compressional forcerequiredtoprevent therodfrom expandingalongits lengthis :(Neglectthechange of cross-sectional area) (A) EAt (B) EAt/(1 + t) (C) EAt/(1t) (D) E/t Q.14 Thelossinweightofasolidwhenimmersedinaliquidat0°CisW0 andat t°CisW.Ifcubicalcoefficient of expansion of the solid and the liquid by S and 1 respectively, then W is equal to : (A) W0 [1 + ( s – l ) t] (B) W0 [1 - (s – l )t] (C) W0 [( s – l ) t] (D) W0 t/(s – l ) Q.15 A thin walled cylindrical metal vessel of linear coefficient of expansion 10–3 °C–1 contains benzenr of volume expansion coefficient 10–3 °C–1 . If the vessel and its contents are now heated by 10°C, the pressure due to the liquid at the bottom. (A) increases by2% (B) decreases by 1% (C) decreases by 2% (D)remainsunchanged Q.16 A rod of length 2m at 0°C and having expansion coefficient  = (3x + 2) × 10–6 °C–1 where x is the distance (in cm) from one end of rod. The length of rod at 20°C is : (A) 2.124 m (B) 3.24 m (C) 2.0120 m (D) 3.124 m Q.17 Acopper ring has a diameter of exactly 25 mm at its temperature of 0°C.An aluminium sphere has a diameter ofexactly25.05 mm at its temperature of 100°C. The sphere is placed on top of thering and two are allowedto come to thermal equilibrium, no heat beinglost to the surrounding.The sphere just passes throughthe ringat theequilibrium temperature. The ratioofthemass ofthe sphere & ringis : (given : Cu = 17 × 10–6 /°C, Al = 2.3 × 10–5 /°C, specific heat of Cu = 0.0923 Cal/g°C and specific heat ofAl = 0.215 cal/g°C) (A) 1/5 (B) 23/108 (C) 23/54 (D) 216/23
3. Question No. 27 to 31 (5 question) Solids andliquidsbothexpandonheating.Thedensityofsubstancedecreases on expanding according totherelation ) T T ( 1 1 2 1 2       where, 1 — densityat T1 2 — density at T2  —coeff. of volumeexpansion of substances whenasolidissubmergedinaliquid, liquidexertsanupwardforceonsolidwhichisequalto theweight of liquiddisplaced bysubmergedpart of solid. Solidwillfloat orsink dependsonrelativedensities ofsolidand liquid. Acubicalblockofsolidfloatsinaliquidwithhalfofits volumesubmerged in liquid asshownin figure (at temperature T) S — coeff.oflinear expansion ofsolid L — coeff.ofvolumeexpansion ofliquid S — densityofsolid at temp. T L — densityofliquid at temp. T Q.27 Therelationbetweendensities ofsolid and liquidat temperatureT is (A) S = 2L (B) S = (1/2)L (C) S = L (D) S = (1/4)L Q.28 Iftemperatureofsystemincreases, thenfraction ofsolid submergedin liquid (A)increases (B) decreases (C)remains the same (D)inadequateinformation Q.29 ImaginefractionsubmergeddoesnotchangeonincreasingtemperaturetherelationbetweenL andS is (A) L = 3S (B) L = 2S (C) L = 4S (D) L = (3/2)S Q.30 Imaginethedepthoftheblocksubmerged in theliquiddoes not changeonincreasing temperature then (A) L = 2 (B) L = 3 (C) L = (3/2) (D) L = (4/3) Q.31 Assume block does not expand on heating. The temperature at which the block just begins to sink in liquidis (A) T + 1/L (B) T + 1/(2L) (C) T + 2/L (D) T + L/2 Q.32 The coefficient ofapparent expansion of aliquid in a coppervessel is C and in a silver vessel is S. The coefficient ofvolume expansionof copperis c. What is thecoefficientoflinearexpansionofsilver? (A) ( ) C S c    3 (B) ( ) C S c    3 (C) ( ) C S c    3 (D) ( ) C S c    3 Q.33 An aluminium container of mass 100 gm contains 200 gmof ice at –20°C. Heat is addedto the system at the rateof 100 cal/s. Thetemperature of the system after 4 minutes will be (specific heat ofice = 0.5 and L= 80 cal/gm, specific heat ofAl = 0.2 cal/gm/°C) (A) 40.5°C (B) 25.5°C (C) 30.3°C (D) 35.0°C
4. Q.44 Twoverticalglasstubesfilledwithaliquidareconnectedbyacapillary tube as shown in the figure. The tube on the left is put in an ice bath at 0°C while the tube on the right is kept at 30°C in a water bath. The difference in the levels of the liquid in the two tubes is 4 cm while the heightoftheliquidcolumnat 0°Cis 120cm.Thecoefficientofvolume expansionofliquidis (Ignoreexpansionofglass tube) (A) 22 × 10–4/°C (B) 1.1 × 10–4/°C (C) 11 × 10–4/°C (D) 2.2 × 10–4/°C Q.45 Asystem S receives heat continuouslyfrom an electrical heater of power 10W.The temperature of S becomes constant at 50°C when the surrounding temperature is 20°C.After the heater is switched off, S cools from 35.1°C to 34.9°C in 1 minute. The heat capacityof S is (A) 100J/°C (B) 300J/°C (C) 750J/°C (D) 1500J/°C Q.46 Ablockofice with mass mfalls intoalake.After impact, a massof ice m/5 melts.Both theblock of ice and thelakehave atemperatureof 0°C. If Lrepresents theheat offusion, theminimum distancethe ice fellbeforestrikingthesurfaceis (A) g 5 L (B) g L 5 (C) m 5 gL (D) g 5 mL Q.47 Pure water super cooled to 15°C is contained in a thermally insulated flask. Small amount of ice is thrown intotheflask. Thefractionofwaterfrozen intoice is : (A) 3/35 (B) 6/35 (C) 6/29 (D) 2/35 Q.48 The specific heat of a metal at low temperatures varies accordingto S = aT3 where a is a constant and T is the absolute temperature. The heat energy needed to raise unit mass of the metal from T = 1 K to T = 2 K is (A) 3 a (B) 4 a 15 (C) 3 a 2 (D) 5 a 12 Q.49 Thegraphshowninthefigurerepresent changeinthetemperatureof5 kg of a substance as it abosrbs heat at a constant rate of 42 kJ min–1. The latent heat of vapourazationof thesubstanceis : (A) 630 kJ kg–1 (B) 126 kJ kg–1 (C) 84 kJ kg–1 (D) 12.6 kJ kg–1 Q.50 The densityof amaterialAis 1500 kg/m3 and that of anothermaterial B is 2000 kg/m3. It is found that the heat capacityof 8 volumes ofAis equal to heat capacityof 12 volumes of B.The ratio of specific heats ofAand B will be (A) 1 : 2 (B) 3 : 1 (C) 3 : 2 (D) 2 : 1 Q.51 Find the amount of heat supplied to decrease thevolume of an ice watermixtureby1 cm3 withoutany change in temperature. (ice = 0.9 water, Lice = 80 cal/gm). (A) 360 cal (B) 500 cal (C) 720 cal (D) none of these
5. Q.59 Two sheets of thickness d and 2d and same area are touchingeach otheron their face. TemperatureTA,TB,TC shown are in geometric progressionwith common ratio r= 2. Thenratioofthermal conductivityofthinnerandthickersheet are (A) 1 (B) 2 (C) 3 (D) 4 Q.60 Thewallwithacavityconsistsoftwo layersofbrickseparated byalayerofair.Allthreelayershavethe samethicknessandthethermal conductivityofthebrickismuch greaterthan thatofair.Theleftlayeris at a higher temperature than the right layer and steadystate condition exists. Which of the following graphs predicts correctlythe variationof temperatureT with distanced insidethecavity? (A) (B) (C) (D) Q.61 Awall has twolayerAand B eachmadeof different material, boththe layers have the same thickness. ThethermalconductivityofthematerialAis twicethatofB.Underthermalequilibrium thetemperature difference across the wall B is 36°C.The temperature difference across thewallAis (A) 6°C (B) 12°C (C) 18°C (D) 72°C Q.62 Aringconsistingof twopartsADBandACBof sameconductivityk carries an amount of heat H.TheADB part is now replaced with another metal keeping the temperatures T1 and T2 constant. The heat carried increases to 2H. What should be the conductivityofthe newADB part? Given ADB ACB = 3: (A) 3 7 k (B) 2 k (C) 2 5 k (D) 3 k Q.63 Threeconductingrodsofsamematerialandcross-sectionareshowninfigure. Temperatures ofA, D and C are maintained at 20°C, 90°C and 0°C. The ratioof lengths of BD and BC if thereis no heat flow inAB is: (A) 2 / 7 (B) 7 / 2 (C) 9 / 2 (D) 2 / 9 Q.64 Threerodsmadeofthesamematerial and havingsamecross-sectional areabut different lengths 10cm,20cm and30cm arejoinedasshown. Thetemperature ofthejointis: (A) 20°C (B) 23.7°C (C) 16.4°C (D) 18.2°C Q.65 Twelveconductingrodsform theridersofauniformcubeofside'l'.Ifin steady state, B and H ends of the rod are at 100°C and 0°C. Find the temperature ofthe junction 'A'. (A) 80°C (B) 60°C (C) 40°C (D) 70°C Q.66 Sixidenticalconductingrodsarejoinedasshowninfigure.PointsAand D aremaintained at temperature of 200°C and 20°C respectively.The temperatureofjunctionBwillbe: (A) 120°C (B) 100°C (C) 140°C (D) 80°C
6. Q.74 If TA and TB are the temperature drops across the rodAand B, then (A) B A T T = 1 3 (B) B A T T = 3 1 (C) B A T T = 4 3 (D) B A T T = 3 4 Q.75 If GA and GB are the temperature gradients across the rodAand B, then (A) B A G G = 1 3 (B) B A G G = 3 1 (C) B A G G = 4 3 (D) B A G G = 3 4 Q.76 Twosheets ofthicknessdand3d,aretouchingeachother.Thetemperaturejust outsidethethinnersheet side isA, and on the side of the thicker sheet is C. The interface temperature is B.A, B and C are in arithmeticprogressing, theratioofthermalconductivityofthinnersheetandthickersheetis (A) 1 : 3 (B) 3 : 1 (C) 2 : 3 (D) 1 : 9 Q.77 Acylindricalrodwithoneendinasteamchamberandtheouterendiniceresultsinmeltingof0.1gmofice persecond.Iftherodisreplacedbyanotherwithhalfthelengthanddoubletheradiusofthefirstandifthe thermalconductivityofmaterialofsecondrodis1/4thatoffirst,therateatwhichicemeltsisgm/secwillbe (A) 3.2 (B) 1.6 (C) 0.2 (D) 0.1 Q.78 A composite rodmadeof threerods of equal length and cross-section as shown in the fig. The thermal conductivities of the materials of the rods are K/2, 5K and K respectively. The endAand end B are at constanttemperatures.AllheatenteringthefaceAgoes outofthe end Btherebeingnolossof heat from thesides of thebar.Theeffective thermal conductivityofthebar is B A K 5K K/2 (A) 15K/16 (B) 6K/13 (C) 5K/16 (D) 2K/13. Q.79 A rod of length L with sides fully insulated is of a material whose thermal conductivity varies with temperature as K= T  , where  is a constant. The ends of the rod are kept at temperature T1 and T2 . The temperature T at x, where x is the distance from the end whose temperature is T1 is (A) L x 1 2 1 T T T         (B) 1 2 T T n L x l (C) L T x T 1 1 2 e T (D) x L T T T 1 2 1   Q.80 The power radiatedbya black bodyis P and it radiates maximum energyaround the wavelength 0 . If thetemperatureoftheblackbodyisnowchangedsothatitradiatesmaximumenergyaroundwavelength 3/40 , the power radiated byit will increase bya factor of (A) 4/3 (B) 16/9 (C) 64/27 (D) 256/81 Q.81 A black metalfoil is warmed byradiation from a small sphere at temperature 'T' and at a distance 'd'. It is foundthat thepowerreceivedbythefoil isP . Ifboththe temperature and distancearedoubled, the power receivedbythe foil will be : (A) 16 P (B) 4 P (C) 2 P (D) P
7. ONE OR MORE THAN ONE OPTION MAY BE CORRECT Take approx. 3 minutes for answering each question. Q.1 Four rodsA,B,C, Dof samelengthandmaterial but ofdifferent radii r, 2 r , 3 r and 2r respectively are held betweentwo rigid walls. Thetemperature of all rods is increased bysame amount. If the rods donot bend, then (A) the stress in the rods are in the ratio 1 : 2 : 3 : 4. (B) the force on the rod exerted bythe wall are in the ratio 1 : 2 : 3 : 4. (C) the energystored in the rods due to elasticityare in the ratio 1 : 2 : 3 : 4. (D) the strains produced in the rods are in the ratio 1 : 2 : 3 : 4. Q.2 AbodyofmassM isattachedtothelowerendofametal wire,whoseupperendisfixed.Theelongation of thewire is l. (A)Loss ingravitational potential energyofM is Mgl (B)The elasticpotential energystoredin thewire is Mgl (C) The elastic potential energystored in the wire is 1/2 Mgl (D) Heat produced is 1/2 Mgl. Q.3 When the temperature of a copper coin is raised by80°C, its diameter increases by0.2%. (A) Percentage rise in the area of a face is 0.4 % (B) Percentage rise in the thickness is 0.4 % (C) Percentagerise in the volume is 0.6 % (D) Coefficient of linear expansion of copper is 0.25 × 10–4 C° –1. Q.4 An experiment is perfomed to measure the specific heat of copper.Alump of copper is heated in an oven, then dropped into a beaker of water. To calculate the specific heat of copper, the experimenter must know ormeasure the value of all of the quantities belowEXCEPT the (A) heat capacityof water and beaker (B) original temperature of the copperand the water (C) final (equilibrium)temperature ofthe copperand thewater (D) time takento achieve equilibrium afterthe copper is dropped into the water Q.5 One end of a conducting rod is maintained at temperature 50°C and at the other end, ice is melting at 0°C.The rateofmeltingoficeis doubled if: (A) the temperature is made 200°C and the area of cross-section of the rod is doubled (B) the temperatureis made 100°C andlength of rod is made four times (C) areaof cross-section of rodis halved and length is doubled (D) the temperature is made 100°C and the area of cross-section of rod and length both are doubled. Q.6 Twometallic sphereAandB aremade ofsamematerial andhavegot identical surfacefinish.Themass of sphereAis four times thatof B. Both thespheres are heated to the same temperature and placed in a room havinglowertemperaturebut thermallyinsulatedfromeachother. (A) The ratio of heat loss ofAto that of B is 24/3. (B) The ratio of heat loss ofAto that of B is 22/3. (C)The ratio of the initial rate of cooling ofAto that of B is 2-2/3. (D)The ratio of the initial rate of cooling ofAto that of B is 2-4/3.
8. Answer Key ONLY ONE OPTION IS CORRECT. Q.1 E Q.2 B Q.3 D Q.4 A Q.5 B Q.6 B Q.7 C Q.8 C Q.9 B Q.10 B Q.11 A Q.12 B Q.13 B Q.14 A Q.15 C Q.16 C Q.17 C Q.18 C Q.19 D Q.20 C Q.21 D Q.22 B Q.23 C Q.24 B Q.25 A Q.26 C Q.27 B Q.28 A Q.29 A Q.30 A Q.31 A Q.32 C Q.33 B Q.34 A Q.35 B Q.36 D Q.37 A Q.38 D Q.39 A Q.40 C Q.41 B Q.42 A Q.43 D Q.44 C Q.45 D Q.46 A Q.47 B Q.48 B Q.49 C Q.50 D Q.51 C Q.52 A Q.53 C Q.54 A Q.55 C Q.56 D Q.57 B Q.58 B Q.59 A Q.60 D Q.61 C Q.62 A Q.63 B Q.64 C Q.65 B Q.66 C Q.67 B Q.68 C Q.69 C Q.70 A Q.71 A Q.72 A Q.73 A Q.74 B Q.75 B Q.76 A Q.77 C Q.78 A Q.79 A Q.80 D Q.81 B Q.82 A Q.83 C Q.84 B Q.85 D Q.86 B Q.87 B Q.88 B Q.89 A ONE OR MORE THAN ONE OPTION MAY BE CORRECT Q.1 B,C Q.2 A,CD Q.3 A,C,D Q.4 D Q.5 D Q.6 A,C Q.7 A,B Q.8 D Q.9 A,B Q.10 A,B,C,D Q.11 B
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