1.

2. or

3. The area of the faces will increased by 0.02% and thevolume by 0.03%.

4. This is because platinum begins so evaporate above

5. White clothes absorb very little heat radiation andhence they are comfortable in summer. Colored clothesabsorb almost whole of the incident radiation and keepthe body warm in water.

6. No the process of transfer of heat by convection is baseon the fact that a liquid becomes lighter on becominghot and rise up in condition or weightlessness this is notpossible so transfer of heat by convection is not possiblein the earth satellite.

7. The neck expands but not the stopper due to poorconductivity of glass. Thus the stopper can be taken outeasily.

8. Water is performed to any other liquid in the hot waterbottles because due to high specific heat it does not coolfast also for the given mass of water the amount of heatcontained is higher and it can provide more warmth ascompared to any other liquid.

9. The two bodies may have different masses and differentmaterials i.e. they may have different thermalcapacities.In case the two bodies have equal thermal capacities

they would settle at the mean temperature10. The thermal conductivity of cooper is much larger than

that of steel the copper bottom always more hear toflow into the pan and hence helps in cooking the foodfaster.

11. The specific heat is the heat capacity per units masswhereas the molar specific heat is the hard capacityper mole.

12. When the birds swell their feathers, they are able toenclosed air in the feathers air being a poor conductorof heat so it prevents the loss of heat from the bodiesof the birds to the surrounding and as such they do notfeel cold in water.

13. The object at 3000c will cool faster than the object at1000C. this is an accordance with Newton’s law ofcooling .As we know rate cooling of an object temperaturebetween the object and its surroundings.

14. According to the Prevost theory of heat exchanges allthe objects (above 10 K) not only radiateelectromagnetic energy but also absorb at the same ratefrom their surroundings thus they do not becomecolder.

15. The statement is true. A black body absorb radiations ofall wavelengths when heated to a suitable temperature.It emits radiation of all wavelengths. Hence a black bodyradiation is white.

16.

17. This is because metal are good conductors of heat andhave law specific heat capacity.

18.

19.

20.

21.

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23.

24.

25. Let lengths of brass and copper rodsrespectively, their correspondingcoefficients of linear expansion.If the temperature of both the rods is changed from T to(T + DT),change in length of brass rod =and change in length of copper rod =For the difference between their lengths to be constant,

or

26. We know that the coefficient of linear expansion forbrass is more than for steel, as

Thus, on cooling, the brass disc shrinks to a greaterextent than the hole in the iron plate and hence the discgets loose.

27. The cylindrical bulb responds quickly to temperaturechange as it has larger surface area than a spherical bulbof the same volume.

28. The wires expand with the hotter temperature insummer and therefore hang lower.

29. A huge amount of thermal energy is required to changethe temperature of water in the oceans.

30. The mixture freezes if heat is removed from it and meltsif heat is added to it.

31. The water vaporizes instantly when it attains the boilingpoint.

32. Thermal energy is distributed throughout the water byconvection currents.

33. A temperature of 310 K = 370C = 98.60 F, which is thenormal human body temperature and as such is not tobe worried about.

34. A temperature of 860 F is approximately equal to 300 C.Above this temperature, chemical reactions may takeplace resulting in a change in the composition of themedicine. The medicine may then become ineffective oreven harmful.

35. It is less than one as the specific heat of water ismaximum and is equal to 1 cal/gC0.

36. The triple point of water is 0.010 C and not 00C.37. The diameter of the opening in the plate of the

kitchen-stove increases when the stove is heated. Theincrease in the diameter (DD) given by

where = coefficient of linear expansion of cast iron,D = original diameter of the opening and = increasein temperature of the plate on heating.38. The flow of heat as well as the flow of electricity is dueto free electrons. Obviously, a good conductor of heat(which possesses a large number of free electrons) isalso a good conductor of heat.

39. This is due to the drop getting insulated from the iron bya layer of bad conducting water vapours. But in case thedrop falls on an iron which is not very hot, it evaporatesas it comes in direct contact with the iron.

40. The reason for this is that the thermal conductivity ofhydrogen is more than that for air.

41. Woollen clothes are warm as they enclose a largenumber of air pockets in them. Because air has very lowthermal conductivity, the clothes as a whole have a lowconductivity. Thus, the clothes prevents the loss of heatfrom the body and keep us warm in the winter.

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42. A layman wrongly thinks that fur is a source of heat toour body. In fact, the fur is a poor conductor of heat. Itprevents the loss of heat from our body to thesurroundings and as a result of this the body remainswarm.

43. Sawdust encloses a large quantity of air in it. Air, as weknow, is a very poor conductor of heat. No air isenclosed in wood from which the sawdust is made.

44. In winter, a metal piece is at a temperature lower thanthat of our body. As a metal is a good conductor of heat,on touching the metal piece, heat flows from our bodyto it. Consequently, the metal piece feels colder than apiece of wood, which being a bad conductor of heat,takes only a small amount of heat from our body.

45. If in arctic cold, metal piece is touched with finger, thefinger freezes to the metal piece as heat is quicklytransferred from the finger to the metal piece.

46. The thermal conductivity of marble is more than that ofcement. Thus, marble floor which absorbs more heatfrom our feet than the cement floor, appears colder.

47. In front of the fire, heat is received only by radiation.But at the same distance over the top of the fire, heat isreceived both due to radiation as well as convection.

48. The beaker will lose heat mainly due to radiation. Asmall part of heat will be lost to the wooden table onaccount of conduction also.

49. An ink dot on a white porcelain dish appears dark as it isa better absorber of radiations than the rest of the dish.But when this dish is heated, the ink dot appearsbrighter than the background because of its being abetter absorber of light and hence also a better emitter.This is in a accordance with Kirchhoff’s law which statesthat good absorbers are good radiators.

50. No, a polished black surface is not a blackbody as itreflects radiations incident on it. On the other hand, Sun,which is dazzling white, is a blackbody.

51. This is due to the reason that compared to a polishedsurface, a blackbody is a good emitter (as well as a goodabsorber).

52. Self (teacher)53. Self (teacher)54. 55 K, 99 F0

55. 0.6670 C56. 4.5 C0

57. 0.40 m & 0.60 m58. 58.4 N59. 2.69 cm3

60. 1.371 L61. 7298 cal62. In modern thermometry, the triple point of water

standard fixed point.63. No. Because absolute zero of temperature is the

minimum possible temperature on Kelvin scale.64. No. When milk is poured into tea, some work is done ich

is not recoverable. So process is not reversible.65. 00 C, 40 C.66. Earth loses heat by convection and radiation.67. As invar has low value of coefficient of linear expansion,

length of pendulum almost remains same in differentseasons hence gives correct time.

68. The temperature

69. Due t decreases in internal energy, a gas is cooled,70. The black and rough surface is a better absorber of heat

in a highly polished surface.71. Because they protect them from both heat and cold.72. Charcoal will shine more as it is a good absorber and

good miter, so it will emit more energy.

73. Zero , because use c= .

74. This is because a gas can be heated under differentconditions of pressure and volume. The amount of heatrequired to raise the temperature of unit mass throughunit degree is different under different conditions ofhating.

75. A Cooking utensil should be the suitable material whichpossesses small value of specific heat (C), large value ofthermal conductivity (K) and low coefficient ofexpansion ( )

76.

77.

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SaraNextGen.Com

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78.

79.

80.

81.

82.

83.

84.

85.

86.

87.

88.

89.

90. Glass transmit about 50% of heat radiation coming froma hot source like the sun but does not allow theradiation from moderately hot bodies to pass through itdue to this when a car is left in the sun heat radiationfrom the sun gets into the car but as the temperatureinside the car is moderate they do not pass back throughits window hence inside of the car becomesconsiderably warmer.

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91. Since the speed is constant so there is no change ofkinetic energy . The loss in gravitational potential energyis partially the gain the heat energy of the brake drum.

92. Newton’s law of cooling - It states that the state of lossof at by a body is directly proportional to thetemperature difference between the body and thesurroundings provided the difference is not o large.It should be noted that this law is approximately in stillair only are a temperature excess of 20 K or 30 K .Cooling Curve - It is defined as a graph between thetemperature a body and the time. It is as shown in figurehere.The slope of the tangent to the curve at any point givesthe rate fall of temperature.

93. Wool is a bad conductor of heat. Moreover woolenclosed air in it which is a bad conductor. There canalso be no loss of hear by convections. The woolenblanket keeps us warm by preventing then heat of thehuman body to flow outside and hence our bodyremains warm.In the case of ice, the heat from outside is prevented toflow inside and thus ice remains cold.

94. When a drop of water falls on a very hot iron, it getsinsulated form the hot iron due to the formations of athin layer of water vapour, which is a bad conductor innature. It takes quite long to evaporate as heat isconducted from hot iron to the drop through the layerof water vapour very slowly.On the other hand, if a drop of water falls on an ironwhich is no very hot, then it comes in direct contact withthe iron and evaporates immediately.

95. Water boils with flame by the process of convections.Hot lighter particles raise up and heavier particles raiseup and heavier particles move down under gravity. In agravity free space in the satellite, the particles cannotmove dose hence, water can’t be hearted byconvections. It will be hearted by conduction.

96.

97. Hot case is a double walled vessel. The space betweenthe walls is evacuated in good hot case. The foodcontainer place inside the hot case is made of crowningsteel thus, neither the outside low temperature air canenter the container not the heat form inside can escapethrough the hot case by conductions or convections.Highly polished shining surface of food container helpsin stopping loss of heat due to radiations. Thus, the heatof the food is preserved for long time and food remainshot in winter.

98. When water falls form a height it looses its potentialenergy. This is converted into the kinetic energy of thewater molecules. It is a known fact form kinetic theoryof gases that increases in kinetic energy of the substanceincreases its temperature , hence the temperature ofwater at the bottom of the falls raises and it does notremain as cold the top. therefore, people taking bathdown below the Kempty fall do not get frozsen, theyrather feel warm and enjoy bathing.

99. Heat conductibility in solids apart from temperaturedepends the availability of conducting particles, i.e., freeelectrons. In metals copper, brass and iron freeelectrons are available but in insulators wood,cardboard and ply free electrons are not available, sometal good conductor of heat.

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100. On hills people make wooden houses or put woodenlining house walls to insulate the house from extremecold of winter cause wood being a bad conductor ofheat does not allow the heat house to escape out orexchange low outside temperature with the iftemperature inside, in plains even though woodenhouses are helpful in fulfilling the odd weatherconditions yet because of other actors such as (i) nonavailability of plenty of wood and (ii) chances catchingfire etc. Wooden houses are generally not built .

101. After hail storm, the ice balls melt by absorbing lotof hear energy form the atmosphere, thus reduces itstemperature. hence there is very cold after the hailstorm.

102.

103.

104.

105.

106.

107. 0.42 Wm-1 K-1.108. -400C109. -5.8 kg/m3

110. Self (teacher)111. Self (teacher)112. Self (teacher)

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113. Self (teacher)114. Self (teacher)115. Self (teacher)116. 1.35 × 104 W117. 42 s118. (i) - it si defined as the change in surface area per

unit original surface area per unit change in thetemperature of the material of the solid.

i.e.,

(ii) - it is defined as the change in volume per unitoriginal volume per unit change in the temperature ofthe material of the solid.

i.e.,

119.

120.

121.

122.

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124.

125.

126.

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127. 128.

129.

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130. 131.

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132. 133.

134.

Generated From SaraNextGen App

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135.

136.

137. This is due to the reason that the copper gauze,being a good conductor of heat, conducts the heat awayfrom the flame so rapidly that the temperature abovethe gauze is lowered below the ignition temperatureabove the gauze is lowered below the ignitiontemperature of the gas. (However, when the gauze isitself heated to the ignition temperature of the gas, itcan no longer prevent the combustion of the gas aboveit and the flame is able to go up the gauze).

138. Vacuum is created between the two walls of aDewar flask (i.e., thermos flask) so as to prevent the lossof heat due to conduction as well as convection. Bothconduction and convection require a material medium.The loss of heat due to radiation is minimized bysilvering the surfaces bounding the vacuum. The tea inthe thermos flask remains hot for a long time as the lossof heat due to all the three known processes is greatlyminimized. The same considerations apply to the entryof heat from the surroundings when the flask contain acold liquid. Thus, a liquid in the flask keeps hot or coldfor a long time.

139. The windows of a car are made of glass and glasspossesses the property of selective absorption of heatradiation. The amount of heat transmitted through glassdepends upon the temperature of the heat source. Forexample, it transmits about 50% of heat radiation whenit is coming from a source like Sun which is at a hightemperature. But when the radiation comes from asource which is below 1000C, glass is athermnous (i.e.,opaque) to it. The glass windows of the car allow theheat radiation of Sun to pass through them and heat theinside of the car. But the inside of the car is at atemperature below 1000C. The radiation emitted by theinside of the car is not allowed by the windows to passthrough. Thus, the inside of the car becomes hot.Glass thus serves to trap the sunrays.

140. The rate of emission increases by 16 times as

(as )

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141. When the temperature of the object is equal to thatof the human body, no transference of heat takes placebetween the body and the object. Thus, when thetemperature of the block of wood or block of metal isequal to 370C, i.e., the temperature of the human body,these appear equally hot or cold on touching on accountof non-transference of heat.

142.

143. Free air is able to transmit heat by convectioncurrents. But in case of felt, there are fine pores whichtrap air and do not allow its movement. Obviously,convection currents cannot be set in the felt.

144. Self (teacher)145. Self (teacher)146. Self (teacher)147. Self (teacher)148. Self (teacher)149. Self (teacher)150. 0.128 kJ/kg K151. (a) 13.60C (b) 00C152. 320 cal/s.153. 400C154.

155.

156. 1.5 g/s157. 44.40C158. 1824 s159. 10 min160.

161. 1.452 × 103W/m2, 1.452 × 107 W/m2

162. 43.59 cal/s.163. 10.46 Kw164. 9170C165. ,

166. 1000 K

167. 14400 Å. Infrared region.168.

169. Here C = 1 Cal g-1.c-1

M = 2 × 103 gm=55 - 20 = 350C

M = 10gIf Q be the heat produced, then

Q = mc =2 × 103× 10 × 35 = 70 × 103 cal.if Q1 be the heat produced, then

170.

171.

172.

173. ‘J’ represents Joule’s mechanical equivalent of heat,it is not a physical constant . It s a conversion factor i.e.,1 calories = 4.18 joule. It means 4.18 joule of energy and1 calories of heat are equivalent. Thus amount of work(in J) is obtained form the quaintly of heat (in cals) bymultiplying the latter by 4.18 and vice-versa.

174. Self (teacher)175. Self (teacher)176. 1.9 × 10-5 0C-1

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178.

179.

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181.

182. Self (teacher)183. Self (teacher)184. Self (teacher)185. Self (teacher)186. 1000C; 572.2 g of water187. 53 g188. 19.24 g/cm3

189. 0.62380 m,

190. (a)

(b)

191.

192.

193. 27 mW/m2

194.

195. 5800 K196. Self (teacher)197. 1800 W198. 5773 K199. 2616 K

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