2 Thermal Physics. Thermal Physics. 1. Simple kinetic molecular model of matter 2. Thermal properties 3. Transfer of thermal energy

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1 2 Thermal Physics 1. Simple kinetic molecular model of matter 2. Thermal properties 3. Transfer of thermal energy 1. A swimmer climbs out of a swimming pool on a warm, dry day. Almost immediately he begins to feel cool. Why is this? A. The water allows a convection current to remove heat from his skin. B. The water takes latent heat from his body in order to evaporate C. The water on his skin is a good conductor of heat D. The water prevents infra-red radiation from reaching his body A B C D Bulb Thick glass Thick glass Thin glass Thin glass Bore Narrow Wide Narrow wide 4. A glass jug is designed so that it does not break when boiling water is poured into it. What sort of glass should be used? 2. Ice at -10 C is heated at a constant rate until it is water at + 10 C. Which graph shows how the temperature changes with time? 5. A substance consists of particles that are close together and moving past each other at random. Te average speed of the particles gradually increasing. What best describes the substance? A. a liquid being boiled to form a gas B. a liquid being heated C. a solid being heated D. a solid being melted to from a liquid 6. A liquid-in-glass thermometer consists of a bulb containing a liquid. The liquid can expand into a very thin capillary tube. 3. A clinical thermometer is designed to respond quickly to a change in temperature and to have a high sensitivity. Which design features should the clinical thermometer have? The liquid in the thermometer is replaced by another liquid that expands more for the same temperature rise. The new thermometer will have A. greater sensitivity and greater range B. greater sensitivity but less range IGCSE Physics 1 Namrata David Publications

2 C. the same sensitivity and the same range D. the same sensitivity but grater range 7. The diagram shows a vacuum flask and an enlarged view of a section through the flask wall. needed to raise the temperature of a 2 Kg block by 20 0 C. What value for specific heat capacity is given by these results? A. 130 J/(kg C) B. 520 J/(kg C) C J/(kg C) D J/(kg C) 11. A person cannot unscrew the lid of a pot of jam. He finds that the lid can be unscrewed after it has been held under hot, running water for a few seconds. The main reason for the silvering is to reduce heat transfer by A. conduction only B. radiation only C. conduction and convection D. conduction and radiation 8. What factors increase the rate of evaporation of a liquid? Why is this? A. the air pressure in the jar falls B. the glass expands C. the jam melts D. the lid expands 12. The diagram shows a thick copper plate that is very hot. One side is black and the other is shiny. A student places her hands the same distance from each side as shown. 9. Four mercury-in-glass thermometers are made with different dimensions Which will have the greatest sensitivity? A. 10 cm long and bore 0.75 mm wide B. 15 cm long and bore 0.50 mm wide C. 25 cm long and bore 0.10 mm wide D. 30 cm long and bore 0.25 mm wide Her left hand feels warmer than her right hand. Which statement is the correct conclusion from the experiment? A. the black side is the hotter than the shiny one B. the black side radiates more heat C. the shiny side radiates more heat D. the shiny side is cooling down faster than the black side 10. In an experiment to find the specific heat capacity of a metal, is found that 5200 J is IGCSE Physics 2 Namrata David Publications

3 13. Some of the more energetic molecules in a liquid leave the surface, leaving the rest of the liquid slightly cooler. What is the name given to this process? A. boiling B. condensation C. evaporation D. freezing 14. A substance consists of particles that are close together and moving past each other at random. The average speed of the partials is gradually increasing. What best describes the substance? A. a gas being heated B. a liquid being heated C. a solid being heated D. a solid being melted 15. Which thermometer is the best foe measuring rapidly changing temperature? A. a clinical thermometer B. a liquid-in-glass thermometer C. a thermo couple D. all thermometers are equally good 16. Some ice cubes are taken from a deep freeze and placed in a metal container. The container is heated at a constant rate and readings of temperature and time are taken. The results are recorded on a graph. Which temperature corresponds to 0 C? The change in shape occurs because A. a brass contracts more than invar B. brass expands when it cools down C. invar and brass contract by equal amounts D. invar contracts more than brass 18. Density changes are responsible for which method of thermal energy transfer? A. conduction only B. convection only C. radiation only D. conduction, convection and radiation 19. A liquid is heated. Which statement is incorrect? A. the molecules expand B. the molecules gain energy C. the molecules move further apart D. the molecules move faster 20. What describes the molecular structure of a liquid? 21 A thermocouple thermometer uses a voltmeter to measure the e.m.f generated between two junctions. The junctions are at temperatures t 1 and t 2. To calibrate the thermometer, fixed points are needed. 17. The diagram show a bimetallic strip when it is at room temperature after it has been cooled. What are the values of t 1 and t 2 when the thermometer is calibrated at the steam point? A B C D t 1 t 2 0 C 0 C 25 C 25 C 0 C 100 C 0 C 125 C IGCSE Physics 3 Namrata David Publications

4 21. What is the definition of heat capacity? A. the quantity of heat required to raise the temperature of an object through 1 C B. the quantity of heat required to raise the temperature of 1 kg substance through 1 C C. the quantity of heat required to convert an object from solid to liquid with out a change in temperature D. the quantity of heat required to change 1 kg of substance from solid to liquid with out a change in temperature 22. Fillings in teeth should made from a material which A. expands more than the tooth when heated B. expands by the same amount as the tooth when heated C. expands less then the tooth when heated D. does not expand when heated C. Fewer molecules are left in the liquid D. Some of the most energetic molecules leave the liquid 25. When ice melts to become water, which force must be overcome? A. the attraction between electrons and the nucleus B. the attraction between the atoms in the molecule C. the force between molecules D. the force of gravity 26. A substance is heated in an enclosed space until it becomes a gas After heater is removed, the temperature is recorded in regular intervals. The graph plotted temperature against time graph. 23. A double glazed window has two sheets of glass separated by a layer of air. Thermal energy is conducted through the layer of the air. The amount of conduction and convection varies with thickness of the layer of air, as shown in the graph Which thickness of air produces the smallest energy transfer A. 0.5 cm because there is little convection B. 1.0 cm because the total thermal energy transfer is least C. 1.5 cm because the total thermal energy transfer is small and conduction is low D. 2.0 cm because there is little conduction 24. A liquid evaporates rapidly. Why does it cool? A. Air molecules remove heat by contact with the liquid surface B. Energy is lost by convection currents What does the section PQ represents? A. boiling B. condensing C. melting D. solidifying 27. A student is given a thermometer that reads 1 C in pure melting ice and 101 C in pure boiling water. She uses it to measure the temperature of some water before and after it is heated. The increase in temperature of water calculated from her results is A. 1 C is too low B. Correct C. 1 C is too high D. 2 C is too high 28. Fiber is used for home insulation in cold country, as shown in the diagram. IGCSE Physics 4 Namrata David Publications

5 Heat cannot easily escape through the ceiling because the fiber A. traps air B. is warm C. is tightly packed D. heats the roof space 29. The diagram shows four similar cans. Each can contains the same volume of water initially at 80 C. After five minutes, which can will contain the coolest water? 31. Assuming the temperature remains constant, which combination correctly describes the volume and shape of a gas or liquid? A B C D Gas or liquid Gas Gas Liquid liquid Volume Fixed Not fixed Fixed Not fixed Shape Not fixed Not fixed fixed fixed 32. An axle is too large to fit into the hole in a wheel that is made of the same metal. How can the axle be made to fit into the hole. A. By cooling the axle alone B. By cooling the wheel alone C. By cooling both the axle and the wheel D. By heating both the axle and the wheel 30. Which graph shows the relationship between the pressure and volume of a fixed mass of gas at constant temperature? 33. A 2 kg mass of copper is heated for 40 s by a heater that produces 100 J/s. The specific heat capacity of copper is 400 J/(kg K) What is the rise in temperature? A. 5K C. 20 K B. 10K D. 50 K 34. In a vacuum flask, which methods of heat transfer are prevented by the vacuum? A. conduction only B. convection only C. conduction and convection only D. conduction,convection and radiation IGCSE Physics 5 Namrata David Publications

6 35. A student has three sealed plastic bags. One bag is full of gas, one of liquid and one of solid. The student squeezes each bag to see if it changes shape, and warms each bag to see if it expands. Which bag contains gas? A. the one that changes shape easily and expands the least when heated B. the one that changes shape easily and expands the most when heated C. the one that is fixed in shape and expands the least when heated D. the one that is fixed in shape and expands the most when heated C. Expands less than the hole in the tooth D. Does not expand when heated 39. Hat energy is supplied at the same rate to 100 g of paraffin and to 100 g of water in similar containers. Why does the temperature of the paraffin rise more quickly? A. the paraffin has a larger specific heat capacity than water B. the paraffin has a smaller specific heat capacity than water C. the paraffin is less dense than water D. the paraffin is more dense than water 40. A teacher has a large tank of water in which he wants to set up a convection current. 36. The diagram shows a cross-section through a rain-water puddle formed in a shallow hole in a road surface. Over a period of time air temperature, wind speed and wind direction remain constant. What happens to the rate of evaporation of water from the puddle? A. it decreases, because the surface area decreases B. it increases, because the puddle gets shallower C. it increases, because the surface area decreases D. it remains constant 37. A new liquid is tested to decide whether it is suitable for use in a liquid-in-glass thermometer. It is found that the liquid does not expand uniformly with temperature. What will be the effect of this on the scale of the thermometer? A. it has a short range B. it is not linear C. the markings are too close together D. the marking are too far apart 38. The fillings for a hole in a tooth should be made from a material that A. Expands more than the hole in the tooth B. Expands by the same amount as the hole in the tooth Which of the following arrangements would do this? A. cooling at X C. heating at Y B. cooling at Y D. heating at Z 41. What will not affect the rate of evaporation from the surface of a liquid? A. Depth of the liquid B. Draughts above the surface of the liquid C. Surface area of the liquid D. Temperature of the liquid 42. What makes a thermometer sensitive to small changes in temperature? A. A bulb with a thin glass wall B. A shiny liquid in its bore C. A stem with a thick glass wall D. A very narrow bore 43. A hot liquid is carefully poured into a beaker. The graph shows how its temperature changes as it cools towards room temperature. A. IGCSE Physics 6 Namrata David Publications

7 Which processes are taking place at region X? A. boiling and evaporation B. condensation only C. evaporation only D. solidification and evaporation 44. The diagram shows a room seen from above. It is cold outside the room. The room is heated by a small fire in the fireplace. 47. What conditions of temperature and surface area would produce the most rapid evaporation from a pool of water on a road surface? Temperature Surface area A High Large B High Small C Low Large D Low small 48. The sensitivity of a liquid-in-glass thermometer depends on the volume of the liquid used and the diameter of the bore of the thermometer. Which change will produce the greatest increase in sensitivity? Where is most heat lost by convection? A. carpet B. chimney C. glass window D. solid wall 45. An experiment is carried out as shown in the diagram. Why does the ice take a long time to melt, even through the water at the top of the tube is boiling? A. convection never occurs in water B. ice is a poor conductor of heat C. the gauze prevents the energy reaching the ice D. water s a poor conductor of heat 46. What is a property of both liquids and gases? A. they always fill their containers B. they are incompressible C. they can flow D. they have molecules in fixed positions Volume of Bore diameter liquid A High Large B High Small C Low Large D Low small 49. The energy required to change liquid water into water vapour at the same temperature is called latent heat of vaporization. What does this energy do? A. increases the average separation of the water molecules B. increases the average speed of the water molecules C. raises the temperature of the air near the water D. splits the water molecules into their separate atoms 50. A 2 kw kettle containing boiling water is placed on a balance. It is left there and continues to boil for 5 minutes. The balance reading changes by 0.2 kg. What does this information give as a value for the specific latent heat of vaporization of water? A J/ kg B J/kg C J /kg D J /kg 51. The heat from the hot water in a metal radiator passes through the metal and then spreads around the room? What are the main processes by which the heat is transferred through the radiator and then spread around the room? IGCSE Physics 7 Namrata David Publications

8 Through the Metal radiator Around the Room A conduction conduction B conduction Convection C Radiation Conduction D Radiation convection 52. Which of the following correctly compares the forces between the molecules in steam, water and ice? Weakest strongest forces forces A ice steam water B ice water steam C steam water ice D water steam ice 53. On a hot day, a drink in a bottle can be kept cool by standing it in a bowl of water and placing a wet cloth over it. In which part of the curve is latent heat released? A. PQ C. RS B. QR D. ST 56. The diagram shows the design for an alarm. The mercury pellet moves and completes the circuit. Why does this happen? Why is the drink kept cool? A. Hot air cannot escape from the bottle B. The cloth conducts heat from the bottle into the water C. The drink cannot evaporate from the bottle D. Water evaporating from the cloth cools the drink 54. Which instrument is most suitable for measuring a rapidly changing temperature? A. alcohol-in-glass thermometer B. clinical thermometer C. mercury-in-glass thermometer D. thermocouple 55. The graph shows the cooling curve of a hot substance. 57. Water at the top of a hot-water tank is heated and the water becomes hot. No water enters or leaves the tank. Water at the bottom of the tank stays cold for some time. Why is this? A. cold water at the top of the tank falls to the bottom B. hot water at the top of the tank rises to the top C. water is a poor conductor of heat D. the insulation is a poor conductor of heat 58. The diagram represents molecules in a liquid. A and C are molecules in a liquid. IGCSE Physics 8 Namrata David Publications

9 B and D are molecules with a low amount of energy. Which molecule is most likely to be leaving the liquid by evaporation? 62. A bar made of half wood and half copper has a piece of paper wrapped tightly round it. The bar is heated strongly at the center for a short time, and the paper goes brown on one side only. 59. The size of a balloon increases when the pressure inside it increases. The balloon gets bigger when it is left in the heat from the Sun. Which side goes brown, and what does this show about and copper? Why does this happen? A. the air molecules inside the balloon all move outwards when it is heated B. the air molecules inside the balloon are bigger when it is heated C. the air molecules inside the balloon move more quickly when it is heated D. the number of air molecules inside the balloon increases when it is heated 60. What must expand in order to show the temperature rise in a mercury-in-glass thermometer? A. the glass bulb B. the glass stem C. the mercury D. the vacuum 61. The table shows the melting points and boiling points of four substances. Which substance is a liquid at room temperature of 20 C? 63. The diagrams show part of a water-heating system which is working by convection. Which diagram shows the most likely flow of water in the system? 64. When water evaporates, some molecules escape? Which molecules escape? A. the molecules at the bottom of the liquid with less energy than others B. the molecules at the bottom of the liquid with more energy than others C. the molecules at the surface with less energy than others D. the molecules at the surface with more energy than others 65. Two metal boxes containing air are standing in a room. Box X is on top of a heater. Box Y is on a bench. The boxes are left for a long time. IGCSE Physics 9 Namrata David Publications

10 Which line in the table best describes the average speed of the molecules in the containers? 68. A person holds a glass beaker in one hand and fills it quickly with hot water. It takes several seconds before his hand starts to feel the heat. Why is there this delay? A. glass is a poor conductor of heat. B. Glass is a good conductor of heat C. water is a poor conductor of heat D. water is agood conductor of heat 69. The diagram shows a heater used to heat a tank of cold water. 66. The top of the mercury thread in a mercury-inglass thermometer reaches point X at 0 C and point Z at 100 C Where might it be at a temperature below the ice-point? A. point W B. point X C. point Y D. point Z 67. The same quantity of heat energy is applied to four different blocks. The temperature rise produce is shown on each block. Which block has the highest thermal capacity? What is the main process by which heat moves through the water? A. conduction B. convection C. evaporation D. radiation 70. A balloon is inflated in a cold room. When the room becomes much warmer, the balloon becomes larger. How does the behaviour of the air molecules in the balloon explain this? A. the molecules become larger B. the molecules evaporate C. the molecules move more quickly D. the molecules repel each other 71. A substance is heated at a steady rate. It changes from a solid to a liquid, and then to a gas. The graph shows how its temperature changes with time? IGCSE Physics 10 Namrata David Publications

11 72. An engineer wants to fix a steel washer on to a steel rod. The rod is just too big to fit into the hole of the washer. Which thermometer reading changes and why? How can the engineer fit the washer onto the rod? A. cool the washer and put it over the rod B. cool the washer and rod to the same temperature and push them together C. heat the rod and then place it in the hole D. heat the washer and place it over the rod 73. An experiment is set up to find out which metal is the best conductor of heat. Balls are stuck with wax to rods made from different metals, as shown in diagram X. The rods are heated at one end. Some of the balls fall off, leaving some as shown in diagram Y. Which lebelled metal is the best conductor of heat? 75. Viewed through a microscope, very small partials can be seen moving with Brownian motion. Which line in the table is correct? 76. A measured mass of gas is placed in a cylinder at atmospheric pressure and is then slowly compressed. The temperature of the gas does not change. What happens to the pressure of the gas? A. it drops to zero B. it decrease, but not to zero C. it stays the same D. it increases 77. The graph shows the change in temperature of a material as it is heated. Which part of the graph shows when the material is boiling? 74. Thermometer X is held above an ice cube and thermometer Y is held the same distance below the ice cube. After several minutes, the reading on one thermometer changes. The ice cube does not melt. IGCSE Physics 11 Namrata David Publications

12 78. An experiment set up is shown. What does the pressure gauge show as the air in the flask becomes hotter? A. a steady pressure B. a decrease in pressure C. an increase in pressure D. an increase and then a decrease in pressure 79. an iron bar is held with one end in a fire. The other end soon becomes too hot to hold. How do the smoke particles move in Brownian motion? A. all in the same direction B. at random C. in circles D. vibrating about fixed points 82. Driving a car raises the temperature of the tyres. This cause the pressure of the air in the tyres to increase. Why is this? A. air molecules break up to form separate atoms B. air molecules expand with the rise in temperature C. the force between the air molecules increases D. the seed of the air molecules increases 83. To mark a temperature scale on a thermometer, fixed points are needed. Which is a fixed point? A. The bottom end of the thermometer tube B. The top end of the thermometer tube C. The temperature of pure melting ice D. The temperature of pure warm water 84. Four blocks, made of different materials, are each given the same quantity of internal(heat) energy. How has the heat traveled along the iron bar? A. by conduction B. by convection C. by expansion by radiation Which block has the greatest thermal capacity? 80. The diagram shows a block of ice places in a warm room. At which point is the temperature the lowest? 81. Brownian motion is seen by looking at smoke particles through a microscope. 85. A long thin bar of copper is heated evenly along its length. IGCSE Physics 12 Namrata David Publications

13 C. Aluminium has a higher thermal capacity than water D. Aluminium has lower thermal capacity than water What happens to the bar? A. becomes lighter B. it becomes longer C. it becomes shorter D. it nebs at the ends 89. Diagram 1 shows apparatus being used to observe smoke particles. Diagram 2 shows how a smoke particle moves randomly. 86. A beaker contains water at room temperature. How could a convection current be set up in the water? A. Cool the water at X B. Cool the water at Y C. Stir the water at X D. Stir the water at Y 87. Two plastic cups are placed one inside the other. Hot water is poured into the inner cup and a lid is put on top as shown. What statement is correct? A. Heat loss by radiation is prevented by the small air gap B. No heat passes through the sided of either cup C. The bench is heated by convection from the bottom of the outer cup D. The lid is used to reduce heat loss by convection kg of water and 1 kg of aluminium are heated to the same temperature and then allowed to cool in a room. Why does the aluminium cool more quickly than the water? A. Aluminium contracts more than water B. Aluminium does not evaporate but water does Why do the smoke particles move randomly? A. they are hit b y air molecules B. they are less dense than air C. they are moved by convection currents D. they gain energy from the light 90. Bread can be cooked by placing it below, but not touching, a heating element. Which process transfers thermal energy from the heating element to the bread? A. Conduction C. insulation B. Convection D. radiation IGCSE Physics 13 Namrata David Publications

14 91. The graph shows how the temperature of hot liquid wax changes with time as the wax is allowed to cool. At which labeled point on the graph are both liquid wax and solid wax present? 94. A measured mass of gas is placed in a cylinder at atmospheric pressure and is then slowly compressed. If the temperature of the gas does not change, what happens to the pressure of the gas? A. it drops to zero B. it decreases, but not to zero C. it stays the same D. it increases 92. The diagram shows a refrigerator. The cooling unit is places at the top. The cooling unit cools the air near it. 95. A mercury-in-glass thermometer is to be used to measure temperature from 0 C to 100 C Why is mercury suitable? A. mercury expands when heated B. mercury has a boiling point below 100 C C. mercury has a melting point above 0 C D. mercury is poor conductor 96. A block is heated at a constant rate. Eventually the melted ice boils. The graph shows how the temperature changes with time. What happens to the density of this air as it cools and how does it moves? 93. Some gas sealed in plastic bag is placed in a refrigerator to cool down. How do the gas molecules behave when this happens? A. they move more quickly and are closer together B. they move more quickly and are further apart C. they move more slowly and are closer together D. they move more slowly and are further together apart How many minutes did it take to melt all the ice? A. 4 C. 11 B. 7 D How does thermal energy(heat energy) travel through the vacuum between the Earth and Sun? A. by conduction B. by convection C. by radiation D. by radioactive decay 98. Which line in the table correctly describes whether the molecules of a solid, liquid and gas are moving or stationary? IGCSE Physics 14 Namrata David Publications

15 D. conduction, convection and radiation 102. The diagrams show four identical pieces of ice that are heated in test tubes of water. In which test-tube will the ice take the longer time to melt? 99. The diagram shows how the atoms in a substance rearrange themselves during a change of state. Which change of state is shown? A. gas to liquid B. liquid to gas C. liquid to solid D. solid to liquid 100. Equal masses of two different liquids are put into identical beakers. They are heated from 20 to 30 by heaters of the same power. Liquid 2 takes twice as long to heat as liquid Some water molecules escape from the surface of a lake. Which name is given to this process? A. boiling B. convection C. evaporation D. radiation Which statement is correct? A. both liquids receive the same amount of energy B. liquid 1 receives more energy than liquid 2 C. the thermal capacity of liquid 1 is equal to the thermal capacity of liquid 2 D. the thermal capacity of liquid 1 is less than the thermal capacity of liquid There is a vacuum between the double walls of a vacuum flask. Which type of heat transfer are reduced by the vacuum? A. conduction and convection B. conduction and radiation C. convection and radiation 104. The diagram represents gas molecules contained in a cylinder. The pistion is moved slowly downwards and the temperature of the gas stays the same. Whys does the pressure of the gas increase? A. The molecules collide harder with the walls IGCSE Physics 15 Namrata David Publications

16 B. The molecules collide more often with the walls C. The molecules move more quickly D. The number of molecules increases To mark the lower fixed point of a Celsius scale on a thermometer, the thermometer should be placed in A. pure alcohol B. pure distilled water C. pure melting ice D. pure mercury 106. A glass flask full of cool water is placed in a container of hot water. What will happen to the level of water at X as the cool water becomes warmer? A. it will fall B. it will rise C. it will rise then fall D. it will stay the same 107. A beaker of water is heated at its base. Why does the water at the base rise? A. It contracts and becomes less dense B. It contracts and becomes more dense C. It expands and becomes less dense D. It expands and becomes more dense 108. A drop of liquid falls on a student s skin and quickly evaporates. What is the effect on the skin and the reason? A. the skin cools because the most energetic molecules escape from the liquid. B. the skin cools because the most energetic molecules remain in the liquid C. the skin warms because the most energetic molecules escape from the liquid D. the skin warms because the most energetic molecules remain in the liquid 109. A suspension of pollen grains in water is observed under a microscope. The pollen grains are seen to be moving all the time. Which diagram illustrates this motion? 110. A knife is being sharpened on a rotating sharpening-stone. A spark flies off and lands on the operator s hand. The spark is very hot, very small piece of metal. The operator feels nothing. What does this show about the piece of metal? A. it has a high thermal capacity B. it has a low thermal capacity C. it is a good conductor of heat D. it is a poor conductor of heat 111. Which substance is a liquid at a room temperature of 25 C? 112. How does heat from the Sun reach the Earth? A. Conduction only B. Convection only C. Radiation only D. Conduction, convection and radiation 113. A gas cylinder is left outside on a sunny day. The Sun heats the gas inside the cylinder. What happens to the gas molecules? A. they collide less often B. they expand C. they move closer together D. they move more rapidly IGCSE Physics 16 Namrata David Publications

17 114. Water spilled on the ground on a hot day evaporates. Which diagram represents the change in arrangement of the particles in water as it evaporates? 117. A thermometer with no scale is taped to a ruler as shown. When placed in steam, the mercury level rises to 22 cm. When placed in pure melting ice, the mercury level falls to 2 cm A block of ice heated until it has all melted. The water that is produced is then heated until it boils. Which line in the table states what happens to the temperature of the ice while it is melting, and to the temperature of the water while it is boiling? Which temperature is shown by the mercury level in the diagram? A. 6 C C. 30 C B. 8 C D. 40 C 118. Which line in the table is correct about conduction and convection? 119. The table lists the melting points and the boiling points of four different substances A,B,C and D. Which substance is a gas at 25 C? 116. A heating element is positioned in a narrow sealed tube of liquid. What would be the best place to position the heating element in order to obtain the best circulation of the liquid through the tube? 120. The diagram shows four blocks of steel. The same quantity of heat is given to each block. Which block shows the greatest rise in temperature? IGCSE Physics 17 Namrata David Publications

18 124. A beaker of water is heated at its base. Why does the water at the base rise? A. It contracts and becomes less dense B. It contracts and becomes more dense C. It expands and becomes less dense D. It expands and becomes more dense 121. A wooden wheel can be strengthened by putting a tight circle of iron around it. Which action would make it easier to fit the circle over the wood? A. cooling the iron circle B. heating the iron circle C. heating the wooden wheel D. heating the wooden wheel and cooling the iron circle 122. Which statement refers to convection? A. it does not involve energy transfer B. it is transfer of heat energy without the movement of particles C. it only occurs in liquids or gases D. it only occurs in solids 123. Spoons made of different materials were placed in four cups of coffee poured from the same jug. Which spoon will be hottest to touch at end X? 125. A drop of liquid falls on a student s skin and quickly evaporates. What is the effect on the skin and the reason? A. the skin cools because the most energetic molecules escape from the liquid. B. the skin cools because the most energetic molecules remain in the liquid C. the skin warms because the most energetic molecules escape from the liquid D. the skin warms because the most energetic molecules remain in the liquid 126. A double glazed window has two sheets of glass separated by a layer of air. Thermal energy is conducted through the layer of the air. The amount of conduction and convection varies with thickness of the layer of air, as shown in the graph Which thickness of air produces the smallest energy transfer A. 0.5 cm because there is little convection B. 1.0 cm because the total thermal energy transfer is least C. 1.5 cm because the total thermal energy transfer is small and conduction is low D. 2.0 cm because there is little conduction IGCSE Physics 18 Namrata David Publications