CLASSIFIED 2 PRESSURE THERMAL PHYSICS MR. HUSSAM SAMIR

CLASSIFIED 2 PRESSURE THERMAL PHYSICS MR. HUSSAM SAMIR

1. The diagram shows a simple mercury barometer. If atmospheric pressure increases, what happens to level X and to level Y? 2. Four flower vases have circular bases. They are filled with water so that they all have the same weight. Which vase exerts the greatest pressure on its base? 3. (a) A stone falls from the top of a building and hits the ground at a speed of 32 m/s. The air resistance-force on the stone is very small and may be neglected. (i) Calculate the time of fall. time =... (ii) On Fig. 1.1, draw the speed-time graph for the falling stone. 1

(iii) The weight of the stone is 24 N. Calculate the mass of the stone. mass =... (b) A student used a suitable measuring cylinder and a spring balance to find the density of a sample of the stone. (i) Describe how the measuring cylinder is used, and state the readings that are taken. (ii) Describe how the spring balance is used, and state the reading that is taken. (iii) Write down an equation from which the density of the stone is calculated. (iv) The student then wishes to find the density of cork. Suggest how the apparatus and the method would need to be changed. 2

4. The IGCSE class is investigating the swing of a loaded metre rule. The arrangement of the apparatus is shown in Fig. 2.1. The load is attached to the metre rule so that its centre is 90.0 cm from the pivot. The rule is displaced a small distance to one side and allowed to swing. The time t taken for 10 complete swings is recorded. This is repeated using different values of the distance d. The readings are shown in the table. (a) Complete the column headings in the table. (b) Calculate the period T for each value of d. The period is the time taken for one complete swing. Enter the values in the table. (c) On the grid below, plot a graph of T / s (y-axis) against d / cm (x-axis). Start the x-axis at d = 70.0 cm and the y-axis at a suitable value of T / s to make best use of the graph grid. 3

(d) A student suggests that T is proportional to d. State whether or not the results support this suggestion and give a reason for your answer. statement...... reason..... (e) Explain why the student takes the time for ten swings and then calculates the time for one swing (the period), rather than just measuring the time for one swing...... 4

5. The diagram shows four models of buses placed on different ramps. How many of these models will fall over? A) 1 B) 2 C) 3 D) 4 6. A manometer is being used to measure the pressure of the gas inside a tank. A, B, C and D show the manometer at different times. At which time is the gas pressure inside the tank greatest? 7. A long thin bar of copper is heated evenly along its length. What happens to the bar? A) It becomes lighter. B) It becomes longer. C) It becomes shorter. D) It bends at the ends. 5

8. Fig. 3.1 shows a pond that is kept at a constant depth by a pressure-operated valve in the base. The pond is kept at a depth of 2.0 m. The density of water is 1000 kg/m3. Calculate the water pressure on the valve. pressure =.. (b) The force required to open the valve is 50 N. The valve will open when the water depth reaches 2.0m. Calculate the area of the valve. area =.. (c) The water supply is turned off and the valve is held open so that water drains out through the valve. State the energy changes of the water that occur as the depth of the water drops from 2.0m to zero....... 9. 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 6

10. A man standing at the top of a cliff throws a stone. Which forms of energy does the stone have at X and at Y? 11. 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. 12. Fig. 5.1 shows some apparatus designed to compare the ability of two surfaces to absorb infra-red radiation. The containers, which are identical, are painted on the outside. One is dull black, the other is shiny white. Both are filled with water, initially at the same temperature. (a) (i) Describe how you would use the apparatus to compare the abilities of the two surfaces to absorb infra-red radiation. 7

... (ii) State the result that you would expect.... (b) The thermometers used have high sensitivity and linear scales. (i) State what is meant by high sensitivity.... (ii) Explain why a high sensitivity is important for this experiment.... (iii) State what is meant by a linear scale.... 13. A block of ice is heated at a constant rate. Eventually the melted ice boils. The graph shows how the temperature changes with time. How many minutes did it take to melt all the ice? A) 4 B) 7 C) 11 D) 13 14. (a) In an experiment to find the specific latent heat of water, the following readings were taken. m1 mass of water at 100 C, before boiling starts 120 g m2 mass of water at 100 C, after boiling finishes 80 g V voltage across the heater 12V I current through the heater 2.0A t time that the heater was supplying energy 3750 s (i) Using the symbols above, write down the equation that must be used to find the value of the specific latent heat L of water. (ii) Use the equation to calculate the specific latent heat of water from the readings above. specific latent heat =... (b) Explain, in terms of the energy of molecules, why the specific latent heat of water has a high value. 8

15. 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. 16. The table shows the melting points and boiling points of four substances. Which substance is a liquid at a room temperature of 20 oc? 17. 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? 9

18. The diagram represents molecules in a liquid. A and C are molecules with a high amount of energy. B and D are molecules with a low amount of energy. Which molecule is most likely to be leaving the liquid by evaporation? 19. 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. 20. Fig. 4.1 shows water being heated by an electrical heater. The water in the can is not boiling, but some is evaporating. 10

(a) Describe, in terms of the movement and energies of the water molecules, how evaporation takes place....... (b) State two differences between evaporation and boiling. 1...... 2..... (c) After the water has reached its boiling point, the mass of water in the can is reduced by 3.2 g in 120 s. The heater supplies energy to the water at a rate of 60W. Use this information to calculate the specific latent heat of vaporisation of water. specific latent heat =... 21. Fig. 3.1 shows water falling over a dam. (a) The vertical height that the water falls is 7.0 m. Calculate the potential energy lost by 1.0 kg of water during the fall. potential energy =... (b) Assuming all this potential energy loss is changed to kinetic energy of the water, calculate the speed of the water, in the vertical direction, at the end of the fall. speed =... (c) The vertical speed of the water is less than that calculated in (b). Suggest one reason for this....... 11

22. The IGCSE class is investigating the temperature changes that occur when hot and cold water are mixed. (a) A student pours 50 cm3 of water into a beaker. He then measures the temperature θ1 of the water in the beaker. Write down the value of θ1 shown on the thermometer in Fig. 1.1. (b) The student then measures the temperature θ2 of some hot water. He pours 50 cm 3 of this hot water into the beaker of water at room temperature. He then records the temperature θ3 of the water in the beaker. His readings are θ2 = 76 C, θ3 = 42 C. Calculate (i) the temperature rise of the cold water,... (ii) the temperature fall of the hot water.... (c) A theoretical calculation based on the equation thermal energy lost by hot water = thermal energy gained by cold water predicts a higher value for the temperature θ3 than the value that is obtained by this experiment. Suggest (i) a practical explanation for the difference in values, (ii) two practical improvements that you could make to the procedure for this experiment to obtain a result that is closer to the theoretical result. 1.... 2.... 12

23. a) Two identical open boxes originally contain the same volume of water. One is kept at 15 C and the other at 85 C for the same length of time. Fig. 4.1 shows the final water levels. With reference to the energies of the water molecules, explain why the levels are different............. (b) In an experiment to find the specific latent heat of vaporisation of water, it took 34 500 J of energy to evaporate 15 g of water that was originally at 100 C. A second experiment showed that 600 J of energy was lost to the atmosphere from the apparatus during the time it took to evaporate 15 g of water. Calculate the specific latent heat of vaporisation of water that would be obtained from this experiment. specific latent heat = 24. A block of ice is 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? 13

25. 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. Which temperature is shown by the mercury level in the diagram? A) 6 C B) 8 C C) 30 C D) 40 C 26. Which line in the table is correct about conduction and convection? 27. 1 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. C) Aluminium has a higher thermal capacity than water. D) Aluminium has a lower thermal capacity than water. 28. 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 B) convection C) insulation D) radiation 14

29. Water spilled on the ground on a hot day evaporates. Which diagram represents the change in arrangement of the particles in the water as it evaporates? 30. A cylinder is filled with a gas and then sealed, so that the gas has a fixed volume. The gas molecules are given energy so that their average speed increases. What happens to the pressure and to the temperature of the gas in the cylinder? 15

31. The graph shows how the temperature of hot liquid wax changes with time as the wax is allowed to cool. At which labelled point on the graph are both liquid wax and solid wax present? 32. Fig. 4.1 shows a sealed glass syringe that contains air and many very tiny suspended dust particles. (a) Explain why the dust particles are suspended in the air and do not settle to the bottom............. (b) The air in the syringe is at a pressure of 2.0 105Pa. The piston is slowly moved into the syringe, keeping the temperature constant, until the volume of the air is reduced from 80 cm3 to 25 cm3. Calculate the final pressure of the air. pressure =... 16

33. Fig. 5.1 shows a thermocouple set up to measure the temperature at a point on a solar panel. (a) X is a copper wire. (i) Suggest a material for Y.. (ii) Name the component Z.. (b) Explain how a thermocouple is used to measure temperature.... (c) Experiment shows that the temperature of the surface depends upon the type of surface used. Describe the nature of the surface that will cause the temperature to rise most. 34. The pressure of a gas is measured using a manometer as shown in the diagram. The mercury in the manometer is replaced with a liquid which is less dense. How does the value of h change? A It becomes zero. B It decreases, but not to zero. C It stays the same. D It increases. 17

35. The diagram represents the molecules of a gas in a closed container of constant volume. What happens to the molecules when the gas is heated? A They expand. B They hit the walls less often. C They move further apart. D They move more quickly. 36. A liquid is left in an open dish. After several days there is less liquid in the dish. Which statement explains this? A The least energetic molecules leave the surface and escape into the air. B The least energetic molecules leave the surface and return. C The most energetic molecules leave the surface and escape into the air. D The most energetic molecules leave the surface and return. 37. A thermometer has a scale which starts at 10 C and ends at 110 C. What is the value of the lower fixed point and of the upper fixed point of the scale? 38. Hot liquid in a vacuum flask cools extremely slowly. This is because some methods of heat transfer cannot take place in a vacuum. Which methods cannot take place in a vacuum? A conduction and convection only B conduction and radiation only C convection and radiation only D conduction, convection and radiation 18

39. A teacher demonstrates convection currents using a box with two chimneys and a lighted candle. She holds a smoking taper at point P. In which direction does the convection current cause the smoke to move? 40. A certain substance is in the solid state at a temperature of 36 C. It is heated at a constant rate for 32 minutes. The record of its temperature is given in Fig. 5.1. (a) State what is meant by the term latent heat.... [2] (b) State a time at which the energy is being supplied as latent heat of fusion.... [1] (c) Explain the energy changes undergone by the molecules of a substance during the period when latent heat of vaporisation is being supplied.... [2] (d) (i) The rate of heating is 2.0 kw. Calculate how much energy is supplied to the substance during the period 18 22 minutes. energy supplied =... [2] 19

(ii) The specific heat capacity of the substance is 1760 J / (kg C). Use the information in the table for the period 18 22 minutes to calculate the mass of the substance being heated. mass heated =... [3] 41. Which change is condensation? 42. An electric heater is placed inside a metal box which has one side open. The diagram shows four possible positions for the box. The heater is switched on for several minutes. In which position does the box become the hottest? 43. Fig. 4.1 represents part of the hydraulic braking system of a car. 20

The force F1 of the driver s foot on the brake pedal moves piston X. The space between pistons X and Y is filled with oil which cannot be compressed. The force F2 exerted by the oil moves piston Y. This force is applied to the brake mechanism in the wheels of the car. The area of cross-section of piston X is 4.8 cm2. (a) The force F1 is 90 N. Calculate the pressure exerted on the oil by piston X. pressure =... [2] (b) The pressure on piston Y is the same as the pressure applied by piston X. Explain why the force F2 is greater than the force F1.... [1] (c) Piston Y moves a smaller distance than piston X. Explain why.... [2] (d) Suggest why the braking system does not work properly if the oil contains bubbles of air.... [2] 44. During a period of hot weather, the atmospheric pressure on the pond in Fig. 3.1 remains constant. Water evaporates from the pond, so that the depth h decreases. (a) Study the diagram and state, giving your reason, what happens during this hot period to (i) the force of the air on the surface of the pond,....[1] (ii) the pressure at the bottom of the pond.....[1] (b) On a certain day, the pond is 12 m deep. (i) Water has a density of 1000 kg / m3. Calculate the pressure at the bottom of the pond due to the water. pressure due to the water =...[2] 21

45. Which statement is explained by reference to pressure? A Objects with greater mass have greater weight. B One kilogram of water occupies more volume than one kilogram of lead. C Spikes on running-shoes sink into the ground. D Water cooled to a low enough temperature turns to ice. 46. The diagram shows a mercury manometer used to measure the pressure of gas in a container. Atmospheric pressure is 76 cm of mercury. What is the pressure of the gas? A 56 cm of mercury B 68 cm of mercury C 84 cm of mercury D 96 cm of mercury 47. A heater supplies 80 J of energy to a block of metal. The temperature of the block rises by 20 C. What happens to the block of metal when its temperature falls by 10 C? A Its internal energy decreases by 40 J. B Its internal energy decreases by 160 J. C Its internal energy increases by 40 J. D Its internal energy increases by 160 J. 48. (a) Two students hang out identical T-shirts to dry at the same time in the same neighbourhood. The only difference between the drying conditions is that one T-shirt is sheltered from any wind and the other is in a strong breeze, as shown in Fig. 6.1. 22

State and explain, in terms of water molecules, the difference between the drying times of the T-shirts.... [2] (b) Fig. 6.2 shows another occasion when a student hangs out two identical T-shirts to dry next to each other on a line. One T-shirt is folded double as shown in Fig. 6.2. State and explain, in terms of water molecules, the difference between the drying times of the T-shirts.... [2] (c) A runner in a hot country feels cooler if she pours water over her hair to keep it wet, even when the water is at the same temperature as the air around her. Explain, in terms of a change of state of water, why she feels cooler.... [2] 49. A heavy table has six legs. The area of cross-section of each leg is X. The legs of the table make marks in a carpet. These marks become deeper with increased pressure. What would reduce the depth of the marks for a table of a fixed weight? A using three legs, each of an area smaller than X B using four legs, each of an area the same as X C using six legs, each of an area smaller than X D using eight legs, each of an area the same as X 23

50. The diagram shows the cross-section of a vacuum flask containing a hot liquid in a cold room. X and Y are points on the inside surfaces of the walls of the flask. How is thermal energy transferred between X and Y? A by conduction and convection B by conduction only C by radiation and convection D by radiation only 51. The diagram shows a simple mercury barometer. Which length is used to find the value of atmospheric pressure? A 12 cm B 74 cm C 86 cm D 100 cm 24

53. A thermometer uses the value of a physical property to indicate the temperature. (a) A particular thermometer is sensitive, linear and has a wide range. Draw a straight line from each characteristic of this thermometer to the appropriate feature. (b) (i) In the space below, draw a diagram to show the structure of a thermocouple thermometer. (ii) Explain why a thermocouple thermometer is particularly well suited to measure 1. high temperatures,.. 2. very rapidly changing temperatures... [2] 25

53. (a) (i) State two ways in which the molecular structure of a gas differs from the molecular structure of a liquid. 1.... 2.... [2] (ii) Compressibility is the ease with which a substance can be compressed. State and explain, in terms of the forces between the molecules, how the compressibility of a gas differs from that of a liquid...... [2] (b) Fig. 6.1 shows a weather balloon being inflated by helium from a cylinder. (i) The helium that inflates the balloon had a volume of 0.035 m3 at a pressure of 2.6 106 Pa, inside the cylinder. The pressure of the helium in the balloon is 1.0 105 Pa and its temperature is the same as it was when in the cylinder. Calculate the volume occupied by the helium in the balloon. volume =... [3] (ii) As the balloon rises up through the atmosphere, the temperature of the helium decreases. State the effect of this temperature change on the helium molecules..... [1] 26

54. The IGCSE class is investigating the rate of cooling of water. Fig. 2.1 shows the apparatus. (a) Record the value of room temperature θr shown on the thermometer. (b) A student pours approximately 200 cm3 of hot water into the beaker. She measures the temperature θ of the water. She starts a stopclock and records the temperature θ of the water at 30 s intervals up to time t = 150 s. The readings are shown in Table 2.1. 27

(c) As you read these words, this experiment is actually being carried out by candidates in many different countries, using identical apparatus. Suggest two differences in the conditions in the various laboratories that might lead to different graphs. 1.... 2.... [2] 28

55. (a) Define specific latent heat of fusion.... [1] (b) (i) A tray of area 0.25 m2, filled with ice to a depth of 12 mm, is removed from a refrigerator. Calculate the mass of ice on the tray. The density of ice is 920 kg / m3. mass =... [2] (ii) Thermal energy from the Sun is falling on the ice at a rate of 250 W / m2. The ice absorbs 60 % of this energy. Calculate the energy absorbed in 1.0 s by the 0.25 m2 area of ice on the tray. energy =... [2] (iii) The ice is at its melting temperature. Calculate the time taken for all the ice to melt. The specific latent heat of fusion of ice is 3.3 105 J / kg. time =... [3] 56. (a) Explain why a liquid cools when evaporation takes place from its surface.... [2] (b) Fig. 7.1 shows five vessels each made of the same metal and containing water. Vessels A, B, C and D are identical in size and shape. Vessel E is shallower and wider. The temperature of the air surrounding each vessel is 20 C. The table shows details about each vessel and their contents. 29

The following questions are about the time taken for the temperature of the water in the vessels to fall by 10 C from the initial temperature. (i) Explain why the water in B takes longer to cool than the water in A..... [1] (ii) Explain why the water in C cools more quickly than the water in A..... [1] (iii) Explain why the water in D cools more quickly than the water in A..... [1] (iv) Suggest two reasons why the water in E cools more quickly than the water in A. 1..... 2..... [2] 57. A swimmer feels cold after leaving warm water on a warm, windy day. Why does she feel cold even though the air is warm? A The less energetic water molecules on her skin escape quickly. B The more energetic water molecules on her skin do not escape quickly. C The water on her skin does not evaporate quickly enough to keep her warm. D The water on her skin evaporates quickly and cools her skin. 58. Which physical property is used to measure temperature in a liquid-in-glass thermometer? A the length of the thermometer B the thickness of the glass bulb C the volume of the glass bulb D the volume of the liquid 59. A heavy table has six legs. The area of cross-section of each leg is X. The legs of the table make marks in a carpet. These marks become deeper with increased pressure. What would reduce the depth of the marks for a table of a fixed weight? A using three legs, each of an area smaller than X B using four legs, each of an area the same as X C using six legs, each of an area smaller than X D using eight legs, each of an area the same as X 60. Evaporation occurs when molecules escape from a liquid surface into the air above it. During this process the temperature of the liquid falls. Why does the temperature of the liquid fall? A The molecules in the vapour expand because the pressure is less. B The molecules left in the liquid have more space to move around. C The molecules move more slowly when they escape into the air. D The molecules with the highest energies escape into the air. 30

61. 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. 62. The diagram shows an electric heater being used to heat a beaker of water and an identical beaker of oil for several minutes. The temperature of the water and the temperature of the oil increase constantly. The rise in temperature of the oil is much greater than that of the water. Why is this? A The oil has a higher boiling point than water. B The oil has a higher thermal capacity than water. C The oil has a lower boiling point than water. D The oil has a lower thermal capacity than water. 63. Two identical copper cans are filled with boiling water. One can is insulated with wool. The temperature of the water in each can is taken every minute for several minutes. Graphs of the results are plotted. Which graph shows the results obtained? 31

64. (a) Suggest (i) an example of a change of state resulting from the removal of thermal energy from a quantity of material,... [1] (ii) the effect of this change of state on the temperature of the material.... [1] (b) Define the thermal capacity of a body.... [2] (c) A polystyrene cup holds 250 g of water at 20 C. In order to cool the water to make a cold drink, small pieces of ice at 0 C are added until the water reaches 0 C and no unmelted ice is present. [specific heat capacity of water = 4.2 J / (g C), specific latent heat of fusion of ice = 330 J / g] Assume no thermal energy is lost or gained by the cup. (i) Calculate the thermal energy lost by the water in cooling to 0 C. thermal energy lost =... [2] (ii) State the thermal energy gained by the ice in melting. thermal energy gained =... [1] (iii) Calculate the mass of ice added. mass of ice =... [2] 32