Heat

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Heat

  1. 1. HEAT
  2. 2. Heat as a form of energy • The Sun is the primary source of heat energy. • Most of the Sun’s heat is radiated back into space and only a small amount of it reaches the Earth to keep it warm.
  3. 3. Rubbing or Friction• Heat can be produced when two objects are rubbed together.• Example, the ancient human produced fire by rubbing two pieces of wood together.
  4. 4. Burning• Burning is one of the most common ways of producing heat.• When something burns, it produces a flame and also heat.
  5. 5. Electricity• Electricity can be used to produce heat.• Example, the bulb of a lighted table releases heat
  6. 6. HEAT A form of energy which flows from a hotter region to a cooler region
  7. 7. ENVIRONMENT 25 oC Heat flows from the container CONTAINER (hotter) to theHEAT oC HEAT 70 surrounding (cooler)
  8. 8. ENVIRONMENT 25 oC Heat flows from surrounding CONTAINER (hotter) intoHEAT oC HEAT 10 container (cooler)
  9. 9. THERMOMETER A thermometer is an instruments used to measure temperature.
  10. 10. When temperaturerises, the mercury level will riseWhen temperaturefalls, the mercury level will fall
  11. 11. The SI unit of temperature is Kelvin (K). But we commonly use Celsius (oC) instead. Conversion of Kelvin to Celsius: Kelvin (K) = Celsius (oC) + 273Example 1: Example 2:55 Celsius to Kelvin 339 Kelvin to CelsiusKelvin = Celsius + 273 Celsius = Kelvin - 273 = 55 + 273 = 339 - 273 = 328 K = 66 oC
  12. 12. Exercise 1: Exercise 2:250 Kelvin to Celsius 383 Celsius to Kelvin
  13. 13. Heat vs temperature Heat Temperature A form of energy The degree ofwhich flows from a Definition hotness and coldnesshotter region to a of a body cooler region Joule (J) Unit of Kelvin (K) measurement Celsius (oC) - Increases when Flows from a hot heated Propertyarea to a cold area - Decreases when cooled
  14. 14. The effect of heat Heat only flows from a hotter object (or place) to a cooler object (or place)COOL HOT Effects on Matter: In general, solids, liquids and gaseous: (1) Expand when they gain heat and; (2) Contract when they lose heat
  15. 15. Expansion & Contraction of Solids COLD HOTExpansion of SolidsAs the temperature increases, the atoms vibratemore vigorously and these vibrations push theatoms further apart. Thus, the volume of the solidincreases.
  16. 16. HOT COLDContraction of SolidsWhen the solid is cooled down, the atoms vibrateless vigorously and they become closer together.Thus, the volume of the solid decreases.
  17. 17. Different solids expand and contract at different rate Metal A BIMETALLIC STRIP Bimetallic strip Metal B (made up of two different metals strips welded together) is used, to find out how different solid expand or contract.
  18. 18. After heating, metal B expanded more than metal A. This causes the bimetallic strip to bend. Metal A Metal B
  19. 19. METAL BALL & RINGWhen the ring and ball are at When the brass ring is heat, the room temperature, the ball ring expands and the ball willwill not pass through the ring. easily pass through the ring Metal ring and metal ball Bunsen burner
  20. 20. Expansion & Contraction of Liquids COLD HOTExpansion of LiquidsWhen the liquid is heated, the molecules have moreenergy and move more vigorously. The movement of themolecules overcome the forces of attraction between themolecules, allowing them to move freely. Thus, the volumeof the liquid increases.
  21. 21. HOT COLDContraction of LiquidsAt lower temperature, the molecules have lessenergy and move closer to each other. This causesthe volume of the liquid to decrease.
  22. 22. Expansion and Contraction of Mercury in the Thermometer When the beaker is heated, the water molecules gains heat and expands. This causes the mercury in the thermometer to rise.
  23. 23. Expansion & contraction of gases COLD HOTExpansion of Gaseous Contraction of GaseousWhen the gas is heated, the At a lower temperature, themolecules gain more energy molecules have move slowerand move faster and further and have less energy. They areapart. This causes the volume closer together causing theto increase volume to decrease.
  24. 24. Expansion and Contraction of Gaseous in Volumetric Flask LIQUID The experiment LIQUID above shows that gaseous expand when heated and glass glass contract whenair air cooled. The liquid rises Heat once the volumetric flask(a) Before heating is heated. (b) After heating
  25. 25. Heat transfers CONDUCTION CONVECTIONRADIATION RADIATION
  26. 26. conduction Conduction: Heat transfer in which energy of the particles in the warmer region isParticles of the passed on to the fish particles of the cooler regionParticles of the pan
  27. 27. Region AThe particles (atoms)vibrates faster as heat is applied to it A B C
  28. 28. Region B The particles from region A passed on heat to the particles of region BA B C
  29. 29. Region C The particles of region B will then pass the heat to particles of region CA B C
  30. 30. States Of Matter● The gaseous are very bad in conducting the heat.● This is because the particles of the gaseous are further apart.● Therefore, the energy passed on to the neighboring particles is slow
  31. 31. Metals are good heat conductor ● The particles in solid are closely packed as compared to those in gaseous. ● Thus, more particles can collide with each other to pass on the energy to their neighboring particles.
  32. 32. Mercury is a good heat conductor ● Mercury, a metal and a liquid at 20oC, conducts heat much better than water. ● This is because they have many electrons to move about. ● When these electrons gain heat, they move around faster and collide more with neighboring electrons and atoms.
  33. 33. Heat conductorsMaterial which allow heat flow through it quickly
  34. 34. Heat insulatorsMaterial which do not allow heat flow through it quickly
  35. 35. Application of conduction (1) Increasing heat transfer Good heat conductors are used to make electrical appliances such as cooking utensils and iron. This is because, heat can be transferred quickly Heat from the source toconductors targeted object
  36. 36. Heatinsulators (2) Reducing Heat Transfer The handle of the electrical appliances are made from heat insulators such as wood and plastic to avoid unwanted transfer of heat
  37. 37. Another example of heat insulators used to reduce heat transfer is a cork mat. It reduces heat loss from the pan to the table by conduction.Cork mat
  38. 38. Double-glazed windows reduce heat gain from outside the houseduring the hot day .It also reduces heat loss from inside during winter season.
  39. 39. Air Air is a good heatOutside Inside insulator. Some air are trapped between two layers of glass and this prevent heat gain or heat loss between outside and inside of the house.
  40. 40. convection Heat transfer by the circulation of currents from one region to another in a liquid or a gas. The cool water from thetop is denser than the hot Convectionwater. This causes the cool current water to sink.When the water is heated the hot water float because it is less dense than the cool water Bunsen burner
  41. 41. Application of convection Hang gliders • The hang gliders can fly without using any energy to push them. • They ride on air currents. • When ground gets heated hot and expands. • The hot air rises from the ground and lifts the hang gliders in the air.
  42. 42. Sea Breeze
  43. 43. Land Breeze
  44. 44. RefrigeratorThe freezer is usually located at the top of the refrigerator FREEZER The warmer air from bottom is less dense thus floats to the top The cold air from the freezer is denser thus sinks to the bottom
  45. 45. HEATER IN A ROOM COLD WINDThe warmer air from the radiator is less dense thus floats to the topHOT RADIATORThe cold air from the outside is denser thus sinks to the bottom
  46. 46. RADIATIONThe transfer of heat in the form of infrared waves emitted by one body and absorbed by another body Your hands feel hot when placed close to the flame, because the heat from the flame reaches your hand by radiation.
  47. 47. In a similar way, theheat from the Sun isreaches the Earth by radiation.
  48. 48. RadiateRadiate Radiate If the object is hotter than the surroundings, it will radiate more heat than it absorbs.
  49. 49. AbsorbAbsorb Absorb If the object is cooler than the surroundings, it will absorb more heat than it radiates.
  50. 50. The Rate of Radiation and Absorption Depends On: (1) Temperature • The hot drink radiates more heat per unit time than the cold drink. • It loses heat more quickly to the surroundings than the cold drink
  51. 51. Which one loses more heat ? Can A Can B 40 oC 78 oC
  52. 52. (2) Nature of the surface The hot water in the black and dull cup loses heatmore quickly than the water in the silver or white cup.(a)Black and dull surface - a good radiator of heat.(b)Silvery (or white) surface - a poor radiator of heat.
  53. 53. Application of RADIATION Reducing heat gain The fuel tank of the truckhas silvery surface to reflectheat radiation and keeps the fuels inside the tank cool.
  54. 54. Reducing heat loss• Kettles and teapots usually have shiny and silvery surfaces, which are poor radiators of heat.• Thus, they will not lose heat too quickly by radiation.
  55. 55. Reducing heat loss or gain• White or light colored uniforms are commonly worn in hot climate places because white surfaces reflect heat well and are poor absorbers of heat.• This helps the students cool on hot days
  56. 56. The space shuttle and the space suitof the astronaut are white in color to reduce heat gain and heat loss.
  57. 57. Increasing heat gainSolar heaters are painted black to absorb heat quickly from the Sun. Black surfaces are good absorbers of heat.
  58. 58. Efficiency in Preventing Heat Gain/Loss A vacuum flask is designed to prevent energy transfer between the content inside and its surroundings outside
  59. 59. Stopper The stopper is made from cork or plasticsVacuum (heat insulators). wall This can prevent Double heat loss and gainglass shell through conduction Silver and convectioncoating Casting
  60. 60. Stopper The vacuumVacuum prevents any wall energy transfer Double throughglass shell conduction and convection. Silvercoating Casting
  61. 61. Stopper Double glassVacuum wall shell reduces heat gain and Doubleglass shell heat loss by conduction Silver because glass iscoating an insulator. Casting
  62. 62. StopperVacuum wallDouble glass shell The silver coating reduces heat gain Silvercoating and loss by radiation. Casting
  63. 63. StopperVacuum wallDouble glass shell Shiny or light Silvercoating colored case reduces heat Casting gain or loss by radiation
  64. 64. EFFECT OF HEAT GAIN & HEAT LOSS Why does the ice cube melt? What changes when the ice melts?
  65. 65. MELTING• Matters can change its state when it is cooled or heated.• When a matter is heated, its particles absorbed heat energy and vibrate or move faster HEAT SOLID LIQUID
  66. 66. Attraction forces Solid has a fixed shape because the molecules are hold together by attraction forces between themSOLID STATE
  67. 67. When a solid is heated,the particles gain energy and vibrate faster
  68. 68. Until the attractionSOLID STATE forces between them fail to hold them together in their fixed position
  69. 69. The attraction forcesLIQUID STATE between them break, which release the particles
  70. 70. BOILING / Evaporation • Matters canGAS HEAT change its state when it is cooled or heated. • When a matter is heated, its particles absorbed heat energy and vibrate or move faster LIQUID
  71. 71. LIQUID STATE Until the attractionforces between them failto hold them together in their fixed position
  72. 72. Until all of the attractionGASES STATE forces between them break and allowing the particles to move freely
  73. 73. differences Boiling Evaporation State at which change At any temperature andAt its boiling point only occurs at any time Throughout the liquid On the surface of the liquid only Where it takes place Rate at which it takes Quick process Slow process place Bubbles are formed Formation of bubbles Bubbles are not formed Energy is supplied fromSource energy is needed Is energy needed? the surrounding
  74. 74. condensation • When a matter isGAS HEAT cooled, its particles emit heatHEAT energy and vibrate or move slower. • If the released energy is sufficient, the matter will change its state. LIQUID
  75. 75. When the temperature drops, the particlesGASES STATE move slower and become closer to each other.
  76. 76. When the particles are close enough to eachGASES STATE other, attraction forces are formed between these particles.
  77. 77. More particles comeLIQUID STATE close to each other and more attraction forces are formed between them
  78. 78. FREEZING• When a matter is cooled, its particles emit heat energy and vibrate or move slower.• If the released energy is sufficient, the matter will change its state. HEAT LIQUID SOLID
  79. 79. More particles comeLIQUID STATE close to each other and more attraction forces are formed between them
  80. 80. Finally all the particles are bounded together and it gives solid a definite shapeSOLID STATE
  81. 81. sublimation• Some substances change directly from solid to gas or solid to gas without going through liquid state.• Example: iodine, dry ice, sulphur and naphthalene. SOLID STATE GAS STATE During heating process, the particles of solid absorb the heat and move about freely and far apart from each other. The solid sublimates to a gaseous form.
  82. 82. Heating Curve Of WaterTemperature GAS BOILING POINT Temperature where liquid  gas LIQUID Temperature where MELTING POINT solid  liquid SOLID Time
  83. 83. The Amount Of Heat Contained In An Object Depends On: (a) The type of material of an object (b) The mass or size of an object (c) The temperature of an object
  84. 84. What happens to the closely packedatoms of the solid if expansion and contraction occur frequently??
  85. 85. The undesirable effects The expansion andcontraction during hot day and cold night, caused undesirabledamages to structures.Cracks may appear on concrete pavement.
  86. 86. Ways to reduce undesirable effects Gaps between the materials The bricks or concrete slabs are arrange with some gaps in between to allow expansion in the hot day and contraction during the cold night.
  87. 87. Railway tracksMetalbridge
  88. 88. Sagging of the transmission line Electric transmissioncable sag on a hot day due to expansion of metals. However,these cables lifted on a cold night due tocontraction of metals
  89. 89. Sagging electrical cable
  90. 90. Bending of the pipesPipes have bends in them so they can expand during thehot days or contractduring the cold night without cracking.
  91. 91. Application of expansion & contraction (1) RivetingA hot rivet is inserted When the rivet cools, The end of the rive through the holes it contracts and is hammered to of 2 metals, which pulls the metal pieces form a new head. are to be fastened tightly together
  92. 92. (2) Heat and Smoke Detector The heat and smoke detector uses the application of heat expansion of bimetallic strip to detect the presence of heat during a fire.
  93. 93. ❶ The heat from the fire causes the bimetallic strip to bend towards the contact point. Bimetallic strip Clamp Brass Contact Iron point Battery
  94. 94. ❷ When the bending strip touches the contactpoint to complete the circuit, the alarm rings. Bimetallic strip Clamp Brass Contact Iron point Battery
  95. 95. (3) Hot air balloon The hot air rises because it is lessdense than the coolerair in the surrounding When the fire is lighted the air isheated & it expands
  96. 96. The cold air sinks because it is moredense than the coolerair in the surrounding When the fire is turned off the air iscooled & it contracts

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