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Heat
Heat is a form of energy that flows from hotter objects to cooler ones. It can be transferred through conduction, convection, or radiation. During conduction, heat transfers through direct contact of particles. Convection involves the circulation of currents in fluids (liquids and gases) from hotter to cooler regions. Radiation transfers heat through electromagnetic waves even without direct contact. Materials expand when heated and contract when cooled. Changes of state between solid, liquid, and gas occur at melting, boiling, condensation, and freezing points depending on temperature and pressure.
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Heat
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- 2. Heat as aform 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. 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. Burning • Burning isone of the most common ways of producing heat. • When something burns, it produces a flame and also heat.
- 5. Electricity • Electricity canbe used to produce heat. • Example, the bulb of a lighted table releases heat
- 6. HEAT A form of energy which flows from a hotter region to a cooler region
- 7. ENVIRONMENT 25 oC Heat flows from the container CONTAINER (hotter) to the HEAT oC HEAT 70 surrounding (cooler)
- 8. ENVIRONMENT 25 oC Heat flows from surrounding CONTAINER (hotter) into HEAT oC HEAT 10 container (cooler)
- 9. THERMOMETER A thermometer is an instruments used to measure temperature.
- 10. When temperature rises, themercury level will rise When temperature falls, the mercury level will fall
- 11. The SI unitof temperature is Kelvin (K). But we commonly use Celsius (oC) instead. Conversion of Kelvin to Celsius: Kelvin (K) = Celsius (oC) + 273 Example 1: Example 2: 55 Celsius to Kelvin 339 Kelvin to Celsius Kelvin = Celsius + 273 Celsius = Kelvin - 273 = 55 + 273 = 339 - 273 = 328 K = 66 oC
- 12. Exercise 1: Exercise 2: 250 Kelvin to Celsius 383 Celsius to Kelvin
- 13. Heat vs temperature Heat Temperature A form of energy The degree of which flows from a Definition hotness and coldness hotter region to a of a body cooler region Joule (J) Unit of Kelvin (K) measurement Celsius (oC) - Increases when Flows from a hot heated Property area to a cold area - Decreases when cooled
- 14. The effect ofheat 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. Expansion & Contractionof Solids COLD HOT Expansion of Solids As the temperature increases, the atoms vibrate more vigorously and these vibrations push the atoms further apart. Thus, the volume of the solid increases.
- 16. HOT COLD Contraction of Solids When the solid is cooled down, the atoms vibrate less vigorously and they become closer together. Thus, the volume of the solid decreases.
- 17. Different solids expandand 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. After heating, metalB expanded more than metal A. This causes the bimetallic strip to bend. Metal A Metal B
- 19. METAL BALL &RING When the ring and ball are at When the brass ring is heat, the room temperature, the ball ring expands and the ball will will not pass through the ring. easily pass through the ring Metal ring and metal ball Bunsen burner
- 20. Expansion & Contractionof Liquids COLD HOT Expansion of Liquids When the liquid is heated, the molecules have more energy and move more vigorously. The movement of the molecules overcome the forces of attraction between the molecules, allowing them to move freely. Thus, the volume of the liquid increases.
- 21. HOT COLD Contraction of Liquids At lower temperature, the molecules have less energy and move closer to each other. This causes the volume of the liquid to decrease.
- 22. Expansion and Contractionof 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. Expansion & contractionof gases COLD HOT Expansion of Gaseous Contraction of Gaseous When the gas is heated, the At a lower temperature, the molecules gain more energy molecules have move slower and move faster and further and have less energy. They are apart. This causes the volume closer together causing the to increase volume to decrease.
- 24. Expansion and Contractionof Gaseous in Volumetric Flask LIQUID The experiment LIQUID above shows that gaseous expand when heated and glass glass contract when air air cooled. The liquid rises Heat once the volumetric flask (a) Before heating is heated. (b) After heating
- 25. Heat transfers CONDUCTION CONVECTION RADIATION RADIATION
- 26. conduction Conduction: Heat transfer in which energy of the particles in the warmer region is Particles of the passed on to the fish particles of the cooler region Particle s of the pan
- 27. Region A The particles(atoms) vibrates faster as heat is applied to it A B C
- 28. Region B The particles from region A passed on heat to the particles of region B A B C
- 29. Region C The particles of region B will then pass the heat to particles of region C A B C
- 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. Metals are goodheat 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. Mercury is agood 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. Heat conductors Material whichallow heat flow through it quickly
- 34. Heat insulators Material whichdo not allow heat flow through it quickly
- 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 to conductors targeted object
- 36. Heat insulators (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. 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. Double-glazed windowsreduce heat gain from outside the house during the hot day . It also reduces heat loss from inside during winter season.
- 39. Air Air is a good heat Outside 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. convection Heat transfer by the circulation of currents from one region to another in a liquid or a gas. The cool water from the top is denser than the hot Convection water. 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. 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.
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- 44. Refrigerator The freezer isusually 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. HEATER IN AROOM COLD WIND The warmer air from the radiator is less dense thus floats to the top HOT RADIATOR The cold air from the outside is denser thus sinks to the bottom
- 46. RADIATION The transfer ofheat 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. In a similarway, the heat from the Sun is reaches the Earth by radiation.
- 48. Radiate Radiate Radiate If the object is hotter than the surroundings, it will radiate more heat than it absorbs.
- 49. Absorb Absorb Absorb If the object is cooler than the surroundings, it will absorb more heat than it radiates.
- 50. The Rate ofRadiation 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. Which one losesmore heat ? Can A Can B 40 oC 78 oC
- 52. (2) Nature ofthe surface The hot water in the black and dull cup loses heat more 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. Application of RADIATION Reducing heat gain The fuel tank of the truck has silvery surface to reflect heat radiation and keeps the fuels inside the tank cool.
- 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. Reducing heat lossor 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. The space shuttle and the space suit of the astronaut are white in color to reduce heat gain and heat loss.
- 57. Increasing heat gain Solarheaters are painted black to absorb heat quickly from the Sun. Black surfaces are good absorbers of heat.
- 58. Efficiency in PreventingHeat Gain/Loss A vacuum flask is designed to prevent energy transfer between the content inside and its surroundings outside
- 59. Stopper The stopper is made from cork or plastics Vacuum (heat insulators). wall This can prevent Double heat loss and gain glass shell through conduction Silver and convection coating Casting
- 60. Stopper The vacuum Vacuum prevents any wall energy transfer Double through glass shell conduction and convection. Silver coating Casting
- 61. Stopper Double glass Vacuum wall shell reduces heat gain and Double glass shell heat loss by conduction Silver because glass is coating an insulator. Casting
- 62. Stopper Vacuum wall Doubleglass shell The silver coating reduces heat gain Silver coating and loss by radiation. Casting
- 63. Stopper Vacuum wall Doubleglass shell Shiny or light Silver coating colored case reduces heat Casting gain or loss by radiation
- 64. EFFECT OF HEATGAIN & HEAT LOSS Why does the ice cube melt? What changes when the ice melts?
- 65. MELTING • Matters canchange 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. Attraction forces Solid has a fixed shape because the molecules are hold together by attraction forces between them SOLID STATE
- 67. When a solidis heated, the particles gain energy and vibrate faster
- 68. Until the attraction SOLIDSTATE forces between them fail to hold them together in their fixed position
- 69. The attraction forces LIQUIDSTATE between them break, which release the particles
- 70. BOILING / Evaporation • Matters can GAS 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. LIQUID STATE Until the attraction forces between them fail to hold them together in their fixed position
- 72. Until all ofthe attraction GASES STATE forces between them break and allowing the particles to move freely
- 73. differences Boiling Evaporation State at which change At any temperature and At 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 from Source energy is needed Is energy needed? the surrounding
- 74. condensation • When a matter is GAS HEAT cooled, its particles emit heat HEAT energy and vibrate or move slower. • If the released energy is sufficient, the matter will change its state. LIQUID
- 75. When the temperature drops, the particles GASES STATE move slower and become closer to each other.
- 76. When the particlesare close enough to each GASES STATE other, attraction forces are formed between these particles.
- 77. More particles come LIQUIDSTATE close to each other and more attraction forces are formed between them
- 78. FREEZING • When amatter 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. More particles come LIQUIDSTATE close to each other and more attraction forces are formed between them
- 80. Finally all theparticles are bounded together and it gives solid a definite shape SOLID STATE
- 81. sublimation • Some substanceschange 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. Heating Curve OfWater Temperature GAS BOILING POINT Temperature where liquid gas LIQUID Temperature where MELTING POINT solid liquid SOLID Time
- 83. The Amount OfHeat 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. What happens tothe closely packed atoms of the solid if expansion and contraction occur frequently??
- 85. The undesirable effects The expansion and contraction during hot day and cold night, caused undesirable damages to structures. Cracks may appear on concrete pavement.
- 88. Ways to reduceundesirable 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.
- 90. Railway tracks Metal bridge
- 92. Sagging of the transmission line Electric transmission cable sag on a hot day due to expansion of metals. However, these cables lifted on a cold night due to contraction of metals
- 93. Sagging electrical cable
- 94. Bending of the pipes Pipes have bends in them so they can expand during the hot days or contract during the cold night without cracking.
- 95. Application of expansion& contraction (1) Riveting A 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
- 96. (2) Heat andSmoke Detector The heat and smoke detector uses the application of heat expansion of bimetallic strip to detect the presence of heat during a fire.
- 97. ❶ The heatfrom the fire causes the bimetallic strip to bend towards the contact point. Bimetallic strip Clamp Brass Contact Iron point Battery
- 98. ❷ When thebending strip touches the contact point to complete the circuit, the alarm rings. Bimetallic strip Clamp Brass Contact Iron point Battery
- 99. (3) Hot airballoon The hot air rises because it is less dense than the cooler air in the surrounding When the fire is lighted the air is heated & it expands
- 100. The cold airsinks because it is more dense than the cooler air in the surrounding When the fire is turned off the air is cooled & it contracts