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F4: Transmission of Heat Textbook page 128 to 143
Objectives At the end of this lesson you will be able to: State how heat energy flow State the 3 mechanisms of heat energy to flow
How does heat move from one place to another? When you stir a cup of hot chocolate with a metal spoon, what happens? After awhile the metal spoon will be hot How does the heat move? From region of high temperature to region of lower temperature High temperature (cup of hot chocolate) and low temperature (metal spoon)
Different ways heat can move through different medium Solid Conduction Liquid and Air Convection No medium (does not require solid, liquid or air) Radiation
Conduction in Solid Define conduction Movement of heat through a material without the obvious movement of the material itself
Conduction in Solid Example: heating of metal rod Heat energy moves along the metal rod From hot end to the cool end of the rod The metal atoms gain energy from the flame and vibrate faster These atoms hit neighbouring atoms causing them to vibrate faster  It is like a book is passed from student to student
Animation – Conduction http://www.phy.cuhk.edu.hk/contextual/heat/hea/condu/conduction_e.html
Are all conductors the same? Example: heating of metal rod Heat energy moves along the metal rod From hot end to the cool end of the rod The metal atoms gain energy from the flame and vibrate faster These atoms hit neighbouring atoms causing them to vibrate faster  It is like a book is passed from student to student
Are all conductors the same? Some materials conduct heat faster than others Metal: good conducter Poor conductor conduct heat slowly example, wood, plastic, ceramics, air and glass Poor conductor = insulator Vacuum (empty space) is perfect insulator. No heat moves through a vacuum by conduction
Uses of conductors Electric iron Metal pan
Uses of insulators An ice box Air has many uses as an insulator, to use air as insulator, it must be trapped Oven gloves Blankets Jackets
Do inquiry time page 131 The air trapped between the two layers and prevent heat loss by conduction Conductor = metal pan/pot and kettles, rice cooker, electric iron Insulators = oven gloves, plastic handles, blankets
Do checkpoint page 131 Conduction. Conductor. Metals. Insulator. Plastics Electric iron/cooking pots
Convection Liquids and gases are poor conductors of heat It moves through convection Convection is the movement of heat energy from one place to another by the movement of the material itself It is like a student walk to the back of the room carrying the book and pass it to another student
Animation Convection in liquids
Objectives At the end of this lesson you will be able to: State how convection occur State the applications of convection
How does convection take place in liquids? As water get heated, it rises from bottom of beaker to the top Cooler water from beaker sink to take the place of the heated water that has risen Convection current
Using particulate model of matter to explain As water get heated, molecules move faster and spread apart Volume of water increases and density decreases Hot water less dense so it will move up Cold water more dense it will sink
How does convection take place in gases? Same as liquid Hot air rises and cooler air sinks Convection current form, similar as in liquid
Using particulate model of matter to explain As gas get heated, molecules move faster and spread apart Volume of gas increases and density decreases Hot air less dense so it will move up Cold air more dense it will sink
Application of convection Electric kettle Heater at the bottom Hot water rises and cold water sinks Convection current forms, eventually all the water becomes warm
Application of convection Hot water system Hot water rises from the boiler Cold water from the tank sinks into the boiler Convection cycle Supply of hot water
Application of convection Air conditioner Placed at the top of the wall Cool air sinks Hot air rises Convection currents are set up in the room
Application of convection Warming a room Heater is places as low as possible Hot air rises Cold air from the room get heated by the heater and rises up Convection currents is form
Sea breeze – During the day Hot day, land heats up faster than the sea Hot air rises from the land The hot air replaced by cold, denser air from the sea Produce sea breeze
Land breeze – During the night At night, land cools quicker than the sea Hot air rises from the sea The hot air replaced by cold, denser air from the land Produce land breeze
Do checkpoint pg 136 Convection Convection current Rise. Hot air/water is less dense. At the top. Because cold air sinks and hot air rises, it causes convection current to occur. Hot water system, electric kettle, heater
Objectives At the end of this lesson you will be able to: State how radiation occur State the application of radiation
How does heat from the sun reach the earth? Radiation Space between Sun and Earth is a vacuum Cannot transfer by conduction or convection Radiation is the transfer of energy without the need for a medium It is like a book can be thrown to the back of the room
How radiation is absorbed? When we stand outdoors, our body absorb radiation from the Sun All objects are able to absorb radiation Black, dull or rough surface are good absorbers of heat Shiny, white or smooth surfaces are poor absorbers of heat
How radiation is emitted? All objects give out heat Black, dull or rough surface are good radiators of heat Shiny, white or smooth surfaces are poor radiators of heat
In conclusion Shiny, white surfaces reduce the amount of energy absorbed from the surroundings by reflecting radiation It also reduce heat from losing to the surrounding Dull and rough surfaces, absorb heat from the surrounding better It also lose heat to the surrounding faster
Do checkpoint 139
Application of Absorbers and Radiators of heat Refrigerator Surface is black So it can radiate heat faster to the surrounding
Application of Absorbers and Radiators of heat Hot water containers Shiny kettle is poor radiators So heat remain in the container and thus water remain hot longer
Application of Absorbers and Radiators of heat Petrol tanks Shiny and white  So it will reflect heat from the Sun Prevent petrol from heating up Thus the tanks remain cool
Do checkpoint 140

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Transmission Of Heat

  • 1. F4: Transmission of Heat Textbook page 128 to 143
  • 2. Objectives At the end of this lesson you will be able to: State how heat energy flow State the 3 mechanisms of heat energy to flow
  • 3. How does heat move from one place to another? When you stir a cup of hot chocolate with a metal spoon, what happens? After awhile the metal spoon will be hot How does the heat move? From region of high temperature to region of lower temperature High temperature (cup of hot chocolate) and low temperature (metal spoon)
  • 4. Different ways heat can move through different medium Solid Conduction Liquid and Air Convection No medium (does not require solid, liquid or air) Radiation
  • 5. Conduction in Solid Define conduction Movement of heat through a material without the obvious movement of the material itself
  • 6. Conduction in Solid Example: heating of metal rod Heat energy moves along the metal rod From hot end to the cool end of the rod The metal atoms gain energy from the flame and vibrate faster These atoms hit neighbouring atoms causing them to vibrate faster It is like a book is passed from student to student
  • 7. Animation – Conduction http://www.phy.cuhk.edu.hk/contextual/heat/hea/condu/conduction_e.html
  • 8. Are all conductors the same? Example: heating of metal rod Heat energy moves along the metal rod From hot end to the cool end of the rod The metal atoms gain energy from the flame and vibrate faster These atoms hit neighbouring atoms causing them to vibrate faster It is like a book is passed from student to student
  • 9. Are all conductors the same? Some materials conduct heat faster than others Metal: good conducter Poor conductor conduct heat slowly example, wood, plastic, ceramics, air and glass Poor conductor = insulator Vacuum (empty space) is perfect insulator. No heat moves through a vacuum by conduction
  • 10. Uses of conductors Electric iron Metal pan
  • 11. Uses of insulators An ice box Air has many uses as an insulator, to use air as insulator, it must be trapped Oven gloves Blankets Jackets
  • 12. Do inquiry time page 131 The air trapped between the two layers and prevent heat loss by conduction Conductor = metal pan/pot and kettles, rice cooker, electric iron Insulators = oven gloves, plastic handles, blankets
  • 13. Do checkpoint page 131 Conduction. Conductor. Metals. Insulator. Plastics Electric iron/cooking pots
  • 14. Convection Liquids and gases are poor conductors of heat It moves through convection Convection is the movement of heat energy from one place to another by the movement of the material itself It is like a student walk to the back of the room carrying the book and pass it to another student
  • 16. Objectives At the end of this lesson you will be able to: State how convection occur State the applications of convection
  • 17. How does convection take place in liquids? As water get heated, it rises from bottom of beaker to the top Cooler water from beaker sink to take the place of the heated water that has risen Convection current
  • 18. Using particulate model of matter to explain As water get heated, molecules move faster and spread apart Volume of water increases and density decreases Hot water less dense so it will move up Cold water more dense it will sink
  • 19. How does convection take place in gases? Same as liquid Hot air rises and cooler air sinks Convection current form, similar as in liquid
  • 20. Using particulate model of matter to explain As gas get heated, molecules move faster and spread apart Volume of gas increases and density decreases Hot air less dense so it will move up Cold air more dense it will sink
  • 21. Application of convection Electric kettle Heater at the bottom Hot water rises and cold water sinks Convection current forms, eventually all the water becomes warm
  • 22. Application of convection Hot water system Hot water rises from the boiler Cold water from the tank sinks into the boiler Convection cycle Supply of hot water
  • 23. Application of convection Air conditioner Placed at the top of the wall Cool air sinks Hot air rises Convection currents are set up in the room
  • 24. Application of convection Warming a room Heater is places as low as possible Hot air rises Cold air from the room get heated by the heater and rises up Convection currents is form
  • 25. Sea breeze – During the day Hot day, land heats up faster than the sea Hot air rises from the land The hot air replaced by cold, denser air from the sea Produce sea breeze
  • 26. Land breeze – During the night At night, land cools quicker than the sea Hot air rises from the sea The hot air replaced by cold, denser air from the land Produce land breeze
  • 27. Do checkpoint pg 136 Convection Convection current Rise. Hot air/water is less dense. At the top. Because cold air sinks and hot air rises, it causes convection current to occur. Hot water system, electric kettle, heater
  • 28. Objectives At the end of this lesson you will be able to: State how radiation occur State the application of radiation
  • 29. How does heat from the sun reach the earth? Radiation Space between Sun and Earth is a vacuum Cannot transfer by conduction or convection Radiation is the transfer of energy without the need for a medium It is like a book can be thrown to the back of the room
  • 30. How radiation is absorbed? When we stand outdoors, our body absorb radiation from the Sun All objects are able to absorb radiation Black, dull or rough surface are good absorbers of heat Shiny, white or smooth surfaces are poor absorbers of heat
  • 31. How radiation is emitted? All objects give out heat Black, dull or rough surface are good radiators of heat Shiny, white or smooth surfaces are poor radiators of heat
  • 32. In conclusion Shiny, white surfaces reduce the amount of energy absorbed from the surroundings by reflecting radiation It also reduce heat from losing to the surrounding Dull and rough surfaces, absorb heat from the surrounding better It also lose heat to the surrounding faster
  • 34. Application of Absorbers and Radiators of heat Refrigerator Surface is black So it can radiate heat faster to the surrounding
  • 35. Application of Absorbers and Radiators of heat Hot water containers Shiny kettle is poor radiators So heat remain in the container and thus water remain hot longer
  • 36. Application of Absorbers and Radiators of heat Petrol tanks Shiny and white So it will reflect heat from the Sun Prevent petrol from heating up Thus the tanks remain cool