Transmission Of Heat

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Transmission Of Heat

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

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