Heating And Cooling L2

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Conduction of heat Year 8

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Heating And Cooling L2

  1. 1. Conduction of heat <ul><li>Target </li></ul><ul><li>To know how heat flows by conduction in substances. </li></ul>Thursday 5 November 2009
  2. 2. Thinking task <ul><li>Why does a piece of metal feel cold but a piece of wood at the same temperature feels warm? </li></ul>Answer: The metal conducts heat away from the hands but wood stops heat flowing from the hand.
  3. 3. Experiment to show conduction of heat <ul><li>Attach some drawing pins to a metal rod using Vaseline. </li></ul><ul><li>Heat the rod with a Bunsen flame – when the heat reaches the pins the Vaseline melt and the pins fall off. </li></ul>
  4. 4. Showing conduction <ul><li>The experiment showed how heat was conducted through a metal rod. </li></ul>There are moving particles (electrons) inside the metal – the faster they move the higher the temperature – they bump into each other to allow the heat to flow through the metal.
  5. 5. Liquids are poor conductors of heat [ insulators ]. WEAR SAFETY GLASSES What about gases? Carefully put your finger 1cm away from a Bunsen burner flame. If gases were good conductors, you’d burn your finger - you don’t. Gases are good insulators. Conduction
  6. 6. Copy this summary table into your book : Conduction
  7. 7. Bad points about conduction <ul><li>Allows heat to flow out of buildings in winter. </li></ul><ul><li>Can cause burns when touching something hot (pan handle). </li></ul>
  8. 8. Good points about conduction <ul><li>Allows heat to flow through the bottom of a cooking pan. </li></ul>
  9. 9. Using insulators <ul><li>We put gloves and jumpers on to keep warm in winter. </li></ul><ul><li>We use place mats to protect tables from damage from hot plates. </li></ul><ul><li>We reduce heat loss from houses with loft insulation. </li></ul>
  10. 10. A model for conduction <ul><li>In metals ‘free’ electrons easily carry the kinetic energy from one side to the other. </li></ul><ul><li>In non metals inter atomic collisions are needed to carry the kinetic energy from one end of the material to the other. </li></ul>Questions: Hodder B Pages 28 and 29
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