Heating And Cooling L2
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Heating And Cooling L2

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Conduction of heat Year 8

Conduction of heat Year 8

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    Heating And Cooling L2 Heating And Cooling L2 Presentation Transcript

    • Conduction of heat
      • Target
      • To know how heat flows by conduction in substances.
      Thursday 5 November 2009
    • Thinking task
      • Why does a piece of metal feel cold but a piece of wood at the same temperature feels warm?
      Answer: The metal conducts heat away from the hands but wood stops heat flowing from the hand.
    • Experiment to show conduction of heat
      • Attach some drawing pins to a metal rod using Vaseline.
      • Heat the rod with a Bunsen flame – when the heat reaches the pins the Vaseline melt and the pins fall off.
    • Showing conduction
      • The experiment showed how heat was conducted through a metal rod.
      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.
    • 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
    • Copy this summary table into your book : Conduction
    • Bad points about conduction
      • Allows heat to flow out of buildings in winter.
      • Can cause burns when touching something hot (pan handle).
    • Good points about conduction
      • Allows heat to flow through the bottom of a cooking pan.
    • Using insulators
      • We put gloves and jumpers on to keep warm in winter.
      • We use place mats to protect tables from damage from hot plates.
      • We reduce heat loss from houses with loft insulation.
    • A model for conduction
      • In metals ‘free’ electrons easily carry the kinetic energy from one side to the other.
      • In non metals inter atomic collisions are needed to carry the kinetic energy from one end of the material to the other.
      Questions: Hodder B Pages 28 and 29