Heat KS3 Y8

Heat KS3 Y8

Conduction
1. An object which has more HEAT or THERMAL ENERGY than another has molecules which vibrate quicker
  1. A thermometer has a rough idea of the amount of thermal energy
  2. Heat transfersfrom a higher to a lower temperature
  3. Solids are better heat conductors than liquids
    1. Stronger bonds in the solids than liquids
  4. Liquids are better than gases
  5. Heat transfers by comduction are when the objects are in contact and the particles don't move.
2. Metals are the best conductors
  1. Free electrons
Convection
1. Heat transfers thanks to the movement of matter (Liquids and gases)
  1. Heat doesn't rise
    1. Hot air rises
2. Hot water/air rises because it is less dense than cold water/air
  1. Hot water is less dense than cold
    1. Has less particles per unit of volume
    2. Hot materials expand and the particles vibrate more and push each other away
Radiation
1. Heat transfers by radiation
  1. Without...
    1. Movement
    2. Presence of matter
  2. Thermal energy is transferred by light
    1. Electromagnetic Waves called infared
  3. Using black and shiny surfaces
    1. Black surfaces are better infrared emitters than shiny ones.
      1. Black surfaces are good absorbers
      2. Shiny surfaces are good reflectors
Vacuum flask
1. Stops heat transfers from higher temperatures to lower ones
  1. Insulators reduce heat loss by conduction
    1. Need to trap air
      1. No convection
        Carpets on the floor (traps air)
      2. gases are better insulators than solids and liquids
        less conduction
      3. Can use glazed windows
        Fibre glas son the loft
      4. Cavity wall insulation
  2. Vacuum stops it by conduction and convection
  3. Shiny glass reflects infrared light and reduces heat loss by radiation
  4. Bung stops heat loss by convection

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