Transfer of thermal energy

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  • Transfer of thermal energy
    • Convection
      • Occurs mostly in fluids (Liquids and Gases)
      • Heat is transferred through the movements of heated particles
      • The heated portions of the fluid becomes less dense and rise up, while the colder portions of fluids become denser and sink.
        • This creates the convection current
      • Applications
        • Electric kettle
          • Heating coil is placed at the bottom to allow hot water to rise and cold water to sink
        • Air conditioners
          • They are fixed close to the ceiling as cold air sinks
    • Conduction
      • Occurs mostly in solids
      • Heat is transferred through the vibrations of particles or diffusion of free electrons in solids
      • A material with a high value of thermal conductivity is a better conductor of heat
      • Metals  have higher thermal conductivity, hence metals are better conductors compared to non-metals and air
      • Applications
        • Metals (eg. stainless steel/aluminium)
          • Used as cooking utensils and saucepans
        • Insulating materials (eg. wood/plastic)
          • Used for handles of saucepans and cooking utensils
    • Radiation
      • Heat is transferred by electromagnetic waves or infrared waves
      • No medium required for heat transfer
      • Factors affecting the rate of radiation
        • colour and texture of surface
          • Dull and black are better emitters and absorbers of radiation
        • Surface temperature
          • Higher temperature =higher rate of radiation
        • Surface area
          • Larger surface area = higher rate of radiation
      • Applications
        • Wearing brightly-coloured clothing on a hot day
          • Bright surfaces reflect most of the radiant heat
        • Greenhouse used i cold countries
          • keep heat in, warming the plants

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