Physics : Energy transfer by heating

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  • Created by: Bexxmay
  • Created on: 03-04-14 13:15
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  • Energy transfer by heating
    • Infrared radiation
      • Objects emit radiation
      • Can detect infrared radiation- it is warm against out skin
      • Can travel through a vaccume - Sun
    • Surfaces and Radiation
      • Matt surfaces-- absorbe radiation
        • Good emitters of infrared radiation
        • Rough surface
      • Light , shiny surfaces are good reflectors of infrared radiation
        • Smooth surface
    • States of Matter
      • Solid
        • Particles vibrate about fixed positions- has a fixed shape
      • Liquid
        • Particles are in contact but move about randomly , so doesnt have a fixed shape
      • Gas
        • Particles far apart and move randomly really fast. Doesnt have a fixed shape and can flow
    • Conduction
      • Mainly solids- good conductors
    • Convection
      • occurs in fluids
      • when a fluid is heated, it expands , therefore becomes less dense and rises. the warm fluid is replaced by cooler , denser fluid.
        • Resulting to a convection current transfers energy throughout the fluid
    • Evaporation and Condensation
      • Evaporation
        • When a liquid turns into a gas. Energetic molecules escape from the liquids surface and enter the air. This is because they become too hot. As the energetic molecule touches a cold surface,it condenses and turns back into a liquid
      • Condensation
        • When a gas turns into a liquid. When a warm air molecule touches a cold surface, it turns into a liquid.
    • Energy Transfer by design
      • The Greater the temperature difference between an object and its surroundings, the greater the rate at which energy is transfered.
        • -Materials the object is in contacts wtg
        • - The objects shape
        • - The objects surface area
      • We want to minimise the rate of energy transfer to keep things warm. Reduce conduction, convection and radiation
        • Need a cood insulator
        • White , shiny objects
        • Prevent conduction currents by trapping the air in small pockets
    • Specific heat capacity
      • SHC of a substance in the amount of energy required to raise the temperature
      • The higher the SHC, the more enery required for each degree temperature change
      • E = M x C x O
        • E: energy transferred , J
        • M: Mass , KG
        • C: SHC, J/Kg
        • O: temperature change,  C
    • Heating and insulating Buildings
      • Fibre glass: reduce energy transfer by conduction
      • Cavity Walls: Traps air in small pockets to reduce energy transfer by convection
      • Double Glazing: reduce energy transfer by condction
      • Drought Proof: reduce energy transfer by convection
      • Aluminium foil behind radiators: Reflect infrared radiation back into room
  • Insulators
  • Conduction
    • Mainly solids- good conductors


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