Conduction, Convection, Condensation, Evaporation and Radiation (P1)

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  • Heat Radiation
    • heat energy transferred by:
      • radiation
      • conduction
        • solids
      • convection
        • liquids and gases
      • transfer of energy by particles
    • the transfer of heat energy by infrared radiation
      • emitted by solids, liquids and gases
    • The bigger the temperature difference between a body and its surroundings, the faster energy is transferred by heating
      • Hotter than surroundings- emits more radiation than it absorbs
      • Cooler than surroundings- absorbs more radiation than it emits
      • The hotter an object, the more radiation it radiates in a given time
    • Dark, matt surfaces
      • absorb and emit radiation well
      • Solar hot water panels
        • washing up
        • radiators
    • Light, shiny surfaces
      • reflect most infrared radiation
        • vacuum flask- silver inner surfaces to keep heat in or out (dependent)
  • Kinetic Theory and Concuction
    • Solids
      • strong forces of attraction
      • particles close in a fixed, regular arrangement
      • not much energy
      • vibrate about fixed positions
    • Liquids
      • weaker forces of attraction
      • particles can move and form irregular arrangements
      • more energy
      • move in random directions at low speeds
    • Gases
      • almost no forces of attraction
      • most energy and free to move
      • travel in random directions at high speeds
    • Conduction of heat energy is where vibrating particles pass on their extra kinetic energy to neighbouringparticles
      • causes a rise in temperature at the other side of the solid
        • increase in heat radiating from its surface
          • faster in denser solids because particles are closer together and so will collide more often
      • Metals are good conductors
        • electrons are free to move inside the metal
        • At the hot end, electrons move faster and collide with other electrons, transferring heat
    • Insulators
      • materials that have larger spaces between their particles
      • conduct heat more more slowly
  • Convection
    • occurs when the more energetic particles move from the hotter region to the cooler region- and take their heat energy with them
    • Immersion heaters
      • kettes
      • radiators
  • Condensation
    • gas turns to a liquid
    • gas cools, particles slow down and lose kinetic ernergy
    • attractive forces pull particles together
    • If the temperature gets cold enough and the gas particles get close enough, condensation can take place
    • water vapour in the air condenses when it comes into contact with cold surfaces
      • drinks glasses
    • Gets faster if:
      • temperature of gas is lower
      • temperature of the surface the gas touches is lower
      • density is higher
      • airflow is less
  • Evaporation
    • liquid turns into gas
    • when particles escape from a liquid
    • Particles near the surface of a liquid can escape and become gas particles if:
      • travelling in the right direction
      • travelling fast enough to overcome attractive forces of other particles
    • the fastest particles evaporate so the average speed and kinetic energy of the remaining particles decreases
      • temperature of the remaining liquid falls
        • cooling effect
    • Faster if:
      • temperature is higher
      • density is lower
      • surface area is larger
      • airflow over the liquid is greater

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