Energy Transfer by Heating - P1 Unit 1

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  • Energy Transfer by Heating - P1 Unit 1.1 - 1.6
    • Infrared Radiation
      • All objects emit infrared radiation
        • The hotter the object the more it emits in a given time
      • It is energy transfer by electromagnetic waves
        • (It's part of the electromagnetic spectrum)
      • We can detect it with our skin as heat
      • It can travel through a vacuum
        • How we get energy from the sun
    • Surfaces and Radiation
      • Dark Matt surfaces
        • Good absorbers of infrared radiation
          • Will become hotter than a white shiny surface
        • Good emitters of infrared radiation
          • Will cool down quicker than a shiny white object
      • Light Shiny Surfaces
        • Good reflectors of infrared radiation
    • States of Matter
      • Three states of matter
        • Solid
          • Particles vibrate in fixed positions, has a fixed shape
        • Liquid
          • Particles in contact with each other, move at random, no fixed shape and can flow
        • Gas
          • Particles far apart, move at random faster, no fixed shape and can flow
          • Low density compared to solid or liquid
      • Properties used to describe state of matter are: Flow, shape and volume
    • Conduction
      • Conduction occurs mainly in solids
      • When heated, particles gain kinetic energy and vibrate more.
      • Metals are good conductors
        • They have free electrons which gain kinetic energy and move through the metal, colliding with other particles and passing on the energy
      • Opposite of conductor is insulator
        • Examples are wool and fibreglass as they have trapped air
    • Convection
      • Convection occurs in fluids
        • (liquids and gases)
      • When fluids are heated they expand and become less dense.
        • This causes them to rise, to where it is cooler
          • It then falls again, forming a convection current
    • Evaporation and Condensation
      • Evaporation is a liquid turning into a gas
        • It is caused by the most energetic liquid molecule escaping the liquid's surface
          • The average kinetic energy of the remaining is less
            • This causes it to cool
        • The rate of evaporation can be increased by
          • Increasing the surface area
          • Increasing the temperature
          • Creating a draught across the surface
      • Condensation is a gas turning into a liquid
        • This often takes place on cold surfaces
        • The rate of condensation is increased by
          • Increasing surface area
          • Reducing the surface temperature
        • The particles lose kinetic/heat energy so move slower
          • The lack of resistance means the particles are pulled back together
  • Energy Transfer by Heating P1 - Unit 1.7 - 1.9
    • Energy Transfer by Design
      • Examiners love asking questions on the vacuum flask
        • This will have glass walls with silver surfaces to reduce radiation
        • A vacuum pocket so that air cannot circulate so there is no convection and poor conduction.
        • A plastic cap to prevent evaporation.
      • The greater the temperature difference between an object and its surrounding the greater the rate energy is transferred.
      • The rate at which energy is depends on:
        • Materials object in contact with
        • Objects shape
        • Objects surface area
      • We maximise energy transfer to keep things cool
        • Good conductors
        • Painted dull black
        • Increased air flow around the object
      • We minimise energy transfer to keep things warm
        • We minimise conduction, convection and radiaiton
        • Good insulators
        • White and shiny
        • Prevent convection currents by trapping air in small pockets or vacuums
    • Specific Heat Capapcity
      • Definition
        • The amount of energy required to raise the temperature of 1 kilogram of a substance by 1 degree celsius
      • Equation
        • E = m x c x delta
          • E = Energy transferred
          • M = mass (kg)
          • c = specific heat capacity (J/kg degrees Celsius)
          • Delta = temperature change (degrees c)
      • The greater the mass of the substance being heated the more energy needed to raise it by 1 degree.
    • Heating and Insulating Buildings
      • The rate of energy transfer in and out of our house can be reduced with various methods
        • Lost insulation prevents conduction
        • Cavity wall insulation prevents convection
        • Double glazing reduce conduction
        • Draught proofing reduce convection
        • Aluminium foil behind radiators reflects infrared radiation
      • The U-value of an object tells us how much energy per second passes through it.
        • This allows us to compare different materials
        • The lower the U-value the better the insulator
      • Solar Heating Panels contain water that is heated by the sun
        • This can provide domestic hot water or used to heat buildings

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