AQA GCSE Physics unit 1.1 Heat

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  • Heat
    • Transfer- Heat is transferred when there is a temperature difference
      • Conduction
        • 1. when materials are heated the paritcles gain energy
        • 2. they vibrate more
        • 3. so collide succesfully with more particles
        • 4. Pass their energy onto them
        • 5. so they vibrate more too
        • Metals are the best conductors because there are electrons in them that pass energy on
      • Infrared radiation- transfer of heat using electromagnetic waves
        • The hotter an object is the more infrared radiation it radiates in a given time
        • Dark, matte surfaces are good absorbers and good emmiters of radiation
        • Light, shiny surfaces are poor absorbers and poor emitters of radiation
          • also good reflectors
      • Convection
        • Heating... HELDR
        • Cooling... CCMDS
      • Evaporation
        • The particles in a liquid have different energies. Some will have enough energy to escape from the liquid and become a gas. The remaining particles in the liquid have a lower average kinetic energy than before, so the liquid cools down as evaporation happens.
      • Condensation
        • Particles may not have enough energy to remain as separate particles, particularly if the gas is cooled down. They come close together and bonds form between them. Energy is released when this happens.
          • Factors affecting rate
            • The particles in a liquid have different energies. Some will have enough energy to escape from the liquid and become a gas. The remaining particles in the liquid have a lower average kinetic energy than before, so the liquid cools down as evaporation happens.
            • -the surface area of the liquid is increased-air is moving over the surface of the liquid.
      • rate at which an object transfers heat depends on:
        • the material from which the object is made
        • The nature of the surface which the object is in contact with
        • SA and volume
    • Measuring and insulating buildings
      • U values
        • How effective a material is as an insulator
        • lower the U-value the better the insulator
      • Specific heat capacity
        • the energy needed to raise the temperature of 1 Kg of a material by 1*C
          • High mass, lots of energy can be transferred without raising the temp

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