P1.1 The Transfer Of Energy By Heating Processes

P1.1.1 Infrared Radiation
1. All objects emit and absorb infrared radiation.
  1. The hotter an object is the more infrared radiation it radiates in a given time.
    1. Dark, matt surfaces are good absorbers and good emitters of infrared radiation. Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation. Light, shiny surfaces are good reflectors of infrared radiation.
P1.1.2 Kinetic Theory
1. The kinetic particle theory explains the properties of the different states of matter. The particles in solids, liquids and gases have different amounts of energy. They are arranged differently and move in different ways.
  1. Particles in a solid are close together in a set pattern, particles in a liquid are close together and random and particles of a gas are far apart and random.
    1. The movement of particles in different states of matters are: in a solid, vibration about a fixed position; in a liquid, movement around each other; in a gas, movement quickly in any direction.
P1.1.3 Energy Transfer By Heating
1. The transfer of energy by conduction, convection, evaporation and condensation involves particles.
  1. Heat energy can move through a substance by conduction. Metals are good conductors of heat but non-metals and gases are usually poor conductors. Poor conductors are called insulators.
    1. The electrons in metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now charged metal ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have. This kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons. These move through the structure of the metal, colliding with ions as they go.
      1. Liquids and gases are fluids and their particles can move from place to place. Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy.
        Liquids and gases expand when heated because the particles move faster when at higher temperatures. As a result, the particles take up more volume because the gap between particles widens, while the particles themselves stay the same size. The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas. The denser cold liquid or gas falls into the warm areas. In this way, convection currents that transfer heat from place to place are set up.
        Evaporation and condensation are changes of state: evaporation involves a liquid changing to a gas and condensation involves a gas changing to a liquid.
        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 particles in a gas have different energies. Some 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.
        The rate of condensation increases if the temperature of the gas is decreased. The rate of evaporation increases if the temperature of the liquid is increased. It is also increased if the surface area of the liquid is increased or air is moving over the surface of the liquid.
        The rate at which an object transfers energy by heating depends on surface area and volume, the material from which the object is made and the nature of the surface with which the object is in contact.
        The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating.
        Small animals like mice have a large surface area compared to their volume. They lose heat to their surroundings very quickly. Large animals like elephants have a small surface area compared to their volume. They lose heat to their surroundings more slowly and may even have difficulty avoiding overheating. Elephants have large ears with a large surface area compared to their volume. These allow heat to be transferred from the elephant to its surroundings, helping to keep the animal cool. In general, similar animals have different ear sizes depending on the climate in which they live. The arctic fox has much smaller ears than the fennec fox, which lives in the desert. The arctic fox must conserve its heat energy in the cold climate, while the fennec fox must avoid overheating in the hot climate.
P1.1.4 Heating And Insulating Buildings
1. U-values measure how effective a material is as an insulator; the lower the U-value, the better the material is as an insulator.
  1. Solar panels may contain water that is heated by radiation from the Sun. This water may then be used to heat buildings or provide domestic hot water.
    1. The specific heat capacity of a substance is the amount of energy required to change the temperature of one kilogram of the substance by one degree Celsius; E=m×c×θ.
      1. E is energy transferred in joules, m is mass in kilograms, θ is temperature change in degrees Celsius and c is specific heat capacity in J / kg °C.

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P1.1 The Transfer Of Energy By Heating Processes

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