Heating and Cooling

Heating and Cooling

Infra Red Radiation
1. All objects are continuously absorbing and emitting thermal radiation
  1. The hotter an object the more radiation it emits
  2. Different surfaces are better at absorbing or emitting radiation than others
    1. Dark matt surfaces are the best emitters and absorbers of infra red radiation
    2. Light, shiny surfaces are the worst emitters and absorbers of infra red radiation
      1. Light, shiny surfaces are able to reflect infra red radiation well
Kinetic Theory
1. The kinetic particle theory helps to explain the way in which the different states of matter behave
  1. The particles in solids, liquids and gases have different amounts of energy,are arranged differently and move in different ways
    1. Particles in solids are arranged closely in a regular pattern and vibrate around a fixed position
      1. This means that they: they have a fixed shape, cannot flow, and cannot be squashed or compressed.
    2. Particles in a liquid are arranged close together in a random pattern and move around each other
      1. This means that they; they flow taking the shape of the shape of the container and cannot be squashed or compressed
    3. Particles in gases are far apart, random and move quickly and freely in any direction
      1. This means that they: can be squashed and compressed, and take the shape of their container completely
Energy Transfer by Heating
1. Conduction
  1. Metals are good conductors of heat whereas non-metals are insulators
  2. The particles in a metal have a kinetic energy and the hotter the metal is the more kinetic energy they have
    1. The electrons in the metal leave their atoms making them charged metal ions
      1. The ions are packed tightly and vibrate contiually
        The kinetic energy moves from the hot area of the metal to the cool by free electrons which move through the structure of the metal, colliding with the ions as they go
2. Convection
  1. Convection occurs in fluids (fluids and gases)
  2. Convection occurs when when hot particles in a fluid take the place of particles with little heat energy
    1. Fluids expand when they get hotter because the particles move more and take up more volume
      1. This is because the gap between particles get bigger when the particles stay the same size making them less dense
        The rarer particles in the hot areas then rise in to the cooler areas, taking the place of the denser particles
        The denser particles then fall to the hot area where they grow warmer and rarer so that they can take the place of the denser articles and so on
        This is called a convection current
3. Changes of State
  1. Evaporation is when a liquid changes to a gas
    1. Some particles in a liquid have more energy than others, so they are able to escape from the liquid and become a gas
      1. The remaining particles of the liquids have less energy so the liquid cools down
        This is why we sweat
    2. The rate of evaporation is increased as the temperature of the liquid is increased
      1. The rate of evaporation is also increased if air moves over the particles and if the surface area of the liquid is increased
  2. Condensation is when a gas changes to a liquid
    1. Particles in a gas have different energies and some of the particles don;t have enough energy remain separate so they move closer and form bonds
      1. Energy is released when this happens
    2. The rate of condensation increases when the temperature of the gas is decreased
4. The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred
Heating and insulating buildings
1. U-values are simple ranking system which measures the effectiveness of a material as an insulator
  1. The lower the U-value the better the material is as an insulator
2. Solar panels can be used to heat water, which is contained in the panel, using radiation from the sun in order to heat buildings or provide domestic hot water
3. Specific heat capacity is the amount of energy needed to change the temperature of a 1kg substance by 1 degree celsius
  1. The equation for specific heat capacity is: E = m × c × θ
    1. E is the energy transferred in joules, J m is the mass of the substances in kg, c is the specific heat capacity in J / kg °C θ (‘theta’) is the temperature change in degrees Celsius, °C

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	Criado por seth.bragg mais de 11 anos atrás