Heat Transfer + specified experiments

• Heat travels from hot to cold (doesn't always rise)
• Conduction = the transfer of heat energy from one solid to another through the movement of touching particles
• Conductors = good at transferring heat (lose heat faster): Insulators = bad at transferring heat (lose heat slower)
• Insulators contain materials that are non-metals
• Air is an excellent insulator. It is used in jumpers to keep heat trapped in the small air pockets; why more layers is warmer than one thick layer
• All metals are good conductors
• Metal atoms vibrate more when heated, passing on vibrations when they collide with their neighbors. Kinetic energy passes along the metal. More dense metals = faster transfer rate. Metals have free electrons so there is more chance of collision and a faster rate of transfer
• Convection occurs in liquids and gases
• Solids have no room for the particles to move so no convection can occur
• when a liquid or gas is heated, kinetic energy is increased = particles move outwards = density decreases as there is more volume but same mass.

  Convection occurs because of changes in density. The warm liquid/gas becomes less dense when heated so rises.
• Convection current = Less dense, heated air moves away from heat source, cools, becoming more dense and sinking.

  
• Radiation = heat that moves as an infrared wave.
• Radiation can move through a vacuum - it doesn't need particles to move (how we get heat from the sun)
• Black = good absorbers and emitters
• Silver = good reflectors
• White = bad emitters and absorbers
• A black mug will stay hot longer than a white mug
• Quilts keep us warm because they have air pockets and air is an insulator
• Heat passes through a radiator through conduction, and as it is a metal it transfers heat faster through free electrons
• Ice in a drink makes it cool because the cold air is dense so sinks to the bottom of the glass where the water is warm, cooling it, and any left over warmth is less dense so rises and is then cooled by the ice cube and sinks again ---> convection current occurs until glass is cold
• Houses in hot countries are painted white because white is a bad absorber and emitter of heat
• The best colour for a radiator is black because it is a good emitter of heat so will make a room hotter
• more insulation = less energy on heat = save on bills + help environment as less fossil fuels are burned
• All insulation questions = Contain trapped air, air is an insulator
• 1. Specified experiment for conduction
  2. Different metals conduct heat at different rates - depends on how many free electrons + how dense
  3. The pins will fall off once the heat reaches the the end and the wax melts; first to drop= best conductor

  
• 1. Specified experiment for Convection
  2. The purple crystal will move up and around the beaker.
  3. As water is heated, it becomes less dense and rises
  4. Once away from flame, it becomes more dense and sinks (crystal colours water)

  
• 1. Specified experiment for radiation
  2. Using a radiation, heat up the 2 thermometers.
  3. Black one should heat up quicker