Thermal Properties

• Conduction is the flow of heat through matter from places of higher temperature to places of lower temperature without movement of the matter as a whole
• In non-metals - when heat is supplied to something, its atoms vibrate faster and pass on their vibrations to the adjacent atoms.
• Bad conductors (insulators) are used to reduce the amount of heat lost to the surroundings
• Convection is the flow of heat through a fluid from places of higher temperature in places of lower temperature by movement of the fluid itself.
• As a fluid (liquid or gas) warms up, the particles which are warmer become less dense and rise.
• After particles have become less dense and risen, they then cool and fall back to the heat source, creating a cycle called convection current.
• As particles circulate they transfer energy to other particles. If a cooling object is above a fluid it will create a convection current as well.
• Radiation is the flow of heat from one place to another by means of electromagnetic waves. It does not require a medium.
• Thermal radiation is mainly infra-red waves, but very hot objects also give out light waves. Infra-red radiation is part of the electromagnetic spectrum.
• Matt black is the best emitter, the worst reflector and the best absorber of radiation
• White is between black and silver as an emitter, a reflector and an absorber of radiation
• Silver is the worst emitter, the best reflector and the worst absorber of radiation
• An emitter sends out thermal radiation.
• A reflector reflects thermal radiation, therefore is a bad absorber.
• An emitter will cool down quickly, an absorber will heat up more quickly and a reflector will not heat up quickly.
• The amount of radiation also depends on the surface temperature and surface area of a body.
• • Consequences of energy transfer include:
  • Metal spoon in a hot drink will warm up because it conducts heat
  • Convection currents create sea breezes. During the day the land is warmer and acts as heat source. During the night the sea acts as the heat source.
  • A black saucepan cools better than a white one, white houses stay cooler than dark ones.