Efficiency

• efficiency = useful output energy / input energy
• Dissipated energy is energy that is no longer useful. (When heating a beaker, energy goes to surroundings)
• Dissipated energy by:

  • reducing friction (eg. by using a lubricant)
  • less collisions on objects surface = less energy loss
  • reducing air resistance (eg. make more streamlined)
  • using an insulator (eg. cotton wool)
  • less lost to surroundings
• Convection - occurs when liquids and gases are heated.

  • Particles gain KE and move apart
  • Less dense hotter fluid rises
  • This starts a convection current
• Radiation - when infrared radiation carries heat energy from one place to another.
• Conduction - heat transfer in solids

  • Transfers KE from one particle to the next
  • Always from higher temperature to lower temperature
  • Free electrons transfer energy rapidly (make metals good conductors)
• Ways to reduce heat loss in a house:

  • Double glaze windows
  • Cavity wall insulating
  • Draught blockers
  • Thick curtains
  • Loft insulation