Conservation and Dissipation of Energy

• Energy cannot be created or destroyed (it can only be transferred into different forms)
• The total energy of the system remains constant due to the conservation of energy
• Waste energy


  The energy that is not used by the device for its desired purpose
• Energy changes in a filament light-bulb


  1. Electrical energy is transferred into light and heat energy

  2. Light is a useful energy form, heat is waste energy
• Efficiency equation 1


  Useful Output Energy Transfer/Total Input Energy Transfer
• Efficiency equation 2


  Useful Power Output/Total Power Output
• Increasing efficiency of a system

  1. Reducing waste output (by lubrication, thermal insulation etc.)

  2. Recycling waste output (eg. recycling thermal waste energy as input energy)
• High thermal conductivity of a material

  The rate of energy transfer through the material is higher than for a material with a lower thermal conductivity
• Double-glazed windows have a lower thermal conductivity than single-glazed windows
• Factors affecting rate of cooling of a building

  • The thickness of the walls
  • The thermal conductivity of the walls
• Methods of reducing heat loss in a building

  • Double glazing
  • Loft and wall insulation
  • Thicker walls
• Improving efficiency of a mechanical machine with moving parts

  Lubricate any moving parts to reduce the friction and therefore energy loss due to heating
• Improving efficiency of a radiator

  Installing metal foil sheets behind the radiator to reflect the heat back into the room rather than it being absorbed into the walls
• Improving efficiency of boiling water in a pan

  By placing a lid on the pan to reduce the heat loss from the top