Conservation and dissipation of energy

• State the law of energy conservation

  Energy cannot be created or destroyed (it can only be transferred into different forms)
• What is waste energy

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

  • Electrical energy is transferred into light and heat energy
  • light is a useful energy form,heat is waste energy
• State two equations to calculate efficiency

  =useful output energy transfer/ total input energy transfer

  =useful power output/ total power output
• How can the efficiency of a system be increased

  1. Reducing waste output(by lubrication, thermal insulation)
  2. Recycling waste output(recycling thermal waste energy as input energy)
• State the consequence for energy transfer of a material with a high thermal conductivity

  The rate of energy transfer through the material is higher than for a material with a lower thermal conductivity
• Do double-glazed windows have a higher or lower thermal conductivity than single-glazed windows

  Lower, meaning less energy transfers through them
• What key factors affect the rate of cooling of a building

  • The thickness of the walls
  • the thermal conductivity of the walls
• State three methods of reducing heat loss in a building

  • Double glazing
  • loft and wall insulation
  • thicker walls
• How can the efficiency of a mechanical machine with moving parts be improved

  lubricate any moving parts to reduce the friction and therefore energy loss due to heating
• How can the efficiency of a radiator be improved

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

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