Conservation and dissipation of energy

Cards (13)

  • State the law of energy conservation
    Energy cannot be created or destroyed (it can only be transferred into different forms)
  • State any changes in the total energy of a ball that is kicked, assuming that no external forces act.
    The total energy of the system remains constant due to the conservation of energy
  • 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?
    • reducing waste output (by lubrication, thermal insulation etc)
    • recycling waste output (eg 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