1.2 Conservation and dissipation of energy
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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 (e.g. recycling thermal waste 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? (Higher)
Lubricate any moving parts to reduce the friction and therefore energy loss due to heating
How can the efficiency of a radiator be improved? (Higher)
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? (Higher)
By placing a lid on the pan to reduce the heat loss from the top