T1 conservation and dissipation of energy Flashcards
state the law of energy conservation
energy cannot be created or destroyed, it can only be transferred or dissipated into the surroundings
state any changes in the total energy of a ball that is kicked, assuming that no external forces act
total energy of the system remains constant due to the conservation of energy
what is waste energy
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 2 equations to calculate efficiency
= useful output energy transfer / total input energy transfer
= useful power output / total power output
how can efficiency of a system be increased
- reducing waste output (lubrication, thermal insulation etc)
- recycling waste output (recycling thermal waste energy as input energy etc)
state the consequence for energy transfer of a material with a high thermal conductivity
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
- thickness of the walls
- thermal conductivity of the walls
state 3 methods of reducing heat loss in a building
- double glazing
- loft and wall insulation
- thicker walls
how can 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
