P7.2 Flashcards
how doe electric current transfer energy
electrical charge moves from a chemical store (battery)
or from a nuclear or chemical store from a power station used to power homes
what are power ratings
electrical items work at certain power ratings. this tells us how quickly they transfer between stores. it s measured in watts
larger power rating mean they transfer more energy and the battery would go dead quicker
how do we measure the power ratings of domestic appliances
kilowatt-hour. this is how much energy is transferred in an hour
how do you calculate the kilowatt-hour of an appliance
kilowatt-hour (KwH) = power (Kw) X time (h) one hour
what do electrical appliances do
they transfer energy from a chemical store to an electrical store then uses electricity to perform a task.
how is energy in the thermal store increased
you can do this by heating something usually achieved by burning fuel or using and electric current
how do analyse the cooling of objects
you analyse how the thermal store of the surroundings change and how the thermal store of the object changes
what is dissipation energy
this is the energy released from the appliance and what happens to it after we are done. the answer is it gets absorbed
how can we reduce energy displacement and why would you want to
we want to reduce the amount of energy displacement because once energy has dispersed it is practically useless.
we can reduce it through:
lubrication - reduces energy loss through friction
insulation - reduces energy lost through heating
why does your house cool down
because energy is lost to the surroundings. energy loss can be reduced with insulation or temperature can be maintained through heating systems by burning fuels
how does the thickness of the wall affect how quickly your house cools down
if two houses were the same temperature then the heating was switched off the one with the thinner walls would cool down much faster
what is thermal conductivity and how does it affect the temperature of the house
the thermal conductivity of a material tells you how much energy will pass through a wall with:
an area on 1m^2
a thickness of one metre
a temperature difference across it of 1 degree Celsius
what is efficiency and how do we calculate it
the more efficient and item is the better at transferring energy from one store to another useful store without wasting energy.
efficiency = useful output energy / input energy
how is useful and wasted energy shown
through Sankey diagrams these indicate the amount of energy by the thickness of the arrows.
state 3 ways we can increase efficiency
reduce energy loss - eg insulation and lubrication
make devices from materials that reduce unwanted energy transfer
- produce devices that are better at there job
