topic 4 - energy resources and energy transfers Flashcards
8 energy stores
- chemical
- electrostatic
- gravitational
- thermal
- nuclear
- elastic
- kinetic
- magnetic
4 energy transfers
- mechanically
- electrically
- heating
- radiation
what is the principle of conservation of energy
In any process energy is never created or destroyed. (It is just transferred from one store to another.)
how to calculate efficiency
efficiency = useful energy output/total energy output
how to draw a Sankey diagram
The energy flow is shown by arrows whose width is proportional to the amount of energy involved. The wasted and useful energy outputs are shown by different arrows.
what is conduction
the transfer of thermal energy through a substance by the vibration of the atoms within the substance. Metals are good conductors because they have free electrons that can move easily through the metal, making the transfer of energy happen faster.
what is convection
Convection occurs in a liquid or gas. These expand when heated because the particles move faster and take up more volume – the particles remain the same size but become further apart. The hot liquid or gas is less dense, so it rises into colder areas. The denser, colder liquid or gas falls into the warm areas. In this way, convection currents are set up which transfer heat from place to place.
what is thermal radiation
Thermal radiation is the transfer of energy by infrared (IR) waves. These travel very quickly in straight lines.
how are emission and absorption of radiation related to surface and temperature
- light, shiny surfaces are good reflectors of IR and so are poor at absorbing it.
- dark, matt surfaces are poor reflectors and good at absorbing IR.
- this means that placed next to a heat source, a dark object would heat up faster than a light one.
- dark matt surfaces are also best at emitting IR. This means that a hot object with a light shiny surface will emit less IR than a dark matt object at the same temperature.
- hotter objects emit more IR per second. The type of EM wave emitted also changes with temperature – the higher the temperature the higher the frequency of EM wave emitted.
what makes a good insulating material
a poor conductor that contains trapped air, e.g. foam, feathers, glass fibre. Being a poor conductor (non-metal) prevents heat transfer by conduction and the trapped air prevents convection currents.
how to calculate work done
work done = force x distance
W = F x d
what is work done equal to
energy tranferred
how to calculate GPE
gravitational potential energy = mass (kg) x gravitational field strength x height
GPE = m x g x h
how to calculate kinetic energy
kinetic energy = 1/2 x mass x velocity^2
KE = 1/2 x m v^2
relationship between GPE and KE
decrease is GPE = increase is KE because energy is conserved
