Section 4 - Energy Resources and Energy Transfer Flashcards
energy stores: kinetic
anything moving has energy in kinetic energy store
energy stores: thermal
any object - more if hotter
energy stores: chemical
anything that can release energy by chem reaction (ie. foods, fuel)
energy stores: gravitational potential
anything in a gravitational field (anything that can fall)
energy stores: elastic potential
anything streched (like springs and rubber bands)
energy stores: electrostatic
two charges that attract or repel each other
energy stores: magnetic
two magnets that attract or repel each other
energy stores: nuclei
atomic nuclei release energy from this store in nuclear reactions
how can energy be transfered between stores
mechanically (due to a force)
electrically (due to a charge moving through p.d)
by heating ( hot to cold)
by radiation (by waves)
principle conservation of energy
energy can be stored, transfered between stores, and dissipated but never created or destroyed. Total energy of a closed system has no net change.
total energy input = useful energy output + wasted energy
useful energy
energy is only useful when it is transferred from one store to a useful one
some of input energy is always wasted (usually heating)
efficiency of energy transfer
useful energy output
—————————— x 100
total energy output
energy stores
kinetic
thermal
chemical
gravitational potential
elastic potential
electrostatic
magnetic
nuclear
(sound?)
sankey diagram
thicker arrow = more energy
this then divided into smaller arrows representing energy outputs
width of arrow is proportionate to amount of Joules it represents, energy input = total output
energy transfer by heating
through
radiation
convection
conduction
bigger temp difference = faster
thermal radiation
consists of EM infrared waves
- all objects are continiously absorbing and emmiting infrared radiation
- an object hotter than surroundings emmits more radiation than it absorbs and vice versa
- some colours are surfaces emit and absorb radiation better than others
conduction
thermal conduction is the process where vibrating particles transfer energy from their kinetic energy store to the kinetic energy stores of neighboring particles
occurs mainly in solids. when a particle vibrates its causes a ripple effect in the lattice structure creating rise in temp which means it transferes energy to surroundings
convection of heat
convection occurs when the more energetic particles more from the hotter region to the cooler region and transfer energy as they do
covection: immersion heater example
- particles near coils get more energy so they move faster, more distance between them means water expands and becomes less dense, causing it to rise.
- as it rises it displaces the colder water making it sink towards coils which repeats the procces
- this results in convection currents circulating energy (most efficient in roundish or squarish containers)
reducing rate of energy transfer
object should be designed with a surface that is a poor emmiter
(ie. white instead of black)
use insulation to stop movement of fluid
thermal conductivity
describes how well an object transferes energy by conduction. (high = quick trnasfer)
work done
when a force moves an object through a distance work is done on the object and energy is transfered
move needs force needs energy (gets mechanically)
power
the rate at which energy is transfered
missing last pages and formula
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