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Chemical energy store
Anything that can release energy by chemical reaction
e.g. food, fuels
Kinetic energy store
Anything moving has energy in kinetic energy store
Gravitational energy store
Anything in a gravitational field
Elastic energy store
Anything stretched, like springs and rubber bands
Thermal energy store
Any object - hotter = more energy in thermal store
Magnetic energy store
Magnets interacting with each other have energy in magnetic store
e.g. two magnets attract/repel each other
Electrostatic energy store
Charged objects interacting with each other have energy in electrostatic store
e.g. two charges attract/repel each other
Nuclear energy store
Atomic nuclei release energy from nuclear store in nuclear reactions
Mechanical energy transfer
Object moving due to force acting on it
e.g. pushing, pulling, stretching
Electrical energy transfer
Charge moving through p.d.
e.g. charges moving around circuit
Energy transfer by heating
Energy transferred from hotter object to colder object
e.g. heating pan of water on hob
Energy transfer by radiation
Energy transferred by EM waves
e.g. energy from Sun reaching Earth as light
Principle of conservation of energy
Energy can be stored, transferred between stores and dissipated - but never created/destroyed
Total energy of closed system has no net change
Formula: Efficiency
Efficiency = useful energy output / total energy output x 100%
Ball rolling up slope
Energy transferred mechanically from kinetic store of ball to its gravitational potential store
Some energy is transferred mechanically to thermal energy stores of ball and slope (due to friction) and then by heating to thermal energy stores of surroundings - energy is wasted
Bat hitting ball
Some energy usefully transferred mechanically from kinetic store of bat to kinetic store of ball
Rest of energy is wasted
Some energy in kinetic energy store of bat is transferred mechanically to thermal stores of bat, ball and surroundings
Remaining energy is carried away by sound
Electric kettle boiling water
Energy transferred electrically from mains to thermal store of kettle’s heating element
Then transferred by heating to thermal store of water
Some energy wasted, and transferred by heating from thermal stores of heating element and water to thermal stores of surroundings
Battery-powered toy car
Energy usefully transferred electrically from chemical store of battery to kinetic store of car and carried away by light from headlights
Energy wasted by transferring to thermal stores of car and surroundings, and wastefully carried away by sound
Bunsen burner and beaker
Energy usefully transferred by heating from chemical store of gas to thermal store of beaker and water
Energy wastefully transferred by heating to thermal stores of stand and surroundings
Some energy carried away by light
Sankey diagrams
Thicker arrow = more energy it represents - thick arrow going in, then several smaller arrows going off it to show different energy transformations occurring
Example of Sankey diagram
Conduction
In solid, particles are held tightly together
When one particle vibrates, it collides with nearby particles and vibrations quickly pass from particle to particle
Process continues throughout solid and gradually some energy is passed all the way through solid, causing rise in temp at other side of solid
Convection
When more energetic particles move from hotter region to cooler region, transferring energy as they do so
Only in liquids/gases
Radiation
All objects emit IR radiation
Hotter object = more IR radiation emitted
Immersion heater
Energy is transferred from heater coils to thermal energy store of water by conduction
Particles near coils get more energy, so they move faster
Meaning there’s more distance between them i.e. water expands and becomes less dense
Reduction in density means that hotter water rises above denser, cooler water
As hot water rises, it cools and becomes denser
Cold water is heated by coils and rises - process repeats
Results in convection currents going up, round and down, circulating energy through water
Emission and absorption of radiation
Hotter object = more IR radiation emitted
Black objects are best at emitting + absorbing thermal radiation
Shiny objects are worst at emitting + absorbing thermal radiation
Investigating thermal conduction
Attach beads at regular intervals (e.g. every 5cm) to one half of a long (at least 30cm) metal bar using wax
Hold metal bar in clamp stand and heat side of bar (using Bunsen burner) with no beads attached from end
As time passes, energy is transferred along bar by conduction and temp increases along rod
Wax holding beads will gradually melt and beads will fall as temp increases, starting with bead closest to point of heating
Investigating thermal convection
Place some purple potassium permanganate crystals in one side of beaker of cold water
Using Bunsen burner, gently heat side of beaker with crystals at bottom
As temp of water around potassium permanganate crystals increases, they begin to dissolve, forming bright purple solution
Purple solution is carried through water by convection, so traces out the path of convection currents in beaker
Investigating thermal radiation
Place an empty Leslie cube (its four vertical faces have different surfaces) on heat-proof mat
Boil water in kettle and fill Leslie cube with boiling water
Wait a while for cube to warm up, then hold thermometer against each of four vertical faces of cube
All four faces should be same temp
Hold IR detector a set distance (e.g. 10cm) away from one of cube’s vertical faces, and record amount of IR radiation detected
Repeat measurement for each of cube’s vertical faces
Make sure detector is same distance from cube each time
More IR radiation should be detected from black surface than white, and more from matt than shiny
Repeat experiment for reliability
Reducing rate of thermal energy transfer
Reduce conduction by using materials with low thermal conductivity
Reduce convection by stopping fluid from moving and preventing convection currents from forming
Reduce radiation by designing object with surface that is poor emitter, e.g. shiny and white
Insulation
such as clothes, blankets, foam cavity wall insulation, work by trapping pockets of air
Air can’t move so energy has to conduct very slowly through air pockets, as well as material in between, both of which have low thermal conductivity
Equation: Work done, Force and Distance
W = Fd
Work done = Force x Distance moved
[J] = [N] x [m]
Work done =
energy transferred
Equation: Gravitational potential energy
GPE = mgh
Gravitational potential energy = Mass x Gravitational field strength x Height
[J] = [kg] x [N/kg] x [m]
Equation: Kinetic energy
KE = ½mv²
Kinetic energy = ½ x Mass x (Speed)²
[J] = ½ x [kg] x ([m/s])²
Falling objects transfer energy
When something falls, energy from GPE store is transferred to its KE store
For a falling object when there’s no air resistance:
Energy lost from GPE store = Energy gained in KE store
Related to Principle of Conservation of Energy
Power
Rate of transfer of energy
Equation: Power, Work done and Time
P = W/t
Power = Work done / Time taken
[W] = [J] / [s]
Non-renewable energy sources
They will all run out one day
They all damage environment
But provide most of our energy
Sources
Coal
Oil
Natural gas
Nuclear fuels
Fossil fuel power stations
As fossil fuel burns (in oxygen), energy in chemical energy store is transferred to thermal energy store of water by heating
Water boils to form steam, which turns a turbine, transferring energy mechanically to KE store of turbine
As turbine revolves, so does the generator, producing electric current
Generator transfers energy electrically away from power station, via national grid
Fossil fuels + and -
Advantages:
Releases a lot of energy, relatively cheaply
Energy from fossil fuels doesn’t rely on weather, like most renewable energy, so it’s reliable
Fossil fuel power stations are already built, so don’t need to spend money on new tech to use them
Disadvantages:
Release carbon dioxide into atmosphere, contributing to global warming + climate change
Burning coal + oil also releases sulfur dioxide, causing acid rain, which can harm trees + soils and can have impact on wildlife
Will eventually run out
Nuclear reactors
Nuclear fission produces the heat to make steam drive turbines, rather than burning, so the boiler is different
During process, energy is transferred from nuclear energy stores to thermal energy stores by heating, then mechanically to KE stores, and finally transferred electrically to national grid
Nuclear power + and -
Advantages:
Doesn’t produce greenhouse gases which contribute to global warming
Plenty of uranium left in the ground
Disadvantages:
Nuclear reactors are expensive to build + maintain, and take longer to start up than fossil fuel ones
Processing uranium before use causes pollution, and risk of leaks of radioactive material
Radioactive waste
When they’re old and inefficient, nuclear power stations must be decommissioned (expensive)
Wind farms
Involves putting wind turbines in exposed places - like on moors, around coast or at sea
Wind turbines use energy from KE store of moving air to generate electricity
Wind turns blades, which turn a generator inside
Wind power + and -
Advantages:
Cheap to run
Tough and reliable
Wind is free
Doesn’t produce polluting waste
Renewable
Disadvantages:
Spoil the view
Inefficient - need 1500 wind turbines to replace one coal-fired power station
Can be very noisy - disturbance for local people
Sometimes wind isn’t strong enough to generate power
Expensive to set up wind farm, especially at sea
Geothermal power
Only possible in certain places where hot rocks lie near the surface
Source of most of the energy is slow decay of radioactive elements deep inside Earth
Water is pumped in pipes down to hot rocks and forced back up due to pressure to turn a turbine which drives a generator
So energy is transferred from thermal energy stores to KE stores and used to generate electricity
Geothermal power + and -
Advantages:
Geothermal energy can be used to heat buildings directly
Free
Renewable
No environmental problems
Disadvantages:
Cost of drilling down several km
Cost of building power plant often high compared to amount of energy we can get from it
Few places where this is an economic option
Solar cells
Solar cells use energy from Sun to directly generate electricity
They generate direct current
Solar cells + and -
Advantages:
Renewable
After initial costs, energy is free and running costs almost nothing
Disadvantages:
Very expensive initially
No pollution
Often too expensive or impractical to connect to national grid - cost of connecting to national grid can be huge compared to value of electricity generated
Can only generate enough electricity to be useful if they have enough sunlight - can be a problem at night
Solar water heating panels
More simple than solar cells
Black water pipes inside glass box
Glass lets energy from Sun in, which is absorbed by black pipes and heats up water
Cooking with solar power
Can focus Sun’s light using curved mirror
Solar heating systems + and -
Advantages:
Renewable
Free after setup cost
Disadvantages:
Solar water heating is only for small-scale energy production
Solar ovens are slow, bulky and unreliable - need strong sunlight to work
Wave power
Lots of small wave converters located around coast
As waves come in to shore, they provide up and down motion which can be used to drive generator
Energy is transferred from KE store of waves to KE store of turbine, and used to generate electricity
Wave power + and -
Advantages:
No pollution
Renewable
No fuel costs + minimal running costs
Disadvantages:
Spoils view
Hazard to boats
Fairly unreliable, as waves usually die out when wind drops
High initial cost
Can’t be used on large scale, but can be useful on small islands
Tidal barrages
Big dams built across river estuaries, with turbines in them
As tide comes in, it fills estuary to height of several metres
Water can be allowed out through turbines at controlled speed
Energy is transferred from KE stores of water to KE store of turbine, and used to generate electricity
Tidal barrages + and -
Advantages:
No pollution
Renewable
Fairly reliable
No fuel costs + minimal running costs
Disadvantages:
Prevents free access by boats
Spoils view
Alters habitat of wildlife
Height of tide is variable so lower tides provide less energy than higher ones
Moderately high initial costs
Hydroelectricity
Often requires flooding of valley by building a big dam
Rainwater is caught and allowed out through turbines, transferring energy from GPE store of water to KE stores as it falls, which is used to generate electricity
Hydroelectric power + and -
Advantages:
Renewable
No pollution
Immediate response to increased demand - if more energy is needed than national grid can supply, water is released
Reliable
No fuel costs + low running costs
Disadvantages:
Big environmental impact due to flooding valley (rotting vegetation releases greenhouse gases) and possible loss of habitat for some species
Reservoirs can look bad when they dry up
High initial costs
Pumped storage
Most large power stations have huge boilers which must be kept running all night even though demand is very low → surplus of electricity at night - very difficult to keep spare energy for later use
‘Spare’ night-time electricity is used to pump water up to a higher reservoir
This can be released quickly during periods of peak demand, such as evenings, to supplement the steady delivery from big power stations
‘Spare’ electricity is used to transfer energy back to water’s GPE stores, so it can generate more electricity when needed by flowing through dam
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