Energy Flashcards
what is a system?
an object or collection of objects
Name the 8 energy stores
- Kinetic
- gravitational potential
- elastic potential
- internal/thermal
- chemical
- nuclear
- magnetic
- electrostatic
What are the 4 energy transfer pathways?
- mechanical work - force mving an object
- electrical work - charges moving due to potential difference
- heating - due to temperature rise
- radiation - energy transferred as a wave like light or infrared
what does work done mean?
energy has been transferred
what is the energy change that happens when an object is projected upwards?
kinetic energy store -> gravitational potential energy store
what is the energy change that happens when water is boiled in an electric kettle?
electricity -> internal energy of heating element -> thermal energy store of water
what is the energy change that happens when a car accelerates by constant force of the engine?
chemical energy store (of engine) -> kinetic energy store (of car)
what are 2 ways to show how energy is transferred as a diagram?
- transfer diagrams
- Sankey diagrams
what does a transfer diagram show?
- boxes show energy stores
- arrows show energy transfers
what does a Sankey diagram look like?
it starts off as one big arrow which then splits into 2 or more arrows
Why are Sankey diagrams useful?
- they show where energy is being transferred to in a system
- the width of the arrows are drawn to scale so show the amount of energy transferred everywhere
what is the law of conservation?
energy can be transferred usefully, stored or dissipated but it can’t be created or destroyed
what is the energy change in a closed system after energy transfers?
there is no net change because of the law of conservation
what is energy dissipation?
the spreading out and transfer of energy into less useful forms - often thermal energy
how is energy dissipated in radio speakers?
- useful: electrical work -> sound waves
- dissipated: infrared radiation - thermal energy
what is dissipated energy often called?
wasted energy
how is conservation of energy demonstrated through a skydiver jumping out of a plane?
- when they jump - gravitational potential energy lost (they are losing height), kinetic energy gained (speed increases)
- wasted energy - transferred to thermal energy store of surroundings (work is done pushing against air particles)
what are some ways to reduce energy dissipation?
- adding lubricant between surfaces reduces friction and therefore energy wasted as heat
- use LED bulbs instead of filament bulbs
- use thermal insulation in cavity walls to reduce heat loss in a building
the higher the thermal conductivity of a material…
…the higher the rate of energy transfer by conduction across the material
what affects the rate of cooling of a building?
- thickness of walls
- thermal conductivity of walls
what is the formula for kinetic energy?
kinetic energy = 1/2 x mass x speed^2
KE = (1/2)mv^2
KE = J
m = kg
v = m/s
how do you know if an object gains kinetic energy?
it gets faster
what is the formula for gravitational potential energy?
gravitational potential energy = mass x height x gravitational field strength
PE = mgh
PE = J
m = kg
g = N/kg
h = m
how do you know if something gains gravitational potential energy?
it gets higher
what is the formula for elastic potential energy?
elastic potential energy = 1/2 x spring constant x extension^2
PE = (1/2)ke^2
PE = J
k = N/m
e = m
how do you know if something is gaining elastic potential energy?
it is stretched or compressed
what determines how much work is done?
- the size of the force acting on the object
- the distance that the force causes the object to move in the direction of the force
what is the formula for work done?
work done = force x distance
W = Fs
W = J
F = N
s = m
why is direction of force and distance important in the work done equation?
distance must be parallel to the force
one joule of work is done when…
…one newton of force causes a body to move one metre
what is power?
the rate at which energy is transferred - the more powerful a device, the more energy it will transfer each second
what is the formula to work out power?
Power = work done/time or power = energy transferred/time
P = W/t or P = E/t
P = W (watts)
W = J
E = J
t = s
one watt equals…
…one joule per second
Two electric motors are used to lift a 2 N weight through a vertical height of 10 m.
Motor one does this in 5 seconds.
Motor two does this in 10 seconds.
Show the difference in power.
For both motors:
W = Fs = 2*10 = 20J
For motor 1:
P = W/t = 20/5 = 4W
For motor 2:
P = W/t = 20/10 = 2W
Motor one transfers twice as much energy per second, so motor one is twice as powerful as motor 2
what is efficiency?
the proportion of input energy transfer which is usefully transferred/the proportion of input power that is usefully output
how do you work out the efficiency of an energy transfer?
efficiency = useful output energy transfer / total input energy transfer (ans x 100 for a percentage instead of decimal)
how do you work out the efficiency of a device when you know the power input and output?
efficiency = useful power output / total power input (ans x 100 for a percentage instead of decimal)
what are some methods of improving efficiency of things?
- insulating them
- lubricating them
- making them more streamlined
what are the useful and wasted energy transfers of an electric fan and how could it be made more efficient?
- useful: kinetic energy store of blades
- wasted: friction between axle and supports, friction between blades and air
- improvement: lubricate the axle
what are the useful and wasted energy transfers of an electric kettle and how could it be made more efficient?
- useful: thermal energy store of water
- wasted: heating the surroundings, letting steam escape once water boils
- improvements: insulate kettle more, switch off quicker once water has boiled
what device is usually almost 100% efficient?
an electric heater - all energy is transferred electrically to useful thermal energy stores
what is conduction?
the process by which vibrating particles transfer energy to neighbouring particles
in what states of matter does conduction happen?
solids - the particles in liquids and gases are more spaced apart so don’t collide as frequently
how does conduction work?
- particles in the part of the object being heated have more energy transferred to their kinetic energy store - they vibrate more and collide with each other
- the collisions cause energy to be transferred between particles’ kinetic energy store - conduction
what is thermal conductivity?
a measure of how quickly energy is transferred through a material through conduction
the higher a material’s thermal conductivity…
…the faster energy can be transferred through it by conduction
what is convection?
where energetic particles move away from hotter to cooler regions
in what states of matter does convection happen?
liquid and gas - particles are much freer to move than in solids
how does convection work? (in the context of a radiator)
- air near the radiator becomes warmer and less dense (particles move quicker)
- warm air rises and is replaced by sinking cooler air which gets heated by the radiator
- previously heated air warms the surroundings, cools, becomes denser and sinks
- then the cycle repeats - making a convection current
what is specific heat capacity?
the amount of energy needed to raise the temperature of 1kg of a substance by 1°C
what is the formula of specific heat capacity?
change in energy = mass x specific heat capacity x change in temperature
ΔE = mcΔθ
ΔE = J
m = kg
c = J/kg°C
Δθ = °C
what is temperature?
it is the average kinetic energy of molecules
what are the 4 non-renewable energy resources?
- coal
- oil
- (natural) gas
- nuclear fuels (uranium and plutonium)
what is a fossil fuel?
natural resources that form underground over millions of years
non renewable fuels…
…are not being made at the same rate they are being used and so will run out one day
what are the 7 renewable energy sources?
- wind
- tides
- solar
- biofuel
- water waves
- hydroelectricity
- geothermal
renewable energy sources…
…can be made at the same rate they are used so therefore will never run out
what are the 3 main uses of energy?
- transport
- electricity generation
- heating
how is energy used for transport?
- petrol and diesel - created from oil to power many vehicles (inc. cars)
- coal - some old fashioned steam train (boil water to produce steam)
- renewable sources like biofuel/combination of biofuel and petrol or diesel
how is energy used for heating?
- natural gas (most widely in the UK) - heats water which is pumped into radiators
- oil - some homes (mainly in remote areas) are heated by by burning oil from a tank
- coal - common in fireplaces
- geothermal - ground sourced heat pumps to heat buildings
- solar - solar water heaters use electromagnetic radiation from the sun to heat water for radiators
how is energy used for electricity generation?
- renewables + non-renewables
- electric-powered vehicles - transport
- electric heaters - heating
Key facts about wind power
(energy store, power output, environmental impact, reliability, other issues)
- energy store: kinetic
- power output: very low
- reliability: not very - no wind = no power + can’t scale up with demand + need to stop if it is too windy
- environmental impact: take up lots of land that could be used for farming, spoils the landscape, noisy BUT no pollution except in manufacturing
key facts about solar power
(energy store, power output, environmental impact, reliability, other issues)
- energy store: nuclear
- power output: depending on weather and only during daylight
- reliability: very reliable, so long as it is daytime, can be cost-effective even when it is cloudy, but best used small-scale
- environmental impact: lots of energy is used to make the solar cells, afterwards not much
key facts about goethermal energy?
(energy store, power output, environmental impact, reliability, other issues)
- energy store: internal/thermal
- power output: medium
- reliable: yes
- environmental impact: very little
- problem: not many suitable locations, a good one is Iceland - lots of volcanoes + hot rocks near the surface
key facts about hydroelectricity?
(energy store, power output, environmental impact, reliability, other issues)
- energy store: gravitational potential
- power output: medium
- reliable: yes except when there is drought
- environmental impact: no pollution BUT rotting vegetation in the flooded valley releases carbon dioxide and methane, habtitat loss, displace whole villages to flood them
key facts about wave power?
(energy store, power output, environmental impact, reliability, other issues)
- energy store: kinetic
- power output: low
- reliability: not very - waves die out when the wind drops
- environmental impact: no pollution, no fuel costs and little running costs BUT disturbs seabeds/ marine habitats, spoils the view, is a hazard to boats
key facts about tidal power?
(energy store, power output, environmental impact, reliability, other issues)
- energy store: kinetic
- power output: high, but hard to harness
- reliability: quite - tides come twice a day always but some are bigger than others - differences in energy generation
- environmental impact: no pollution, no fuel and little running costs BUT restricts free access for boats, spoils the view and alters the habitat for wildlife
key facts about bio-fuels?
- energy store: chemical
- power output: medium
- reliability: fairly - crops grow quick and can grow all year round, but can’t respond to immediate energy demands
- environmental impact: theoretically carbon neutral BUT there may not be enough space to grow crops for biofuel, expensive, creates methane and CO2 emissions, can cause deforestation
key facts about fossil fuels?
(energy store, power output, environmental impact, reliability, other issues)
- energy store: chemical
- power output: high
- reliability: yes - enough to meet current demand, but may run out in the future
- environmental impact: all release greenhouse gases, coal + oil release sulfur dioxide causing acid rain, coal mining damages the landscape, oil spillages cause lots of environmental problems
key facts about nuclear fuels?
(energy store, power output, environmental impact, reliability, other issues)
- energy store: nuclear
- power output: very high
- reliability: yes - enough fuel o meet current demand
- environmental impact: doesn’t release any harmful chemicals into the atmosphere BUT produces dangerous nuclear waste
How has reliance on fossil fuels changed over time?
- 20th century - usage increased - bigger population + more uses of electricity
- 21st century - slowly decreasing usage - more energy efficient appliances + more careful spending
why do we burn fossil fuels?
- producing electricity
- fueling cars
- heat homes
- cook food
why are renewables being used more?
- we now know the negatives of burning fossil fuels on the environment
- people are becoming aware that non-renewables will run out one day
- pressure from people and countries for governments to transition to renewables
what are the effects of transitioning to renewables?
- energy companies build new power plants for renewables to not lose customers
- electric cars and hybrid cars have hit the market and are becoming more popular
why can’t scientists push for a complete shift to renewables?
They can only give the science, they can’t make people, companies and governments change their behaviours. There are also political, social, ethical and economic issues that are out of their control
what factors limit changing to renewables?
- reliability and cost - fossil fuels are so much more cost-effective
- people can’t agree where to put new power plants - protest if it is near their house
- making personal changes like buying a hybrid car is expensive and out of reach for many
- research into making renewables better is very expensive and time consuming
