Energy Transfers Flashcards
How is energy lost in an electric heater?
Energy is lost to heat the copper that the tank is made from and to the atmosphere.
Where is energy lost in a car?
Energy is used to overcome the various friction forces that oppose motion. This can also cause energy to be transferred to heat.
Lost as sound (engine noise)
Lots of energy is converted to heat which is lost or heats the surroundings
What is the law for Conservation of energy?
Energy is not created or destroyed in any process. Only transferred from one form to another.
What is the equation for efficiency?
useful output/total input x 100%
Electrical energy
whenever a current flows
Light energy
from the sun, luminous objects, light bulbs
Sound energy
loudspeakers etc
Kinetic energy
anything that possesses motion
Nuclear energy
released only from nuclear reactions
Thermal energy
flows from hot objects to cooler ones
GPE
possessed by anything that can fall
EPE
possessed by springs, elastic, rubber bands
Chemical
possessed by foods, fuels, batteries
What are gravitational and elastic potential and chemical energy?
Forms of stored energy
An appliance is more efficient if it…
wastes less energy
What happens to wasted energy?
It is always dissipated as heat
What are the energy transfers for a microphone to and amplifier to a speaker?
sound - electrical - sound
What does a TV transfer?
electrical - light and sound
What do toy car batteries transfer?
chemical - electric - kinetic, sound, heat, light
What does a batter charge transfer?
electrical to chemical
What are GPE and Potential energy always transferred to first?
kinetic energy
How will a Sankey diagram show if something is more efficient?
It will have thick arrow for the useful energy output
What does a filament lamp sankey diagram look like?
Most energy is wasted as heat; only small % is useful output
What is IR radiation?
transfer of heat energy by electromagnetic waves
What do convection and conduction involve?
The transfer of energy by particles
Conduction occurs mainly in…
solids
Convection is the main method of heat transfer in…
fluids (liquids and gases)
What can emit/absorb IR radiation?
all objects
What makes heat transfer quicker?
the bigger the temperature difference
All objects are continually doing what?
emitting and absorbing heat radiation
What will an object do that is cooler than its surroundings?
It will absorb more radiation than it emits
What will an object that is warmer than its surroundings do?
Emit more radiation than it absorbs
What happens in the conduction of heat in terms of particles?
Vibrating particles which have gained more KE pass this gain in KE to neighbouring particles
How does heat transfer via conduction lead to an increase in the heat radiating from the surface of the solid?
The process of particles sharing their KE is passed on throughout the solid causing rise in temp at the other side of the solid. This rise in temp means than the object now loses more heat from its surface as a means of cooling down again.
What method of heat transfer works in a vacuum?
IR radiation
When does convection occur?
When more energetic particles move from the hotter region to the cooler region and take their heat energy with them.
How does convection work in an immersion heater?
Heat energy transferred from heater coils to water via conduction.
Particles near coils get more energy and move faster and because there is more distance between the particles, the water expands and becomes less dense.
Hotter, less dense water rises above the denser, cooler water and displaces it out of the way in doing so making it sink to the heater coils
Process repeats with convection currents and all water will be heated
Where is convection most efficient?
In roundish/squarish containers because they allow the convection currents to work best
Why is the water below the heater cold?
Because any hot water rises due to its low density - it wouldn’t sink down to displace cooler water!
How is heat loss reduced in loft?
Thick layer of fibreglass wool laid out across loft floor and ceiling reduces heat loss from CONDUCTION AND CONVECTION
What is draught-proofing?
Strips of foam/plastic around doors and windows to stop heat loss via CONVECTION
How does a hot water tank jacket reduce heat loss?
Lagging such a fibreglass wool reduced conduction and radiation
How does double glazing help reduce heat loss?
Two layers of glass for insulation with an air cavity to reduce CONDUCTION AND CONVECTION
How do thick curtains reduce heat loss?
Reduce by stopping radiation and conduction
How does cavity wall insulation help against heat loss?
Foam squirted into the gap between inner and outer bricks stop CONVECTION AND RADIATION by being lined with shiny foil to reflected the heat back in.
Insulating foam and trapped air pockets in it (air is an insulator) reduce CONVECTION
How do humans reduce heat loss?
Clothes - trap air near skin to reduce convection and conduction because air is not a solid
Hair stands on end to trap a thicker layer of insulating air around the body - reduce CONVECTION
Clothes also reduce radiation as the material absorbs some of the heat radiated out by our bodies
What happens when a force moves an object?
energy is transferred and work is done
When is work done?
when energy is transferred
What happens when work is done against friction?
most energy is transformed into heat and some sound
This is “wasted” energy
WORK EQUATION
work = force x distance
What is power?
the rate of doing work i.e. how much energy is transferred / second
What is a powerful machine?
one that transfers a lot of energy in a short space of time
POWER EQUATION
P = E/t
What does kinetic energy depend on?
mass
velocity
What is GPE?
the energy stored in an object of mass m when you raise it to height h against gravity g
GPE EQUATION
m x g x h
What is the kinetic energy gained equal to?
The GPE lost
What are the non-renewable resources?
coal
oil
gas
nuclear
What are the basic energy transfers in a power station?
fuel (chemical)
steam (heat energy)
turns a turbine (kinetic)
drives a generator (kinetic)
makes electricity (electrical)
What are the advantages of burning fossil fuels?
Releases lots of energy relatively cheaply
Energy from fossil fuels not reliant on the weather - RELIABLE
We have lots of fossil fuel plants already so no money needs to be spent on new technology to use them
What are the disadvantages of f fuels?
release CO2 into atmosphere when burned - global warming and climate change
burning coal and oil release S02 which causes acid rain; this damages tree, buiding and life
NON-RENEWABLE
How is nuclear power generated?
TRANSFER FLOW CHART
Nuclear fission of uranium produces heat to make steam to drive turbines rather than burning.
NUCLEAR - HEAT - KINETIC - ELECTRICAL
Disadvantages of nuclear power?
reactors are expensive to build and maintain - longer to start up than fossil fuel ones
processing of uranium before use causes pollution
risk of radioactive material leak
radioactive waste
expensive to decommission when they are old and inefficient
Advantages of nuclear?
no greenhouse gases - NO GLOBAL WARMING
still plenty of uranium fuel reserves
How does wind power work?
Put up lots of wind turbines in exposed places.
Wind turbines convert kinetic energy of moving air to electrical energy.
WIND TURNS BLADES WHICH TURN A GENERATOR INSIDE
Advantages of wind power?
cheap to run
tough and reliable
free
no polluting waste and RENEWABLE
Disadvantages of wind power?
spoil the view
noisy
wind not always strong enough to generator power when demand increases UNRELIABLE
Expensive to set up farms - especially out at sea
How does geothermal energy work?
Hot rocks lie under ground
Water is pumped under ground and forced back up to pressure to turn a turbine and generator
HEAT - KINETIC - ELECTRICAL
What else can geothermal be used for?
heat building directly
What is the heat from rocks under ground made from?
slow decay of radioactive materials like uranium deep inside the Earth
Advantages of Geothermal?
free
renewable
no real environmental issues
Disadvantages of geothermal?
cost of drilling down
cost of building a plant is greater than the energy given out
few places where this is an economic option
How do solar cells work?
transform light energy from the Sun directly into electrical energy
generate direct current
Benefits of solar cells?
renewable energy source
expensive initially but after energy from sun is free and no running costs really
no pollution
good in remote places where there is not much choice and satellites
good to power calculators and watches
CAN BE CONNECTED TO RECHARGEABLE BATTERIES TO CREATE A SYSTEM THAT CAN STORE ENERGY DURING THE DAY FOR USE AT NIGHT
Disadvantages of solar cells?
very expensive initially
used to generate electricity on a small scale
not practical and too expensive to connect to the National Grid - cost of doing so is more than achieved from the electricity generated
unreliable - NO SUN AT NIGHT
How do solar panels work?
Black water pipes in a glass box. Glass traps heat and light that is absorbed by the black pipes and heats water.
Ad/Disadvantages of solar panels?
Expensive to set up
renewable and free after time
good for small scale production
How can solar power be used for cooking?
Curved mirror directs Sun’s heat and light on a pan.
Renewable energy source for outdoor cooking but slow, bulky and unreliable and needs strong sunlight to work!
How does wave power work?
small wave converters take the up and down motion of waves and use it to drive a generator.
KINETIC - ELECTRICAL
Advantages of wave power
no pollution
renewable
no fuel costs
minimal running costs
useful for small scale production on small islands
Disadvantages of wave power?
spoil view
hazard to boats
UNRELIABLE - waves stop when wide and tide affected
high initial costs
How does tidal power work?
FLOWCHART OF ENERGY CONVERSION
Tidal barrages are big dams built over estuaries with turbines in them.
Tide comes in and fills up estuary - driving turbines as it comes in
Water is then let out through turbines at a controlled speed and drives turbines
KINETIC - ELECTRICAL
Advantages of tidal?
no pollution
renewable
predictable although not up to demand!!
no fuel cost
minimal running cost
Disadvantages of tidal?
prevents free access by boats
spoils view
alters habitat for wildlife
height of tide is variable - low tide = LESS ENERGY
high initial costs
How does HEP work?
Requires flooding of valley by building a dam
Rainwater caught and allowed through turbines converting GPE of water to KE as it falls.
This is converted to Electrical energy by a generator
Advantages of HEP?
renewable
no pollution
no fuel and running costs
immediate response to INCREASED DEMAND
NO RELIABILITY ISSUES EXCEPT IN DROUGHT
Disadvantages of HEP?
BIG Impact on the environment due to flooding the valley (rotting vegetation releases methane and CO2)
loss of habitat for some species
reservoirs unsightly
high initial costs
How does pumped storage help with surplus electricity?
Spare electricity is used to pump water up to a higher reservoir
This can be released quickly during peak demand to supplement the steady delivery from big power stations
Why is there surplus electricity at night with low demand?
large power stations have boilers that are left running all night leading to surplus electricity build up
How is pumped storage different to HEP?
HEP generates power
Pumped storage is a way of storing energy which has already been generated
What does a dynamo do?
converts kinetic energy of moving bicycle wheel into electrical energy. Lamp converts electrical energy to heat and light
What are the energy conversions due to friction?
heat and sound
How can you show conduction?
ICE, MATCH AND PAPER
- Block of ice put into test tube under gauze so it doesn’t rise again and water at top is heated. Ice not melted because conduction doesn’t occur efficiently in fluids
- Hold match away from flame. Only light when very near to flame; air is a poor conductor of heat.
- cylinder of brass fitted onto some wood and paper around middle.
Paper is heated over flame.
Paper doesn’t brown on brass side as metal conducts heat away from the paper. Paper scorched on wooden side as wood is a bad conductor (heat just builds up under paper and scorches it)
How do particles in a solid share their heat energy with particles around them?
they collide and share their KE
Why does convection occur in fluids?
because convection requires particles that can move about and create convection currents
How does convection help in mines?
A lit candle is placed in a mine with 2 chimneys. As the flame burns , air around it heats up, expands and becomes less dense.
This heated air rises up out of the mine through one chimney.
Low pressure in mine so fresh air rushed in to replace the lost air.
What happens when heating water in a pan?
metal pan conducts heat from the flame which heats water particles.
Heated water rises because it is less dense and so cooler air replaces the water that rose
What is IR radiation?
the transfer of heat energy by IR waves and does not involve particles.
What does the rate at which objects emit IR depend on?
SA
difference in temp between object and surroundings
texture of surface
colour
Best reflector of IR?
shiny, white
Best absorber of IR?
matt black
Summary of IR emitter and absorbers?
Black is better at absorbing than white.
Shiny is better at reflecting than matt
How is a vacuum flask adapted for function?
PLASTIC STOPPER
- doesn’t conduct heat (insulator)
- prevent convection from taking place
VACUUM
- no particles so no convection or conduction
THIN SILVERED WALLS
-reduce radiation by reflected heat back into flask
How does carpet prevent heat loss?
Air trapped in fibred prevents CONVECTION
Cost efficiency?
Savings - initial cost
Payback time?
initial cost/annual saving
Explain what is meant by a non-renew energy source?
one that is not replaced at the same rate as it is used
What is the greenhouse effect?
insulating effect of certain gases in Earth’s atmosphere.
They allow short-wavelength IR from Sun into Earth’s atmosphere but absorb the re-emitted long-wavelength IR.
This is trapped and heats the Earth.
Why are fossil fuels not a clean way of producing energy?
They all have carbon in them and when burnt, release CO2. Damaging effect on environment
Advantages of nuclear power?
There is enough to meet our energy requirements and with ‘breeder’ nuclear reactors to generate more nuclear fuel, meet demand indefinitely.
Compare power stations for GAS, COAL, NUCLEAR AND HEP and how quickly they respond to changes in demand
gas - quite quick response
coal - longer to respond as takes longer to fire up
nuclear - only suited to steady supply as the reactors cannot be quickly run up to operating temp or closed down
HEP - very quick
Light to chemical?
PHS
Sound to electrical?
microphone
Systematic error?
every result is wrong by the same amount
Random error?
do same thing, repeat it but get different results
Zero error?
instrument is not set to zero
What is efficiency?
the fraction of energy supplied to a device which is transferred into a useful form
If you throw an object vertically upwards with u of 20m/s how high will it reach before returning to Earth?
1/2mv2 = mgh (cancel m)
so 0.5 x (20)2 = 10 x h
so h = 20m
