Energy Flashcards
What is a system?
An object or group of objects.
What happens when a system changes?
The way that energy is stored changes.
Name the 8 main energy stores
Chemical
Kinetic
Gravitational potential
Elastic
Thermal
Magnetic
Electrostatic
Nuclear
Chemical energy
The energy held in chemical bonds (that connect atoms and molecules together).
Kinetic energy
To do with the motion or movement of an object.
Law of conservation of energy
Energy cannot be created or destroyed, only transferred between different forms and objects.
Gravitational potential energy
The energy that an object possesses because of its position in a gravitational field.
Thermal energy
The heat energy trapped within an object, related to temp of that object.
Elastic energy
The energy held in an already-stretched spring.
Magnetic energy
Energy associated with a magnetic field.
Nuclear energy
Energy gained from breaking atoms apart.
In what ways can energy be transferred?
Mechanically
Electrically
By heating
By radiations (light/sound waves)
What is the change in the way energy is stored when an object is projected (thrown) upwards?
The kinetic store decreases and the gravitational potential energy store increases.
What is the change in the way energy is stored when a moving object hits an obstacle?
Kinetic energy can be transferred and energy can be dissipated as sound and thermal energy.
What is the change in the way energy is stored when an object accelerates at a constant speed?
The kinetic energy store of the object will increase when it’s accelerated by a force.
What is the change in the way energy is stored when a vehicle slows down/breaks?
The kinetic store decreases and the thermal energy store increases due to friction in the brakes.
What is the change in the way energy is stored when water is brought to the boil in an electric kettle?
Energy is transferred electrically to increase the thermal store in the water.
What is a closed system?
An isolated system where no energy flows in and out of the system.
The kinetic energy of a moving object can be calculated using what
equation?
Ek = 1/2 m v²
what is the unit for energy?
joules, J
what is the unit for mass, m ?
kg
what is the unit for speed, v ?
m/s
The amount of elastic potential energy stored in a stretched spring
can be calculated using what equation?
Ee = 1/2 k e²
What must we assume when calculating the amount of elastic potential energy stored in a stretched spring?
That the limit of proportionality has not been exceeded.
What is the unit for extension, e?
metres (m)
The amount of gravitational potential energy gained by an object
raised above ground level can be calculated using what equation?
Ep = m g h
What is the unit for gravitational field strength, g ?
N/kg
The amount of energy stored in or released from a system as its
temperature changes can be calculated using what equation?
∆ E = m c ∆ θ
What is the symbol for change in thermal energy?
∆ E
What is the symbol for specific heat capacity?
c
What is the unit for specific heat capacity?
J/kg °C (joules per kilogram per degree Celsius)
What is the symbol for temperature change?
∆θ
What is the unit for temperature change?
°C
What is specific heat capacity?
The amount of energy required to raise the temperature of one kilogram of a substance by one degree Celsius.
Power definition
The rate at which energy is transferred or
The rate at which work is done.
What are the two key power equations?
P = E/t
P=W/t
What is the symbol for work done?
W
What is the unit for work done?
J (joules)
What is the unit for power, P ?
W (watts)
What is the symbol for energy transferred?
E
What is the unit for energy transferred?
J (joules)
What do we measure time in?
Seconds.
An energy transfer of 1 joule per second is equal to what?
A power of 1 watt.
A power of one watt is equal to what?
An energy transfer of 1 joule per second.
How do we work out the work done by a force?
Use the equation W = F s
Two electric motors both lift
the same weight through the same height, but one does it faster
than the other. Which of the motors has a greater power rating?
The second, faster motor because it transfers more energy per second.
What can energy be?
Transferred usefully, stored or dissipated, but cannot be created or destroyed.
The law of conservation of energy means that when there are energy transfers in a closed system…
…there is no net change to the total energy
How is most energy wasted?
As heat energy
What three things does the rate at which thermal energy is transferred through the walls of a house depend on?
-The difference in temperature between the warmer interior and the colder exterior of the house
-The thickness of the walls
-The thermal conductivity of the walls
What factor affects the rate of energy transfer by conduction across a material?
The material’s thermal conductivity (the higher the thermal conductivity, the higher the rate of energy transfer by conduction across the material/the better conductor the material is).
How does the thickness and thermal conductivity of a building’s walls affect the rate of the building cooling?
The thicker the walls and lower the thermal conductivity, the more slowly a building will cool.
The energy efficiency for any energy transfer can be calculated using what equations?
efficiency = useful output energy transfer ÷ total input energy transfer
or
efficiency = useful power output ÷ total power input
What do we mean by efficiency?
How good a machine is at transferring energy into useful forms. (a very/highly efficient machine will have an efficiency of nearly 100%).
How can we reduce unwanted energy transfers?
-Lubrication to reduce friction (hence energy lost as heat to the surroundings)
-Using wires with low resistance in electrical circuits
-Streamlining shapes for moving objects to reduce air resistance
This can also increase the efficiency of an intended energy transfer.
How does resistance lead to wasted energy?
Energy is lost as heat to the surroundings because there is friction between two objects (even if one of them is air).
What are the main energy sources available for use on Earth?
Fossil fuels (coal, oil, gas)
Nuclear fuel
Biomass (Bio-fuel)
Wind
Hydroelectricity
Geothermal
Tidal power
Solar power
Water waves
Define ‘renewable energy resource’
A resource that is being (or can be) replenished as it is used and will not run out.
What are some uses of energy resources?
-Transport
-Electricity generation
-Heating
Biomass
Taken from living or recently living organisms including methane gas from animal waste and sewage.
Used for fuels such as methanol is transport and as fuel in power stations.
Wind
Wind turbines transfer the kinetic energy of the wind to electrical energy by turning a generator.
Hydroelectricity
Water stored in a reservoir is used to generate electrical energy when it flows downhill through a generator.
Geothermal energy
Radioactive decay of some of the elements in the Earth’s core and mantle generates a lot of heat. This heats surrounding rocks.
Water is pumped down to be heated by the rocks.
The resulting hot water or steam is used to heat homes or turn generators to generate electrical energy.
Tidal power
Kinetic energy of tidal streams or sea water flowing through barrages is used to turn turbines and generate electrical energy.
Define ‘Non - renewable energy source’
A resource that cannot be replaced and that will eventually run out.
Solar power
Solar panels use radiation from the Sun to heat water for use in homes or to generate electricity.
Water waves
Water waves turn a generator to generate electricity.
Fossil fuels (NR)
Coal, oil, and gas are burned in power stations to heat water, which evaporates to steam. This steam turns turbines to generate electricity.
Fuels such as petrol. kerosene, diesel, and oil are used in transport and heating homes.
Nuclear power (NR)
Uranium or plutonium release energy from the fission of their nuclei. The energy released is used in power stations to generate electricity.
Does conduction or convection take place in solids?
Conduction
Does conduction or convection take place in fluids?
Convection
Conduction
The process of transferring heat energy.
Explain the process of conduction.
One end of a solid object is heated, transferring energy to the kinetic energy stores of the particles in that end.
This causes the particles to vibrate faster, and so they collide more frequently with neighbouring particles.
The collisions transfer kinetic energy, so these neighbouring particles also vibrate faster and collide more often with other particles.
This process repeats over and over again, so energy is effectively passed along the object from one particle to the next.
Even though it’s kinetic energy that’s being passed between particles, when considering the object as a whole we say that it’s heat (or thermal energy) that’s being transferred.
Which material has a higher thermal conductivity: metal or plastic?
Metal (it conducts energy better when heated).
What do we mean by the term ‘fluid’, and which states of matter are considered fluids?
A fluid is a substance in which the particles are free to move around. They include both liquids and gases.
Explain the process of convection.
As a fluid is heated the particles gain kinetic energy and spread further apart.
This causes the fluid to become less dense and so it will rise above any cooler fluid that hasn’t been heated (because that fluid is more dense).
As the fluid cools down it will become more dense again, and so sink back down.
If this process takes place in a limited space, like a container or a room, it can create a convection current.
How can we reduce heat loss via convection?
-Closing windows
-Using a blanket at night
When we say heat energy is transferred by ‘radiation’, what are we referring to?
Infrared radiation
What is infrared radiation?
-A form of electromagnetic radiation
-That can travel through a vacuum
-Hotter objects emit more infrared radiation than cooler ones (hotter objects have more energy, so also emit more energy.)
Explain why environmental problems are not always solved by science. (3)
Science can identify environmental issues like global warming, but political, ethical, and economic factors may not allow these to be addressed. There may be resistance from people not wanting wind turbines near their homes or animal habitats to be destroyed, for example. There may also be financial constraints meaning politicians don’t allow resources to be built due to cost, or other social, political, and economic issues.
Solar power evaluation
Positive - Can be used to supply energy to people in remote areas.
Negative - Does not work when not sunny.
Biomass evaluation
Meh - Carbon neutral: carbon dioxide released when burnt is the same amount that the organism took in when living.
Wind energy evaluation
Negative - Do not work if it’s too windy or if it’s not windy enough.
Positive- produces no air pollution and the energy source is free
Hydroelectricity evaluation
Partial - Generally reliable but will not be used if the reservoir runs dry in a drought.
Geothermal energy evaluation
Positive - Reliable due to constant heat supply.
Tidal power evaluation
Partial - Tidal power is available at predictable times, but not all of the time.
Negative - There are few places where these can be situated and they may affect wildlife habitats.
Water waves evaluation
Negative - unreliable due to small or no wave motion on calm days.
Fossil fuels evaluation
Partial - Reliable, but produces carbon dioxide which leads to global warming.
Nuclear power evaluation
Positives:
- Reliable
-Produces around 10,000 x more energy per kilogram compared with fossil fuels
Negative:
-Produces large amounts of dangerous radioactive waste.
Word equation for work done
work done = force x distance
Doubling speed increases kinetic energy by what?
A factor of 4 (Ek = 1/2 m vsquared)
Does work done by the breaks of a car increase or decrease when stopping it?
Increase (by a factor of 4 if speed is doubled)
Because work done = force x distance , if work done increases by a factor of 4 then what happens to the (breaking) distance if force remains constant?
It increases by a factor of 4
What eventually happens to wasted energy?
It dissipates into the surroundings.
What is a kilowatt hour?
Electrical energy equal to a power of one thousand watts for one hour.
Give an environmental advantage to turning off electrical appliances when they are not being used.
Conserves fossil fuels
Less fossil fuels burned
Less greenhouse gas produced
Why might a students results only be an estimate of mean power?
Energy transfer to the surroundings
What surfaces do the best emitters of infrared radiation have?
Dark matt
What surfaces do the worst emitters of infrared radiation have
Light shiny
Dark matt cans are the best absorbers of what?
Infared radiation
Controls thermal insulation practical
Material of can
Volume of water
Starting temperature
Area of can
Surrounding temperature
Same surface underneath cans
What do smaller ears and thicker fur minimise?
Energy transfer
Why might the temperature of a room remain constant despite a heater switched on?
The room is losing heat/energy at the same rate the heater supplies it.
Is plastic a poor or good conductor?
Poor
What does a plastic cap do for a vacuum flask?
Stops convection currents forming at the top of the flask stopping energy transfer by convection.
Is glass a good or poor conductor?
Poor
Glass reduces energy transfer by…
conduction
What does a vacuum between two walls do?
Stop energy transfer by both conduction and convection because both require particles.
What do silvered surfaces do?
They are poor emitters of infrared radiation so reduce energy transfer by radiation.
Which type of fossil fuel power station has the shorted start-up time?
gas
What forms the national grid?
cables and transformers
Give one environmental advantage of generating electricity using solar cells rather than generating electricity in a coal burning power station.
Less/no atmospheric pollution
No harmful gases
