1. Energy Flashcards
What are the nine types of energy?
Kinetic sound light thermal electrical gravitational potential elastic potential chemical nuclear
What are the two ways that energy can be transferred?
From place to place or from one form into another
What is ‘waste energy’?
not useful energy that transferred to another store wastefully and is usually dissipated to the surroundings
What is ‘useful energy’?
The energy transformed to where it is wanted in the form wanted
What is an efficient device?
A device where most of the energy is usefully transformed
What form is waste energy nearly always in?
Heat energy given to the surroundings
Equation for efficiency?
(Useful energy output / total energy input) x100
What is work done equal to?
Energy transferred
Equation for work done?
Work done (J) = power (W) x time (s)
What is the rate at which energy is transformed?
Power
When is work done?
When any object is moved around ie energy is supplied
Equation for power?
Power (W) = work done (J) / time taken
What is 1 watt equal to?
1 Joule per second
What do you pay for when you pay for electricity?
The energy transferred
Equation for kinetic energy?
Ek=1/2mv²
Equation for gravitational potential energy?
Ep=mgh
How to calculate weight?
Mass x gravitational field strength
How to calculate a change in kinetic energy?
Ek=1/2mv²-1/2mu²
What is change in kinetic energy equal to?
Work done and kinetic energy transferred
Equation for elastic potential energy?
Ee=1/2ke²
Why does a compression still act like an extension?
The same amount of energy is stored
What is internal energy?
The energy stored by the particles of a substance
What is internal energy a sum of?
The kinetic energy of all the particles and the potential energy of all the particles due to their relative positions and forces between them
What does internal energy not include?
Gravitational potential energy or the kinetic energy caused by motion of the whole substance
What is the average kinetic energy of the molecules related to?
The temperature of a gas
What happens to kinetic energy if the temperature of a substance is increased?
The total kinetic energy of the particles increases and so the internal energy increased
What is latent heat?
The energy transferred to or from a substance when it changes state
What happens to the temperature during change of state?
The temperature is constant, so the total kinetic energy of particles does not change
What happens to the energy of particles when a substance melts or boils?
The total potential energy of the particles increased because energy is needed to break the bonds
What is happening when a substance is heating?
- temperature increases
- kinetic energy increases
- potential energy is constant
- internal energy increases
What is happening when a substance is changing state?
- temperature is constant
- kinetic energy is constant
- potential energy increases
- internal energy increases
What factors affect how much energy must be gained by an object as its temperature increases?
- temperature increase
- mass
- material
What is specific heat capacity?
The amount of energy required to heat 1kg of a material by 1 degree C
What is the specific heat capacity of water?
4200 J/kg*c
What is the specific heat capacity of copper?
390 J/kg*c
What is the equation for specific heat capacity?
Specific heat capacity = change in thermal energy / mass x temperature change
Why is the filling of a pie hotter than the crust?
The pastry and filling have the same temperature however the filling contains water and has a higher specific heat capacity so transfers more heat energy
What is latent heat measured in?
Joules per kilogram
What is the specific latent heat of fusion (lf)?
The energy needed to change state of 1kg of the substance from solid to liquid
What is the specific latent heat of vaporisation (lv)?
The energy needed to change the state of 1kg of the substance from liquid to gas
How to work out specific latent heat?
Latent heat = energy / mass
What is specific latent heat measured in?
J/kg
How can heat be transferred?
Conduction, convection and radiation
What direction does thermal energy travel in?
Hot to cold
What is conduction?
Particles that are very close together can transfer heat energy as they vibrate
Which is the method of heat transfer in solids?
Conduction
How do non-metals conduct?
As a non-metal is heated at one end, the atoms near the heat source gain kinetic energy and vibrate more and collide with each other so the energy is passed on
How do metal conduct?
When a metal is heated, free electrons gain kinetic energy so they move faster and diffuse through the metal - energy is transferred when electrons collide with other electrons or ions
Why is the rate of energy transfer greater in copper than steel?
Copper a higher thermal conductivity
What is the best insulator?
A vacuum
Why can’t conduction occur in a vacuum?
There are no particles to collide and pass on the energy
What do many insulating materials contain?
Pockets of trapped air
Why is air a good insulator?
It is a gas and particles are too far apart to transfer energy effectively
Why do steel pans have wood or plastic handles?
They do not get hot and burn your hand because they are made of material that cannot conduct heat so is an insulator
Why is felt a better insulator than paper?
It has air pockets and air is a good insulator as it is a gas
How to test different materials as insulators?
Fill 3 containers with boiling water, put a thermometer in each, wrap 3 different types of insulator and the hot water and measure temperature of each container in intervals
Why are wood and fibre glass good insulators?
They have trapped air in pockets - air is a gas so a poor conductor
Which are the best insulating materials?
The ones with the lowest thermal conductivity
What are fluids?
Substances that can flow i.e. Liquids and gases
What happens when fluid particles are heated?
They move around more and spread out
What happens when a fluid is heated?
Becomes less dense - same number of particles take up more space
How is wind an example of convection?
On a beach, the air above sand is heated, becomes less dense and rises. Cold air above the sea is sucked inland as wind
How is a freezer an example of convection?
A freezer cools air at the top and cools food on the way down. Warmer air at the bottom rises and a convection current is set up inside the fridge
Where can’t convection occur?
- in solids because particles are not free to flow
* in vacuums because there are no particles to flow and carry energy
How does trapped air reduce heat loss by convection?
Convection causes heat to be lost through the roof - loft instillation helps to reduce this. Trapped air in fibre glass is not free to flow so this helps to prevent convection currents
Where can energy be lost from in the home?
Through the roof, windows, floors, walls, doors and gaps
How can energy loss be reduced through the roof?
Loft insulation
How can energy loss be reduced through walls?
Cavity wall insulation
How can energy loss be reduced through doors and gaps?
Draught excluders
How can energy loss be reduced through floors?
Carpets
How can energy loss be reduced through windows?
Curtains and double glazing
What type of heat transfer does double glazing reduce?
Conduction
What type of heat transfer does cavity wall insulation reduce?
Conduction and convection
What type of heat transfer does loft insulation reduce?
Conduction and convection
What type of heat transfer does foil behind radiators reduce?
Radiation
What type of heat transfer does draught excluders reduce?
Convection
What type of heat transfer do curtains reduce?
Convection (and radiation, conduction)
What type of heat transfer do carpets reduce?
Conduction (and convection)
How does double glazing reduce heat transfer?
2 layers so it is further for heat to travel
Air between glass which is a gas so a good insults
How does cavity wall insulation reduce heat transfer?
2 layers so it is further for heat to travel
Air between walls which is a good insulator
Foam which has pockets of air which reduce flow in convection
How does loft insulation reduce heat transfer?
Fibre glass has pockets of trapped air
How does foil behind radiators reduce heat transfer?
Silver is a good reflector so heat from back radiator is reflected into room
How do draught excluders reduce heat transfer?
Close gaps around doors and windows so air cannot flow through
How do curtains reduce heat transfer?
Block gaps so air cannot flow through
Opaque so heat is not passed through
How do carpets reduce heat transfer?
Made of insulating materials which have a lot of air between fibres
What is payback time?
A way to calculate how cost effective types of insulation are. It is the time taken to save the money that it cost to buy
How to calculate pay back time?
Payback time = cost of insulation/ annual saving
What is a renewable energy resource?
One that can be replenished as it is used
What are some types of renewable energy resources?
Tidal Solar Geothermal Biofuel Wind Hydroelectric Wave
How does geothermal power work?
Hot rocks underground heat water to produce steam. Holes are drilled down to the hot region, steam comes up and used to drive turbines which drive electric generators
Energy transformations in geothermal power?
Heat -> Kinetic -> Electrical
Where can geothermal power stations be built?
Near hot reservoirs beneath the earth’s surface
Advantages of geothermal power?
- No pollution
- Low running costs
- Don’t take up much room - no impact on environment
Disadvantages of geothermal power?
- Difficult to find suitable sites for power stations
- Rocks have to be certain type and depth
- Rocks above have to be soft enough to drill through
- If not carefully managed a borehole can ‘run out of steam’ and not usable for decades
- Some dangerous gases and minerals come out of boreholes and are hard to dispose of
How does wind power work?
The wind turns blades which tune a rotor shaft. The resultant mechanical power is used to drive an electricity generator
Energy transformations in wind power?
Kinetic -> Electrical
Where can wind power stations be built?
In windy places e.g. the sea
Advantages of wind power?
- Dovetails with other systems
- Simple technology
- Once constructed, low running costs
- Occupied land can still be used for farming
- Cheap electricity
- Suitable for less sunny regions
- Safe, if properly maintained
- Plentiful wind supply
- No pollution
Disadvantages of wind power?
- No wind = no power
- Wind farms create a constant low level noise
- Can interfere with TV and radar
- Aesthetically disturbing
- Small electricity production from each windmill
How does wave power work?
Friction develops between air and water as wind blows across the water. Energy is transferred between the two elements. Taking the motion of the waves and translating it to mechanical/electrical energy generates energy from the waves
Energy transformations in wave power?
Kinetic -> Electrical
Where can wave power stations be built?
In the sea
Advantages of wave power?
- No waste or pollution
- Wave energy generators can produce large amounts of energy
- Once constructed, low running costs
Disadvantages of wave power?
- Can be noisy
- Must be able to withstand very rough weather
- Wave energy generators are only effective when exposed to strong waves
- May be a hazard to ships and leisure craft
How does tidal power work?
A bay dammed with gates and turbines fitted along the length of the dam. Gates are opened to let the tide in and turn the turbines to produce electricity
Energy transformations in tidal power?
Gravitational potential -> Kinetic -> Electric
Where can tidal power stations be built?
In an estuary
Advantages of tidal power?
- Amount of energy produced is predictable
- Low running costs
- No waste or pollution
- Reliable technology
- No fuel
Disadvantages of tidal power?
- Early stages of development
- Only produced energy for 10 hours a day as tide moves in and out
- Expensive to install
- Few suitable places
How does biofuel work?
- Energy crops - plants grown specifically for fuel e.g. wood. Some crops are fermented to produce ethane
- Waste - as material rots it gives off methane which is burnt to produce steam and turn a turbine
Energy transformations in biofuel?
Chemical -> Heat -> Kinetic -> Electrical
Where can biofuel power stations be built?
Fields or factories - waste underground
Advantages of biofuel?
- Fuel is cheap
- Methane is a greenhouse gas and burning it would reduce the amount in the atmosphere
- Using waste material makes good environmental and economical sense
Disadvantages of biofuel?
- Creating enough waste is difficult
- CO2 produced by bio-energy production
- Some waste materials not available all year round
How does solar power work?
Sonar cells are devices that convert light energy into electrical energy directly.
Sonar water heating uses heat from the sun to heat water in glass panels on a roof. Water is pumped through pipes in the panel.
Sonar furnaces use mirrors to concentrate the sun’s energy and produce high temperatures
Energy transformations in solar power?
Light -> Electrical
Where can solar power stations be built?
On roofs
Advantages of solar power?
- Safe
- Can generate energy in remote places
- Handy for low-power uses like garden lights
- Once constructed, low running costs
Disadvantages of solar power?
- Doesn’t work at night
- Electricity produced is more expensive
- Energy has to be stored in batteries, hydrogen or water
- Can’t be used as the only system in cloudy places
How does hydroelectric power work?
Flowing waters create energy that can be captured. When demand increases water is released back into a lower reservoir through a turbine. The water comes from behind a dam. The water drives electrical generators which may be built inside the dam
Energy transformations in hydroelectric power?
Gravitational potential -> Kinetic -> Electrical
Where can hydroelectric power stations be built?
Upland water areas above the ground because it is a store of gravitational potential energy
Advantages of hydroelectric power?
- No pollution
- Can produce electricity on demand
- More reliable than wind and solar
Disadvantages of hydroelectric power?
- Fish cannot migrate upstream, or downstream to the ocean
- Can impact water quality and flow
- Can be impacted by drought and variation in water flow
- Often change the paths of rivers which can move people out of houses and harm local wildlife
What is a fuel?
A material that can be burnt to provide energy (light and heat)
Energy transformation in a fuel?
Chemical -> Light + Heat
How does coal form?
Coal formed when old plants from millions of years ago died and formed layers at the bottom of swamps, to form peat
How do oil and natural gas form?
Oil and natural gas are formed when layers of sediment, plants and bacteria become buried and pressure is added over millions of years
What are the fossil fuels?
Oil, natural gas and coal
How do fossil fuels produce electricity?
The fuel is burned and heat produced boils water, creating high pressure which turns a turbine. The turbine turns a generator
How does natural gas produce electricity?
It is burnt and the hot gases produced are used directly to turn a turbine
What is the start up time of coal?
7 hours
What is the start up time of oil?
4 hours
What is the start up time of natural gas?
1 hour
How long will coal last?
About 300 years
How long will oil last?
About 45 years
How long will gas last?
25-30 years
Which fossil fuel creates the most pollution?
Coal
Which fossil fuel creates the least pollution?
Natural gas
What is the difference between first and second generation biofuels?
First generation have been derived from starches, sugars or animal fats
Second generation are derived from more advanced sources and are renewed as part of the carbon cycle
What are the different types of biofuels?
Bioethanol, biodiesel, biomethane
