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Chapter 1: Energy
1.1-Energy Stores and Systems
Energy is never used up, instead it is transferred between different energy stores and different objects.
Energy is Transferred between stores
When energy is transferred to an object, the energy is stored in one of the object’s energy stores.
There are eight energy stores:
Thermal energy stores
Kinetic energy stores
Gravitational potential energy stores
Elastic potential energy stores
Chemical energy stores
Magnetic energy stores
Electrostatic energy stores
Nuclear energy stores
Energy is transferred mechanically(by a force doing work, electrically(work done by moving charges), by heating or by radiation(e.g. light or sound)
When a System Changes, Energy is Transferred
A system is just a fancy word for a single object or a group of objects that you are interested in.
When a system changes, energy is transferred.
It can be transferred into or away from the system, between different objects in the system or between different types of energy stores.
Closed systems are systems where neither matter nor energy can enter or leave.
The net change in the total energy of a closed system is always zero.
Energy can be transferred by heating
Take the example of boiling water in a kettle - you can think of the water as the system.
Energy is transferred to the water(from the kettle’s heating element) by heating, into the water’s thermal energy stores(causing the temperature of the water to rise).
You could also think of the kettle’s heating element and the water together as a two-object system.
Energy is transferred electrically to the thermal energy store of the kettle’s heating element which transfers energy by heating to the water’s thermal energy store.
Energy can also be transferred by doing work
Work done is just another way of saying energy transferred. Work can be done when current flows(against resistance in a circuit) or by a force moving an object.
1.2-Kinetic and Potential Energy
The three most common energy stores are: Kinetic energy, Elastic potential energy and gravitational potential energy.
Movement means energy in an object’s kinetic energy store
Anything that is moving has energy in its kinetic energy store.
Energy is transferred to this store when an object speeds up and is transferred away from this store when an object slows down.
The energy in the kinetic energy store depends on the object’s mass and speed.
The greater the mass and the faster its going, the more energy it will have.
Formula: E=1/2mv(2)
Kinetic energy= 1/2 mass x velocity(2)
Example: A car of mass 2,500kg is travelling at 20mph. Calculate the energy
(1/2 x 2500) x 20(2)=500,000 Joules
Raised objects store energy in gravitational potential energy stores
Lifting an object in a gravitational field requires work, which causes a transfer of energy to the gravitational potential energy store of the raised object.
The higher the object, the more gravitational potential energy.
The amount of energy depends on the object’s mass, height and strength.
Formula: E= mgh
Gravitational potential energy= Mass x Gravitational Strength x Height
Falling objects also transfer energy
When something falls, energy from its gravitational potential energy store is transferred into its kinetic energy store.
For a falling object when there’s no air resistance:
Energy lost from the g.p.e store = Energy gained in the kinetic energy store
In real life, air resistance acts against all falling objects- causing some energy to be transferred to other energy stores, e.g. thermal energy store of the objects and surroundings'.
Stretching can transfer energy to elastic potential energy stores
Stretching or squashing an object can transfer energy to its elastic potential energy store.
So long as the limit of proportionality has not been exceeded, energy in the elastic potential energy store can be found.
Formula: E=1/2ke(2)
Elastic potential energy= 1/2 spring constant x extension(2)
1.3-Specific Heat Capacity
In simple terms it means, how hard it is to heat something up.
Different Materials have Different Specific Heat Capacities
More energy needs to be transferred to the thermal energy store of some materials to increase their temperature than others,
e.g. you need 4,200J to warm 1kg of water by 1c, but only 139J to warm 1kg of mercury.
Materials that need to gain lots of energy in their thermal energy stores to warm up also transfer loads of energy when they cool down again.
They can ‘store’ a lot of energy.
Specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1c.
Formula: CE = mcC0
Change in thermal energy= Mass(kg) x Specific Heat Capacity(J/kgc) x Change in temperature
You can investigate Specific Heat Capacity
To investigate a solid material(e.g. Copper), you’ll need a block of the material with two holes in it(for the heater and thermometer to go into)
Measure the mass of the block, then wrap it in an insulating layer to reduce the energy dissipating from the block into the surroundings, and Insert the thermometer and heater.
Measure the initial temperature of the block and set the potential difference,V, of the power supply to 10V.
When you turn on the power, the current in the circuit does work, transferring energy electrically from the power supply to the heaters thermal energy store.
This causes the material’s temperature to increase.
Take readings as the block heats up of the temperature and current every 10 minutes.
The reading though the current shouldn’t change.
After 10 readings, turn off the power supply.
Using your measurements of the current, and the potential difference of the power supply, you can calculate the energy transferred to the heater. E=Pt
You can then plot a graph of energy transferred to the thermal energy store of the block against temperature.
To find the gradient you can use the equation Change in Temperature / Change in Energy
To calculate the specific heat capacity do 1/(gradient x the mass of the block).
You can then repeat the experiment with different materials to see how their specific heat capacity compares.
1.4-Conservation of Energy and Power
The Conservation of energy principle:
Energy can be transferred usefully, stored or dissipated but can never be created or destroyed.
When energy is transferred between stores, not all the energy is transferred usefully(where you want it to go). Some energy is always dissipated when an energy transfer takes place.
Dissipated is sometimes called ‘wasted energy’, because the energy is being stored a way that is not useful(usually energy has been transferred into the thermal energy store).
Example:
A mobile phone is a system.
When you use the phone, energy is usefully transferred from the chemical energy store of the battery in the phone.
But some energy is dissipated in this transfer to the thermal energy store of the phone(that’s why it feels warm after a while).
Understand to describe energy transfers of a closed system(does not allow transfer of matter in and out the system):
A cold spoon is dropped into an insulated flask of hot soup, which is sealed.
If you assume the flask is a perfect thermal insulator so the spoon and soup form a closed system.
Energy is transferred from the thermal energy store of the soup to the useless thermal energy store of the spoon(causing the soup to cool down slightly).
Energy transfers have occurred within the system, but no energy has left the system- so the net energy is zero.
Power is the ‘rate of doing work’-i.e. how much per second
Power is the rate of energy transfer, or the rate of doing work.
Power is measured in watts. One watt = 1 joule of energy transferred per second.
Equation P=E/t or P=W/t
Power(watts) = Energy transferred(J) / time(s) or Power(watts)=Work done/time(s)
A powerful machine is one which transfers a lot of energy in a short space of time.
I.e In a car the faster one is the one that transfers the same amount of energy in less time.
Example:
It takes 8,000J of work to lift a stunt performer to the top of a building. Motor A can lift the performer in 50s. Motor B would take 300s to lift the performer. Which motor is more powerful?
1.5-Conduction and Convection
Conduction occurs mainly in solids
Conduction is the process where vibrating particles transfer energy to neighbouring particles.
Energy transferred to an object by heating is transferred to the thermal store of the object.
This energy is shared across the kinetic energy stores of the particles in the object.
The particles in the part of the object being heated vibrate more and collide with each other.
These collisions cause energy to be transferred between particles’ kinetic energy stores.
This is conduction.
This process continues throughout the object until the energy is transferred to the other side of the object.
It’s then usually transferred to the thermal energy store of the surroundings(or anything else touching the object).
Thermal conductivity is a measure of how quickly energy is transferred through a material in this way.
Materials with a high thermal conductivity transfer energy between their particles quickly.
Convection occurs only in liquids and gases
Convection is where energetic particles move away from hotter to cooler regions.
Convection can happen in gases and liquids.
Energy is transferred by heating to the thermal store of the liquid or gas.
This energy is shared across the kinetic energy stores of the gas or liquid’s particles.
Unlike in solids, the particles in liquids and gases are able to move.
When you heat a region of a gas or liquid, the particles move faster and the space between individual particles increases.
This causes the density of the region being heated to decrease.
Because liquids and gases can flow the warmer and less dense region will rise above denser, cooler regions.
If there is a constant heat source, a convection current can be created.
Radiators create convection currents
Heating a room with a radiator relies on creating convection currents in the air of the room.
Energy is transferred from the radiator to the nearby air particles by conduction(the air particles collide with the radiator surface).
The air by the radiator becomes warmer and less dense, as the particles move quicker.
This warm air rises and is replaced by cooler air, which is then heated by the radiator.
At the same time, the previously heated air transfers energy to the surroundings, like the walls and contents of the room. It cools and becomes denser and sinks.
This cycle repeats, causing a flow of air to circulate around the room- this is a convection current.
1.6-Reducing Unwanted Energy Transfers
Lubrication reduces frictional forces
Whenever something moves, there’s usually at least one frictional force acting against it.
This causes some energy in the system to be dissipated,
e.g. air resistance can transfer energy from a falling object’s kinetic energy store to its thermal energy store.
For objects that are being rubbed together, lubricante can be used to reduce the friction between the object’s surfaces when they move.
Lubricants are usually liquids(like oil), so they can flow easily between objects and coat them.
Insulation reduces the rate of energy transfer by heating
There are a few things you can do to prevent energy lost:
Have thick walls that are made from a material with a low thermal conductivity.
The thicker the walls and the lower their thermal heat conductivity, the slower the rate of energy transfer will be(so the building will cool more slowly).
Use thermal insulation, such as:
Have cavity walls, which are made up of an inner and outer wall with an air gap with air in the middle, this reduces the amount of energy transferred by conduction through walls.
Loft insulation can reduce convection currents.
Double-glazed windows-air gap between two sheets of glass to prevent energy transfer by conduction.
Draught excluders around doors and windows to reduce energy transfers by convection.
Investigate the effectiveness of materials as thermal insulators:
Boil water in a kettle. Pour some of the water into a sealable container(e.g. a beaker and lid) to a safe level.
Measure the mass of water in the container.
Use a thermometer to measure the initial temperature of the water.
Seal the container and leave it for five minutes. Measure this time using a stopwatch.
Remove the lid and measure the final temperature of the water.
Pour away the water and allow the container to cool to room temperature.
Repeat, but wrap the container in a different material.
You could investigate how the thickness of the material affects how good a thermal insulator it is.
Results:
You should find that the thicker the insulating layer, the smaller the temperature change of the water, and so the less energy is transferred. This means thicker layers make better thermal insulators.
1.7-Efficiency
Most energy transfers involve some waste energy
Useful devices are only useful because they can transfer energy from one store to another.
The less energy that is ‘wasted’ in this energy store, the more efficient the device is said to be.
You can improve the efficiency of energy transfer by insulating objects, lubricating them or making them more streamlined.
The efficiency for any energy transfer can be worked out using:
Efficiency=Useful output energy transfer / Total input energy transfer
You don’t need to know energy inputs and outputs as long as you know the power input and output:
Efficiency=Useful power output / Total power input
Useful energy output isn’t usually equal to total energy input:
NO device is 100% efficient and wasted energy is usually transferred to useless thermal energy stores
.However, electric heaters are the exception as they’re usually 100% efficient because all the energy in the electrostatic energy store is transferred to 'useful energy store’.
1.8-Energy Resources and their Uses
Energy resources, both renewable and non-renewable, are mostly used to generate electricity
Non-Renewable Energy Resources will run out one day:
Non-Renewable energy resources are fossil fuels and nuclear fuel(uranium and plutonium).
Fossil fuels are natural resources that form underground over millions of years.
Normally, burnt to provide energy.
The three main fossil fuels are:
Natural Gas
Coal
Oil
They all:
Will run out some day
Do damage to our environment
But they provide most of our energy
Renewable energy resources will never run out:
Renewable energy resources are:
Wind
Solar
Water-waves
Hydro-electricity
Bio-fuel
Tide
Geothermal
These will never run out-they energy can be renewable as it is used
Most of them do damage the environment, but in less significant ways than non-renewable energy
Problem is they dont provide much energy and some are unreliable because they depend on the weather
Energy Resources can be used for transport
Transport in the most obvious thing where fuel is used.
There are non-renewable energy resources:
Coal is used in some old-fashioned trains to boil water to produce steam
Petrol and diesel powered vehicles use fuel created from oil
There are also renewable energy resources:
Vehicles that run on pure bio-fuel or a mix of a bio-fuel and petrol or diesel(only the bio-fuel bit is renewable)
And for heating:
There are non-renewable energy resources:
Coal is commonly burnt in fireplaces
Natural gas is the most widely used fuel for heating homes in the UK.
The gas is used to heat water, which is then pumped into radiators throughout the home
Electric heaters(or storage heaters) use electricity generated from fossil fuels
There are also renewable energy resources:
A geothermal heat pump used geothermal energy resources
Solar water heaters work by using the sun to heat water which is then pumped into radiators
Burning bio-fuel/using electricity generated from renewable resources can also be used
1.9-Wind, Solar and Geothermal
Renewable energy resources, such as wind, solar and geothermal will never run out.
However, they don’t generate as much power
Wind Power-Lots of Little Wind Turbines
Involves putting lots of wind turbines up in exposed places like on moors or round coasts
Each turbine has a generator inside it-the rotating blades turn the generator and produces electricity
There’s no pollution, except for when they are manufactured
However they do spoil the view, as you need 1,500 to replace one coal-fired power station, which would effect the scenery
They can also be very noisy, annoying people that live nearby
They also stop working when the wind stop or if its too strong meaning its impossible to increase supply when demand is high.
On average, they produce electricity 70-85% of the time.
The initial costs are quite high, but there are no fuel costs and little maintenance costs
Also there’s no permanent damage to the landscape, as they don’t leave a mark
Solar Cells-Expensive but No Environmental Damage
Solar cells generate electric currents directly from sunlight.
Solar cells are often the best source of energy to charge batteries in calculators and watches which don’t use much electricity.
Solar power is often used in remote places where there’s not much choice, such as the Australian outback) and to power electric road signs and satellites
There’s no pollution, although they use energy to produce
In sunny countries solar power is a very reliable source, but only in daytime.
However, it can also be cost-effective in cloudy countries like Britain
Like wind, you can’t increase power output when there is high demand
Initial costs are high but after that the energy is free and running costs almost zero
Solar cells are used to generate electricity on a small scale
Geothermal Power-Energy in Underground Thermal Energy Stores
This is possible in volcanic areas or where hot rocks lie quite near the surface.
The source of much of this energy is the slow decay of various radioactive elements, including uranium, deep inside the Earth
This is actually free energy that is reliable and does very little damage to the environment
Used to generate electricity or heat buildings directly
The main drawbacks are that there aren’t many suitable locations and the cost of building one is high compared to the amount of energy it produces
1.10-Hydro-electricity, Waves and Tides
Hydro-electric Power uses Falling Water
Hydro-electric power usually requires the flooding of a valley by building a big dam.
Water is allowed out through turbines. There is no pollution.
But theres a big impact on the environment due to the flooding, rooting vegetation releases methane and CO2, and possible loss of habitat for some species.
The reservoirs can also look very ugly when they dry up.
Putting hydroelectric power stations in remote villages tends to reduce their impact on humans.
A big advantage is it can provide an immediate response to an increased demand for electricity
There’s no problem with reliability except in times of drought-but remember this is Great Britain we’re talking about
Initial costs are high, but there are no fuel costs and minimal running costs
It can be a useful way to generate electricity on a small scale in remote areas
Wave Power-Lots of Little Wave-Powered Turbines
You need lots of small wave-powered turbines located around the coast.
Like with wind power, the moving turbines are connected to a generator.
There is no pollution.
The main problems are disturbing the seabed and the habitats of marine animals, spoiling the view and being a hazard to boats.
They are fairly unreliable, since waves tend to die out when the wind drops
Initial costs are high, but there are no fuel costs and minimal running costs.
Wave power is never likely to provide energy on a large scale, but it can be very useful on small islands.
Tidal Barrages-Using the Sun and Moon’s Gravity
Tides are used in lots of ways to generate electricity.
The most common method is building a tidal barrage
Tidal barrages are big dams built across river estuaries, with turbines in them.
As the tide comes in it fills up the estuary. The water is then allowed out through the turbines at a controlled speed.
Tides are produced by the gravitational pull of the Sun and Moon
There is no pollution.
The main problems are preventing free access by boats, spoiling the view and altering the habitat of the wildlife.
Tides are pretty reliable as they happen twice a day without fail.
The only drawback is that the height of the tide is variable so lower tides will provide significantly less energy than the bigger spring tides.
They also don’t work when the water is the same either side of the barrage-this happens four times a day because of the tides
Initial costs are moderately high, but there are no fuel costs and minimal running cots.
Even though it can only be used in some of the most suitable estuaries tidal power has the potential for generating a significant amount of energy.
1.11-Bio-fuels and Non-renewables
Bio-fuels are made from Plants and Waste
Bio-fuels are renewable energy resources created from either plant products or animal dung. They can be solid, liquid or gas and can be burnt to produce electricity or run cars in the same way as fossil fuels
Are supposedly carbon neutral, although there is some debate about this as its only true if you are planting plants at the rate you a burning things
Bio-fuels are fairly reliable, however they cannot respond to immediate energy demand. To combat this, they are continuously produced
The cost to refine bio-fuels is very high and some worry that growing crops specifically for bio-fuels will mean there isn’t enough space or water for crops for food
In some regions, large areas of forest have been cleared to make room for bio-fuels, resulting in lose of habitat and increasing methane and C02 emissions
Non-Renewables are Reliable
Fossil fuels and nuclear energy are reliable. There’s enough to meet current demand and can respond to changes in demand.
However, they are slowly running out.
While the set-up costs of power plants can be quite high, the running costs aren’t.
But they create Environmental Problems
Coal,oil and gas release CO2 into the atmosphere when they’re burnt. All this CO2 adds to the greenhouse effect, contributing to global warming
Burning coal and oil also release sulfur dioxide, which causes acid rain-which can be harmful to trees and soils
Acid rain can reduced by taking the sulfur out before the fuel is burned or cleaning up the emissions
Coal mining makes a mess of the landscape
Oil spillages cause serious environmental problems, affecting mammals and birds that live in and around the sea
Nuclear power is clean but the waste is very dangerous and difficult to dispose of and carries the risk of a major disaster
1.12-Trends in Energy Resources Use
Currently we still depend on Fossil Fuels
Over the 20th century the electricity use of the UK hugely increased as the population grew and people began to use electricity for more and more things
Since the beginning of the 21st century, electricity use in the UK has been decreasing(slowly), as we get better at making appliances more efficient and become more careful with energy use in our homes
Most of our electricity is produced using fossil fuels and from nuclear power
Generating electricity isn’t the only reason we burn fossil fuels-oil(diesel and petrol) is used to fuel cars, and gas is used to heat homes and cook food
However, we are trying to increase our use of renewable energy-the UK pledged to use renewable energy for 15% of yearly energy use). This move towards renewable energy resources has been triggered by many things…
People want to use More Renewable Energy Resources
We now know that burning fossil fuels is very damaging to the environment. This makes many people want to use more renewable energy resources that affect the environment less
People and the government are also becoming increasingly aware that non-renewables will run out one day. Many people think it’s better to learn to get by without non-renewable before this happens
Pressure from other countries and the public has meant governments gave begun to introduce targets for using renewable resources. This in turn puts pressure on energy providers to build new power plants that use renewable resources to make sure they do not lose business and money
Car companies have also been affected by this change in attitude towards the environment. Electric cars and hybrids are already on the market and their popularity is increasing
The use of Renewables in Limited by Reliability, Money and Politics
There’s a lot of scientific evidence supporting renewables, but although scientists can give advice, they don’t have the power to make people, companies or governments change their behaviour
Building new renewable power plants cost money, so some energy providers are reluctant to do this, as its more expensive
Also some people don’t like living near them and there’s a question about whether its ethical
Also there not as reliable and we would have to research new ways which is expensive