Physics
Double Award
Double Award
Cambridge IGCSE
TOPIC 1B: ENERGY and PRESSURE
Much of the energy we use at home is transferred as electrical energy. But where does this electrical energy come from? What about the energy we use for transport and heating? In this section, you will learn about the wide range of energy resources available to us, and the advantages and disadvantages of each one. You will also learn about the energy transfers involved in each resource.
The vast majority of the energy we use comes from burning fossil fuels - coal, oil and natural gas. These fuels are made from the fossilised remains of plants and animals created millions of years ago. It takes a long time to produce fossil fuels, so once we use up our fossil fuel resources, they will be effectively gone for the foreseeable future. These are called non-renewable resources.
Our transport system relies heavily on the combustion of petrol and diesel from fossil fuels, and converting the stored chemical energy into kinetic energy. Fossil fuel power stations produced electricity from fossil fuels. The video below outlines how this process works:
Youtube - How a power station works (energynownews)
As can be seen from the video, fuel is burned, transferring chemical energy in the fuel to thermal. This thermal energy is used to produce steam. This produces mechanical work on the turbine and generator, making it spin quickly (kinetic energy) and then generating electrical energy for transfer to our homes.
Fossil fuel power stations can produce a large power output, 24 hours a day. For this reason, the majority of the World's electrical energy is still produced in this way. However the fossil fuels will run out eventually, and they are highly polluting, contributing to the greenhouse effect and global warming. Power stations using gas are more efficient and less polluting than coal. Scientists and engineers are working hard to move away from our reliance on fossil fuels and seeking alternative energy sources.
There are three methods used to generate electricity using water:
1. The most widely used of these is a hydroelectric power station. This uses the G.P.E. stored in water that is held in a dam high up above the river below, as shown in figure 1.
Figure 1. Hoover Dam, USA - hydroelectric plant
Energy stored as G.P.E. transfers to kinetic energy as it flows down through pipes to turbines and a generator, which convert this to electrical energy.
The process is very efficient and there is no pollution produced. A large dam has a high power output and works 24 hours a day. This energy resource is renewable and will not run out like fossil fuels. However, there is an environmental impact in building such a large structure across the river, affecting wildlife and flooding a large area upstream.
2. A tidal power station uses the rising and falling of water in the sea to generate electricity. The tides are produced by the gravitational pull of the Moon and Sun on the seas, and the original source of this energy is the vast quantity of kinetic energy stored in the motion of the Earth and Moon. A tidal power station traps high tide water, and otherwise works in exactly the same way as a hydroelectric power station. Only a few regions in the world have a high enough tide for an effective power station. Otherwise, the advantages and disadvantages are very similar to hydroelectric power.
3. Waves at sea are produced by the wind blowing across the water surface, and winds are caused by convection and heat from the Sun, as discussed in section 4.4. Wave power stations have very different designs, but all of them tap in to the stored gravitational energy created with tall waves moving across the sea. This height difference between the top and bottom of the wave can produce mechanical work that drives a generator, producing electrical energy. Wave power stations are renewable and pollution-free, but are unreliable and do not generate power every day of the year. They are not widely used at the moment as the power output is small, and costs are high.
Solar heating systems consist of water-filled black panels. Heat from the Sun warms the panels, and the hot water can be used directly, for central heating systems or for hot water at home. This is an efficient way to use the radiant heat energy from the Sun, but is not that reliable - it only works well on sunny days!
Solar panels as shown in figure 2 work in a different way. They convert sunlight directly into electricity using silicon crystals. These panels contain smaller photovoltaic cells which generate a current.
Solar panels have the advantage of creating electricity directly from light (although this process is not very efficient). They are also non-polluting and a renewable resource. Large amounts of panels are needed to generate a significant power output, and they are expensive. Also, they need a sunny day, will not work 24 hours a day.
Figure 2. Solar cells
Wind turbines are becoming a common feature around the world. They are relatively cheap to produce for a renewable resource, and a large number of wind turbines in a 'wind farm' can generate a significant power output. Wind is produced by convection currents from the Sun's radiant heat and light. The kinetic energy in the wind turns the turbine blades and generator directly, thus producing electricity. This is a relatively simple process so is quite efficient, and pollution-free. However, some people do not like the visual impact of so many wind turbines on the top of surrounding hills, and they can be noisy if you live nearby. They are also unreliable -they do not give a constant output day to day as the wind varies.
Many locations in the world like Hawaii and Iceland are volcanic - there are active volcanoes on the islands and geothermal activity underground. In these locations, steam can be generated by pumping cold water underground, instead of burning fossil fuels. The jets of steam coming back to the surface can then drive generators and produce electricity. The Earth's core should have cooled down billions of years ago, but is kept hot by nuclear decay of radioactive substances. (See topic 7). Therefore, geothermal power is using radioactive decay in the Earth as it's source of energy. This nuclear energy store is converted to thermal energy, and then kinetic energy as the hot steam does mechanical work on the generator. Finally it is converted to electrical energy for transfer to our homes.
Geothermal power stations work 24 hours a day and are reliable, with a high output. The hot water produced can also heat homes directly, as it does in Iceland. No pollution is produced and it is a renewable resource. (The radioactive isotopes underground stay active for billions of years).
However, only a few countries can realistically use geothermal power safely. It is not an option for most countries in the world.
Figure 3. A geothermal power station, Iceland
A nuclear power station works in much the same way as a fossil fuel power station. The key difference is that nuclear fuel stores nuclear energy that is then used to produce heat energy. You will learn more about nuclear fuels in topic 5. The heat produced then boils water to make steam and drive a turbine and generator, generating electrical energy.
Nuclear power stations have a huge power output and are also reliable, working 24 hours a day. They do not produce any gases or other pollution that contributes to global warming. However, the nuclear fuel waste is highly radioactive and is dangerous for thousands of years, making it extremely difficult to dispose of. In addition, there have been several serious accidents at nuclear power plants, and many people believe nuclear power is too dangerous to be used widely. Nuclear fuels are also non-renewable, and will eventually run out if widely used.
When an unstable heavy nuclei like uranium decays, it slowly releases energy. In a chain reaction, it is forced to disintegrate by a collision. Both these processes involve the release of energy from the splitting of a heavy nuclei, and we call this nuclear fission. However, nuclear fusion is quite different.
Heavy nuclei are held together by a strong force like a nuclear glue. This force only acts over a short range. If you can get two light nuclei close together, then this force makes them snap together like strong magnets, and this releases energy. The energy comes from a small quantity of mass that is lost in the process, and converted to energy.
This process - of light nuclei fusing together - is called nuclear fusion. It only works with light nuclei like hydrogen and helium, and only when they are put very close together. Unfortunately, these nuclei have protons in them that repel each other, so they really do not want to be close together! The electrostatic repulsion works over longer distances, so initially the protons repel unless they are forced very close together.
Fusion needs very high pressures and temperatures. This makes light nuclei move very fast and close together, causing some to fuse. This is the energy source that keeps the Sun and all stars producing heat and light! The temperature needed to do this for hydrogen in stars is millions of degrees Celcius, and even then the process is slow.
One day, physicists hope to be able to generate electricity using fusion - we could even use the hydrogen from water to do this which would be pollution free! Unfortunately, fusion will not work at low temperatures and pressures. The experimental reactors being built require dangerously high temperatures and the fuel inside will melt any container if it touches the sides. This is still a work in progress.....!
Figure 5: An experimental fusion reactor.
Oak Ridge Labs (CC by 2.0 licence)
Note that nearly all of the energy resources listed above rely on energy from the Sun as the original source. For example, coal comes from the fossilised remains of plants and animals. The animals ate plants, and all plants get their energy from the Sun.
The only sources that DO NOT use energy originally from the Sun are:
Questions:
1. The table below gives some information about nuclear power.
| Energy Resource | Renewable or non-renewable? | One Advantage | One Disadvantage |
|---|---|---|---|
| Nuclear | Non-renewable | High power output | Nuclear waste is difficult to dispose of safely. |
| Coal | |||
| Wind |
Complete the rows in the table for coal and wind energy. Add one advantage and one disadvantage for each row. (Do not include 'renewable' and 'non-renewable' in the advantages / disadvantages columns).
| Energy Resource | Renewable or non-renewable? | One Advantage | One Disadvantage |
|---|---|---|---|
| Nuclear | Non-renewable | High power output | Nuclear waste is difficult to dispose of safely. |
| Coal | non-renewable | One of: |
One of: |
| Wind | renewable | One of: - non-polluting - Cheap (for renewable) -efficient |
One of: Unreliable /does not work every day of the year /only works when windy Large numbers of turbines needed to generate high power output -visual pollution |
*Top tip - try to complete this table for all the energy resources when you are revising.
2. Describe the energy transfers that take place in a hydroelectric power station.
Water high up behind the dam has stored gravitational energy / G.P.E.
It flows downhill, moves quickly through the turbines and making the generator spin, which is kinetic energy.
The generator produces electrical energy for transfer.
(There is some wasted thermal energy lost to the surroundings).
3. Electricity can be generated in many ways. State two advantages of using geothermal power to generate electricity.
Any two advantages from:
Now test your understanding using these quick, 10 minute questions on this topic from Grade Gorilla:
