Mains electricity

  • Where does mains electricity come from?
  • What are fossil fuels and how did they form underground?
  • Why should we save energy and how can we do it?
  • Why are illegal electrical connections so dangerous?
  • What is the difference between renewable and non-renewable energy resources?

This unit lends itself to searching for information, pictures, simulations and videos on the Internet, in the Library, in magazines and books. The basic information about the main topic is provided here, but teachers and learners should explore the topic further.

We are so used to switching on electrical appliances that we hardly think what makes it possible to have these things. Our focus turns to appliances that need a mains electrical supply. You have listed examples like a television, a computer, a kettle and many others before.

The big question here is `Where does mains electricity come from?'

Fossil fuels

A battery has stored energy which can provide electrical energy. However, our homes, schools, shops and factories cannot run on batteries because they cannot store or provide large amounts of energy. We use electricity every day. The main supplier of electrical energy is from power stations. We call this `mains electricity'. Power stations also need a source of energy to make electricity. In South Africa, this is mostly from fossil fuels.

What are fossil fuels?

Coal, oil and natural gas are fossil fuels. Some people think that fossil fuels are the remains of dead dinosaurs but this is not true! Actually, most of the fossil fuels we find today were formed millions of years before even the first dinosaurs. Fossil fuels were once alive!

Do you remember learning about fossils in Gr. 5 Earth and Beyond? Write down what you think a fossil is.

A fossil is the remains of a dead organism (plant or animal) from millions of years ago.

So fossil fuels are actually the remains of prehistoric organisms that lived millions of years ago!

Wow, that's amazing! So the coal we burn was actually a real tree millions of years ago?!

Yes, that is right Jojo. But different fossil fuels come from different organisms and formed in slightly different ways.

Let's take a trip back in time, millions of years ago!

This activity is meant as a comprehension for reading appreciation. Ideally the learners should read the text themselves and then answer the questions that follow. The ability to read a lot of text, identify the main facts, and then answer questions or summarise text is an important skill.


  • Read the text below about how fossil fuels were formed and study the pictures
  • Then answer the questions that follow.

300 million years ago...

Think about what the Earth must have looked like back then! There were swamps and marshes everywhere and it was warmer than it is today. Ancient trees, ferns and plants grew everywhere. Very weird looking animals roamed the earth, and even stranger looking fish lived in the rivers and deep in the oceans and seas.

An ancient, prehistoric world

When these prehistoric plants and animals died their bodies their bodies decomposed just in the same way as organisms decompose today. The dead organisms became buried under layers and layers of mud, rock, sand and water. Over time, these layers built up and became very deep and they pushed down with a great pressure on the layers below it.

Millions of years passed, and the dead plants and animals slowly decomposed and formed fossil fuels. Different types of fossil fuels were formed depending on different factors. For example, whether it was the remains of plants or animals or a combination and how long the remains of the organisms had been buried for. The type of fossil fuels that formed also depended on the temperature and pressure conditions during the decay of the organisms.

Oil and natural gas

Oil is a dark, thick liquid that can be used to make petrol to burn in vehicles, such as cars, buses and trucks. Natural gas is colourless and it is used mostly in homes for heating and cooking food.

Oil and natural gas formed from organisms (plants and animals) that lived in the oceans before there were dinosaurs. When these organisms died, they settled on the bottom of the river bed or ocean floor and the layers built up under mud and sand (silt). The mud and sand slowly changed into rock and the rock and water pressure pushed down on the remains of the dead plants and animals.


Over millions of years of being under heat and pressure, the dead plants and animals changed into a thick liquid, called crude oil. In deeper, hotter places tiny bubbles of natural gas formed. These were trapped under the rocks.

Over time, some of the oil and natural gas began to work its way up through the rock and to the Earth's crust and into rock formations called `caprocks'. Today, most of the oil and natural gas is collected from these caprocks by drilling down through the layers of rock.


Coal is a black rock that can be burnt to produce energy in power stations all over the world.

Coal was formed from the dead remains of trees, ferns and some other plants that lived 300 to 400 million years ago. This was when the Earth was mostly covered in swampy forests. These kinds of plants were very different to the plants that we get today. Over time, the layer of dead plants at the bottom of swamps was covered with layers of water and mud. The top layers squashed down on the dead plants. Over millions of years the heat and pressure turned the plants into the coal that we mine today.

Ferns were very common in the prehistoric world of plants.
Much of the Earth was covered in swamps millions of years ago.

The energy in coal originally comes from energy from the Sun. Plants on Earth used the energy of the Sun for photosynthesis and to grow. This energy was stored in the leaves, flowers and stems of the plants. As the plants died the energy was trapped.


What are the three fossil fuels discussed in the above story.

coal, oil and natural gas

The organisms that fossil fuels were formed from lived many years ago and are different to the organisms that we get today. How many millions of years ago was this?

300 million years ago

The dead organisms are covered in sediments over time. Do you remember learning about sediments in Gr. 5 Earth and Beyond and how sedimentary rock forms? Write a description of what sedimentation is.

Sedimentation is when particles (either sand, rock, or organic material) settle on the bottom of a river or the ocean floor and over time form layers which begin to compact.

What are the two main factors which turned the remains of organisms into fossil fuels deep under the layers of rock and mud?

high pressure and heat

Explain why we say that all our energy originally comes from the sun, even in fossil fuels.

The organisms that fossil fuels are made from lived millions of years ago. The plants used the Sun's energy to make food by photosynthesis. When they died this energy was trapped in the plants' remains which then turned into fossil fuels. The animals that ate the plants got their energy indirectly from the Sun through the plants. When these tiny animals died, the energy was also trapped in their remains which became fossil fuels.

Do you remember learning about the states of matter in Matter and Materials. Each of the three fossil fuels discussed here is a different state of matter. Say what they are.

coal - solid, oil - liquid, natural gas - gas

The process of coal formation and natural gas and oil formation have similarities, but also differences. Draw a table where you compare these two processes. Give your table a heading.

Possible answers:

A comparison of the process of coal formation, and natural gas and oil formation (different fossil fuels)

Coal formation

Oil and natural gas formation

Millions of years ago that the organisms died to start forming fossil fuels

300 million years

300 million years

Organisms from which fossil fuel is formed

Plants (trees, ferns and other plants)

Tiny plants and animals

Place where organisms lived and died


Water - mostly oceans and rivers

Layers that remains were covered in

Sand, mud, water

Sand, silt, water

Factors which contributed to formation

High pressure and heat

High pressure and heat

State of matter of fossil fuel formed

Solid coal

Oil - liquid, Natural gas - gas

The way we obtain the different fossil fuels is also different. Coal is usually obtained by digging mines into the rock and sand to reach the coal deposits deep under the surface. This creates a huge hole in the surface of the earth as you can see in the photograph of a mine.

A coal mine
An oil rig in the ocean which sinks a drill into the ocean floor to reach the oil deposits

Oil and natural gas is obtained by drilling down through the rock. A hole is sunk with a huge drill so that the oil and natural gas can be reached and then brought up to the surface. This normally takes place in the ocean, as you can see in the oil rig in the photo.

  1. Search the Internet to find out which countries in the world have large quantities of coal, oil and natural gas.

  2. Search the Internet to find out which three countries in the world use the most fossil fuels.

So we have spoken about fossil fuels and energy, but how do we then get electrical energy from fossil fuels?

That is a great question Jojo! A good scientist always asks questions!

Fossil fuels and electricity

The main supplier of electricity in South Africa is ESKOM. ESKOM uses mainly coal to produce energy for industrial and household use.

Let's look at a power station to find out how coal is used to produce electricity.

Look at the diagram and the steps which outline the process to make electricity from coal:

  1. Coal is transported from a coal mine to a power station.
  2. At the power station, the coal is ground into a fine powder (pulverised).
  3. The ground coal then goes into a container where it is burned.
  4. The heat generated from the burning coal is used to boil water in a huge boiler.
  5. The boiling water produces steam that turns a turbine (a turbine is a big wheel which turns).
  6. The turbine is linked to a generator which uses a coil to produce energy.
  7. From the generator the electric current is transported ("carried") by a system of electrical transmission lines (also called power lines) and substations to our homes.
The process of making electricity from coal in a power station

Make a poster to trace the source of our electricity


  • poster size paper or cardboard
  • colour pens or pencils


  1. Design and make a poster for your classroom on which you illustrate the chain of objects and processes that allow us to use an appliance in our homes (such as a television set, stove or refrigerator).
  2. Start with a picture or drawing of the Sun in the top left corner and end with the appliance in the bottom right corner of the poster.
  3. Use arrows to show the sequence of objects and processes.
  4. Label each object or process on your poster.
  5. Decide on a heading for your poster and write it in big letters at the top.

The sequence should be something like sun → plants and animals → fossil fuels (coal) → power station → electricity → delivery to home on power lines → TV (or other appliance).

Fossil fuels are non-renewable resources of energy. This is because they take millions of years to form. Once these fuels are burnt, they cannot be recovered or reused. They are non-renewable.

A learner's conception of `millions of years' might not be well grounded. Fossil fuels are not renewable because we use them up far quicker (in a few centuries) than they can form (millions of years). This point will be lost if learners can not distinguish between hundreds and millions. This should be addressed by the teacher to focus on meaning of hundreds and millions.

People on Earth are using up these deposits of fossil fuels much, much faster than they are being made as they take millions of years to be made! Look at the diagram of a power station again. Do you see the smoke that is given off when the coal is burnt? This causes huge environmental concerns as it is polluting our atmosphere. A bit later in this chapter we will look at other ways of producing energy which, unlike fossil fuels, are renewable.

Cost of electricity

Do you hear your parents and other adults talk about the cost of living? Do they remind you to switch off lights and other appliances that are not in use? Electricity is an expensive resource!

A learner might make the reasonable point that the coal is burnt anyway, whether you leave that light on or not. But, the point is to show that cumulatively, saving electricity can have an effect on reducing demand on power stations, and it also reduces the amount that your individual household spends on electricity if you use it efficiently.

Why is electricity expensive?

Electricity is costly because:

  • The production and delivery of electricity requires infrastructure (the structures and facilities) like coal mines, trucks and trains to transport coal, power stations, substations and wiring.
  • All of these buildings, structures, materials and processes are very expensive to build and maintain.
  • Some electrical appliances require a lot of energy, much more than others. For example, a geyser uses a lot of electricity to heat the water and so it becomes expensive.

When electrical energy enters your home, it must pass through a meter. Have you ever seen a white box outside your house? This is the electricity meter. A worker from the city council reads the meter so that they will know how much electricity you used. They then bill you for the cost. The more electricity we use, the more we pay and the more we use up fossil fuels. Some houses now have pre-paid electricity meters where you pay for your electricity before you use it.

This is an electricity meter. Can you see the number recording the electricity usage in kilowatt hours (kWh)?

Running electrical appliances

We already mentioned that some electrical appliances use more electricity to run than others. Appliances that heat use the most energy, such as a geyser or heater. How do we know which electrical appliances use more electricity?

Energy required by electrical appliances and devices

This could be an individual task, each learner should look for this information so that they become familiar with looking for ways to save energy.

This is how we find out!


  1. Find the appliances or devices listed in the table. If you do not have them in your home or school, ask family, friends or neighbours if you could look at theirs.
  2. Have a look at each appliance and check for a label with information like the one below. This information is usually at the back or the bottom of the appliance.

230 V - 240 V; 50 Hz; 2 kW

  1. Record the number that is followed by a W or kW on the label in column 2 of the table. This number indicates how much energy is required by the device in a certain time. It is called the power required by the device. We measure power in watt (W) or kilowatt (kW). The higher the value the more energy the device uses in a specific time.

Make the link between the unit W and kW where a kilowatt is 1000 watts. Similarly, metre (m) and centimetre (cm) and gram (g) and kilogram (kg). As well as metre and millimetre (mm) and ampere (A) and milliampere (A).

  1. Add any other three appliances or devices to the list.
  2. Record all the power values in column 3 in watt. If the power is given in kW, multiply this number by 1000 to get the value in watt (W).

    For example: 2 kW \times 1000 = 2000 W

    If the device does not show a value in W or kW, look for two quantities given in volt (V) and milliampere (mA). Multiply these two numbers and then divide the answer by 1000 to get the power in watt.

    For example: \(\text{240}\) V \times \(\text{150}\) mA = \(\text{36\ 000}\) W

    \(\text{36\ 000}\) \div \(\text{1000}\) = \(\text{36}\) W

You divide by 1000 to correct for using mA instead of A. Power (W) = voltage (V) \times current (A)

Appliance or device

Power in W or kW

Power in watt (W)

Cellphone charger

Electric kettle

Television set

Light bulb (old type)

Energy saving light bulb


Electric iron

Teacher note: The values in the table are not exact, but the order of magnitude should be similar.

Appliance or device

Power in W or kW

Power in watt (W)

Cellphone charger

240 V and 150 mA

36 W

Electric kettle


2000 W

Television set

60 W

60 W

Light bulb (old type)

100 W

100 W

Energy saving light bulb

15 W

15 W


230 V and 500 mA

115 W

Electric iron

1.4 kW

1400 W

Now arrange the appliances in the next table in terms of the power required. The list should be from small to large values of the power.

Appliance or device

Power in watt (W)


What do you see in this table? Which two appliances have the lowest power requirements? What do these appliances have in common?

Possibly the cellphone charger and energy saving bulb. They are small and only require a small amount of energy to work. The bulb is built specifically to use less energy.

Which two appliances have the highest power requirements? What do these appliances have in common?

Possibly the kettle and iron (or any other heating device): they are used to produce heat which uses a lot of electrical energy.

Saving electricity

Just when I am ready to run outside, my mom often makes me come back to turn my bedroom light off.

Good for her, Jojo! Electricity is expensive so we should try and save electricity.

This is not the only reason to try save electricity. Remember when we spoke about the pollution given off by coal power stations? Why else do you think it is important to try save energy and reduce your power usage?

The burning of coal in power stations produces carbon dioxide, a greenhouse gas, which contributes to global warming. If enough people reduce electricity usage in their homes, this will reduce the demand on coal power stations, meaning they have to burn less coal, which will in turn have less of an environmental impact.

There are many different ways to save electricity, from small actions, to larger actions, such as using renewable energy resources. We will discuss this a bit later in the chapter.

How can you prevent wastage of electricity in your home? Name four possible ways.

Use energy saving light bulbs, install a solar water heater, switch off all electrical devices that are not in use, and use as little hot water as possible.

Illegal connections

We discussed a world without electricity and we all realised how dependent we are on this resource. It is illegal for anyone to use electricity that was generated by ESKOM without their permission. Some people make illegal connections because they don't want to pay for the electricity. They cut through the insulation in a power line and attach other cables to this line. They can then direct some electricity to their house or workplace. These connections are dangerous to people as they are often unsafe.

People who make illegal connections try to get electricity for free but the dangers are not worth it. It is not worth your life!

Look at this mess of illegal electrical connections.

Electricity and safety

Accidents caused by electricity happen all the time. People often get hurt or even killed by electricity because they do not use it safely. Not only is it important to know how to use electricity safely, but also what to do if someone is hurt or shocked by electricity.

What types of emergencies can happen at home or at school with electricity?

Someone could get a shock on a plug or exposed wire, someone could put an electrical appliance in or near water and get a shock, there could be a power outage and when someone is trying to fix the problem, they could get shocked, etc

Find out about the emergency services in your area and write down their names and telephone numbers. Also write this information on a piece of paper and stick it to the wall next to your phone or in a central place in your home.

Consider inviting an electrician to talk about electricity and safety to the class.

Accidents with electricity can be avoided. We just need to be smart about working with electricity. Let's formulate some safety rules for working with electricity.

Safety rules when working with electricity!

This was done in Gr. 5, but it is a good idea to revise it again as electrical accidents often happen in the home and at school.


  1. Look at each of the following pictures.
  2. Each one shows someone doing something with electricity, and often the person is doing something dangerous!
  3. Answer the questions about each of the pictures.

Electricity does not flow. Electric current flows. Be careful of introducing misconceptions here.


The person in the illustration above is using a table knife to remove a coin that has fallen in the toaster before switching off the appliance. What are the dangers related to this act?

The person can get shocked as electricity can pass from the toaster, through the metal knife and through the person.

What safety rule can you formulate regarding this?

First turn the toaster off and unplug it and use a wooden or plastic knife.

Why is this an unsafe cable to use ? Circle the area that makes it unsafe.

What could be done to the cable to make it safe to use?

Replace the cord, or else wrap insulation tape around the broken cord. However, this will not prevent a short if the wires inside also have perished insulation. It is best to replace the cord.

What safety rule can you formulate regarding this?

Never use an appliance that has a broken cord or has some of the metal wire showing through the cord casing.

Why is it dangerous to pull the boy from the electric wire?

Electric current can flow from one person to the next, so you will also get shocked.

What can the helper do to save the boy without being shocked by the electricity?

Use a non plastic/non metal object to separate them from the electrical source.

What safety rule can you formulate regarding this?

NEVER try to pull someone who is being shocked away from the appliance.

Why is this not a safe place to play?

High voltage fences can shock you even if you stand near them without actually touching them, or you might accidentally bump against the fence.

What safety rule can you formulate regarding this?

Never play near to or on electric fences or power lines.

Why is this connection dangerous?

Too much electric current flowing to one plug is dangerous. One multi-plug adapter is safe, but do not put adapters into each other. Rather use 2 different plug points.

Teacher's note: The real danger is that overloading the plug causes heating of the circuit which can result in fire.

What safety rule can you formulate regarding this?

Never put too many appliances into one socket.

Why is it dangerous for the children to play outside during the lightning storm?

If this powerful natural electricity strikes close to you, it will try to get to the ground through you. Our bodies are good conductors of electricity.

Why should no one play under a tree when it is storming?

The lightning is attracted to high points such as a tree and can shock the tree and also kill anyone underneath it.

Explain why it is not a good idea to be swimming when there is lightning in the sky?

Lightning could strike the water. Water with dissolved substances, such as salt or chlorine, is a good conductor of electricity and you can get shocked, and possibly die if you are swimming.

What safety rules can you formulate regarding lightning?

Do not play outside when there is thunder and lightning.

Why is the gardener unsafe when mowing the lawn in the rain? Give at least two reasons.

Water is able to conduct electricity, so you can get a shock if you are touching an appliance and water drips into the socket, cord or motor. Secondly, he is not wearing shoes which is dangerous as he could cut himself and the current can flow through him and into the Earth.

What safety rules can you formulate regarding using electrical appliances outside in the garden?

Never use electrical appliances outdoors in wet weather or if you are wet. Wear shoes when using electrical appliances.

Renewable ways to generate electricity

We have seen above that fossil fuels are non-renewable resources of energy.

What do you understand by the word `non-renewable'?

This means it cannot be renewed, reused. There is a finite supply which will be used up one day.

So, if we are using an energy resource which is non-renewable, then this will be a problem in the future when these resources run out. Are there other sources of energy?

Scientists and engineers are looking for ways to harness energy from renewable resources. A renewable resource is the opposite to a non-renewable resource. It will not run out and can be used over.

Renewable energy sources include natural phenomena such as sunlight, wind, tides and plant growth. The energy comes from natural processes that happen over and over.

Why do you think natural phenomena such as sunlight and wind can be considered as renewable?

This is because the sunlight and the wind will not `run out'. They are not used up or depleted in our time line. They will always be present on Earth (at least for a time frame relevant to human existence - the sun might extinguish one day in the far future, but this is not relevant when thinking of a renewable resource).

This is another place to speak of orders of magnitude. These resources are available so long as the solar system lasts in its current form, roughly 3.5 billion years they say. So these are renewable because they will always be available to us as a species even if we last a few million years more (having only really been around about 150 000 years or so).

Examples of renewable energy resources are:

  • solar (energy from the sun),
  • wind,
  • ocean (tides and waves),
  • hydropower (waterfalls or fresh water dams),
  • biomass (energy from plants and other organic material), and
  • geothermal (energy from steam underneath the surface of the earth).

Sun, wind and water can be used as sources of energy. Solar panels can be fitted to houses but this source of renewable energy works best on sunny days, and is less effective on cloudy days. Wind energy can be collected with a windmill or wind-turbine which can be big and noisy. Hydroelectric power stations harness the energy in water stored in high dams. It is only possible in areas where there are high mountains and rivers.

Wind turbines use wind to generate electricity.
A water wheel uses the flow of water to push the wheel around which can then do work.
As the water flows through this large hydroelectric power station, from the higher dam to the lower dam, electricity is made.
Solar panels

Renewable versus non-renewable energy

Learning how to debate is an important skill. After doing this activity, you could practise debating skills in the class by getting two groups to discuss opposing sides of the story. Each group must understand that they have to justify an argument for each side of the debate.

What are the advantages and disadvantages of renewable and non-renewable sources? There is a lot of debate around the use of renewable and non-renewable sources for energy. Let's join this debate!


  1. Work in groups of four.
  2. Discuss whether your house uses renewable or non-renewable sources of energy.
  3. Does anyone in the group have solar panels at home?
  4. Think about the advantages and disadvantages of renewable and non-renewable sources. You can use the Internet or other information sources to check for more ideas here.
  5. Write some of your answers in the spaces below.
  6. Report back to the class and see what others think about this debate.





If time permits, learners can do a mini research project on one of the renewable energy resources and present a poster in which they answer questions such as, `How is this renewable energy resource harvested and used to produce electricity?', `Is this resource used in South Africa?', etc. These can be stuck up as posters in the classroom for others in the class to read and learn from.

  • Most of our electricity comes from fossil fuels such as coal, oil and natural gas.
  • Fossil fuels are the remains of dead plants and animals from millions of years ago.
  • The energy in fossil fuels originally comes from the Sun which was captured by the plants that lived millions of years ago.
  • Electricity is expensive due to the infrastructure required to produce and deliver it.
  • Fossil fuels are non-renewable meaning they will run out.
  • We should try to be energy-efficient and not waste electrical energy.
  • Illegal connections pose a huge threat to people as they can be unsafe.
  • There are other resources which are renewable and can be used to generate electricity, such as wind power, solar power and hydropower.

Look at the flow diagram below. Describe what it is showing using what you have learnt in this chapter.

The Sun produces energy which plants capture and use to make food through the process of photosynthesis. Animals eat the plants. When these prehistoric plants and animals died millions of years ago, their remains were turned into fossil fuels (such as coal, oil and natural gas) over a long time. This was due to being covered in layers of sediment of mud and water which over time turned into rock and exerted a great pressure and heat on the remains. Today, these fossil fuels are mined and collected from inside the Earth's crust. Oil is processed to make petrol and diesel and the energy from the fossil fuels is used, for example in cars, where it is burnt and the energy released powers the cars.

Why are fossil fuels considered non-renewable resources?

This is because there is a limited supply of fossil fuels which will run out one day as we are using fossil fuels faster than they are made (which takes millions of years). They cannot be reused.

Write a paragraph in which you explain why you think humans should investigate alternative energy sources, such as renewable energy sources and how this might help the Earth.

Learner dependent answer, but assess whether learner has the ability to present an argument and justify their reasoning. One of the reasons which learners could present includes the fact that our reliance on non-renewable energy resources is not sustainable and poses a problem for the future if they run out. Furthermore, burning fossil fuels has a severe environmental impact as the carbon dioxide released contributes to greenhouse gases and global warming.

What type of electrical appliances in our homes use the most energy in a specific time?

This depends on the activity and usage, but the most energy will probably be used by heating devices such as a geyser or heater.

Imagine that you are writing an article for your local newspaper on how to save electricity in your homes. Use your imagination to write your article telling people how to save electricity. Use the space below. Give your article a catchy heading.

Assess learner's ability to write creatively about a science related topic. They are required to use the knowledge they have learnt in this chapter to write something creative. Tips to save electricity could be turning off lights when not in the room, using energy saving lights, reducing shower time to use less hot water, turning off the geyser during the day, using a gas stove instead of electrical stove, and bigger actions such as installing solar power, etc.

How do you think saving electricity will reduce the demand on ESKOM's power stations?

The more electricity you use, the more coal needs to be burned at the power stations to produce electricity. Saving electricity means that you use less electricity so there is less demand on the power stations.

What is an illegal electrical connection? How do you think the local government could stop or reduce the amount of illegal connections?

An illegal connection is when someone accesses electricity by cutting a power line and attaching another line and then not paying for it. The local government could try stop this by firstly trying to supply the poorer areas with appropriate electricity access points, going around and checking that there are not any dangerous connections, raising awareness about the dangers of illegal connections through advertising boards, on radio, in the newspaper, etc. Assess any other viable answers that the learner may come up with.

That is all from me for Energy and Change!

Join Sophie next to learn more about our planet Earth and outer Space!