Chapter 5 of 8

All 8 chapters
  1. 1What magnets pull, readunderstood
  2. 2North and south poles, readunderstood
  3. 3Magnetic force through things, readunderstood
  4. 4Making a compass, readunderstood
  5. 5Electricity: safe and unsafe, readunderstood
  6. 6A simple circuit, readunderstood
  7. 7Conductors, insulators and switches, readunderstood
  8. 8Circuit drawings, readunderstood

S2.8.5 Chapter 5

Electricity: safe and unsafe

Why can I hold a cell but not touch a wall socket?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Name things at home that use cells and things that use mains
  • Explain why we never experiment with wall sockets or mains wires

Electricity makes a torch shine and a fan turn. It comes from two kinds of place.

One place is a cell. A cell makes electricity from the chemicals inside it. Many people call a cell a battery. Torches, clocks and toys use cells.

The other place is the mains. The mains is electricity sent to buildings along wires. It comes out of wall sockets. It also runs along power lines.

Draw it first

Draw the two kinds of electricity

  1. A picture split by a dashed line. On the left are a torch and a cell, labelled torch and cell, above the word safe. On the right are a wall socket and a power line, labelled wall socket and power line, above the words never touch.torchcell

    1 Draw a torch and a cell. Write torch and cell.

  2. A picture split by a dashed line. On the left are a torch and a cell, labelled torch and cell, above the word safe. On the right are a wall socket and a power line, labelled wall socket and power line, above the words never touch.torchcellwall socketpower line

    2 Draw a wall socket and a power line. Write wall socket and power line.

  3. A picture split by a dashed line. On the left are a torch and a cell, labelled torch and cell, above the word safe. On the right are a wall socket and a power line, labelled wall socket and power line, above the words never touch.torchcellwall socketpower linesafenever touch

    3 Draw a dashed line between them. Write safe on the left and never touch on the right.

A torch cell is small and gentle. It is safe to use in a circuit. The label says 1.5 V. The V is for volts. Volts tell you how hard electricity pushes.

The mains pushes much harder. It is 100 V or more. Mains electricity can kill.

Two bars drawn to the same scale. The tall bar is labelled mains, with 100 V or more under it. The very short bar is labelled cell, with 1.5 V under it. Labels: mains, 100 V or more, cell, 1.5 V.mains100 V or morecell1.5 V
The bars use the same scale. The mains pushes far harder than a cell.

Water and the mains are a deadly pair. Never touch a plug, a switch or a wire with wet hands. You will see why in the chapter on conductors.

Two boxes, labelled wet hands and plug, with a cross between them. Under them are the words never touch.wet handsplugnever touch
Wet hands and a plug must never meet.

A generator or a big solar panel can also make strong electricity. Leave its wires alone too.

See it three ways

As a picture

Two columns of boxes. The left column is headed cells and holds the boxes torch, clock and toy car. The right column is headed mains and holds the boxes kettle, iron and fridge.cellstorchclocktoy carmainskettleironfridge

In words

Small things you carry often run on cells. Big things and things that make heat use the mains.

In symbols

A torch cell: 1.5 V. The mains: 100 V or more.

Two columns of boxes. The left column is headed use and holds the box AA cell 1.5 V. The right column is headed never use and holds the boxes car battery and cut open cell.useAA cell 1.5 Vnever usecar batterycut open cell
Use a small torch cell. Never use a car battery. Never cut a cell open.

Try it

Hunt for cells and mains at home

You need: paper and a pencil, a grown up to walk round with you.

Be safe: Look only. Never touch a socket, a plug or a mains wire.

  1. Walk round your home with a grown up. Look, but do not touch.
  2. Find things that run on cells. Think of a torch, a clock or a toy.
  3. Find things that use the mains. Look for a plug and a wire to the wall.
  4. Do not touch plugs, sockets or wires. Do not open anything.
  5. Make a table with two columns. Write thing and cell or mains.
  6. List what you find. If your home has no mains, list the cells you find.

What you will see: Small things you carry often run on cells. Big things and things that make heat use the mains. A phone has a cell inside, but it charges from the mains. If you cannot do this, read the table.

If you cannot try it, this is what happens.
A table with two columns, headed thing and cell or mains. Row one: torch, cell. Row two: clock, cell. Row three: kettle, mains. Row four: iron, mains. Row five: fan, mains.thingcell or mainstorchcellclockcellkettlemainsironmainsfanmains

A wrong idea many people have

A cell and the mains are the same, so both are safe.

Why it feels right: Both can light a bulb. A torch and a lamp look alike when they shine.

The test that breaks it: Read the label on a torch cell. It says 1.5 V. Ask a grown up to show you an electric kettle label. It says 100 V or more. Only read the labels. Do not plug anything in.

What is true: The mains pushes at least 60 times harder than a torch cell. A torch cell is safe. The mains can kill.

Key words

cell
a small thing that makes electricity from chemicals. Many people say battery.
mains
the strong electricity sent to buildings along wires. It can kill.

Back to your guess

The answer is B: A torch cell is safe. Mains electricity can kill.

A torch cell is safe to use. Mains electricity from a wall socket or a power line can kill. Never touch it.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. Which of these runs on a torch cell?

    Tap your answer.

    1. Not this one. An electric kettle plugs into the wall. It uses the mains. Try another.

    2. Not this one. An electric iron plugs into the wall. It uses the mains. Try another.

    3. Yes, that is right. A torch has cells inside it. An electric kettle and iron use the mains.

    See the answer

    A pocket torch

    A torch has cells inside it. An electric kettle and iron use the mains.

    • If you chose A: An electric kettle plugs into the wall. It uses the mains.
    • If you chose B: An electric iron plugs into the wall. It uses the mains.

  2. Why must we never push things into a wall socket?

    Tap your answer.

    1. Yes, that is right. The mains pushes very hard. It can stop your heart. Keep away from sockets.

    2. Not this one. The danger is to you, not to the socket. Mains can kill. Try another.

    3. Not this one. A socket has no cell. It is joined to the mains. Try another.

    See the answer

    Mains electricity can kill.

    The mains pushes very hard. It can stop your heart. Keep away from sockets.

    • If you chose B: The danger is to you, not to the socket. Mains can kill.
    • If you chose C: A socket has no cell. It is joined to the mains.

  3. Mei sees a wire on the ground. It fell from a power line. What should she do?

    A person, labelled Mei, stands on the ground at the left. At the right a pole stands with a wire hanging from its top and lying along the ground. The wire is labelled fallen wire, with a line down to it. Labels: Mei, fallen wire.Meifallen wire
    Tap your answer.

    1. Not this one. A damp stick can let electricity pass. Stay far away. Try another.

    2. Not this one. Dry hands are not safe. The mains can kill. Try another.

    3. Not this one. The ground near the wire can carry electricity. Stay far away, not close. Try another.

    4. Yes, that is right. The wire may carry mains electricity. Only trained people go near it.

    See the answer

    Stay far away and tell a grown up at once.

    The wire may carry mains electricity. Only trained people go near it.

    • If you chose A: A damp stick can let electricity pass. Stay far away.
    • If you chose B: Dry hands are not safe. The mains can kill.
    • If you chose C: The ground near the wire can carry electricity. Stay far away, not close.

  4. Which cell is safe for the activities in this book?

    Tap your answer.

    1. Yes, that is right. A small torch cell is gentle. A car battery is not.

    2. Not this one. A car battery can burn you and it can explode. Never use one. Try another.

    3. Not this one. The inside of a cell can burn your skin and eyes. Never cut one open. Try another.

    See the answer

    A small torch cell marked 1.5 V

    A small torch cell is gentle. A car battery is not.

    • If you chose B: A car battery can burn you and it can explode. Never use one.
    • If you chose C: The inside of a cell can burn your skin and eyes. Never cut one open.

  5. From an earlier chapter

    A magnet touches each of these. Which one does it pull?

    Tap your answer.

    1. Not this one. A magnet does not pull plastic. It pulls iron and steel. Go to S2.8.1. Try another.

    2. Not this one. A magnet does not pull wood. It pulls iron and steel. Go to S2.8.1. Try another.

    3. Yes, that is right. A magnet pulls iron and steel. It does not pull plastic or wood.

    See the answer

    An iron nail

    A magnet pulls iron and steel. It does not pull plastic or wood.

    • If you chose A: A magnet does not pull plastic. It pulls iron and steel. Go to S2.8.1.
    • If you chose B: A magnet does not pull wood. It pulls iron and steel. Go to S2.8.1.

  6. Cell or mains? Sort these: torch, electric kettle, toy car, electric iron.

    See the answer

    Cell: torch and toy car. Mains: electric kettle and electric iron.

    A torch and a toy car carry their own cells. The electric kettle and iron plug into the wall.

  7. Joseph says a quick touch of a wall socket is safe. Is he right?

    Tap your answer.

    1. Not this one. The mains is strong. Even a quick touch can hurt or kill. Try another.

    2. Not this one. Shoes do not make a socket safe. Never touch it. Try another.

    3. Not this one. Dry hands are not safe. Never touch a socket, quick or slow. Try another.

    4. Yes, that is right. The mains pushes at least 60 times harder than a torch cell. Never touch a socket.

    See the answer

    No. The mains can kill, even in a moment.

    The mains pushes at least 60 times harder than a torch cell. Never touch a socket.

    • If you chose A: The mains is strong. Even a quick touch can hurt or kill.
    • If you chose B: Shoes do not make a socket safe. Never touch it.
    • If you chose C: Dry hands are not safe. Never touch a socket, quick or slow.

  8. Sipho finds a button cell, a small flat round one. His little sister is near. What should he do?

    Tap your answer.

    1. Not this one. A swallowed button cell burns inside. Keep it away from little children. Try another.

    2. Yes, that is right. A button cell is small enough to swallow. A swallowed one burns inside.

    3. Not this one. What is inside a cell can burn your skin and eyes. Never cut one open. Try another.

    See the answer

    Keep it away from little children and tell a grown up.

    A button cell is small enough to swallow. A swallowed one burns inside.

    • If you chose A: A swallowed button cell burns inside. Keep it away from little children.
    • If you chose C: What is inside a cell can burn your skin and eyes. Never cut one open.

  9. A torch cell is 1.5 V. The mains is 100 V or more. Which is true?

    Tap your answer.

    1. Not this one. The numbers are very different. The mains pushes far harder than a cell. Try another.

    2. Not this one. Size does not matter. 1.5 V is a gentle push. Try another.

    3. Yes, that is right. The mains is 100 V or more. A torch cell is 1.5 V. The mains pushes much harder.

    4. Not this one. Where it comes from does not make it safe. 100 V or more can kill. Try another.

    See the answer

    The mains pushes far harder, so it can kill.

    The mains is 100 V or more. A torch cell is 1.5 V. The mains pushes much harder.

    • If you chose A: The numbers are very different. The mains pushes far harder than a cell.
    • If you chose B: Size does not matter. 1.5 V is a gentle push.
    • If you chose D: Where it comes from does not make it safe. 100 V or more can kill.

Keep it

Copy this into your exercise book.

Torch cells are safe to use. Mains electricity from a wall socket or a power line can kill. Never touch sockets, plugs or mains wires. Never use a car battery. Never cut open a cell.

Draw: Two columns. Cell: a torch and a clock. Mains: a kettle and an iron. Cross out the mains.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (707 KB). It opens on any phone.