Chapter 7 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

S2.8.7 Chapter 7

Conductors, insulators and switches

Which things let electricity pass?

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

  • Test which materials let electricity pass in a circuit
  • Make a switch from paper clips or kitchen foil

Some materials let electricity pass. Others do not. A circuit can tell you which.

A conductor is a material that lets electricity pass. Metals are conductors.

An insulator is a material that does not let electricity pass. Plastic, wood, rubber, glass and dry paper are insulators.

Draw it first

Draw a circuit that tests materials

  1. A cell on the left, labelled cell, and a bulb on the right, labelled bulb. A wire loops from the cell to the bulb with a break in the top wire, labelled gap. The bulb is dark. A nail, labelled nail, is laid across the gap. The bulb is lit. A stick, labelled stick, replaces the nail. The bulb is dark.cellbulb

    1 Draw a cell, a bulb and wires. Leave a gap in the top wire.

  2. A cell on the left, labelled cell, and a bulb on the right, labelled bulb. A wire loops from the cell to the bulb with a break in the top wire, labelled gap. The bulb is dark. A nail, labelled nail, is laid across the gap. The bulb is lit. A stick, labelled stick, replaces the nail. The bulb is dark.cellbulbgap

    2 Write gap. The bulb is dark.

  3. A cell on the left, labelled cell, and a bulb on the right, labelled bulb. A wire loops from the cell to the bulb with a break in the top wire, labelled gap. The bulb is dark. A nail, labelled nail, is laid across the gap. The bulb is lit. A stick, labelled stick, replaces the nail. The bulb is dark.cellbulbnail

    3 Lay a nail across the gap. The bulb lights. Write nail.

  4. A cell on the left, labelled cell, and a bulb on the right, labelled bulb. A wire loops from the cell to the bulb with a break in the top wire, labelled gap. The bulb is dark. A nail, labelled nail, is laid across the gap. The bulb is lit. A stick, labelled stick, replaces the nail. The bulb is dark.cellbulbstick

    4 Swap the nail for a stick. The bulb goes dark. Write stick.

The nail is a conductor. It joins the two ends of the wire. The loop is complete. The stick is an insulator. The gap stays.

Wires have metal inside and plastic outside. The metal carries the electricity. The plastic keeps it in the wire. It keeps you safe too.

A wire seen from the side. Most of it is covered by a coat, labelled plastic coat. At the end, the bare metal inside shows, labelled metal. Labels: plastic coat, metal.plastic coatmetal
Metal inside, plastic outside.

Water with salt or other things mixed in it conducts. Tap water, rain, sea water and sweat all have such things. A wet hand lets electricity pass.

Your torch cell may not light a bulb through water. It pushes too gently. The mains pushes far harder. Through water, it can kill.

See it three ways

As a picture

Two columns of boxes. The left column is headed conductors and holds the boxes nail, foil, paper clip, key and metal spoon. The right column is headed insulators and holds the boxes plastic, wood, rubber, glass and dry paper.conductorsnailfoilpaper clipkeymetal spooninsulatorsplasticwoodrubberglassdry paper

In words

Metals let electricity pass. They are conductors. Plastic, wood, rubber, glass and dry paper do not. They are insulators.

A switch opens or closes a gap in the loop. It lets you turn a bulb on and off.

A switch is closed when its lever touches both contacts. The loop is complete, and the bulb lights.

A loop with a cell on the left, labelled cell, a switch on the right, labelled switch, and a bulb along the bottom, labelled bulb. The lever of the switch lies flat and touches both contacts. The bulb is lit.bulbcellswitch
The switch is closed. The loop is complete. The bulb lights.

A switch is open when its lever is lifted. There is a gap. The bulb is off.

A loop with a cell on the left, labelled cell, a switch on the right, labelled switch, and a bulb along the bottom, labelled bulb. The lever of the switch is lifted away from one contact. The bulb is dark.bulbcellswitch
The switch is open. There is a gap. The bulb is dark.

The switch on a torch slides a metal strip. It joins two parts inside, or breaks them apart.

Try it

Test materials and make a switch

You need: a torch cell marked 1.5 V and a small torch bulb, three strips of kitchen foil, folded long and thin, tape, a nail or a metal spoon, and a metal paper clip, a stick, a piece of plastic, dry paper and a rubber band.

Be safe: Use only a torch cell. Never let strip A touch strip B. That joins the two ends of the cell. The foil gets hot fast.

  1. Use three foil strips and tape. Strip A joins the cell knob to the bulb side.
  2. Strip B starts at the flat end of the cell.
  3. Strip C starts at the bulb tip. Leave a gap between B and C.
  4. Press both free ends on a nail. Does the bulb light?
  5. Test the other things the same way. Write lit or dark for each.
  6. Now lay a paper clip across the gap. A foil strip works too.
  7. Lift it off. That is a switch.

What you will see: The bulb lights with the nail, the spoon and the paper clip. These are metals. It stays dark with the stick, the plastic, dry paper and rubber. A paper clip across the gap is a switch. Lay it down to close the loop. Lift it to open the loop. Rub off paint or rust where the foil touches. No cell or bulb? Read the table. Or switch a torch on and off. Do not open it.

If you cannot try it, this is what happens.
A table with two columns, headed thing and bulb. Row one: nail, lit. Row two: paper clip, lit. Row three: foil, lit. Row four: stick, dark. Row five: plastic, dark. Row six: dry paper, dark. Row seven: rubber band, dark.thingbulbnaillitpaper cliplitfoillitstickdarkplasticdarkdry paperdarkrubber banddark

A wrong idea many people have

Shiny things let electricity pass.

Why it feels right: Shiny foil and spoons let electricity pass. So shine seems to be the clue.

The test that breaks it: Use your tester. Touch the free ends to a glass bead or shiny plastic. It is shiny, but the bulb stays dark. Now rub a dull grey nail clean with paper. Touch the ends to it. The bulb lights.

What is true: Shine does not matter. The material does. Metals conduct. Glass and plastic do not.

Key words

conductor
a material that lets electricity pass. Metals are conductors.
insulator
a material that does not let electricity pass.
switch
a part that opens or closes a gap in the loop.
closed
a closed switch has no gap. The loop is complete.

Back to your guess

The answer is C: Metals do. Plastic and wood do not.

Metals let electricity pass. Plastic, wood, rubber, glass and dry paper do not. Shine does not matter.

Check yourself

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

  1. Which of these is a conductor?

    Tap your answer.

    1. Not this one. Wood is an insulator. Metals are conductors. Try another.

    2. Yes, that is right. Steel is a metal. Metals let electricity pass.

    3. Not this one. Rubber is an insulator. Metals are conductors. Try another.

    See the answer

    A steel nail

    Steel is a metal. Metals let electricity pass.

    • If you chose A: Wood is an insulator. Metals are conductors.
    • If you chose C: Rubber is an insulator. Metals are conductors.

  2. Why do wires have a plastic coat?

    Tap your answer.

    1. Yes, that is right. The metal inside carries the electricity. The plastic coat stops it reaching you.

    2. Not this one. Plastic is an insulator. The metal inside carries the electricity. Try another.

    3. Not this one. The coat has a different job. It keeps electricity in and keeps you safe. Try another.

    See the answer

    Plastic is an insulator. It keeps electricity in the wire.

    The metal inside carries the electricity. The plastic coat stops it reaching you.

    • If you chose B: Plastic is an insulator. The metal inside carries the electricity.
    • If you chose C: The coat has a different job. It keeps electricity in and keeps you safe.

  3. Tariq touches the free ends to a shiny glass bead. The bulb stays dark. Why?

    Tap your answer.

    1. Not this one. Size is not the reason. Glass does not let electricity pass. Try another.

    2. Not this one. Shiny foil does. Shine does not decide. The material does. Try another.

    3. Not this one. Test the bulb with a nail across the gap. If it lights, the bulb is fine. Glass is the reason. Try another.

    4. Yes, that is right. Glass does not let electricity pass, however shiny it is.

    See the answer

    Glass is an insulator.

    Glass does not let electricity pass, however shiny it is.

    • If you chose A: Size is not the reason. Glass does not let electricity pass.
    • If you chose B: Shiny foil does. Shine does not decide. The material does.
    • If you chose C: Test the bulb with a nail across the gap. If it lights, the bulb is fine. Glass is the reason.

  4. A switch is open. What does the bulb do?

    Tap your answer.

    1. Not this one. Open means a gap in the loop. Electricity cannot go round. Try another.

    2. Yes, that is right. An open switch leaves a gap in the loop. Nothing goes round, so the bulb is off.

    3. Not this one. A gap stops all of it. The bulb is fully dark. Try another.

    See the answer

    It is dark, because there is a gap.

    An open switch leaves a gap in the loop. Nothing goes round, so the bulb is off.

    • If you chose A: Open means a gap in the loop. Electricity cannot go round.
    • If you chose C: A gap stops all of it. The bulb is fully dark.

  5. From an earlier chapter

    A loop has a cell and a bulb. One wire has a gap. What happens?

    Tap your answer.

    1. Not this one. A gap stops the electricity completely. The bulb stays dark. Go to S2.8.6. Try another.

    2. Not this one. The loop must be complete. A gap stops the bulb. Go to S2.8.6. Try another.

    3. Yes, that is right. A gap breaks the loop. With no way round, nothing goes through the bulb.

    See the answer

    The bulb stays dark.

    A gap breaks the loop. With no way round, nothing goes through the bulb.

    • If you chose A: A gap stops the electricity completely. The bulb stays dark. Go to S2.8.6.
    • If you chose B: The loop must be complete. A gap stops the bulb. Go to S2.8.6.

  6. Why must your hands be dry near electricity?

    Tap your answer.

    1. Yes, that is right. A wet hand is a conductor. It can let mains electricity go through you.

    2. Not this one. The water we meet has things mixed in it. It lets electricity pass. Try another.

    3. Not this one. Cold is not the danger. Wet hands let electricity into your body. Try another.

    See the answer

    Water with salt or dirt in it lets electricity pass.

    A wet hand is a conductor. It can let mains electricity go through you.

    • If you chose B: The water we meet has things mixed in it. It lets electricity pass.
    • If you chose C: Cold is not the danger. Wet hands let electricity into your body.

  7. Kofi says a switch makes electricity. Is he right?

    Tap your answer.

    1. Not this one. A switch makes nothing. The cell pushes the electricity round. Try another.

    2. Yes, that is right. The cell pushes the electricity. The switch opens or closes the gap.

    3. Not this one. A closed switch does not change the brightness. It joins the loop, and an open one breaks it. Try another.

    See the answer

    No. A switch only opens or closes the loop.

    The cell pushes the electricity. The switch opens or closes the gap.

    • If you chose A: A switch makes nothing. The cell pushes the electricity round.
    • If you chose C: A closed switch does not change the brightness. It joins the loop, and an open one breaks it.

  8. Look at the picture. Ana lays a paper clip across the gap. What does the bulb do?

    A cell on the left, labelled cell, and a bulb on the right, labelled bulb. A wire loops from the cell to the bulb with a break in the top wire. A paper clip, labelled paper clip, lies across the break and touches both ends of the wire. Labels: cell, bulb, paper clip.cellbulbpaper clip
    Tap your answer.

    1. Yes, that is right. The clip joins the two ends of the wire. Metals let electricity pass, so the loop is complete.

    2. Not this one. Size does not matter. The clip touches both ends, and metal lets electricity pass. Try another.

    3. Not this one. Any metal can carry electricity, not only wires. A paper clip is a metal. Try another.

    See the answer

    It lights. A paper clip is metal.

    The clip joins the two ends of the wire. Metals let electricity pass, so the loop is complete.

    • If you chose B: Size does not matter. The clip touches both ends, and metal lets electricity pass.
    • If you chose C: Any metal can carry electricity, not only wires. A paper clip is a metal.

  9. Which of these is an insulator?

    Tap your answer.

    1. Not this one. A paper clip is a metal. Metals are conductors. Try another.

    2. Not this one. Foil is a metal. It is a conductor. Try another.

    3. Yes, that is right. Wood does not let electricity pass when it is dry. It is an insulator.

    4. Not this one. Water with salt in it lets electricity pass. It is a conductor. Try another.

    See the answer

    A dry wooden stick

    Wood does not let electricity pass when it is dry. It is an insulator.

    • If you chose A: A paper clip is a metal. Metals are conductors.
    • If you chose B: Foil is a metal. It is a conductor.
    • If you chose D: Water with salt in it lets electricity pass. It is a conductor.

Keep it

Copy this into your exercise book.

Metals are conductors. They let electricity pass. Plastic, wood, rubber, glass and dry paper are insulators. Water with salt or dirt in it conducts, so keep hands dry. A switch opens or closes a gap in the loop.

Draw: A loop with a cell, a bulb and a gap. Lay a nail across the gap. Draw lines round the bulb.

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

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