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SavannahYear 8
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ScienceYear 9 Science: inheritance, energetics, climate, magnetism and space30 min★★★ difficulty

Magnetic fields and electromagnets

A compass needle swings to the north without anything touching it. Magnetic fields explain that, and the same idea drives every electric motor, doorbell and loudspeaker you use.

Lesson overview

What you'll learn in this lesson

Understand magnetic fields, including Earth's magnetism, compasses and the magnetic effect of a current

Key learning points

  • • Permanent magnets and fields
  • • Earth's field and the compass
  • • The magnetic effect of a current
  • • Electromagnets and their uses

This lesson at a glance

  • 30 minutes
  • 19 parts to scroll through
  • 4 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

magneticfieldsmagnetismcompasseseffect

Scroll down — the lesson carries on below

Part 1 of 19 · Discover5%
1

Watch & discover

Part 1 of 19

Watch first

Magnetic fields and electromagnets

An English teaching video on this topic from LearnScienceWithB. Watch it, then scroll down for the lesson.

In a nutshell

Understand magnetic fields, including Earth's magnetism, compasses and the magnetic effect of a current

2

What you already know

Part 2 of 19

Before we start

What you already know

You should already know that a circuit needs a complete loop and that current flows through a wire.

3

Key words

Part 3 of 19

Key words

Words you'll need today

Magnetic field
The region where a magnetic force acts.
Field line
A line showing the direction a north pole would move.
Induced magnet
A material that becomes magnetic only in a field.
Solenoid
A coil of wire that produces a magnetic field when current flows.
4

Learning cycle

Part 4 of 19

Learning cycle 1 of 2

Fields and compasses

A short piece of teaching, then a check to make sure it has landed.

5

Explore the idea

Part 5 of 19

Learn

Permanent magnets and fields

A magnet has a north and a south pole; like poles repel and unlike poles attract. The field is the region where that force acts, drawn as field lines running from north to south outside the magnet. Lines closer together mean a stronger field, which is why the force is greatest at the poles. Only iron, steel, cobalt and nickel are strongly magnetic.

6

Explore the idea

Part 6 of 19

Learn

Earth's field and the compass

Earth behaves as though a huge bar magnet sits inside it, produced by movement in its liquid iron core. A compass needle is a small magnet free to turn, so it lines up with the field and points roughly to geographic north. That the needle behaves this way is itself the evidence that Earth's core generates a magnetic field.

7

Quick check

Part 7 of 19

Quick check

Field lines run...

8

Quick check

Part 8 of 19

Quick check

A compass points north because...

9

Reset break

Part 9 of 19

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now
10

Learning cycle

Part 10 of 19

Learning cycle 2 of 2

Magnetism from electricity

A short piece of teaching, then a check to make sure it has landed.

11

Explore the idea

Part 11 of 19

Learn

The magnetic effect of a current

A current in a wire creates a circular magnetic field around it, which a plotting compass can trace. Winding the wire into a solenoid concentrates the field so that it resembles a bar magnet's, strong and uniform inside the coil. Reversing the current reverses the field direction, something a permanent magnet cannot do.

12

Explore the idea

Part 12 of 19

Learn

Electromagnets and their uses

Adding an iron core to a solenoid makes an electromagnet, far stronger than the coil alone. Its two useful features are that its strength can be changed by adjusting the current or the number of turns, and that it can be switched off. Scrapyard cranes, relays, electric bells and motors all depend on that control.

13

Quick check

Part 13 of 19

Quick check

The magnetic field around a straight current-carrying wire is...

14

Quick check

Part 14 of 19

Quick check

Adding an iron core to a solenoid...

15

Common mix-ups

Part 15 of 19

Common mix-ups

Things people often get wrong

  • People often think all metals are magnetic. Aluminium and copper are not attracted to magnets.
  • People often think field lines are real objects. They are a way of drawing direction and strength.
16

Challenge round

Part 16 of 19

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

17

Challenge round

Part 17 of 19

Game · Fill the gaps

Finish the sentences

Choose the word that belongs in each gap.

Only iron, steel, cobalt and nickel are strongly ____.

18

Mastery quiz

Part 18 of 19

Marked quiz

End of lesson quiz: Magnetic fields and electromagnets

6 questions, marked with the reasoning shown. No timer.

  1. 1. Like poles...

  2. 2. Which metal is strongly magnetic?

  3. 3. Earth's magnetic field is generated by...

  4. 4. Reversing the current in a solenoid...

  5. 5. An electromagnet is more useful than a permanent magnet because it...

  6. 6. Closer field lines mean the field is...

19

Lesson round-up

Part 19 of 19

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

  1. Name the variable the club changed the second time, and one variable they kept the same.
  2. Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
  3. Write a conclusion for the club's report, saying how far the evidence supports it.

  • Method and results

    Writing

    Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.

    1 page + results table

  • Conclusion

    Writing

    Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.

    6–8 sentences

  • Labelled diagram

    Diagram

    Draw the apparatus or the process in pencil, label it fully, and photograph it.

    1 labelled diagram

  • Reading and notes

    Reading

    Read the lesson text again and write the key ideas in your own words.

    Half a page of notes

Saved as you type.

Part 1 of 19 · Watch & discover

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