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
- 25 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 25
Visual introductionPicture this
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.
In a nutshell
Understand magnetic fields, including Earth's magnetism, compasses and the magnetic effect of a current
What you already know
Part 2 of 25
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.
Key words
Part 3 of 25
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.
Reset break
Part 4 of 25
Pause
That's sitting 1 of 6 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.
Learning cycle
Part 5 of 25
Learning cycle 1 of 2
Fields and compasses
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 6 of 25
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.
Explore the idea
Part 7 of 25
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.
Reset break
Part 8 of 25
Pause
That's sitting 2 of 6 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.
Quick check
Part 9 of 25
Quick check
Part 10 of 25
Learning cycle
Part 11 of 25
Learning cycle 2 of 2
Magnetism from electricity
A short piece of teaching, then a check to make sure it has landed.
Reset break
Part 12 of 25
Pause
That's sitting 3 of 6 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.
Explore the idea
Part 13 of 25
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.
Explore the idea
Part 14 of 25
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.
Quick check
Part 15 of 25
Reset break
Part 16 of 25
Pause
That's sitting 4 of 6 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.
Quick check
Part 17 of 25
Common mix-ups
Part 18 of 25
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.
Challenge round
Part 19 of 25
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
Reset break
Part 20 of 25
Pause
That's sitting 5 of 6 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.
Challenge round
Part 21 of 25
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Only iron, steel, cobalt and nickel are strongly ____.
Challenge round
Part 22 of 25
Game · Recall cards
Field lines run...
Card 1 of 4
Exit quiz
Part 23 of 25
Exit quiz
Show what you've learned
6 questions, marked together at the end. Nothing is timed.
1. Like poles...
2. Which metal is strongly magnetic?
3. Earth's magnetic field is generated by...
4. Reversing the current in a solenoid...
5. An electromagnet is more useful than a permanent magnet because it...
6. Closer field lines mean the field is...
Mastery quiz
Part 24 of 25
Marked quiz
End of lesson quiz: Magnetic fields and electromagnets
4 questions, marked with the reasoning shown. No timer.
1. Field lines run...
2. A compass points north because...
3. The magnetic field around a straight current-carrying wire is...
4. Adding an iron core to a solenoid...
Lesson round-up
Part 25 of 25
Lesson round-up
Ready when you are
Quiz score
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Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 25 · Watch & discover