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Edexcel International GCSE Physics · Section 6 Magnetism and electromagnetism · 6 (d) Electromagnetic induction
Electromagnetic Induction: Making a Voltage with a Magnet
In this lesson you'll learn to: explain that a voltage is induced across the ends of a coil
when it cuts a magnetic field, say what makes the induced voltage bigger, what makes it
change direction and why it is zero when nothing moves, and predict what a
centre-zero voltmeter does each time.
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Prefer to watch? Scroll to the bottom for the video on this topic
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A video walkthrough is coming soon — it will appear at the bottom of this page
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Start here — have a play
Don't read anything yet. On tab 1, drag the magnet into the coil and watch the voltmeter. Push it in fast, then slowly. Hold it still inside the coil. Pull it out. Flip it so the S pole goes in first, add more turns, then switch to moving the coil instead. Each time, ask: which way did the needle go, and how far? Tab 2 is the table on your workbook page: predict, then watch. Tab 3 is the page's exam question.
Drag the
Turns
Into the coil first
Magnet
First, the rule
Direction
Size
What's happening
Pull down
Turns
Magnet
What's happening
Now answer the exam question on your page:
- Why a voltage? The magnet moves, so the coil cuts its magnetic field, so a voltage is induced.
- Why alternating? The trace goes positive and negative because the voltage alternates from one direction to the other: the coil cuts the magnetic field in alternating directions, down and then up.
- Why do the peaks decrease? As the magnet slows down, the coil cuts the magnetic field at a smaller rate, so the induced voltage is smaller.
- Bigger peaks? Use a stronger magnet, more turns, or move the magnet faster (pull it further down before letting go).
The voltage depends on how fast the field lines are cut, not on where the magnet is.
▲ The voltages are realistic for a school bar magnet and a small coil: a few millivolts.
Seen the needle move? Now learn the rules.
There is one sentence to learn word for word, then three ways to make the voltage bigger and two ways to turn it round. The notes below have them all.
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Revision notes
6.15 What is electromagnetic induction?
⭐ Learn this sentence
A voltage is induced across the ends of a conductor when it cuts a magnetic field.
Induced means it is made by the movement: there is no cell or battery in the circuit.
The voltage is only induced while the coil and the magnet are moving relative to each other, so the wire is cutting through the field lines. It does not matter which one moves: pushing the magnet into the coil and pushing the coil onto the magnet do the same thing.
If the coil is part of a complete circuit, the induced voltage makes an induced current flow. That is how a generator makes electricity.
What changes the induced voltage?
⬆
Make it bigger
Move the magnet (or the coil) faster.
Use more turns on the coil.
Use a
stronger magnet.
⇄
Change its direction
Move it the opposite way (in → out).
Or turn the magnet round so the other pole goes in
first.
0
No voltage at all
No movement = no cutting = no voltage. This is true even when the magnet is sitting right inside the coil.
Your workbook page starts from "N pole pushed in → needle to the right" and changes one thing at a time. Compare every row with that.
| What changes | Direction | Size of reading |
|---|---|---|
| Magnet pushed in faster | same (right) | bigger |
| Magnet pushed in more slowly | same (right) | smaller |
| Coil with more turns | same (right) | bigger |
| Magnet pulled out | reversed (left) | same |
| S pole pushed in instead | reversed (left) | same |
| Magnet held still inside the coil | none | zero |
| Magnet still, coil pushed onto it | same (right) | same |
⭐ Exam tip: the word that scores is "cuts"
Write that the coil cuts the magnetic field (or cuts the field lines). "The magnet is near the coil" or "the magnet is in the coil" scores nothing: a magnet sitting still inside a coil induces no voltage.
The size of the voltage depends on how fast the field is cut, so "faster" and "more slowly" are the words to use, not "harder" or "further".
⭐ The magnet on a spring
A magnet bouncing up and down through a coil gives an alternating voltage: one way as it goes down, the other way as it comes up, and zero for an instant at the top and bottom of each bounce, where it stops.
The peaks decrease because, as the magnet slows down, the coil cuts the magnetic field at a smaller rate, so the induced voltage is smaller. Try it on tab 3 of the animation.
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How to write it in the exam
"Explain why a voltage is induced" questions want the same three links every time. Write all three, in order.
The three links for "why is a voltage induced?"
The magnet moves (relative to the coil),
so the coil cuts the magnetic field,
so a voltage is induced across the ends of the coil.
the movementthe cuttingthe induced voltage
Exam-style question · explain · 2 marks
A magnet is dropped through a coil of wire. The coil is connected to a voltmeter. Explain why the voltmeter shows a reading as the magnet falls.
- The magnet moves through the coil, so the coil cuts the magnetic field (1)
- So a voltage is induced across the ends of the coil (1)
Exam-style question · no movement · 2 marks
A student holds the magnet still inside the coil. The voltmeter reads zero. Explain why.
- The magnet is not moving relative to the coil (1)
- So the coil does not cut the magnetic field, and no voltage is induced (1)
Where marks go missing: "the magnet is inside the coil, so there should be a voltage". Being in the field is not enough. It has to be cut.
Exam-style question · factors · 3 marks
Give three ways the student could make the induced voltage bigger.
- Move the magnet faster (1)
- Use a coil with more turns (1)
- Use a stronger magnet (1)
Where marks go missing: "use a bigger magnet" (say stronger) and "use more coils" (say more turns on the coil).
Exam-style question · direction · 2 marks
When the N pole is pushed into the coil the needle moves to the right. The student now pulls the magnet out at the same speed. Describe what the needle does.
- It moves to the left (the opposite direction) (1)
- By the same amount, because the speed is the same (1)
Check your answer has all 3 links whenever the question says "explain": the movement, the cutting, the induced voltage.
📘 Now do it in your workbook
Fill in the key sentence, predict the voltmeter for all six changes in the table, then answer the 6-mark question on the magnet bouncing on a spring.
Edexcel iGCSE Physics Workbook · MAGNETISM & ELECTROMAGNETISM · page 12The full workbook covers the whole of Section 6 Magnetism and electromagnetism, with exam-style questions and worked answers.
✅ Can you do it? Tick as you go
0% complete🎉 Nice work! You've ticked off every objective for this spec point.
Don't forget to hit “Mark complete” at the bottom of the lesson.
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Prefer to watch? Here's the whole thing
Video walkthrough — coming soon
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it.
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it. The video is on its way.
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Video coming soon
The walkthrough for this lesson is being filmed and will appear right here. Until then, the animation and the notes above cover every mark.
Now put it into practice
Page 12 of the workbook has the key sentence, the six-row voltmeter table and the 6-mark magnet-on-a-spring question, with full answers at the back.
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