The shape of the lesson
By the end of the lesson, learners can
- Move the magnet, watch the meter: Move a magnet in and out of a coil and see the induced e.m.f. respond to the speed and direction.
- What makes the e.m.f. bigger: The induced e.m.f. depends on how fast the field changes, how strong it is, and how many turns the coil has.
- The cause: a changing magnetic field through the coil induces an e.m.f.
- The factors: faster movement, more turns, stronger magnet all make it bigger.
- The trap: a magnet held still induces nothing (the reading is zero).
One picture every idea returns to
Moving a conductor across a magnetic field, or changing the field through a coil, induces an e.m.f. The induced e.m.f. is larger when the movement is faster, the field stronger, or the coil has more turns. Reversing the motion reverses the induced current.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Movement makes voltage.. Push a magnet into a coil and a meter flicks, even though no battery is anywhere in sight. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Move the magnet, watch the meter | Move a magnet in and out of a coil and see the induced e.m.f. respond to the speed and direction. Project tab 1 of the lab (Induction) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: What makes the e.m.f. bigger | The induced e.m.f. depends on how fast the field changes, how strong it is, and how many turns the coil has. | Connect-Extend-Challenge |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 15 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in What makes the e.m.f. bigger, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Connect-Extend-Challenge
After the new idea, each student writes three lines: how it connects to what they knew, how it extends their thinking, and what still challenges them. Pairs compare, then the challenges become the plenary.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| An e.m.f. is induced only while the field through the coil is changing. | A magnet held still inside a coil induces nothing. It must be moving, or the current switching, for induction to happen. |
Electromagnetic induction: worksheet
6 questions, 15 marks. Written in the style of the papers; no past paper question is reproduced.
State what is meant by electromagnetic induction, and what must happen for an e.m.f. to be induced in a coil.
Describe a simple experiment to show that moving a magnet near a coil produces an e.m.f.
A magnet is moved into a coil and a small deflection is seen. State three changes that would give a larger deflection.
A magnet is pushed into a coil and then held still inside it. Describe what the meter reads while the magnet is held still, and explain why.
When a magnet is pushed into a coil the meter needle deflects to the right. State what happens to the needle when the magnet is then pulled out, and why.
A bicycle dynamo lights a lamp only while the bike is moving. Explain, in terms of induction, why the lamp goes out when the bike stops, and why it gets brighter as the bike goes faster.
Answer key and marking notes
- Electromagnetic induction is the production of an e.m.f. by a changing magnetic field. ✓
- The magnetic field through the coil must be changing (for example a magnet moving in or out). ✓
- Connect a coil to a sensitive (centre-zero) meter. ✓
- Move a bar magnet into the coil: the meter deflects, showing a current. ✓
- The deflection lasts only while the magnet is moving. ✓
- Move the magnet faster. ✓
- Use a coil with more turns. ✓
- Use a stronger magnet. ✓
- The meter reads zero. ✓
- The field through the coil is no longer changing, so no e.m.f. is induced. ✓
- The needle deflects to the left (the opposite way). ✓
- The field is now changing in the opposite direction, so the induced current reverses. ✓
- The dynamo spins a magnet near a coil, so the field through the coil keeps changing and induces an e.m.f. ✓
- When the bike stops, nothing moves, the field stops changing, so no e.m.f. is induced and the lamp goes out. ✓
- Going faster changes the field more quickly, giving a bigger e.m.f. and a brighter lamp. ✓
2 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
A magnet is pushed into a coil connected to a sensitive meter. The meter deflects. What happens if the magnet is then held still inside the coil?
- AThe meter reads zero, because there is no longer a change in the magnetic field.
- BThe meter reading doubles.
- CThe meter keeps the same steady reading.
- DThe meter reading slowly increases.
A magnet is moved into a coil. Which change would increase the size of the induced e.m.f.?
- Amoving the magnet into the coil faster
- Bmoving the magnet more slowly
- Cusing a coil with fewer turns
- Dholding the magnet still inside the coil
Quiz key
An e.m.f. is induced only when the magnetic field through the coil is changing. A stationary magnet produces no change, so no e.m.f. is induced and the meter reads zero. Movement, not the mere presence of the magnet, is what matters.
A faster movement changes the magnetic field through the coil more quickly, inducing a larger e.m.f. Moving slowly, using fewer turns, or holding it still would all reduce or remove the e.m.f.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.