The shape of the lesson
By the end of the lesson, learners can
- Switch the magnet on: Turn the current on and off and watch the electromagnet field appear and vanish.
- Stronger, and useful: An electromagnet can be made stronger and put to work in switches and speakers.
- Patterns: circles around a wire; a bar-magnet shape for a coil.
- Direction: reverse the current and the field reverses (poles swap).
- Strength: bigger with more current, more turns, and a soft-iron core.
One picture every idea returns to
An electric current produces a magnetic field. A solenoid carrying current acts like a bar magnet whose field can be switched on and off and strengthened with more current, more turns, or a soft iron core. This is the basis of relays and loudspeakers.
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, Current makes a magnet.. Send a current down a wire and a compass nearby swings: the current has wrapped itself in a magnetic field. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Switch the magnet on | Turn the current on and off and watch the electromagnet field appear and vanish. Project tab 2 of the lab (Field and poles) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Stronger, and useful | An electromagnet can be made stronger and put to work in switches and speakers. | Cooperative Concept Mapping |
| 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, 14 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 Stronger, and useful, 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.
Cooperative Concept Mapping
Teams receive the key terms on cards and arrange them on a large sheet, drawing and labelling the links. Compare maps between teams before showing the model map.
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 electromagnet works only while the current flows, which is exactly why it is useful: the magnetism can be switched on and off. | A soft iron core boosts it because soft iron magnetises and demagnetises easily. |
The magnetic effect of a current: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
Describe the shape of the magnetic field around a long straight wire carrying a current.
Describe the magnetic field produced by a current in a solenoid (a long coil).
A plotting compass is placed near a wire carrying a current and the needle points in a certain direction. State what happens to the needle if the current is reversed, and why.
State three ways to increase the strength of the magnetic field of a solenoid.
A scrapyard crane uses an electromagnet to lift cars. Explain why an electromagnet is used instead of a permanent magnet.
A coil with a soft-iron core is connected to a battery. State what happens to the magnetism of the core when the current is switched off, and why a soft-iron core is chosen rather than a steel one.
Answer key and marking notes
- A pattern of circles around the wire. ✓
- The circles are closer together (the field is stronger) nearer the wire. ✓
- The field is like that of a bar magnet. ✓
- It has a north end and a south end, with field lines through the middle of the coil. ✓
- The needle turns to point the opposite way. ✓
- Reversing the current reverses the direction of the magnetic field. ✓
- Increase the current. ✓
- Increase the number of turns on the coil. ✓
- Place a soft-iron core inside the coil. ✓
- An electromagnet can be switched on and off with the current. ✓
- It picks up the car when the current is on. ✓
- It drops the car when the current is switched off; a permanent magnet could not release it. ✓
- The core loses its magnetism almost completely when the current is switched off. ✓
- Soft iron is used because it magnetises and demagnetises easily, while steel would keep its magnetism. ✓
1 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 current is switched on in a long coil (solenoid) wound on a soft iron core. What does the coil behave like?
- Aa bar magnet, with a north and a south pole
- Ban electric heater only
- Ca capacitor that stores charge
- Dan insulator
Quiz key
A current in a solenoid produces a magnetic field just like a bar magnet, with a north and south pole; the soft iron core makes it much stronger. Switching the current off removes the magnetism, which is why it is an electromagnet.
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.