Level 2 · Secondary physics teaching kit · Grades 10–12
Electricity, magnetism, and Maxwell's picture
Use the learner record during the live investigation, then use the instructor guide to facilitate comparison, address misconceptions, and assess evidence-bounded reasoning.
Learner lab record
Faraday induction polarity map
How do flux-change rate and direction determine the magnitude and sign of an induced voltage?
Setup
Use the induction laboratory. Keep coil geometry fixed, compare slow and fast flux changes, then reverse the direction without changing the magnitude.
Predict first
- 1. Predict what doubling the change rate does to emf magnitude.
- 2. Predict what reverses when the flux-change direction reverses.
| Variable | Role | Unit |
|---|---|---|
| Magnetic flux change | independent | Wb |
| Change duration | independent | s |
| Coil turns | controlled, then independent | turns |
| Induced emf | dependent | V |
Observation columns
Analyze
- 1. Which pair isolates change rate?
- 2. Which pair isolates direction?
- 3. How does Lenz's law protect the energy ledger?
- 4. What apparatus property is absent from this ideal model?
Conclusion frame
When flux changed ___ times faster, emf changed from ___ to ___; reversing the change reversed ___ because ___.
Instructor guide · 45–55 minutes
Teach the investigation, not the interface
Learning target: Learners connect induced-emf magnitude to flux-change rate and polarity to opposition of the change.
Prepare
- • Review flux as field through area.
- • Choose a sign convention and display it throughout.
- • Prepare one apparent energy-creation claim for critique.
Facilitation moves
- • Ask what changed in the flux, not merely whether a magnet moved.
- • Separate polarity from magnitude.
- • Trace mechanical input through induced current to dissipation.
Accessibility and participation
- • Describe polarity with words and arrows, not red/blue alone.
- • Provide a tactile coil-and-arrow sketch.
- • Keep motion optional; static parameter states carry the full lesson.
Evidence of learning
- • A controlled rate comparison
- • A correct polarity reversal
- • A complete input-to-output energy explanation
Misconception checks
A stronger magnet always means current without input.
Current requires changing flux and a closed circuit; the driver supplies energy against the induced response.
Negative voltage means energy was destroyed.
The sign records orientation relative to the declared convention.
Extension
Add coil resistance and compare open-circuit emf with delivered electrical power.