VCE Physics — Unit 3 AOS 2
Electromagnetic Induction — Flashcards & Quiz
Electromagnetic induction is the generation of an EMF when the magnetic flux through a coil changes. VCE Physics Unit 3 AOS 2 quantifies the effect with Faraday's law and gives direction with Lenz's law. You need to calculate induced EMF for moving conductors, rotating coils and changing fields, and explain the minus sign as energy conservation.
Key Points
- Magnetic flux: Φ = BA cosθ, measured in webers (Wb).
- Faraday's law: ε = –N dΦ/dt. The minus sign encodes Lenz's law.
- Lenz's law: the induced current flows in a direction that opposes the change in flux causing it — energy conservation.
- Three ways to change flux: change B (moving magnet), change A (stretching loop), change θ (rotating coil — the AC generator).
- Peak EMF for a rotating coil: ε₀ = NBAω; instantaneous EMF ε = NBAω sin(ωt).
- Eddy currents are induced currents in bulk conductors; minimised by lamination in transformer cores.
Common Mistakes to Avoid
- Confusing Faraday's law (magnitude) with Lenz's law (direction).
- Forgetting the minus sign or the N factor.
- Mixing up flux (Φ, through an area) with flux density (B).
- Claiming DC gives an induced EMF — only CHANGING flux induces EMF.
- Using the wrong angle — θ is between B and the NORMAL to the loop, not between B and the loop surface.
Exam Strategy
VCAA Unit 3 AOS 2 induction questions ask you to calculate induced EMF or determine current direction. Method: (1) identify what is changing (B, A, or θ), (2) write Φ = BA cosθ, (3) differentiate to find dΦ/dt, (4) apply ε = –N dΦ/dt, (5) use Lenz's law to determine direction. Clear diagrams with labelled field, motion and current earn method marks.
Revision Tip
Flux-change scenarios are drillable — build a Revizi deck with 8+ setups (moving bar, rotating coil, collapsing field) and practise the same method every time.
Related Concepts
Last updated: March 2026