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.
Sample Flashcards
Q1: State Faraday's law of electromagnetic induction.
Faraday's law states that the magnitude of induced EMF equals the rate of change of magnetic flux: ε = -N(ΔΦ/Δt), where N is number of turns. A changing magnetic flux through a conductor induces an EMF. The faster the flux changes, the greater the induced EMF. This is the fundamental principle behind generators and transformers.
Q2: What is magnetic flux and how does it relate to induced EMF?
Magnetic flux (Φ) is the product of magnetic field strength and perpendicular area: Φ = BA cosθ, measured in webers (Wb). EMF is induced when flux changes through a conductor loop. Flux can change by varying field strength, area, or orientation angle. Zero flux change means zero induced EMF.
Q3: What are the three ways to change magnetic flux through a coil?
Flux can be changed by: (1) varying magnetic field strength B, (2) changing the area A of the coil in the field, or (3) rotating the coil to change the angle θ between field and area normal. All three methods are used in practical applications. Any combination of these changes will induce EMF according to Faraday's law.
Sample Quiz Questions
Q1: According to Faraday's law, the magnitude of induced EMF is proportional to the rate of change of magnetic flux through a conductor.
Answer: TRUE
TRUE. Faraday's law states ε = -N(ΔΦ/Δt): induced EMF equals the rate of change of magnetic flux (multiplied by number of turns). Faster flux change produces greater EMF. This is the fundamental principle of generators and transformers.
Q2: An EMF can be induced in a coil by moving the coil through a magnetic field, changing the magnetic field strength, or rotating the coil in the field.
Answer: TRUE
TRUE. All three methods change the magnetic flux Φ = BA cosθ through the coil. Moving or rotating changes area or angle; changing field strength changes B. Any change in Φ induces EMF according to Faraday's law.
Q3: Magnetic flux through a coil is measured in webers (Wb), where 1 weber equals 1 tesla × 1 square metre.
Answer: TRUE
TRUE. Flux Φ = BA has units of tesla × square metre (T·m²), defined as 1 weber. Since 1 T = 1 Wb/m², we have Φ in webers. This unit is named after Wilhelm Weber, a pioneer in electromagnetism.
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 · 3 flashcards · 3 quiz questions