A Level Electromagnetic Induction Hub
A Level Electromagnetic Induction hub covering magnetic flux and linkage, Faraday’s and Lenz’s laws, motional e.m.f., simple applications and ideal transformers.
Learning goals
- Use magnetic flux and flux-linkage relationships.
- Apply Faraday's and Lenz's laws to induced e.m.f. and direction.
- Explain simple applications of electromagnetic induction, including motional e.m.f. and eddy currents.
- Explain simple iron-core transformer operation and apply ideal transformer ratios.
Electromagnetic induction is about changing magnetic flux linkage. First identify what changes, then use Faraday’s law for magnitude and Lenz’s law for direction.
Prerequisites: Electromagnetic Forces, A Level Currents, and graph gradients.
Route: flux and flux linkage → Faraday and Lenz → motional e.m.f. → simple applications → transformer construction → ideal ratios.
After this hub: take the Electromagnetic Induction Quiz, then the Electromagnetic Induction Structured Set.
Lessons
Work through these lessons in order.
- Magnetic flux and flux linkage
- Induction experiments, Faraday's law and Lenz's law
- Simple applications of electromagnetic induction
- Simple iron-core ideal transformers
- Magnetic Flux
Define magnetic flux Φ and flux linkage NΦ, use Φ = BA cosθ and NΦ = NBA cosθ, and solve induction-style flux questions in exams (A Level Physics).
- Faraday's and Lenz's Laws
Use Faraday’s law ε = −d(NΦ)/dt and Lenz’s law to find induced e.m.f. and predict its direction from changing flux linkage (A Level Physics).
- E.m.f. Induced in a Moving Conductor
Derive and use ε = Blv for a straight conductor moving in a uniform magnetic field, including direction via Fleming’s right-hand rule (A Level Physics).
- Eddy Currents
Explain how eddy currents are induced by changing flux, why they cause heating and magnetic braking, and how lamination/slits reduce losses (A Level Physics).
- Features of an A.C. Transformer
Identify transformer parts and use the ideal transformer ratios Vs/Vp = Ns/Np and VpIp = VsIs to solve basic transformer questions (A Level Physics).
- Ideal Transformer Operation and Ratios
Explain how an a.c. transformer works via changing flux and Faraday’s law, and use Vs/Vp = Ns/Np with power conservation in exam problems (A Level Physics).
- 7 steps to solving electromagnetic induction problems · Supporting
A fast, exam-friendly workflow for electromagnetic induction problems using NΦ, Faraday’s law, Lenz’s law and direction rules (A Level Physics).
- Power Distribution · Supporting
Use P = VI and Ploss = I²R to explain high-voltage transmission and solve questions on transmission current, power loss and efficiency (A Level Physics).
- Induction Stove · Supporting
Explain how an induction stove heats a pan using changing magnetic flux and eddy currents, and why non-conducting cookware does not heat (A Level Physics).
- The Electric Guitar · Supporting
Explain how a guitar pickup uses changing magnetic flux to induce an a.c. signal in a coil that matches the string’s vibration frequency (A Level Physics).
- Subway Braking System · Supporting
Explain electromagnetic (eddy current) braking: motion in a magnetic field induces currents that oppose motion, producing a retarding force (A Level Physics).
- Movement Sensors · Supporting
Explain how movement sensors use changing flux linkage to induce an e.m.f., and how signal size depends on the rate of change (A Level Physics).
- Ground Fault Interrupters · Supporting
Explain the basic idea of a ground fault interrupter: unequal live/neutral currents imply leakage and trigger a fast cut-off (A Level Physics).
Revision
Flux orientation checkpoint
If the question gives the angle to the plane, convert it to the complementary angle to the normal before using cosine.
Quick reference
| Model | Relationship | Fast check |
|---|---|---|
| Magnetic flux | Φ = BA cos θ | θ is between vector B and the surface normal |
| Flux linkage | NΦ = NBA cos θ | turns multiply linkage, not flux per turn |
| Average induced e.m.f. | |E| = |Δ(NΦ)/Δ t| | constant linkage gives zero e.m.f. |
| Instantaneous induced e.m.f. | E = -d(NΦ)/dt | sign depends on the chosen positive convention |
| Motional e.m.f. | E = Blv | perpendicular geometry only |
| Ideal transformer | Vₛ/Vₚ = Nₛ/Nₚ = Iₚ/Iₛ | voltage follows turns; current is inverse |
Transformer checkpoint
The ideal ratios assume the same changing flux links every turn and that input power equals output power.
Exam traps
- Flux and flux linkage differ. Φ is for one surface or turn; a coil has linkage NΦ.
- Lenz’s law opposes the change. State whether flux is increasing or decreasing before choosing the induced field direction.
- No current is not the same as no e.m.f. An open coil can have an induced e.m.f. even though no sustained current flows.
- The negative sign needs a convention. For magnitude-only questions, use the absolute rate of change and determine direction separately.
- A transformer needs changing flux. Steady d.c. produces no continuous secondary e.m.f.
- Power equality is an ideal-model statement. Do not use VₚIₚ = VₛIₛ for a stated non-ideal transformer without accounting for efficiency.
Beyond the syllabus
- Transformer Losses — energy losses in real transformers, beyond the named 9478 transformer outcome.
Practice
Use the quiz to diagnose a weak outcome, then complete one flux-linkage question and one transformer question under timed conditions.
Next hub: Quantum Physics
Continue with the next resource in this course.
Course and syllabus information
- Course
- GCE A-Level H2 Physics
- Edition
- GCE A-Level H2 Physics 2027