IP Physics Notes (Upper Secondary, Year 3-4): 16) Electromagnetic Induction

Study guide30 Sep 2025, 00:00 ZUpdated 30 Nov 2025

Apply Faraday and Lenz, sketch AC generator waveforms, and compute transformer ratios for power transmission questions.

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Q: What does IP Physics Notes (Upper Secondary, Year 3-4): 16) Electromagnetic Induction cover?
A: Apply Faraday and Lenz, sketch AC generator waveforms, and compute transformer ratios for power transmission questions.

Quick recap -- Changing magnetic flux induces emf. Remember: faster change -> larger emf, and the induced current always opposes the flux change (Lenz). Generators and transformers are direct applications.

The core idea is simple: Induction happens when magnetic flux changes.

Use it as a working check: Faster motion, stronger magnets, or more coil turns increase induced emf. Lenz's law says the induced current opposes the change that caused it.

Then go one layer deeper: Use the generator and transformer sections to practise explaining flux change, predicting polarity, sketching AC output, and applying voltage-turns ratios.

Keep your practice loop tight via our Sec 4 IP Physics tuition hub. It links each topic here to quizzes, diagnostics, and WA-style problem sets.

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These notes align with SEAB GCE O-Level Physics (6091) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Physics 6091 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for these notes.

Faraday's & Lenz's Laws

Faraday: magnitude of induced emf $\mathcal{E}$ is proportional to rate of change of magnetic flux linkage.
Lenz: induced current direction opposes the change producing it (conservation of energy).
Practical consequences:
- Move magnet faster -> larger $\mathcal{E}$

Reviewed by

Chee Wei Jie·Academic Advisor (Physics)

Situation	Flux change to name first	Induced face needed	Common trap
North pole moves towards coil	North-going flux through coil increases	Near face becomes north to repel the approach	Saying "opposes the magnet" without naming the increasing flux
North pole moves away from coil	North-going flux through coil decreases	Near face becomes south to attract it back	Using the same current direction as the approach case
South pole moves towards coil	South-going flux through coil increases	Near face becomes south to repel the approach	Forgetting that the pole label flips but the opposition idea stays
Magnet held still inside coil	Flux is not changing	No induced emf or current	Thinking a strong magnet alone is enough for induction

Coil moment	Flux through coil	Rate of change	Graph cue
Coil face is broadside to the field	Maximum or minimum flux	Momentarily zero	Emf crosses zero.
Coil face is edge-on to the field	Flux passes through zero	Greatest rate of change	Emf has maximum magnitude.
Half a turn later	Same orientation but opposite side leading	Same magnitude, opposite direction	Emf has opposite sign.
Faster rotation	Flux pattern repeats more quickly	Greater rate of change	Higher peak emf and higher frequency.

Question clue	First label	Equation move	Trap to avoid
Supply is connected to one coil	That coil is the primary, $p$ .	Put its voltage and turns under $V_p$ and $N_p$ .	Calling the lower-voltage side "primary" just because it is safer.
More turns on secondary	Step-up transformer	$N_s > N_p$ , so $V_s > V_p$
Fewer turns on secondary	Step-down transformer	$N_s < N_p$ , so $V_s < V_p$
Ideal transformer power is assumed	Input power equals output power	Use $V_p I_p = V_s I_s$

IP Physics Notes (Upper Secondary, Year 3-4): 16) Electromagnetic Induction

Faraday's & Lenz's Laws

Induction Setups

Lenz direction checkpoint

Alternating-Current Generator

Generator graph checkpoint

Transformers

Transformer setup checkpoint

Worked Example: Step-Down Calculation

Power Transmission Rationale

Practice Quiz

Key Takeaways

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