Unit Overview

Electromagnetic induction

CIE A-Level Physics· 5 min read 📊 n/a

1. Unit at a glance

This unit reverses the relationship you learned in the previous unit: instead of moving charges creating magnetic fields, we explore how changing magnetic fields create electric effects. We build from foundational definitions up to core laws and practical applications of induction, with each sub-topic relying on the concepts from the previous step.

We cover the following core sub-topics in this unit:

Magnetic flux

Defines magnetic flux and flux linkage, the foundational quantities for all induction calculations.

★★⏱ 3 min

Faraday's law and Lenz's law

Covers the two core laws that describe the magnitude and direction of induced effects.

★★★⏱ 4 min

Induced e.m.f.

Walks through calculation of induced e.m.f. in rotating coils, moving conductors, and other common scenarios.

★★★⏱ 5 min

Self-inductance

Introduces inductance as a circuit property and explores its effects when current changes.

★★★★⏱ 4 min

2. Common Pitfalls

Wrong move:

Assuming a large magnetic flux always produces an induced e.m.f.

Why:

Induced e.m.f. depends on change in flux over time, not the absolute magnitude of flux.

Correct move:

Always confirm that flux is changing before solving an induction problem.

Wrong move:

Misapplying Lenz's law by opposing the original magnetic field instead of the change.

Why:

This leads to incorrect direction for the induced current and e.m.f.

Correct move:

Focus on opposing the change in flux, not the original magnetic field itself.

3. Quick Reference Cheatsheet

Concept	Key Formula/Rule
Magnetic flux	$Φ = B A cos θ$
Flux linkage (N turns)	$N Φ = B A N cos θ$
Faraday's Law	$ε = - \frac{d ( N Φ )}{d t}$
Lenz's Law	Induced current opposes the change that produced it
Self-inductance definition	$ε = - L \frac{d I}{d t}$

What's Next

Begin this unit with the first sub-topic on magnetic flux to build the foundational understanding you need for all subsequent topics. Once you complete all sub-topics in this unit, move on to the next unit on alternating currents to apply your knowledge of induction to AC circuit concepts.