Why is electromagnetic induction so important in daily life?

It's the fundamental principle behind electricity generation in power stations, transformers for changing voltage levels, induction cookers, and many electric motors and generators, powering our modern world.

How do Faraday's Law and Lenz's Law work together?

Faraday's Law tells us the *magnitude* of the induced EMF, based on the rate of flux change. Lenz's Law provides the *direction* of the induced EMF or current, stating it always opposes the change in magnetic flux that caused it.

What is the difference between magnetic flux and magnetic flux linkage?

Magnetic flux ($\Phi$) refers to the magnetic field passing through a *single* loop or area. Magnetic flux linkage ($\lambda$) is the total flux through *all turns* of a coil, so $\lambda = N\Phi$ for a coil with N turns, where N is the number of turns.

Where can I learn Electromagnetic induction for Cambridge 9702?

This free lesson on MarkScheme covers syllabus point 20.5 (Electromagnetic induction) for Cambridge A-Level Physics. It includes visual revision, key points, and links to real past-paper questions with mark-scheme marking at markscheme.app/courses/9702/20-5-electromagnetic-induction.

Is Electromagnetic induction (20.5) on 9702 free to study?

Yes. The Physics 9702 course on MarkScheme is 100% free — including premium visual lessons, exam tips, and past-paper marking. No paywall for Electromagnetic induction.

How do I revise Electromagnetic induction for 9702 exams?

Start with the visual steps on this page, note the key exam points, then attempt a 9702 past-paper question on Electromagnetic induction using MarkScheme's /mark tool. Mark strictly against the official scheme and re-read any marks you lost.

Electromagnetic induction 9702 — Free…

Electromagnetic induction

Ever wondered how electricity is generated in power plants? It's largely thanks to electromagnetic induction! This fundamental principle describes how a changing magnetic field can create an electric current. We'll explore the concepts of magnetic flux, Faraday's Law, Lenz's Law, and the fascinating Hall Effect, all crucial for understanding how generators and sensors work. This pilot aligns with Senpai Corner A Level notes (2025–2027) for topic 20.5.

BY THE END, YOU CAN…

1Define and apply concepts of magnetic flux and flux linkage.
2Explain and use Faraday's and Lenz's Laws to determine induced EMF and current direction.
3Describe the Hall Effect and its application in measuring magnetic fields.

In simple terms

A friendly intro before the formal notes — no formulas yet.

Electromagnetic induction

Cambridge 9702 Paper 4 — Electromagnetic induction (20.5). Senpai Corner diagram-backed pilot with premium structure and live visuals.

1
$\Phi$ is the magnetic flux (in Webers, Wb).
2
B is the magnetic flux density (in Tesla, T).
3
A is the area through which the field lines pass (in m²).
4
$\theta$ is the angle between the magnetic field B and the normal to the area A.

What this topic covers

The official Cambridge syllabus points this lesson works through.

20.5.1
Define magnetic flux as the product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density
20.5.2
Recall and use $Φ = BA$
20.5.3
Understand and use the concept of magnetic flux linkage
20.5.4
Understand and explain experiments that demonstrate: that a changing magnetic flux can induce an e.m.f. in a circuit; that the induced e.m.f. is in such a direction as to oppose the change producing it; the factors affecting the magnitude of the induced e.m.f.
20.5.5
Recall and use Faraday's and Lenz's laws of electromagnetic induction

Explore the concept

Use the live diagram and synced steps — play it or tap a step card to walk through.

Key formulas

Tap any symbol to reveal exactly what it means and its units.

$\Phi = BA \cos \theta$

Tap a symbol — great for exam definitions

$\lambda = N\Phi = NBA \cos \theta$

Tap a symbol — great for exam definitions

$\mathcal{E} = |\frac{\Delta \lambda}{\Delta t}| \quad \text{ or } \quad \mathcal{E} = |N\frac{\Delta \Phi}{\Delta t}|$

Tap a symbol — great for exam definitions

$\mathcal{E} = -\frac{\Delta (N\Phi)}{\Delta t}$

Tap a symbol — great for exam definitions

$V_H = \frac{BI}{nqt}$

Full topic notes

Formal explanation with the rigour you need for the exam.

Magnetic Flux ($\Phi$)

Magnetic flux quantifies the total amount of magnetic field lines passing through a specific area. Think of it as how much 'magnetic field' is piercing through a surface. The angle between the field and the surface is crucial.

$\Phi = BA \cos \theta$

$\Phi$ is the magnetic flux (in Webers, Wb).
B is the magnetic flux density (in Tesla, T).
A is the area through which the field lines pass (in m²).
$\theta$ is the angle between the magnetic field B and the normal to the area A.
Maximum flux occurs when the field is perpendicular to the area ( $\theta = 0^\circ$ , $\cos 0^\circ = 1$ ), so $\Phi = BA$ .
Zero flux occurs when the field is parallel to the area ( $\theta = 90^\circ$ , $\cos 90^\circ = 0$ ).

Magnetic Flux Linkage ($\lambda$)

When a coil has multiple turns, the magnetic flux interacts with each turn. Magnetic flux linkage is the total magnetic flux interacting with the entire coil. It's simply the magnetic flux through one turn multiplied by the number of turns.

$\lambda = N\Phi = NBA \cos \theta$

N is the number of turns in the coil.
$\Phi$ is the magnetic flux through a single turn.
The unit for magnetic flux linkage is also Weber (Wb), or more specifically, Weber-turns.

Faraday's Law of Electromagnetic Induction

Faraday's Law provides the quantitative relationship for induced EMF. It states that the magnitude of an induced electromotive force (EMF) is directly proportional to the rate at which the magnetic flux linkage changes through a conductor or coil.

$\mathcal{E} = |\frac{\Delta \lambda}{\Delta t}| \quad \text{ or } \quad \mathcal{E} = |N\frac{\Delta \Phi}{\Delta t}|$

$\mathcal{E}$ is the induced EMF (in Volts, V).
$\Delta \lambda$ is the change in magnetic flux linkage (in Wb).
$\Delta t$ is the time taken for the change (in seconds, s).
A faster change in flux linkage results in a larger induced EMF.

Lenz's Law

While Faraday's Law tells us how much EMF is induced, Lenz's Law tells us its direction. It states that the induced current will flow in a direction that creates a magnetic field which opposes the original change in magnetic flux that caused it. This is a consequence of the conservation of energy.

$\mathcal{E} = -\frac{\Delta (N\Phi)}{\Delta t}$

The negative sign mathematically incorporates Lenz's Law.
It signifies that the induced EMF opposes the change in flux.
If flux is increasing, the induced field tries to decrease it. If flux is decreasing, the induced field tries to increase it.

The Hall Effect

The Hall Effect describes the induction of a potential difference (called Hall Voltage, $V_H$ ) across a conductor when it carries a current and is placed in a perpendicular magnetic field. This occurs because the magnetic force separates the charge carriers to opposite sides of the conductor.

$V_H = \frac{BI}{nqt}$

B is the magnetic flux density.
I is the current flowing through the conductor.
n is the charge carrier number density.
q is the charge of a single carrier (e.g., electron charge e).
t is the thickness of the conductor slice perpendicular to B and I.

The Hall Probe

A Hall probe is a practical application of the Hall Effect. It's a small, flat device that can be used to accurately measure magnetic field strength (magnetic flux density). By measuring the Hall Voltage for a known current and material, the magnetic field can be determined, as $V_H$ is directly proportional to B.

Worked examples

See the formulas applied — reveal one step at a time, like the exam.

EXAMPLE 1

A coil with 500 turns has a magnetic flux of 2.0 mWb passing through it. If this flux is uniformly reduced to 0.5 mWb in 0.25 seconds, calculate the magnitude of the induced EMF.

1
Calculate the initial magnetic flux linkage:

EXAMPLE 2

A straight conductor of length 25 cm moves at a constant speed of 8.0 m/s at right angles to a uniform magnetic field of flux density 40 mT. Calculate the EMF induced across the ends of the conductor.

1
Identify the formula for motional EMF: $\mathcal{E} = BLv$ , where B, L, and v are mutually perpendicular.

How it all connects

The big idea sits in the middle — tap a linked idea to explore the link.

MAIN IDEAElectromagnetic induction

Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.

Glossary

Try to recall each definition before you reveal it.

Quick check

Answer in your head first — then tap to check. No pressure.

Revision flashcards

Flip the card. Test yourself before the exam.

QUESTION · 1 / 15

What is electromagnetic induction?

TAP OR SPACE TO FLIP

ANSWER

The process of generating an electromotive force (EMF) in a conductor due to a changing magnetic field or relative motion.

TAP OR SPACE TO FLIP BACK

1 / 15 · ← → space

Key takeaways

Review these before you close the topic — retrieval beats re-reading.

✓
$\Phi$ is the magnetic flux (in Webers, Wb).
✓
B is the magnetic flux density (in Tesla, T).
✓
A is the area through which the field lines pass (in m²).
✓
$\theta$ is the angle between the magnetic field B and the normal to the area A.
✓
Maximum flux occurs when the field is perpendicular to the area ( $\theta = 0^\circ$ , $\cos 0^\circ = 1$ ), so $\Phi = BA$ .
✓
Zero flux occurs when the field is parallel to the area ( $\theta = 90^\circ$ , $\cos 90^\circ = 0$ ).

Practice — then mark it

The whole point: a real Cambridge question, marked mark-by-mark.

Real past paper[0]

Mark a past-paper question on this topic

Do it on paper → mark itMARKED MARK-BY-MARK · B1 / M1 / A1 · OFFICIAL SCHEME

Extra simulations & links

PhET, GeoGebra and other curated tools — open in a new tab.

Frequently asked

✓

Checkpoint

One marked question is worth ten re-reads — close the loop before you move on.

Checkpoint

Reading it isn’t knowing it — prove it.

Before you move on: do Mark a past-paper question on this topic on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.

Attempt & get marked →Takes about a minute · you’ll land back on this lesson

← PREVIOUS20.4 Magnetic fields due to currents NEXT →21.1 Characteristics of alternating currents

Electromagnetic induction

BY THE END, YOU CAN…

1Define and apply concepts of magnetic flux and flux linkage.
2Explain and use Faraday's and Lenz's Laws to determine induced EMF and current direction.
3Describe the Hall Effect and its application in measuring magnetic fields.

In simple terms

A friendly intro before the formal notes — no formulas yet.

Electromagnetic induction

Cambridge 9702 Paper 4 — Electromagnetic induction (20.5). Senpai Corner diagram-backed pilot with premium structure and live visuals.

1
$\Phi$ is the magnetic flux (in Webers, Wb).
2
B is the magnetic flux density (in Tesla, T).
3
A is the area through which the field lines pass (in m²).
4
$\theta$ is the angle between the magnetic field B and the normal to the area A.

What this topic covers

The official Cambridge syllabus points this lesson works through.

20.5.1
Define magnetic flux as the product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density
20.5.2
Recall and use $Φ = BA$
20.5.3
Understand and use the concept of magnetic flux linkage
20.5.4
Understand and explain experiments that demonstrate: that a changing magnetic flux can induce an e.m.f. in a circuit; that the induced e.m.f. is in such a direction as to oppose the change producing it; the factors affecting the magnitude of the induced e.m.f.
20.5.5
Recall and use Faraday's and Lenz's laws of electromagnetic induction

Explore the concept

Use the live diagram and synced steps — play it or tap a step card to walk through.

Key formulas

Tap any symbol to reveal exactly what it means and its units.

$\Phi = BA \cos \theta$

Tap a symbol — great for exam definitions

$\lambda = N\Phi = NBA \cos \theta$

Tap a symbol — great for exam definitions

$\mathcal{E} = |\frac{\Delta \lambda}{\Delta t}| \quad \text{ or } \quad \mathcal{E} = |N\frac{\Delta \Phi}{\Delta t}|$

Tap a symbol — great for exam definitions

$\mathcal{E} = -\frac{\Delta (N\Phi)}{\Delta t}$

Tap a symbol — great for exam definitions

$V_H = \frac{BI}{nqt}$

Full topic notes

Formal explanation with the rigour you need for the exam.

Magnetic Flux ($\Phi$)

$\Phi = BA \cos \theta$

$\Phi$ is the magnetic flux (in Webers, Wb).
B is the magnetic flux density (in Tesla, T).
A is the area through which the field lines pass (in m²).
$\theta$ is the angle between the magnetic field B and the normal to the area A.
Maximum flux occurs when the field is perpendicular to the area ( $\theta = 0^\circ$ , $\cos 0^\circ = 1$ ), so $\Phi = BA$ .
Zero flux occurs when the field is parallel to the area ( $\theta = 90^\circ$ , $\cos 90^\circ = 0$ ).

Magnetic Flux Linkage ($\lambda$)

$\lambda = N\Phi = NBA \cos \theta$

N is the number of turns in the coil.
$\Phi$ is the magnetic flux through a single turn.
The unit for magnetic flux linkage is also Weber (Wb), or more specifically, Weber-turns.

Faraday's Law of Electromagnetic Induction

$\mathcal{E} = |\frac{\Delta \lambda}{\Delta t}| \quad \text{ or } \quad \mathcal{E} = |N\frac{\Delta \Phi}{\Delta t}|$

$\mathcal{E}$ is the induced EMF (in Volts, V).
$\Delta \lambda$ is the change in magnetic flux linkage (in Wb).
$\Delta t$ is the time taken for the change (in seconds, s).
A faster change in flux linkage results in a larger induced EMF.

Lenz's Law

$\mathcal{E} = -\frac{\Delta (N\Phi)}{\Delta t}$

The negative sign mathematically incorporates Lenz's Law.
It signifies that the induced EMF opposes the change in flux.
If flux is increasing, the induced field tries to decrease it. If flux is decreasing, the induced field tries to increase it.

The Hall Effect

$V_H = \frac{BI}{nqt}$

B is the magnetic flux density.
I is the current flowing through the conductor.
n is the charge carrier number density.
q is the charge of a single carrier (e.g., electron charge e).
t is the thickness of the conductor slice perpendicular to B and I.

The Hall Probe

Worked examples

See the formulas applied — reveal one step at a time, like the exam.

EXAMPLE 1

A coil with 500 turns has a magnetic flux of 2.0 mWb passing through it. If this flux is uniformly reduced to 0.5 mWb in 0.25 seconds, calculate the magnitude of the induced EMF.

1
Calculate the initial magnetic flux linkage:

EXAMPLE 2

1
Identify the formula for motional EMF: $\mathcal{E} = BLv$ , where B, L, and v are mutually perpendicular.

How it all connects

The big idea sits in the middle — tap a linked idea to explore the link.

MAIN IDEAElectromagnetic induction

Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.

Glossary

Try to recall each definition before you reveal it.

Quick check

Answer in your head first — then tap to check. No pressure.

Revision flashcards

Flip the card. Test yourself before the exam.

QUESTION · 1 / 15

What is electromagnetic induction?

TAP OR SPACE TO FLIP

ANSWER

The process of generating an electromotive force (EMF) in a conductor due to a changing magnetic field or relative motion.

TAP OR SPACE TO FLIP BACK

1 / 15 · ← → space

Key takeaways

Review these before you close the topic — retrieval beats re-reading.

✓
$\Phi$ is the magnetic flux (in Webers, Wb).
✓
B is the magnetic flux density (in Tesla, T).
✓
A is the area through which the field lines pass (in m²).
✓
$\theta$ is the angle between the magnetic field B and the normal to the area A.
✓
Maximum flux occurs when the field is perpendicular to the area ( $\theta = 0^\circ$ , $\cos 0^\circ = 1$ ), so $\Phi = BA$ .
✓
Zero flux occurs when the field is parallel to the area ( $\theta = 90^\circ$ , $\cos 90^\circ = 0$ ).

Practice — then mark it

The whole point: a real Cambridge question, marked mark-by-mark.

Real past paper[0]

Mark a past-paper question on this topic

Do it on paper → mark itMARKED MARK-BY-MARK · B1 / M1 / A1 · OFFICIAL SCHEME

Extra simulations & links

PhET, GeoGebra and other curated tools — open in a new tab.

Frequently asked

✓

Checkpoint

One marked question is worth ten re-reads — close the loop before you move on.

Checkpoint

Reading it isn’t knowing it — prove it.

Before you move on: do Mark a past-paper question on this topic on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.

Attempt & get marked →Takes about a minute · you’ll land back on this lesson

← PREVIOUS20.4 Magnetic fields due to currents NEXT →21.1 Characteristics of alternating currents

Revise Electromagnetic induction for Cambridge 9702 (20.5)

In simple terms

What this topic covers

Explore the concept

Key formulas

Full topic notes

Magnetic Flux ($\Phi$)

Magnetic Flux Linkage ($\lambda$)

Faraday's Law of Electromagnetic Induction

Lenz's Law

The Hall Effect

The Hall Probe

Worked examples

How it all connects

Glossary

Quick check

Revision flashcards

Key takeaways

Practice — then mark it

Mark a past-paper question on this topic

Extra simulations & links

Frequently asked

Checkpoint

Reading it isn’t knowing it — prove it.

In simple terms

What this topic covers

Explore the concept

Key formulas

Full topic notes

Magnetic Flux ($\Phi$)

Magnetic Flux Linkage ($\lambda$)

Faraday's Law of Electromagnetic Induction

Lenz's Law

The Hall Effect

The Hall Probe

Worked examples

How it all connects

Glossary

Quick check

Revision flashcards

Key takeaways

Practice — then mark it

Mark a past-paper question on this topic

Extra simulations & links

Frequently asked

Checkpoint

Reading it isn’t knowing it — prove it.

Discuss Electromagnetic induction