What does Induction cover in IB Physics?

This topic covers the principles of electromagnetic induction, including magnetic flux, Faraday's law, Lenz's law, and induced electromotive force (emf). Magnetic flux Phi through a surface is given by Phi = BA cos θ. Faraday's law of induction states that the induced emf mathcalE is mathcalE = -N (Δ Phi)/(Δ t).

Is Induction SL or HL?

Induction is HL only. SL students are not examined on it.

How does FourtyFive help me practise Induction?

FourtyFive has 4 Induction questions. Every answer you write is marked mark by mark, IB-style, and you see where each mark was won or lost. Every part has a hint, the AI tutor helps you through the step you are stuck on, and your Study Profile picks what to practise next.

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Can I handwrite Induction answers on an iPad?

Yes. In the FourtyFive iPad app you write your working by hand with Apple Pencil, the way you would on paper, and it is marked the same way.

Topic D.4 · HL only

Induction: notes and practice questions

Q: How do I revise Induction for IB Physics?

Start from the core idea: this topic covers the principles of electromagnetic induction, including magnetic flux, Faraday's law, Lenz's law, and induced electromotive force (emf). In the exam: hL Paper 1A and HL Paper 2. May 2025 HL Paper 2 TZ1 question 9(d) closed a long SHM question with induction: discuss two factors that affect the magnitude of the induced emf, with the question stem explicitly listing what each bullet had to cover (4 marks, the largest single part on that paper), then explain why connecting a resistor across the coil damps the oscillation (3 marks). Then practise exam-style questions, easiest first, writing out every step of your working before you check it.

3 min read Jump to 4 practice questions

Summary

This topic covers the principles of electromagnetic induction, including magnetic flux, Faraday's law, Lenz's law, and induced electromotive force (emf).
Magnetic flux $\Phi$ through a surface is given by $\Phi = BA \cos \theta$ .
Faraday's law of induction states that the induced emf $\mathcal{E}$ is $\mathcal{E} = -N \frac{\Delta \Phi}{\Delta t}$ .
Lenz's law determines the direction of induced emf, ensuring energy conservation.
For a straight conductor of length $L$ moving at speed $v$ perpendicular to a uniform magnetic field $B$ , the induced emf is $\mathcal{E} = BvL$ .
A coil rotating in a uniform magnetic field induces a sinusoidal varying emf.

How it is examined

HL Paper 1A and HL Paper 2. May 2025 HL Paper 2 TZ1 question 9(d) closed a long SHM question with induction: discuss two factors that affect the magnitude of the induced emf, with the question stem explicitly listing what each bullet had to cover (4 marks, the largest single part on that paper), then explain why connecting a resistor across the coil damps the oscillation (3 marks).

Given in the booklet

$\Phi = BA\cos\theta$ , Faraday's law with the factor N, $\varepsilon = BvL$ . Lenz's law is a statement to be recalled and applied. Transformers, rectification and RL circuits are not on this syllabus at all: the 2016 course had more of this content than the 2025 course does.

Key ideas

There is no standard level content in D.4.

Not assessed

A discussion of inductance and resistance-inductor (RL) circuits is not required.

Guiding questions

What are the effects of relative motion between a conductor and a magnetic field?
How can the power output of electrical generators be increased?
How did the discovery of electromagnetic induction effect industrialization?

Linking questions

How is the efficiency of electricity generation dependent on the source of energy?
Faraday's law of induction includes a rate of change. Which other areas of physics relate to rates of change? (NOS)

Practice questions

4 questions · 4 medium

Showing 4 of 4

Question 1

MediumPaper 2 · calculator3 marks

A high-speed maglev train travels at $100 \text{ m s}^{-1}$ along a track. The vertical component of the Earth's magnetic field at that location is $4.5 \times 10^{-5} \text{ T}$ . The effective length of the conducting axle connecting the wheels is $2.5 \text{ m}$ .

(a) Determine the maximum potential difference induced across the train's axle.

Question 2

MediumPaper 2 · calculator4 marks

A student is performing an experiment to investigate electromagnetic induction. They use a single-turn circular coil connected to a sensitive voltmeter. The coil is placed in a uniform magnetic field.

(a) The coil has a radius of 5.0 cm and is initially oriented such that its plane is perpendicular to a uniform magnetic field of strength 0.10 T. The student then quickly rotates the coil through 90° in 0.050 s so that its plane becomes parallel to the magnetic field. Calculate the magnitude of the average electromotive force (emf) induced in the coil during this rotation.

Question 3

MediumPaper 1A · calculator1 mark

A small electrical generator contains a coil of wire rotating at a constant angular speed $\omega$ in a uniform magnetic field. The variation with time of the induced emf in the coil is shown in the graph.

Graph showing induced EMF / V on y-axis from -12 to 12, and time / ms on x-axis from 0 to 4.0. A sinusoidal wave is shown with amplitude 12 V and period 4.0 ms.

The angular speed of the coil is now increased to $1.5\omega$ .

What is the amplitude of the emf and the time period for the variation of the emf in the coil after this change?

	Amplitude of emf/V	Time period/ms
A.	$18$	$2.67$
B.	$18$	$6.0$
C.	$8.0$	$2.67$
D.	$8.0$	$6.0$

Question 4

MediumPaper 1A · calculator1 mark

A multi-turn coil is placed in a uniform magnetic field. The coil is initially oriented such that its plane is parallel to the magnetic field lines. It is then rotated through $90^\circ$ so its plane becomes perpendicular to the field lines. An average emf of $4.0\text{ mV}$ is induced in the coil during this rotation. The coil has $100$ turns and encloses an area of $5.0\text{ cm}^2$ . The rotation takes $0.25\text{ s}$ .

What is the magnitude of the magnetic field?

A. $5.0\text{ mT}$

B. $10.0\text{ mT}$

C. $20.0\text{ mT}$

D. $40.0\text{ mT}$

Every Induction question, marked for you

Every answer is marked mark by mark, IB-style, and the AI tutor helps when you are stuck.

Where marks are lost

Stopping one step short of the conclusion. Two numbers and no sentence is two marks out of three.
Answering a procedure question with a platitude.
Losing precision in Paper 1B. Uniquely to this paper, quoting the right number badly loses marks.

Induction: notes and practice questions

How it is examined

Guiding questions

Linking questions