What does Electric and Magnetic Fields cover in IB Physics?

This topic covers electric potential, electric potential energy, and equipotential surfaces in electric fields. Electric potential energy E_p for two point charges is given by E_p = k(q_1q_2)/(r). Electric potential V_e at a point due to a point charge Q is V_e = k(Q)/(r).

Is Electric and Magnetic Fields SL or HL?

Electric and Magnetic Fields is HL only. SL students are not examined on it.

How does FourtyFive help me practise Electric and Magnetic Fields?

FourtyFive has 4 Electric and Magnetic Fields 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.

Is FourtyFive free for Electric and Magnetic Fields practice?

Yes. A free account gives you 50 marked answers a month, and you do not need a card to sign up.

Can I handwrite Electric and Magnetic Fields 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.2 · HL only

Electric and Magnetic Fields: notes and practice questions

Q: How do I revise Electric and Magnetic Fields for IB Physics?

Start from the core idea: this topic covers electric potential, electric potential energy, and equipotential surfaces in electric fields. In the exam: both papers. Field-line sketching is examined directly, and the guidance list above is effectively the list of diagrams that can be asked for. 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 electric potential, electric potential energy, and equipotential surfaces in electric fields.
Electric potential energy $E_p$ for two point charges is given by $E_p = k\frac{q_1q_2}{r}$ .
Electric potential $V_e$ at a point due to a point charge $Q$ is $V_e = k\frac{Q}{r}$ .
Electric field strength $E$ is the negative electric potential gradient, $E = -\frac{\Delta V_e}{\Delta r}$ .
Work done $W$ moving a charge $q$ in an electric field is $W = q\Delta V_e$ .
No work is done moving a charge along an equipotential surface.
Equipotential surfaces can be sketched for various charge configurations.

How it is examined

Both papers. Field-line sketching is examined directly, and the guidance list above is effectively the list of diagrams that can be asked for. Equipotential questions are HL only. The parallel-plate result $E = V/d$ is the bridge into D.3, and most Paper 2 questions use it as the first step of a longer electron-deflection problem. An SL question must not ask about potential or equipotentials in either the gravitational or the electric case.

Given in the booklet

SL: Coulomb's law with $k = 1/4\pi\varepsilon_0$ , $E = F/q$ , $E = V/d$ , plus the elementary charge, $\varepsilon_0$ and k in the constants table, and the electronvolt conversion. HL adds $E_\text{p} = kq_1q_2/r$ , $V_\text{e} = kQ/r$ , the potential gradient and $W = q\Delta V_\text{e}$ . Permittivity values for materials other than free space are supplied in the question.

Key ideas

the direction of forces between the two types of electric charge
Coulomb's law as given by $F = k\dfrac{q_1 q_2}{r^2}$ for charged bodies treated as point charges, where $k = \dfrac{1}{4\pi\varepsilon_0}$
the conservation of electric charge
Millikan's experiment as evidence for quantization of electric charge

Guiding questions

Which experiments provided evidence to determine the nature of the electron?
How can the properties of fields be understood using both an algebraic approach and a visual representation?
What are the consequences of interactions between electric and magnetic fields?

Linking questions

How are electric and magnetic fields like gravitational fields?
What are the relative strengths of the four fundamental forces?
How can moving charges in magnetic fields help probe the fundamental nature of matter?
Charge is quantized. Which other physical quantities are quantized? (NOS)

Practice questions

4 questions · 3 medium · 1 hard

Showing 4 of 4

Question 1

MediumPaper 2 · calculator3 marks

A proton is accelerated from rest in a linear particle accelerator by a uniform electric field. The proton passes through a potential difference of $250\,\text{kV}$ .

(a) Calculate the final speed of the proton.

Question 2

HardPaper 1A · calculator1 mark

The characteristic impedance of free space, $Z_0$ , is a physical constant relating the magnitudes of the electric and magnetic fields of electromagnetic radiation travelling through free space. It is given by the expression $Z_0 = \sqrt{\frac{\mu_0}{\epsilon_0}}$ . What are the fundamental SI units of $Z_0$ ?

A. $\text{kg m}^2 \text{A}^{-2} \text{s}^{-3}$

B. $\text{kg}^{-1} \text{m}^{-2} \text{A}^{2} \text{s}^{3}$

C. $\text{kg}^2 \text{m}^4 \text{A}^{-4} \text{s}^{-6}$

D. $\text{m}^{-2} \text{s}^2$

Question 3

MediumPaper 1A · calculator1 mark

A specialized sensor uses a uniform electric field to accelerate ions. The electric potential changes linearly from $1200 \text{ V}$ to $0 \text{ V}$ over a distance of $2.5 \text{ cm}$ .

What is the magnitude of the electric field strength in this region?

A. $4.8 \times 10^2 \text{ N C}^{-1}$

B. $4.8 \times 10^3 \text{ N C}^{-1}$

C. $4.8 \times 10^4 \text{ N C}^{-1}$

D. $9.6 \times 10^4 \text{ N C}^{-1}$

Question 4

MediumPaper 2 · calculator11 marks

(a)(i)

A robotic arm is used to move a straight conducting wire of length $L = 0.80 \text{ m}$ at a constant velocity to the right perpendicular to a uniform magnetic field of magnitude $B = 0.95 \text{ T}$ . The magnetic field is directed vertically downwards into the page. The wire is connected to a circuit, forming a closed loop, and as it moves, an induced current flows through it. As a result of its motion, the wire experiences a magnetic force of $0.15 \text{ N}$ directed opposite to its velocity (i.e., to the left).

Show that the induced current in the wire is approximately $0.20 \text{ A}$ .

[2]

(a)(ii)

State the direction of the magnetic force on an electron within the moving wire.

[1]

(a)(iii)

Explain why the magnitude of the net magnetic field on the side of the wire towards which it is moving is different from the side it is moving away from.

[3]

(a)(iv)

Outline how Lenz's law applies to this system.

[2]

(b)

A second, long, straight stationary wire carrying a current of $2.0 \text{ A}$ is placed parallel to the moving wire at a distance of $0.15 \text{ m}$ . The current in the stationary wire flows in the same direction as the induced current in the moving wire.

Determine the magnitude of the force per unit length between the two wires. State the fundamental SI units for your answer.

[3]

Every Electric and Magnetic Fields 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.

Electric and Magnetic Fields: notes and practice questions

How it is examined

Guiding questions

Linking questions

Practice questions

Question 1

Question 2

Question 3

Question 4

Every Electric and Magnetic Fields question, marked for you

Where marks are lost

Practise this topic as a session

Questions,
answered.

Start with the IB question
bank built for you.

How it is examined

Guiding questions

Linking questions

Practice questions

Question 1

Question 2

Question 3

Question 4

Every Electric and Magnetic Fields question, marked for you

Where marks are lost

Questions,answered.

Start with the IB questionbank built for you.

Questions,
answered.

Start with the IB question
bank built for you.