D.2 Electric and magnetic fields questions for IB Physics

110 questions on Electric and magnetic fields, written by Augment in the style of IB exam papers. Six of them are below in full, to answer on paper.

IB Physics
Part of D Fields
SL and HL

Questions by paper and level

SL and HL questions are for students at either level. HL only questions cover what only HL students study.

Paper	SL and HL	HL only	All
Paper 1A	27	16	43
Paper 1B	5	2	7
Paper 2	31	29	60
Every paper	63	47	110

Counted on 10 November 2026

Questions to try

Written by Augment in the style of IB exams, not past papers. Answer them on paper, then check each one against its markscheme with a free account.

Question 1 · PHY-00083Paper 1A · 1 mark

A small magnet stays at rest on the vertical steel door of a refrigerator. One of the forces acting on the magnet is the magnetic force exerted on it by the door. Which force forms a Newton's third law pair with this force?

A
the normal force exerted by the door on the magnet
B
the friction force exerted by the door on the magnet
C
the gravitational force exerted by Earth on the magnet
D
the magnetic force exerted by the magnet on the door

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Question 2 · PHY-01215Paper 1B · HL only · 12 marks

A group of students analyse data from an accelerator experiment. A beam of alpha particles is directed at a thin copper foil (proton number $Z = 29$ ) inside an evacuated chamber. A detector at a large fixed scattering angle counts the scattered alpha particles. For each initial kinetic energy $E_{k}$ of the alpha particles, the students calculate

Q = \frac{measured count rate}{count rate predicted using the electric force alone} .

$E_{k}$ / MeV	6.0	8.0	10.0	12.0	14.0	16.0	18.0
$Q$ ± 0.05	1.02	0.98	1.01	0.99	0.76	0.43	0.11

(a)
State why the chamber is evacuated.
1 mark
(b)
Calculate the percentage uncertainty in $Q$ when $E_{k} = 16.0$ MeV.
1 mark
(c)
The graph shows the variation of $Q$ with $E_{k}$ .
Estimate, using the graph, the kinetic energy $E_{T}$ above which the measured count rate deviates from the prediction.
2 marks
(d)
Show that the distance of closest approach of an alpha particle of kinetic energy $E_{T}$ in a head-on collision with a copper nucleus is about $7 \times 10^{- 15}$ m.
2 marks
(e)
Explain why $Q$ falls below 1 when $E_{k}$ is greater than $E_{T}$ .
2 marks
(f)
Assume that the deviation begins when the distance of closest approach equals the sum of the radii of the alpha particle and the copper nucleus. Determine the radius of a copper nucleus.
2 marks
(g)
Estimate the nucleon number of the copper nuclei.
2 marks

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Question 3 · PHY-00387Paper 2 · 10 marks

A small oil droplet of radius 1.5 μm falls vertically through air between two horizontal metal plates that are 6.0 mm apart. The density of the oil is 920 kg m $^{- 3}$ , the density of air is 1.2 kg m $^{- 3}$ and the viscosity of air is $1.8 \times 10^{- 5}$ Pa s. At first there is no potential difference between the plates.

(a)
Show that the terminal speed of the droplet is about 0.25 mm s $^{- 1}$ .
3 marks
(b)
Outline why the buoyancy force on the droplet can be neglected.
1 mark
(c)
A potential difference of 450 V is now applied between the plates, with the upper plate positive. The droplet carries a charge of $- 5 e$ . Calculate the electric force on the droplet.
2 marks
(d)
Determine the new terminal velocity of the droplet.
2 marks
(e)
Determine the potential difference that would make the droplet rise at a constant speed of 0.25 mm s $^{- 1}$ .
2 marks

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Question 4 · PHY-00815Paper 1A · 1 mark

A rubber balloon is rubbed on a wool jumper. The balloon becomes negatively charged. Which describes the transfer of charge?

A
Positive charge moves from the balloon to the wool.
B
Positive charge moves from the wool to the balloon.
C
Electrons move from the balloon to the wool.
D
Electrons move from the wool to the balloon.

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Question 5 · PHY-01405Paper 1B · 12 marks

A group of students test Coulomb's law. A small conducting sphere A is mounted on an insulating rod that stands on a top-pan balance. An identical sphere B is held directly above A by an insulating rod in a clamp. The separation $r$ between the centres of the spheres can be changed by moving the clamp.

Sphere A on a vertical insulating rod standing on a top-pan balance. Identical sphere B is held directly above it on an insulating rod from a clamp and stand. The distance r between the centres of the spheres is marked.

The balance is set to read zero with both spheres uncharged. Both spheres are then given the same positive charge by touching them to the same terminal of a high-voltage supply.

(a)
Outline why the reading on the balance becomes positive when the spheres are charged.
1 mark
(b)
The students record the balance reading $m$ for different values of $r$ .
$r$ / cm ± 0.1 cm
$m$ / g ± 0.01 g
3.0
0.58
4.0
0.33
5.0
0.21
6.0
0.15
8.0
0.08
10.0
0.05
Calculate, for $r = 4.0 cm$ , the electric force between the spheres and its absolute uncertainty.
2 marks
(c)
Calculate the percentage uncertainty in $\frac{1}{r^{2}}$ for $r = 3.0 cm$ .
2 marks
(d)
The graph shows the variation of $F$ with $\frac{1}{r^{2}}$ , where $F$ is the electric force between the spheres. The error bars show the uncertainty in $F$ ; the uncertainty in $\frac{1}{r^{2}}$ is not shown. The line of best fit is drawn.
Determine, using the graph, the charge on each sphere.
3 marks
(e)
The students claim that the data show that $F$ is proportional to $\frac{1}{r^{2}}$ . Discuss this claim.
2 marks
(f)
After taking the last reading, the students return sphere B to $r = 3.0 cm$ . The balance now reads 0.49 g. Suggest a reason for this and an improvement to the procedure.
2 marks

$r$ / cm ± 0.1 cm	$m$ / g ± 0.01 g
3.0	0.58
4.0	0.33
5.0	0.21
6.0	0.15
8.0	0.08
10.0	0.05

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Question 6 · PHY-00388Paper 2 · 10 marks

In a mass spectrometer, singly charged positive ions of neon-20 (mass 20 u) and neon-22 (mass 22 u) all move with a speed of $6.0 \times 10^{4}$ m s $^{- 1}$ . They enter a region of uniform magnetic field of strength 0.20 T through a slit S. The field is directed into the page. The ions travel in semicircles and strike a detector plate.

A horizontal detector plate with a slit S. Ions travel upwards into a region of uniform magnetic field directed into the page, shown by crosses. Two semicircular paths of slightly different radii curve to the left and return to the plate.

(a)
Explain why the ions move in a circular path.
2 marks
(b)
Outline why the kinetic energy of an ion does not change while it is in the field.
1 mark
(c)
Show that the radius of the path of a neon-20 ion is about 6 cm.
2 marks
(d)
Determine the distance between the points where the neon-20 and the neon-22 ions strike the detector plate.
2 marks
(e)
Calculate the time that a neon-20 ion spends in the magnetic field. State, with a reason, whether a faster neon-20 ion would spend more time, less time or the same time in the field.
2 marks
(f)
Calculate the centripetal acceleration of a neon-20 ion in the field.
1 mark

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