About Electromagnetism in O Level Physics
Electromagnetism is one of the 14 main topics in our O Level Physics (Cambridge (CAIE) 5054) question bank, and about 4% of its real questions come from it. Tayyari Karo has 25 real questions on this topic from 2021 to 2025, from Paper 1, Paper 2; 18 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 12 medium, 11 hard, 2 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
Try 7 real questions
These are real past-paper questions. Think of your answer first, then open the explanation.
Oct/Nov 2025 · Paper 1 · Electromagnetism
Two current-carrying conductors are placed next to each other, with the current in each conductor in the same direction.
Which statement about the forces experienced by the conductors is correct?
- The forces are in the same direction, and the conductors are forced apart.
- The forces are in opposite directions, and the conductors are forced apart.
- The forces are in the same direction, and the conductors are forced towards each other.
- The forces are in opposite directions, and the conductors are forced towards each other.
Show answer and explanation
Answer: D. The forces are in opposite directions, and the conductors are forced towards each other.
Parallel conductors carrying current in the same direction attract each other; each conductor experiences a force pulling it towards the other, so the two forces point in opposite directions (towards each other), causing attraction.
Oct/Nov 2025 · Paper 1 · Electromagnetism
A student uses a simple iron-cored transformer. The primary coil has 250 turns and the secondary coil has 200 turns. The input voltage to the primary coil is 12 V.
What is the output voltage?
- 0.069 V
- 0.11 V
- 9.6 V
- 15 V
Show answer and explanation
Answer: C. 9.6 V
Using Vs/Vp = Ns/Np: Vs = 12 × (200/250) = 9.6 V.
Oct/Nov 2023 · Paper 1 · Electromagnetism
A magnet moves at constant speed through a coil of wire connected to an oscilloscope, producing a trace showing a dip followed immediately by a peak. The experiment is changed and a new trace is produced showing a narrower peak followed, after a clear gap, by a dip. Which statement explains why the new trace is different from the original trace?
- The coil is longer and the other pole of the magnet enters the coil first.
- The coil is longer and the same pole of the magnet enters the coil first.
- The coil is shorter and the other pole of the magnet enters the coil first.
- The coil is shorter and the same pole of the magnet enters the coil first.
Show answer and explanation
Answer: A. The coil is longer and the other pole of the magnet enters the coil first.
In the new trace the two pulses are more widely separated in time, showing it takes longer for the magnet to pass through, i.e. the coil is longer; the order of the pulses is reversed (peak then dip, instead of dip then peak), showing the opposite pole now enters the coil first.
Oct/Nov 2023 · Paper 1 · Electromagnetism
A commutator connects the coil of a d.c. motor to the power supply; once every half-turn, the current in the coil reverses. What is the name of the commutator and what is the orientation of the plane of the coil as the current reverses?
- slip ring, parallel to the magnetic field
- slip ring, perpendicular to the magnetic field
- split ring, parallel to the magnetic field
- split ring, perpendicular to the magnetic field
Show answer and explanation
Answer: D. split ring, perpendicular to the magnetic field
A d.c. motor uses a split-ring commutator; the current reverses at the instant the coil plane is perpendicular to the magnetic field, which keeps the turning effect acting in the same rotational direction.
May/June 2022 · Paper 1 · Electromagnetism
A narrow beam of electrons travels horizontally to the right and enters a region of magnetic field that points into the page.
What is the direction of the deflection of the electrons as they enter the magnetic field?
- into the page
- out of the page
- up the page
- down the page
Show answer and explanation
Answer: D. down the page
Using F = qv × B with the negative charge of the electron, a beam moving right through a field into the page experiences a force down the page (the opposite direction to that found for a positive charge moving the same way).
Oct/Nov 2022 · Paper 1 · Electromagnetism
The output from an a.c. generator is displayed on an oscilloscope as a sine wave.
The generator is then turned at a slower rate. The settings on the oscilloscope controls are not changed.
Which description matches the new output?
- the same amplitude but a longer period
- a smaller amplitude and a longer period
- a larger amplitude and a shorter period
- the same amplitude but a shorter period
Show answer and explanation
Answer: B. a smaller amplitude and a longer period
Turning the coil more slowly cuts field lines more slowly, so the peak e.m.f. is smaller, and each revolution takes longer, so the period is longer.
May/June 2024 · Paper 2 · Electromagnetism
Explain why the coil turns.
Show model answer
Each current-carrying side of the coil lying in the magnetic field experiences a force (motor effect, F = BIL). Because the current flows in opposite directions along the two sides of the coil, the forces on the two sides act in opposite directions, forming a couple (a turning moment) that rotates the coil.
Two equal, opposite forces acting on opposite sides of the coil form a couple, producing rotation.
