IGCSE · 26 September 2026 · 6 min read
IGCSE magnetism and induction questions: choose the right effect
Magnetism questions become confusing when every diagram contains a coil, a magnet and arrows. The components alone do not identify the process. Ask what the question supplies and what it asks you to explain: current, field, movement, force or voltage.
These original examples practise the distinctions and calculations used in IGCSE Physics. Check the Core/Supplement or board-specific scope in your own specification, especially for transformer and direction-rule detail. The questions are teaching examples, not copied examination material.
Sort the situation into cause and effect
A current-carrying wire produces a magnetic field around it. A current-carrying conductor placed in an external magnetic field can experience a force: that is the motor effect. A conductor or coil experiencing a suitable change in magnetic field can have an induced voltage: that is electromagnetic induction. These statements describe different starting conditions.
Before applying a hand rule or equation, write a short chain such as changing field → induced voltage → current if the circuit is closed. This prevents a common error: claiming that a magnet always creates current merely because it is near a wire. There must be the relevant change, and current also needs a conducting path.
Worked example: a magnet enters, stops and leaves a coil
A bar magnet is pushed into a coil connected to a sensitive centre-zero meter, held stationary, then pulled out. During entry the changing magnetic field through the coil induces a voltage and a current produces a meter deflection. While both are stationary the change stops, so the induced current returns to zero. Withdrawal produces a deflection in the opposite direction.
The meter's actual left or right direction depends on how the coil and leads are connected; do not invent it from an unlabelled sketch. The reliable prediction is the reversal relative to the first movement. Pushing the magnet in faster generally gives a larger peak induced voltage for the same setup because the field through the coil changes more rapidly.
Transfer the explanation by changing one condition
Now keep the magnet stationary and move the coil towards it. Relative motion can still change the field through the coil, so induction can occur. If magnet and coil move together while their relative arrangement remains unchanged, that movement alone does not create the same changing-field effect. The deciding feature is not movement relative to the room.
Reverse the pole entering the coil while keeping the motion the same. The direction of induced voltage reverses. Reverse both pole and motion and the two reversals restore the original direction. Do not describe this as energy created from nothing: mechanical work done against the interaction supplies the electrical energy transferred in the circuit.
Worked example: predict a motor force
Consider a straight conductor with conventional current directed out of the page, in a magnetic field directed from left to right. The motor-effect direction rule gives an upward force. Reversing only the current changes the force downward. Reversing only the magnetic field also changes the force downward. Reversing both leaves the force upward.
Use the magnetic field direction from north towards south in the external gap, and conventional current rather than electron-flow direction. A wrong arrow may come from applying the generator rule to a motor situation. Check the input first: here an existing current and field produce a force; the question is not asking for an induced voltage from movement.
Worked example: turns ratio and an ideal current check
An ideal transformer has 600 primary turns and 150 secondary turns. Its primary voltage is 240 V. Using Vₛ / Vₚ = Nₛ / Nₚ gives Vₛ = 240 × 150 / 600 = 60 V. The secondary has fewer turns, so a smaller voltage is physically consistent. If you obtain 960 V, you have probably inverted the ratio.
If the ideal secondary supplies 2.0 A, the output power is 60 × 2.0 = 120 W. With no losses, the input current is 120 / 240 = 0.50 A. A real transformer requires more input power than useful output power. A steady direct current does not provide the continually changing magnetic field needed for normal continuous transformer action.
Independent practice and an error diagnosis
Try a second ideal transformer: 800 primary turns, 200 secondary turns and 120 V input. The turns ratio is one quarter, so the output is 30 V. If the output current is 0.40 A, output power is 12 W and ideal input current is 0.10 A. Check both ratios and the power balance before accepting your answer.
For written questions, identify the missing causal link in your answer. Magnet moves is incomplete without a changing magnetic field through the coil; more turns is incomplete without saying what output changes. Keep a correction log with the effect, the direction prediction and the relevant assumption. Then solve a changed setup without looking at the original arrows.
Questions, explained
Choose a question for a direct answer, then explore the explanation and supporting resources. Each answer has its own link to save or share.
Why does a stationary magnet not induce a current in a stationary coil?
Its field through the stationary coil is not changing. Electromagnetic induction requires the relevant change in magnetic field, which can occur through relative motion or a changing current in a nearby coil. A current also requires a closed conducting circuit.
Why does moving a magnet faster increase induced voltage?
For the same magnet and coil arrangement, faster movement changes the magnetic field through the coil more rapidly. This generally increases the peak induced voltage. State the changing-field explanation instead of saying that faster motion simply creates more magnetism.
What is the difference between the motor effect and induction?
The motor effect uses a current in an external magnetic field to produce a force. Electromagnetic induction produces a voltage when the field through a coil changes or a conductor cuts magnetic field lines. Identify which quantities are supplied before choosing a direction rule.
Why does a transformer need alternating current?
Alternating current continually changes the magnetic field produced by the primary coil, allowing a voltage to be induced in the secondary. A steady direct current does not sustain that changing field. Switching transients are different from continuous transformer operation.
Why can a step-down transformer increase current?
For an ideal transformer, input and output powers are equal. If output voltage is lower, the current corresponding to the same transferred power is higher because P = VI. The actual current depends on the connected load, and real transformers have losses; they do not create extra energy.