A maglev train uses powerful electromagnets beneath the train carriage and along the track. When current flows through the electromagnets, the train is levitated above the track and pushed forward. Explain how changing the current supplied to the electromagnets beneath the train affects the force experienced by the train, and state two ways, other than changing the current, that the strength of an electromagnet could be increased.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Maglev (magnetic levitation) trains have no wheels and do not touch the track. They use electromagnets — solenoids with iron cores — to both levitate and propel the carriage. Engineers can adjust the electrical supply to control the levitation force.
Model answer (5 marks)
Increasing the current through the electromagnet increases the magnetic field strength produced by the coil. A stronger magnetic field exerts a larger magnetic force on the train, so the levitation and propulsion forces increase. Conversely, decreasing the current weakens the field and reduces the force.
Other ways to increase electromagnet strength are:
1. Increase the number of turns of wire in the coil.
2. Use a ferromagnetic core (e.g. iron) or increase the core’s cross‑sectional area or length.
Other ways to increase electromagnet strength are:
1. Increase the number of turns of wire in the coil.
2. Use a ferromagnetic core (e.g. iron) or increase the core’s cross‑sectional area or length.
Examiner tips
- Use the phrase ‘increasing the current increases the magnetic field’ to show understanding of the relationship; mention force ∝ B. Include both the effect on levitation and propulsion. List two distinct methods (turns, core material, core size).
- Keep answer concise, avoid unnecessary words; use UK spelling.
- Use bullet points or numbered list for the two methods to show clear structure.
Common mistakes
- Saying the force increases without linking it to the magnetic field strength (B).
- Listing a method that is essentially the same as changing current, e.g. ‘increase the voltage’.
- Using vague terms like ‘make the electromagnet stronger’ without specifying how.
Mark scheme (5 marks)
- Increasing the current increases the strength of the magnetic field produced by the electromagnet
- A stronger magnetic field produces a greater force on the train (force is proportional to the magnetic flux density / field strength)
- Decreasing the current decreases the magnetic field strength and therefore decreases the force (correct direction of change stated)
- First correct method to increase electromagnet strength (other than current): increase the number of turns/coils of wire
- Second correct method to increase electromagnet strength (other than current): use an iron core / change the core material to iron (if not already stated) OR increase the length of the coil OR increase the cross-sectional area of the coil
Key terms in this question
electromagnet · force · current
Related
- All OCR A-Level Physics B: Advancing Physics (H557) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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