A maglev train uses powerful electromagnets beneath the train carriage to levitate it above the track. Explain how the electromagnets are made and how changing the current in them affects the force they exert on the track.

OCR A-Level Physics B: Advancing Physics (H557) — 4.2 Energy, power and resistance · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Maglev trains have no wheels and do not touch the track. Instead, electromagnets on the underside of the train interact with the track to produce a lifting force, allowing the train to float and move with very little friction.

Model answer (5 marks)

An electromagnet is a solenoid – a coil of wire wound around an iron core. When electric current flows through the coil, it creates a magnetic field. The iron core concentrates and amplifies this field, making the electromagnet much stronger than the coil alone.

If the current in the coil is increased, the magnetic field produced by the solenoid becomes stronger. A stronger magnetic field exerts a larger magnetic force on the track, which in turn increases the lifting force that keeps the train levitated.

Examiner tips

  • Use the term "solenoid" and "iron core" to show you know the construction.
  • Explain that current creates a magnetic field and that the core amplifies it.
  • State that increasing current strengthens the field and therefore the lifting force.
  • Keep the answer concise – 5 marks can be earned with 3–4 short points.

Common mistakes

  • Saying the electromagnet is just a magnet without mentioning the coil and core.
  • Confusing the direction of the force with the direction of the current.
  • Omitting the effect of increasing current on the magnetic field strength.

Mark scheme (5 marks)

  1. An electromagnet is made from a solenoid (coil of wire) with an iron core
  2. When current flows through the coil/wire, a magnetic field is generated
  3. The iron core increases the strength of the magnetic field
  4. Increasing the current increases the strength of the magnetic field
  5. A stronger magnetic field produces a greater force on the track / increasing current increases the lifting force

Key terms in this question

electromagnet · current

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