A maglev train uses electromagnets to levitate above a track. Explain how increasing the current through the electromagnets affects the force on the train, and describe one way a maglev train differs from a conventional train that uses permanent magnets attached to the track.

OCR GCSE Physics A: Gateway Science (J249) — P3.3 Magnetism and the motor effect · Explain · 4 marks · View as Markdown

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

Maglev trains use the motor effect and electromagnetic principles to float above the track without wheels. Engineers can adjust the current supplied to the electromagnets to control the levitation force.

Model answer (4 marks)

Increasing the current increases the magnetic field strength of the electromagnet. A stronger field produces a larger magnetic force on the train, giving a greater levitation (upward) force. A maglev train uses electromagnets that can be switched off or reversed, whereas a conventional train relies on permanent magnets that cannot be turned off. Consequently, a maglev train floats without physical contact with the track, eliminating friction, while a conventional train runs on wheels that touch the rails.

Examiner tips

  • Use the term ‘magnetic field strength’ and ‘levitation force’ to show understanding of the motor effect.
  • Mention the ability to switch the electromagnets on/off or reverse polarity as a key difference.
  • Highlight the absence of friction due to no contact with the track.
  • Keep the answer concise and directly linked to the marks listed.

Common mistakes

  • Confusing the magnetic field with the electric current itself.
  • Failing to state that the electromagnets can be turned off or reversed.
  • Lumping all differences into one point instead of separating the control and contact aspects.

Mark scheme (4 marks)

  1. Increasing the current increases the strength of the magnetic field produced by the electromagnet
  2. A stronger magnetic field results in a greater force on the train (greater levitation/upward force)
  3. A maglev train's electromagnets can be switched off (or reversed), unlike a permanent magnet which cannot be turned off
  4. A maglev train has no physical contact with the track (no friction between train and track) whereas a conventional wheeled train does

Key terms in this question

electromagnet · permanent magnet · current

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