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A2 Daily A Level Physics question

2026-06-29 OCR A Electromagnetic induction (M6): Lenz’s law OCR-A Module 6.3.2 Electromagnetic induction: Faraday’s and Lenz’s laws OCR-A Module 6.3.1 Magnetic flux and flux linkage (qualitative)

In a school demo, a strong neodymium magnet is dropped through a vertical copper pipe (the pipe is not part of an external circuit). Which statement must be true?

  1. A It falls faster than in air because currents in the pipe attract the magnet downward.
  2. B It falls at the same rate as in air because copper is not magnetic so no currents form.
  3. C It falls more slowly than in air because currents in the pipe create a magnetic field opposing the magnet’s motion. (correct)
  4. D It briefly speeds up then slows to the same speed as in air because currents only occur when the magnet leaves the pipe.

Answer

The correct answer is C.

Correct: C — It falls more slowly than in air because currents in the pipe create a magnetic field opposing the magnet’s motion. A is wrong: by Lenz’s law the induced magnetic field opposes the change in flux, producing an upward force that resists the fall, not a downward pull that speeds it up. B is wrong: copper being non-magnetic is irrelevant; it is a good conductor, so changing flux induces currents. C is correct as stated by Lenz’s law, leading to a reduced acceleration and often a low terminal speed. D is wrong: induced currents occur whenever the flux through the pipe changes—while the magnet enters, moves within, and exits—not only at the edges.

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