A straight conducting wire is moved downwards through a magnetic field. A small current is detected in the wire. Explain why a current is produced and describe two ways the student could increase the size of the induced current.

Eduqas A-Level Physics — 4.5 Electromagnetic induction · Explain · 5 marks · View as Markdown

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

A straight conducting wire is held between the poles of a horseshoe magnet. When the wire is moved downwards, a sensitive galvanometer connected to the wire shows a reading.

Model answer (5 marks)

A moving wire cuts magnetic flux, producing a potential difference across its ends. This EMF drives a current through the galvanometer.

To increase the current:
1. Move the wire faster through the field.
2. Use a stronger magnetic field (e.g. a stronger magnet).

Examiner tips

Use the phrase ‘cutting magnetic flux’ to show understanding of Faraday’s law.
Mention that EMF ∝ vBℓ to justify speed and field strength effects.
Keep the answer concise – 5 marks can be earned with 3–4 short sentences.

Common mistakes

Confusing the direction of motion with the direction of induced current.
Failing to mention that the EMF is proportional to the rate of change of flux.
Using vague terms like ‘more electricity’ instead of ‘larger EMF’ or ‘larger current’.

Mark scheme (5 marks)

Moving the wire cuts through (or moves through) the magnetic field lines / the wire cuts the magnetic flux
This induces (or generates) a potential difference / voltage across the wire
This potential difference drives a current around the circuit (through the galvanometer)
Move the wire faster (through the magnetic field) to increase the induced current
Use a stronger magnet to increase the induced current

Key terms in this question

magnetic field · induced current