Magnetic fields
4 marks · NormalA student uses iron filings to reveal the magnetic field pattern around a bar magnet. They notice that the filings bunch together at certain locations.
Explain why iron filings gather more closely at the poles of the magnet.
Describe what this observation shows about the magnetic field strength near the poles compared to the middle of the magnet.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) The iron filings are attracted where the magnetic field is strongest, which is at the poles, so they collect there in greater density. · must show Field strength attracts filings, Poles have strongest field
(b) The magnetic field is strongest at the poles and weaker away from the poles in the middle of the magnet. · must show Field is strongest at poles, Field is weaker in the middle
Common mistakes: Suggesting poles have more filings due to shape rather than field strength
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Marking points
B1 (a) · 1 mark · Relates density of filings to strength of magnetic field.
B2 (a) · 1 mark · States that poles are where magnetic field is strongest.
B3 (b) · 1 mark · States magnetic field is strongest at the poles.
B4 (b) · 1 mark · States magnetic field is weaker away from the poles/in the middle.
Worked solution
a) Iron filings gather at the poles because the magnetic field is strongest there and pulls the filings towards those regions.
b) This shows that the magnetic field strength is highest at the poles and is lower in the middle of the magnet.