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GCSE Physics 07 — Magnetism and Electromagnetism

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Topics include Permanent Magnetism and Magnetic Fields, Magnetic Fields around Currents, Electromagnets and their Applications, The Motor Effect and F = BIl, Electric Motors (DC), Loudspeakers and Headphones, Electromagnetic Induction, and Generators: Alternators and Dynamos.

Physics EN
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Permanent Magnetism and Magnetic Fields

Magnets exert non-contact forces on each other and magnetic materials through invisible regions called magnetic fields. The interaction between poles (attraction or repulsion) and the induction of magnetism in materials are fundamental behaviours.

Key points

  • Law of Magnetism: Like poles repel (N-N, S-S); unlike poles attract (N-S).
  • Magnetic Materials: Iron, steel, nickel, and cobalt are the only common magnetic materials.
  • Field Lines: Drawn from North to South. The density of lines indicates field strength (closer lines = stronger field).
  • Induced Magnetism: When a magnetic material is placed in a field, it becomes a magnet. Induction always causes a force of attraction.
  • Hard vs Soft: 'Soft' materials (e.g., pure iron) lose magnetism easily; 'Hard' materials (e.g., steel) retain it.

Worked example

Question

A student plots the magnetic field around a bar magnet using a plotting compass. Explain how the compass indicates the direction of the field and where the field is strongest.

Solution

The plotting compass is a small permanent magnet. Its North pole is attracted to the South pole of the bar magnet and repelled by the North pole. Therefore, the compass needle aligns with the field lines, pointing away from the magnet's North pole and towards its South pole. The field is strongest at the poles, which would be indicated by the compass needle changing direction most rapidly over short distances, corresponding to where field lines are closest together.

Common pitfalls

  • Confusing magnetic poles (N/S) with electric charges (+/-).
  • Thinking that all metals are magnetic (e.g., copper and aluminium are not).
  • Believing induced magnetism can cause repulsion (it is always attractive).

Prerequisites

  • Non-contact forces
  • Vectors (direction and magnitude)
Further resources