Concept of a magnetic field
Section: Magnetic Fields | Syllabus: Cambridge AS Level Physics 9702
Defining a Magnetic Field A magnetic field is a region of space where a force is exerted on: A magnetic pole (e.g., a permanent magnet) A moving electric charge A current-carrying conductor Examiner Definition It is best defined as a field of force produced by moving charges or permanent magnets.
Sources of Magnetic Fields Unlike gravitational fields (mass) and electric fields (charge), magnetic fields are fundamentally produced by moving charges . Permanent Magnets: Result from the spin and orbital motion of electrons within atoms (microscopic currents).
Common magnetic materials include Iron, Nickel, and Cobalt . Currents: Any macroscopic flow of charge produces a magnetic field. Field Type Source Force Acts On Gravitational Mass Mass Electric Charge Charge Magnetic Moving Charge Moving Charge / Magnet Field Lines Representation Magnetic field lines visualize the strength and direction of the field.
Direction: From North (N) to South (S) outside the magnet. Strength: Represented by the density of lines. Closer lines indicate a stronger field (higher magnetic flux density). Loops: Magnetic field lines always form closed loops (they continue from S to N inside the magnet).
Interaction: Field lines never cross . Common Mistake Do not confuse the direction of the field line with the direction of force. The field line shows the direction a "free" North pole would move. Diagram: Field Patterns Show field lines for: 1.
Bar magnet (loops N to S). 2. Uniform field (parallel, equally spaced lines). 3. Earth's magnetic field (similar to a bar magnet).
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