Magnetism Notes

Magnetism

  • An attractive and repulsive phenomenon produced by a moving electric charge.
  • Ability of certain materials to attract iron, cobalt, or nickel.

Nature of Magnetism

  • Electrons possess a characteristic called “spin.”
  • Certain elements have electrons that “spin” in the same direction.
  • The collective motion of the charged atomic particles (the e-) results in a magnetic dipole & force field.
  • The magnetic force field produced is perpendicular to the plane of the motion of the e-.

Magnetic Fields (Lines of Force, Lines of Flux)

  • The force field that exists inside and outside a magnet.
  • Magnetic Field Strength
    • Stronger magnet has more lines 🡪 greater Flux Density (flux lines per square meter).
    • Measured as Tesla or Gauss.
  • Direction of Lines
    • North to South outside the magnet.
    • South to North inside the magnet.
    • Lines never intersect.

Classifications of Magnets

  • Natural
    • Earth
    • Lodestone
  • Artificial permanent
    • Alnico
    • Neodymium
  • Electromagnets
    • Temporary due to moving electric current

Laws of Magnetism

  • Repulsion-Attraction
    • Like poles repel; unlike poles attract
  • Inverse Square Law
    • Force between two magnetic fields directly proportional to product of their magnitudes and inversely proportional to the square of the distance between them.
  • Magnetic Poles
    • Every magnet has 2 poles

Magnetic Induction

  • Non-magnetized iron brought within a magnetic field; domains of iron line up in orderly fashion, iron is temporarily magnetized (magnetic induction)

Magnetic Permeability and Retentivity

  • Permeability
    • Ease with which material can be magnetized
  • Retentivity
    • Ability of material to stay magnetized
  • Inversely Proportional:
    • Soft iron - High permeability, low retentivity
    • Hard steel - Low permeability, high retentivity

Magnetic Classifications of Matter

  • Ferromagnetic
    • High permeability / easy to induce magnetization
    • Iron, Cobalt, Nickel, Alnico
  • Paramagnetic
    • Low permeability / weak attraction to magnet
    • Platinum, Aluminum
  • Diamagnetic
    • Weakly repelled by magnet
    • Beryllium, Bismuth, Lead
  • Nonmagnetic
    • Cannot be magnetized
    • Wood, Glass, Rubber, Plastic