Magnetism: Permanent and Induced Magnets

Magnetism: Permanent and Induced Magnets

Permanent Magnets

  • A permanent magnet produces its own constant magnetic field.
  • This type of magnet retains its magnetic properties for a long period and does not need a continuous supply of electrical energy.
  • They have two poles: a north pole and a south pole.
  • Like poles repel each other while unlike poles attract each other.
  • The geographical north pole of the earth is actually a magnetic south pole and vice versa.
  • The magnetic field is strongest at the poles and weakens with distance.
  • A magnetic field can be represented by magnetic field lines, always directed from North to South.
  • Permanent magnets are commonly used in compasses, fridge magnets, and motors.

Induced Magnets

  • Induced magnetism is the process by which a material becomes a magnet because it is in a magnetic field.
  • Only certain materials, such as iron, cobalt, nickel and steel, can be induced to become magnets.
  • The induced magnetism is temporary and lasts only as long as the material is in the magnetic field. Once removed, it loses its magnetism.
  • An induced magnet always has its induced north pole near the permanent magnet’s south pole and its induced south pole near the permanent magnet’s north pole.
  • The phenomena of induced magnetism is utilized in electromagnets, transformers, electric bells, and switches.

Magnetic Fields

  • Magnetic fields are regions around a magnet where other magnets or magnetic materials will experience a force.
  • They can be visualised using field lines which shows the shape of the field.
  • The field is strongest where the lines are closest together, usually at the poles.
  • Field lines always run from the north pole of a magnet to its south pole.
  • Magnetic fields can also be shown using plotting compasses or iron filings.

Magnetic Materials

  • A magnetic material is one that can be attracted by a magnet and can be magnetised to become a magnet itself.
  • Iron, steel, nickel and cobalt are the most common magnetic materials.
  • The response of a material to a magnetic field depends on its properties. Soft magnetic materials like iron can be easily magnetised and demagnetised, while hard magnetic materials like steel are difficult to magnetise but retain their magnetism for longer.