Introduction to Magnetism (Revision)

In form 3, we learned that
  1. a magnet can attract certain type of metal.
  2. the metals that can be attracted by a magnet are called the “magnetic materials” of “ferromagnetic materials”. Examples of magnetic materials are iron, steel, nickel and cobalt.
  3. a magnet has 2 poles-the North Pole and the South Pole.
  4. there is a magnetic field surrounding the magnet.  A magnetic field is a region in the surrounding of a magnet which a magnetic material experiences a detectable force.

Magnetic Field Line
(The magnetic field is represented by the magnetic field lines)
  1. The magnetic filed of a magnet is represented by the magnetic field lines. The magnetic field lines flow  out from the North pole and flow into the South pole.
  2. The distance between the field lines represent the strength of the field, the closer the field line, the stronger the field. In the diagram, the magnetic field A is stronger than magnetic field B because the line in magnetic field A is closer.

Compass in a Magnetic Field
(Figure(a): The pointer of a compass point towards the North pole of a magnet)

(Figure(b): The direction of the pointer of a magnet is always in the same direction of the magnetic field)

  1. The pattern and the direction of a magnetic field can be determined by a compass.
  2. First of all, we need to know that, in SPM, normally we use a circle with an arrow to represent compass. The arrow represents the pointer of a compass and it always points towards the North pole of a magnet.
  3. Second, we also need to know that the pointer of a compass is always in the direction of the magnetic field.
  4. In figure (b) above, we can see that when a few compasses are put near to a bar magnet, the pointer of the compasses are all in the direction of the magnetic field.
  5. If a compass is placed near to a current carrying wire, the pointer of the compass will point along the direction of the magnetic field generated by the current (as shown in the figure below). This will be discussed in electromagnetism.

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