You should have learned magnetism in form 3. In form 3, you 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.
We also learned that a magnet has 2 poles-the North Pole and the South Pole. 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 filed of a magnet is represented by the magnetic field line. The magnetic field line flowing out from the North pole and flowing into the South pole.

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


The pattern and the direction of a magnetic field can be determined by a compass. The pointer of the compass is always in the direction of the magnetic field. 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.

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. This will discuss in electromagnetism.




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6 comments

  1. Sek // July 18, 2008 at 1:37 AM  

    Visitors are welcomed to post question or give further expiation to the topic at the comment column.

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  2. Shreyas // February 19, 2009 at 8:07 AM  

    OK, first off- Thanks. This site is really helpful, and has cleared quite a few doubts.

    However, I still am a little confused.
    1) Can you explain the change of the compass point direction in a bar magnet and a straight conductor? What do you mean when you say that 'it points in the direction of the field,and so it points to the north?

    Thanks

  3. Sek // February 19, 2009 at 8:15 AM  

    Shreyas, TQ for your question.

    The magnetic field is coming out from the South pole, directing towards the North pole.

    Therefore, if you put a compass in a magnetic field, the pointer of the compass will be in the same direction as the field.

  4. tHe ElIxir // May 5, 2009 at 5:04 AM  

    Sl

    referring to shreyas's question earlier. But i thought the compass pointer always points to the north no matter what? so what do you mean when you say "the pointer of the compass will be in the same direction as the field."?

    thx

  5. Sek // May 5, 2009 at 8:37 AM  

    tHe Ellxir,

    First of All, the compass is always pointing towards the North of Earth, but not the North of the "magnetic field of the Earth". Actually, the pole of the magnetic field of the earth at the North of Earth is the "South Pole" but not the North Pole.

    As you can see in the diagram above, the compass is actually pointing away from the North pole and pointing towards the South pole or it is always pointing in the direction of the field.

  6. shinyiing // June 12, 2009 at 1:21 AM  

    first of all, thank you for posted all of these...
    it's so useful to me to prepare my SPM...

    but i have a few questions...
    what is feromagnetic...it is just only the things that can be attracted by the magnet?
    and...
    can i have some example?