Friday, December 24, 2010


Magnets and magnetic

Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Some are attracted to a magnetic field (paramagnetism); others are repulsed by a magnetic field (diamagnetism); others have a much more complex relationship with an applied magnetic field. Substances that are negligibly affected by magnetic fields are known as non-magnetic substances. They include copper, aluminium, gases, and plastic.

Magnets attract (never repel) the , ferromagnets, "magnetic metals".
Ferromagnetic materials have the highest magnetic susceptibilities.Examples of ferromagnetic materials are Iron, Nickel, Cobalt, hematite, magnetite and ionized gases (such as the material stars are made of). Magnets also attract or repel other permanent magnets,depending on which way they are facing each other. Permanent magnets usually have some iron in them.

There is a kind of dark-gray brittle ceramic called "ferrite" (pronounced like
"fair-right"), which has iron, oxygen, and some other metals with oxygen.
Ferrite can be magnetic too, because of the iron in it.

Properties of magnets

1.Magnetic Poles

The magnetic force surrounding a magnet is not uniform. There exists a great concentration of force at each end of the magnet and a very weak force at the center.

Proof of this fact can be obtained by dipping a magnet into iron filings (fig. 1-8). It is found that many filings will cling to the ends of the magnet while very few adhere to the center.

The two ends, which are the regions of concentrated lines of force, are called the POLES of the magnet. Magnets have two magnetic poles and both poles have equal magnetic strength. The poles are where the magnetic effects are the strongest.

2.North and South Poles

If a bar magnet is suspended freely on a string, it will align itself in a north and south direction. When this experiment is repeated, it is found that the same pole of the magnet will always swing toward the north magnetic pole of the earth. Therefore, it is called the north-seeking pole or simply the NORTH POLE. The other pole of the magnet is the south-seeking pole or the SOUTH POLE.

A practical use of the directional characteristic of the magnet is the compass, a device in which a freely rotating magnetized needle indicator points toward the North Pole.

3.Laws of magnetic poles

The realization that the poles of a suspended magnet always move to a definite position gives an indication that the opposite poles of a magnet have opposite magnetic polarity.The law previously stated regarding the attraction and repulsion of charged bodies may also be applied to magnetism if the pole is considered as a charge.

The north pole of a magnet will always be attracted to the south pole of another magnet and will show a repulsion to a north pole. The law of magnetism is:

Like poles repel, unlike poles attract.

How is magnet identified?

If an object attracts another object, it cannot be concluded to be a magnet as it may either be a magnetic material (not a magnet) that is attracted by the suspended magnet or a magnet itself with the opposite pole on the approaching end. To be certain, we would have to test the other end with the N pole of the suspended magnet to see if repulsion occurs.

1 comment:

  1. it was ok.. not what i was really looking for.. but ok