Download Magnetism Part I

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Magnetism
Molecular theory of Magnetism
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Each and every molecule of a magnetic substance is a complete magnet in itself, having a
north pole and a south pole of equal strength.
In an unmagnetized substance, the molecular magnets are randomly oriented such that
they form closed chains.
When the substance is magnetized, the molecular magnets are realigned so that north
poles of all molecular magnets point in one direction and south poles of all molecular
magnets point in the opposite direction.
When all the molecular magnets are fully aligned, the substance is said to be saturated
with magnetism
During heating the magnetized specimen, molecular magnets acquire some kinetic
energy. Some of the molecules may get back to the closed chain arrangement. That is
why magnetism of the specimen would reduce on heating.
Magnetism
Magnetism is a force that is created when objects are attracted or repelled by one another.
What is a magnet?
A magnet is any material that is able to attract iron or steel. When a piece of material is brought
close to or stroked by a magnet, the material itself becomes magnetic.
There are two classes of magnets:
1. Electro Magnet:
Materials that lose their charge when the magnetic source is removed (soft iron)
2. Permanent Magnet
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Materials that retain their magnetism when the magnetic source is removed (steel)
Magnetic Materials
These materials are greatly influenced by an external magnetic field. They also retain their
magnetic properties after the external field has been removed. Iron, nickel, and cobalt are
examples of ferromagnetic materials.
Non magnetic Materials
Materials that has no obvious magnetic properties are said to be non magnetic. Examples on non
magnetic materials are bronze, lead and plastic.
Diamagnetic
Diamagnetic materials are slightly repelled by a magnetic field and the material does not retain
the magnetic properties when the external field is removed. Examples of diamagnetic materials
are copper, silver and gold.
Laws of Magnets
All magnets have two (2) poles: a North Pole and South Pole. Experiments also show that:
1. Unlike poles attract and like poles repel each other.
2. Forces of attraction decreases as the poles get further apart.
A Magnetic Field
A magnetic field is the area around a magnet. The larger the magnet and the closer an object is to
the magnet, the greater the force of the magnetic field.
Magnetic Shielding
Magnetic shielding is a process that limits the magnetic effect between two locations. Shielding
is usually done using a number of materials, such as sheet metal, metal mesh, ionized gas, or
plasma. The purpose is most often to prevent magnetic fields from interfering with electrical
devices.
Unlike electricity, magnetic fields cannot be blocked or insulated, which makes shielding
necessary. There is no way to block magnetic field lines; nature will find a path to return the
magnetic field lines back to an opposite pole. This means that even if a nonmagnetic object —
for example, glass — is placed between the poles of a horseshoe magnet, the magnetic field will
still exist.
Instead of attempting to stop these magnetic field lines, magnetic shielding re-routes them
around an object. This is done by surrounding the device to be shielded with a magnetic material.
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The magnetic field will tend to flow along this material, avoiding the objects inside. Thus, the
magnetic field lines are allowed to terminate on opposite poles, but are merely redirected.