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Albert Poon 3/10/91
022T SP2
Types of Magnets
Generally, the two broad classes of magnets are permanent
magnets and electromagnets.
An electromagnet is a type of magnets needs currents from an
external source to maintain its magnetic field. The current in a
wire conductor create as associated magnetic field. And these
current and its magnetic field become concentrated in a smaller
space. As the result, it create a strong magnetic field. In other
words, more current and more turns made a stronger magnetic
field.
One of the most common application of electromagnets magnetic
tape recording. The tape is coated with fine particles of iron
oxide. The recording head is a coil that produces a magnetic
field in proportion to the current. As it passes through the air
gap of the head, the small areas of the coating become magnetized
by induction. When you played back the tape, the moving of the
magnetic tape produces variation in electric current.
Permanent magnets are made of hard magnetic material, cabolt
steel. It magnetized by induction in the manufacturing process. A
strong field is needed for induction in these material. When
they removed the magnetizing field. The residual induction makes
the material a permanent magnet.
One of the disadvantage of the permanent magnet is when it
above the curie temperature, the molecular structure can not be
rearrange. The resulting in loss of magnetism that is not
recovered after cooling. For instance, when iron is above 800'C,
it will loss its ferromagnetic properties.
Magnetic Materials.
1 Ferromagnetic materials, like iron, steel, nickel and cobalt.
These materials become strongly magnetized in the same
direction as the magnetizing field, and also with a high
permeability from 50 to 5000.
2 Paramagnetic materials, for example, aluminum and manganese.
The permeability is slightly more than 1, they become weakly
magnetized in the same direction as the magnetizing field.
3 Diamagnetic materials. These includes copper, zinc, gold and
silver. The permeability is less than 1, and they become
weakly magnetized , but in the opposition direction from the
magnetizing field.
4 Ferrites is a nonmetallic material that have the
ferromagnetic properties. Which contains high permeability.
But it made of ceramic material. The permeability is from 50
to 3000.