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