Basic Magnetism

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Basic Magnetism
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• Magnets occur naturally within rocks like
  lodestone. The word magnet is derived form a
  place called Magnesia because magnetic rocks are
  common there.

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Types of Magnets

• Permanent retain magnetism permanently

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Types of Magnets

• 2. Electromagnets when an iron bar is wrapped
  with a current carrying wire, the bar becomes a
  magnet. It ceases to be magnetic when the current
  is off.

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Types of Magnets

• 3. Solenoid A coil of wire itself exhibits
  magnetism when the current is on.

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Lines of Force

• In all cases, the magnet produces magnetic lines
  of force that attract or repel other magnets. The
  magnetic lines of force form a magnetic field.
  All lines are said to originate at the N pole and
  travel to the S. (You may also consider the lines
  to point in the direction that an N pole test
  magnet would be pushed.)

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Lines of Force
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• The Greeks found a rock (magnetite or lodestone)
  that attracted iron. The Chinese used this to
  invent compasses in the 11th century.

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• A few materials (iron, steel) are strongly
  attracted to magnets. Others are less strongly
  (cobalt, and nickel).

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Types of Magnetism

• Ferromagnetic materials with a strong magnetic
  attraction. (iron, steel)

• Paramagnetic materials with a slight magnetic
  attraction. (wood , aluminum, platinum, oxygen)

• Diamagnetic weakly repelled by strong magnets.
  (zinc, bismuth, sodium chloride, gold)

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Theory of Magnetism

• Magnetism is a property of a charge in motion.
  The electrons revolve around the nucleus, causing
  the magnetism. The electrons also spin on their
  own axis (like the Earth), producing a magnetic
  field. However, when the electrons are paired,
  the fields cancel each other out.

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Domains

• Domains are regions of magnetic substances that
  have a free, spinning electron. When these
  domains line up, the substance becomes a magnet.

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Evidence that supports the domain theory

• Rubbing a nail with a magnet turns the nail into
  a magnet.
• Rubbing a test tube of iron filings produces
  North South poles that can be seen with a
  compass.
• When temporary magnets are hit, they lose their
  magnetism.

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Evidence that supports the domain theory

• Breaking a magnet in two, results in 2 magnets
  with North South poles.

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Evidence that supports the domain theory

• 5. The magnetism of a bar magnet can be reversed
  by a strong external magnetic field.