Transcript Basic Magnetism

Basic Magnetism
• Magnets occur naturally within rocks like
lodestone. The word magnet is derived form
a place called Magnesia because magnetic
rocks are common there.
Types of Magnets
Permanent – retain magnetism
permanently
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.
Types of Magnets
• 3. Solenoid – A coil of wire itself exhibits
magnetism when the current is on.
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.)
Lines of Force
N
S
• The Greeks found a rock (magnetite or
lodestone) that attracted iron. The Chinese
used this to invent compasses in the 11th
century.
• A few materials (iron, steel) are strongly
attracted to magnets. Others are less
strongly (cobalt, and nickel).
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)
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.
Domains
• Domains are regions of magnetic substances
that have a free, spinning electron. When
these domains line up, the substance
becomes a magnet.
Evidence that supports the
domain theory
1. Rubbing a nail with a magnet turns the nail into
a magnet.
2. Rubbing a test tube of iron filings produces
North & South poles that can be seen with a
compass.
3. When temporary magnets are hit, they lose their
magnetism.
Evidence that supports the
domain theory
4. Breaking a magnet in two, results in 2
magnets with North & South poles.
S
S
N
N
Evidence that supports the
domain theory
5. The magnetism of a bar magnet can be
reversed by a strong external magnetic field.