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Materials may be classified as:
FERROMAGNETIC
strongly attracted to magnets
iron, steel, cobalt, nickel
PARAMAGNETIC
slightly attracted by strong magnets
wood, aluminum, platinum, oxygen
DIAMAGNETIC
slightly repelled by strong magnets
zinc, bismuth, sodium chloride, gold
Magnetism is a property of charge in motion.
Orbiting electrons (negative charges in motion)
in the atom produce a magnetic field.
The domain theory is used to explain why
some materials are, or may become, magnetic.
No one knows exactly why
moving charges cause magnetism.
BASIC LAW OF MAGNETISM
Like poles repel; unlike poles attract.
Although it is possible to isolate positive
and negative charges, it is impossible to
isolate NORTH and SOUTH magnetic poles.
Magnetic monopoles do not exist.
Even though magnetic properties are
similar to electric properties, it is
erroneous to directly relate positive
and negative electric charges to
north and south magnetic poles.
The north magnetic pole
is not caused by protons,
nor is the south magnetic
pole caused by electrons!!!!
The force between magnetic poles follows a law
similar to the Law of Universal Gravitation
and Coulomb’s Law for Electrostatics.
Universal Gravitation
F = G (m1m2
2
)/d
Electrostatics
F = k (q1q2)/d2
Magnetism
F = k (M1M2)/d2
Magnetic fields surround magnets.
Field lines point from North to South
outside the magnet.
N
S
Click here to view some magnetic fields.
The number of field lines
is known as Magnetic Flux.
The unit of magnetic flux is the WEBER,
named in honor of Wilhelm Weber.
The amount of flux lines
per unit area is known as
Magnetic Flux Density.
Magnetic Flux Density is
measured in TESLAS,
named in honor of
Nikola Tesla.
One Tesla is one Weber per square meter = 1 Weber/m2.
Magnetism became associated
with currents when
Hans Christian Oersted
noticed a compass move
near a wire with a current
in the very early 19th century.
Demo simulation link
A magnetic field surrounds a current-bearing wire.
The direction of the magnetic field can be determined
by the “Right Hand Rule for a Current-Bearing Wire.”
“Grasp wire with right hand so that thumb
points in the direction of conventional
(positive) current. Your fingers circle the
wire in the direction of the magnetic field.”
Click on the following links to view computer
simulated examples of how electricity and
magnetism are necessarily “linked” together.
• magnetic field around a current-bearing wire: Link, link
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Lenz’s Law: Link
Faraday’s Magnetic Field Induction Experiment1: Link
Faraday’s Magnetic Field Induction Experiment2: Link
AC Generator: Link
DC Generator: Link
Lorentz Force: Link
magnet moving in and out of coil (movie): Link
Applications of Electromagnetic Relationships
Electromagnets
Generators
Electric Motors