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Magnetism
What is magnetism?
•Force of attraction or
repulsion due to electron
arrangement
•Magnetic forces are the
strongest at the poles
•Magnets have two poles:
North and South
Magnetic poles and fields
• Magnets always have two poles
• If a magnet is cut it will still have
two poles
• Like magnetic poles repel
• Unlike magnetic poles attract
• A magnetic field is the area in
which magnetic forces act
Magnetic materials
•Natural magnets have
naturally occurring magnetic
properties ex:
LODESTONE (magnetite)
Temporary magnets
•Easy to magnetize
•Lose their magnetism
quickly
•Ex: Soft iron
Permanent magnets
•Hard to magnetize
•Stay magnetized longer
than temporary magnets
•Ex: alnico (cobalt, nickel,
aluminum)
Earth’s magnetic properties
• Gilbert was a scientist that showed
that the Earth behaves as a
magnet
• The Earth’s magnetic field is
strongest at the poles
• Earth’s magnetic field is called the
magnetosphere
Compasses
• Compasses are used to determine
direction
• Compass needles are magnetized
and respond to the magnetic field
of the Earth
• Compasses point to the
MAGNETIC POLES OF THE
EARTH
Magnetic variation
•Magnetic poles of the Earth
are different from the
geographic poles of the
Earth
Magnetic Induction
•Process by which materials
can be magnetized
What affects magnetic
properties?
• Spinning electrons cause some
metals to have magnetic properties
• Magnetic domains are groups of
arranged magnetic fields
• Dropping,hammering or heating a
magnet will cause a magnet to lose
magnetic properties
Atoms themselves have magnetic properties due
to the spin of the atom’s electrons.
Groups of atoms join so that their magnetic fields
are all going in the same direction
These areas of atoms are called “domains”
When an unmagnetized substance is placed in a
magnetic
field, the substance can become magnetized.
This happens when the spinning electrons line up
in the
same direction.
Electromagnetism
• Discovered by Oersted (scientist)
• Relationship between electricity
and magnetism
Electromagnets
• Temporary magnets
• Magnetism can be turned on and
off
• Made by wrapping wire around a
piece of iron and sending a current
through the wire
• Magnetic field is in the same
direction as the electric current
Increasing the strength of
electromagnets
•Increasing the voltage or
current
•Increasing the number of
loops of wire
Electric motors vs. generators
•Electric motors convert
electricity to mechanical
energy in order to do work
•Generators convert
mechanical energy to
electrical energy
Transformers
• Used to increase or decrease
voltage
• Made of primary and secondary
coils
• Two types of transformers:
• “Step-up” (increase voltage)
• “Step-down”(decrease voltage)