ELECTRICITY AND MAGNETISM 22.1 Chapter Twenty-Two: Electricity and Magnetism 22.1 Properties of Magnets 22.2 Electromagnets 22.3 Electric Motors.
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Transcript ELECTRICITY AND MAGNETISM 22.1 Chapter Twenty-Two: Electricity and Magnetism 22.1 Properties of Magnets 22.2 Electromagnets 22.3 Electric Motors.
ELECTRICITY AND MAGNETISM 22.1
Chapter Twenty-Two: Electricity
and Magnetism
22.1 Properties of Magnets
22.2 Electromagnets
22.3 Electric Motors
Chapter 22.1 Learning Goals
Identify properties of magnetic
materials and use interactions
between magnets to explain
attraction and repulsion.
Describe the source of Earth’s
magnetism.
Explain how a compass works.
Investigation 22A
Magnetism
Key Question:
How do magnets and compasses work?
22.1 Properties of Magnets
If a material is magnetic, it has the ability
to exert forces on magnets or other
magnetic materials nearby.
A permanent magnet is a material that
keeps its magnetic properties.
22.1 Properties of Magnets
All magnets have two
opposite magnetic
poles, called the north
pole and south pole.
If a magnet is cut in
half, each half will
have its own north
and south poles.
22.1 Properties of Magnets
Whether the two magnets attract or
repel depends on which poles face
each other.
22.1 Properties of Magnets
Magnetic forces can pass through
many materials with no apparent
decrease in strength.
22.1 Properties of Magnets
Magnetic forces are used
in many applications
because they are relatively
easy to create and can be
very strong.
Large magnets create
forces strong enough to
lift a car or a moving train.
22.1 Magnetic fields
The force from a
magnet gets weaker
as it gets farther
away.
Separating a pair of
magnets by twice the
distance reduces the
force by 8 times or
more.
22.1 Magnetic fields
A special kind of
diagram is used to
map the magnetic
field.
The force points
away from the north
pole and towards the
south pole.
22.1 Magnetic fields
You can actually see
the pattern of the
magnetic field lines
by sprinkling
magnetic iron filings
on cardboard with a
magnet underneath.
22.1 Magnetic field lines
A compass needle is a
magnet that is free to
spin.
Because the needle
aligns with the local
magnetic field, a
compass is a great
way to “see” magnetic
field lines.
22.1 Geographic and magnetic
poles
The planet Earth
has a magnetic
field that comes
from the core of
the planet itself.
22.1 Geographic and magnetic
poles
The names of
Earth’s poles were
decided long before
people understood
how a compass
needle worked.
The compass needle’s “north” end is actually
attracted to Earth’s “south” magnetic pole!
22.1 Declination and “true north”
Because Earth’s geographic north pole
(true north) and magnetic south pole
are not located at the exact same
place, a compass will not point
directly to the geographic north pole.
The difference between the direction
a compass points and the direction of
true north is called magnetic
declination.
22.1 Declination and “true north”
Magnetic declination is measured in
degrees and is indicated on
topographical maps.
22.1 Declination and “true north”
Magnetic declination is
measured in degrees and
is indicated on
topographical maps.
Most good compasses
contain an adjustable
ring with a degree scale
used compensate for
declination.
22.1 Earth’s magnetism
Studies of
earthquake waves
reveal that the Earth’s
core is made of hot,
dense molten metals.
Huge electric
currents flowing in
the molten iron
produce the Earth’s
magnetic field.
22.1 Earth’s magnetism
The gauss is a unit used to measure
the strength of a magnetic field.
The magnetic field of Earth (.5 G) is
weak compared to the field near the
ceramic magnets you have in your
classroom. (300- 1,000 G).
For this reason you cannot trust a
compass to point north if any other
magnets are close by.
22.1 Earth’s magnetism
Today, Earth’s
magnetic field is
losing approximately
7 percent of its
strength every 100
years.
If this trend
continues, the
magnetic poles will
reverse sometime in
the next 2,000 years.