Download magnetic field - s3.amazonaws.com

Magnets
Properties of Magnets
•A magnet is any material that attracts iron
and materials that contain iron.
•Magnets attract or repel other magnets.
•One part of a magnet will always point north
when allowed to swing freely
•Magnets will point towards the North Star or
Polaris, also known as the leading star, or
lodestar.
Magnetic Poles
•A magnetic pole is the end of a magnet
•North pole: end that points North
•South pole: opposite end
•Magnetic poles that are unlike attract each
other, alike poles repel.
•Just like electric charges!
•Magnetic force is the attraction or repulsion
between magnetic poles.
•Produced when magnetic poles interact
•Any material that exerts magnetic force is
considered a magnet
Magnetic Fields
•The magnetic field is the area of magnetic force
around a magnet
•Allows magnets to interact without touching
•Magnetic field lines are the invisible lines that map out
the magnetic field of a magnet
•Form complete loops, never cross
•Always leave north and enter south
•Distance between field lines indicate the strength of the
magnet
•Closer the lines, stronger the lines
Magnetic Domains
•A magnetic domain is a region where the magnetic
fields of all atoms are lined up in one direction
•If the material is NOT magnetized, the magnetic
domain points in random directions
•If the material is considered a magnet, the magnetic
domains are arranged in the same direction
Magnetic Materials
•A ferromagnetic material is a material that shows
strong magnetic properties
•Behaves like a piece of iron
•Iron, nickel, cobalt, samarium
•Alloy magnets - magnets made from several different
metals
•Alnico - aluminum, nickel, iron, cobalt
•Platinum and cobalt
•Ferrite - mixture of substances that contain
ferromagnetic elements
•Most commonly used today
•Brittle material but inexpensive
Making Magnets
•Unmagnetized material can be magnetized
•Placing an unmagnetized ferromagnetic material in
a strong magnetic field
•By rubbing the material with one pole of a magnet
•Magnetizing a paper clip
•Rub the paperclip in one direction along one pole of
the magnet
•Magnetic field of the magnet causes some domains
in the paperclip to line up.
Destroying Magnets
•Temporary magnet is a magnet made from a material
that easily loses its magnetism
•Permanent magnet is a magnet made from a material
that keeps its magnetism for a long time
•No magnet can last forever
•Ways to demagnetize magnets
•Drop it
•Strike it
•Heat it
Breaking Magnets
•Break a magnet in half and you will have two smaller
magnets
•Each smaller magnet has its own north pole and south
pole
•Magnetic poles are lined up in one direction, which will
remain even if the magnet is broken
S
N
MAGNETIC EARTH
Earth as a Magnet
• In the 1500s, Sir William Gilbert decided to investigate
compasses
• Gilbert confirmed that a compass always points in the same
direction, no matter where you are
• Gilbert hypothesized that the Earth is simply a giant magnet
• Was Gilbert correct?
The Compass
• The north pole of the
magnet will point towards
the North Pole
• The poles of the
magnetized needle on the
compass align themselves
with the Earth’s magnetic
fields
• The Earth does not actually
have a bar magnet buried
within its core – just an
analogy!
The Unknown Core
• Seismologists still do not
completely understand
Earth’s magnetism
• They theorize that the
inner core of the Earth is
made up of molten iron
• The circulation of molten
material inside the Earth’s
core is what causes Earth’s
magnetism
Earth’s Poles
• The Earth rotates on its axis
around the geographic poles
• The magnetic poles are located
on Earth’s surface where the
magnetic force is the strongest
• Magnetic North Pole is actually
located in Northern Canada –
about 1,250 kilometers (about
776 miles) from the geographic
North Pole
• Magnetic declination is the
angle between the two lines –
geographic north and magnetic
north
Earth’s Magnetic Field
• Earth’s magnetic field acts on rocks
• Rock is produced in the ocean floor from molten material
that seeps up through the mid-ocean ridge
• The iron in the rock lines up in the direction of the Earth’s
magnetic field
• Rock cools and hardens and the iron is locked in place
• This process creates a permanent record of the magnetic
field
• As scientists have been studying such rocks, they have
discovered that the direction and strength of the Earth’s
magnetic field have changed over time
• Earth’s magnetic field has completely reversed direction
every million years or so
Mid-ocean
ridge
Rock formed when Earth’s
Magnetic field was normal
Rock formed when Earth’s
Magnetic field was reversed
Oceanic crust
Earth’s mantle
Molten Material
The Magnetosphere
Van Allen belts – two regions that contain
electrons and protons traveling at very high
speeds
The Magnetosphere
• Solar wind is a stream of electrically charged
particles flowing at high speeds from the sun
• Pushes against Earth’s magnetic field and
surrounds the field
• The region shaped by the field is known as the
magnetosphere.
Pictures of
The Earth’s
Magnetosphere
Auroras
• When high-speed, charged
particles get close to Earth’s
surface, they interact with
atoms in the atmosphere
• This results in the atoms giving
off light
• A curtain of shimmering bright
light in the atmosphere
• This glowing region caused by
charged particles is called an
aurora.
• Known as The Northern Lights,
or aurora borealis in the North
and the Southern Lights or
aurora australis in the South.