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Transcript
Properties of magnets
 Magnet-
material that can exert forces on
magnets or other magnetic materials, like iron
and steel.
 Poles-
all magnets have 2- North and south
Permanent magnets- keep their magnetic
properties- bar, horseshoe, round..called
“hard magnets.”-
strongest: nickel, cobalt or neodymium.
Temporary magnets- lose their magnetism
easily. Called “soft magnets”
Force of Attraction- opp. Poles( N and S)
Force of Repulsion- like poles (N,N, S,S) repel.
At this pt. all magnets are dipoles(2 poles), and
no monopole(1 pole) exists !
Magnets can exert their forces even thru
insulating materials like wood, plastic, and glass
if they are strong enough.
Conducting materials like iron and steel can
block or change the mag. forces.
USES OF MAGNETS:
•junkyards, weather stripping on doors, zippers,
latches, cabinet and fridge doors, handbags, etc.
•MAGNETIC FIELD: area around a magnet
that exerts a force. ( a force field)
•Magnetic field lines– represent the mag. Field,
and always go from N pole towards the S pole.
The closer the lines, the stronger the force.
ferromagnets
Magnets made of iron, nickel or cobalt with
very strong mag. Properties.
Magnetic domains- millions of atoms align
themselves with other atoms in groups all
facing in the same direction.
If a magnet is near a paperclip, the domains in
the paperclip will realign with the magnet until
the magnet is removed.
SOURCE OF MAGNETISM
 ELECTROMAGNETS-
coil of wire wrapped
around an iron core, connected to a source of
electricity-like a battery—creates a magnet.
N
and S poles are at each end of the coil..You
can switch the poles by switching the
direction of the electricity flow.
 EM
can be much stronger than permanent
magnets, b/c they can use large currents.
Uses: toasters, doorbells, watches, clocks,
Where is the north and south pole?
Right-Hand Rule

If the fingers of your
RIGHT hand curl in
the direction of the
current, your thumb
points toward the
north pole.
•Factors affecting electromagnets:
make them stronger:
a) add more turns of wire ( this
increases the current over and over)
b) increase the current
( more batteries)
If you dbl. the batteries, you dbl .The
current, and the magnet’ strength.
However, more wire makes more heat
c) Increase the iron core—
With an EM, you can turn a switch on and off,
and have it work– our doors for fire drills stay
open with an EM!
SO, MAGNETISM COMES FROM ELECTRIC
CURRENTS!
Some materials, like lead and diamonds are
not magnetic at all, whereas aluminum can
be a weak magnet, but is often nonmagnetic,
b/c the atoms are not aligned naturally.
What destroys magnets?
 Increasing
temperature can ruin the domains
 Dropping
the magnets
 Changing
the domains alignment somehow
•
Compass needles:
As early as 500 B.C., people were using
Lodestone(magnetite) as a compass.
oCompass needle- free moving magnet. It
stops spinning when it is lined up with the
magnetic field present.
o the needle lines up w/ local mag. Field, w/ N
pole of compass attracted to S pole of mag.
Field .
o The N pole of a compass actually points to
the Earth’s SOUTH MAGNETIC POLE, which
is near the NORTH GEOGRAPHIC POLE!!!
oThe S pole of a compass points to the Earth’s
NORTH MAGNETIC POLE, near the S G Pole.
A compass does NOT pt. directly to the geo. N
pole, but near it. It will always be slightly E or
W of the G N Pole.
( mag. S. P is about 600 miles( 1000 km) from
GNP).
Magnetic Declination.
The difference between the direction the
needle points, and True G North, is called You
can measure the “angle of declination.”– PAGE
371 OF TEXT—LOOK TOGETHER !!
INTERESTING FACTS:
GAUSS-unit
to measure the strength of a
mag. Field.
Mag.
Field of Earth is weak compared to a
classroom magnet.
The
poles of our Earth have reversed about
every 500,000 yrs. Last one was about
750,000 yrs. Ago, so we are due!!
Location
of our mag. Poles is always
changing.
Chapter 16.1 Objectives and Vocabulary
Recognize that magnetic
poles always exits in pairs.
 Decide whether two magnetic
poles will attract or repel.
 Describe the magnetic field
and forces around a
permanent magnet.






magnetic
permanent magnet
magnetic poles
magnetic field
magnetic field line
The earth’s magnetic field
 The
earth has an imaginary bar magnet going
thru its’ core.
 The
mag. Field of earth would look just like
the field around the bar magnet; But, the
solar winds from the sun, change its shape
slightly.
 WILLIAM
GILBERT: 1600--discovered that the
E. has a magnetic field around it. The E. core
is mostly iron and nickel, creating the mag.
Field.
Solar winds- from the sun blow on the E. mag.
Field, creating a “tail.”-reshaping the Mag.
Field of Earth -- called the Magnetosphere.
These winds push radioactive particles toward
the E.
•Van Allen Radiation Belts–“trap” most of the
rad. particles from the sun, keeping them from
harming us.
•Any particles that escape the belts, get
attracted to the N and S poles of the Earth,
and react with gases in the atmosphere,
creating Auroras.
Now you draw it with me:
PICTURES OF AURORAS
Auroras- charged part. From Sun react with
gases in the atmosphere at the northern and S.
poles, and create brilliant light shows.
Northern Lights- A. Borealis
Southern lights- A. Australis
FACTS TO KNOW:
 Sunspots:
come in pairs, with poles, and are
dark circular areas that are cooler, and
magnetic.
 Every
11 yrs. the annual # of sunspots varies,
and the sun’s mag. Poles reverse. Jupiter
and Saturn also have mag. Fields.