Transcript How can we explain magnetism?

How can we explain magnetism?
Do Now:
Why does a compass point north?
Magnets
•2 poles:
North and south
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N
•Cannot isolate a pole
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N
S
N
Like Poles
►2
like poles experience a force
of repulsion
S
N
N
N
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S
S
N
Donut magnet Demo
Unlike Poles
►2
unlike signs experience a
force of attraction
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S
N
S
Compass
► Attracted
to magnetic south pole
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N
Therefore this is
magnetic north
Earth
► Earth
is a huge
magnet
► So why does the
north pole of a
compass point to the
north pole of the
Earth?
Geographic
Magnetic South
Pole
Geographic
Magnetic North
Pole
Ferromagnetic substances
►Substances
magnetic
 Iron
 Nickel
 Cobalt
that are naturally
How do things become
magnetized?
Magnetism is caused by the spin of the unpaired
electrons. When they spin in the same direction,
they cause microscopic magnets called domains.
If all the domains are aligned, a magnet is formed.
Temporary Magnet
► Created
when a ferromagnetic substance is
brought into close proximity to an easily
magnetized substance
(domains temporarily align)
► Occurs when the electrons spin in the same
direction
Magnetic Field Lines
If compasses are place around a magnet, we can
visualize the field around the magnet.
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S
Magnetic Fields
►Field
lines are called lines of
flux
►Defined as north to south
►Strongest where the lines of
flux are closest
Magnetic Flux
Magnetic flux describes the lines of a magnetic field
around a magnetized object.
Each magnetic flux line is equal to 1 Weber (Wb).
The strength of the field, or magnetic flux density
(B) is measured in Wb/m2 , or Tesla (T).
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S
If field lines point in the same direction,
N
S
N
S
They repel.
If field lines point in the opposite direction,
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N
N
S
They attract.
So why is the Earth magnetic?
► Magnetic
charges
fields are created by moving
 Any time a charge moves (current) a magnetic
field is created
► Outer
Core of Earth is liquid iron and nickel
 Ferromagnetic substances that have a charge
and are moving
Magnetic Force
•Created when a moving charge
passes through a magnetic field
•Reason: Charge has a magnetic
field and it interacts with another
magnetic field
•Greatest force is when the charge
passes perpendicular to the field
Sidenote:
► Planes,
DeGaussing
ships move through the Earth’s
magnetic field.
► Just as moving a charge through a magnetic
field creates a force, forcing an object to
move through a magnetic field creates
electricity
► This needs to be taken into account or else
navigational equipment gets jacked up
Which produces the greatest force?
B (magnetic lines of flux
B (magnetic lines of flux
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B (magnetic lines of flux
e-
Gamma Rays
► Moving
charges through space
► Enter Earth’s magnetic field
► Magnetic force is created
► Gamma Rays get deflected
► The Earth is safe
► http://www.youtube.com/watch?v=0JYkR17
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