Download Magnetic Fields - Northwest ISD Moodle

Magnetic Fields
A PowerPoint Presentation by
Paul E. Tippens, Professor of Physics
Southern Polytechnic State University
©
2007
Objectives: After completing this
module, you should be able to:
• Define the magnetic field, discussing
magnetic poles
Magnetism
Since ancient times, certain materials, called
magnets, have been known to have the property of
attracting tiny pieces of metal. This attractive
property is called magnetism.
S
Bar Magnet
S
N
N
Magnetism
The domain theory is a simple model of magnetism
which states that all materials are made up of tiny
regions called domains. The domains behave like
magnets.
Random distribution=no magnetic effect
Domains aligned=magnetized
Magnetic Poles
Iron
filings
N
The strength of a magnet is
concentrated at the ends,
called north and south
“poles” of the magnet.
S
A suspended magnet:
N-seeking end and
S-seeking end are N
and S poles.
W
N
S
N
Bar magnet
S
N
E
Compass
Magnetic Attraction-Repulsion
S
S
N
N
N
Magnetic Forces:
Like Poles Repel
S
S
N
N
S
Unlike Poles Attract
Magnetic Field Lines
We can describe
magnetic field lines
by imagining a tiny
compass placed at
nearby points.
The direction of the
magnetic field B at
any point is the same
as the direction
indicated by this
compass.
N
S
Field B is strong where
lines are dense and weak
where lines are sparse.
Magnetic Field Lines
The field lines follow the needle on the compass
Field Lines Between Magnets
Unlike
poles
Attraction
N
S
Leave N
and enter S
N
Like poles
N
Repulsion